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Sample records for dependent plasticity stdp

  1. Spike timing dependent plasticity (STDP) can ameliorate process variations in neuromorphic VLSI.

    Science.gov (United States)

    Cameron, Katherine; Boonsobhak, Vasin; Murray, Alan; Renshaw, David

    2005-11-01

    A transient-detecting very large scale integration (VLSI) pixel is described, suitable for use in a visual-processing, depth-recovery algorithm based upon spike timing. A small array of pixels is coupled to an adaptive system, based upon spike timing dependent plasticity (STDP), that aims to reduce the effect of VLSI process variations on the algorithm's performance. Results from 0.35 microm CMOS temporal differentiating pixels and STDP circuits show that the system is capable of adapting to substantially reduce the effects of process variations without interrupting the algorithm's natural processes. The concept is generic to all spike timing driven processing algorithms in a VLSI.

  2. Questions About STDP as a General Model of Synaptic Plasticity

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    John Lisman

    2010-10-01

    Full Text Available According to spike-timing-dependent plasticity (STDP, the timing of the Na+ spike relative to the EPSP determines whether LTP or LTD will occur. Here, we review our reservations about STDP. Most investigations of this process have been done under conditions in which the spike is evoked by postsynaptic current injection. Under more realistic conditions, in which the spike is evoked by the EPSP, the results do not generally support STDP. For instance, low-frequency stimulation of a group of synapses can cause LTD, not the LTP predicted by the pre-before-post sequence in STDP; this is true regardless of whether or not the EPSP is large enough to produce a Na+ spike. With stronger or more frequent stimulation, LTP can be induced by the same pre-before-post timing, but in this case block of Na+ spikes does not necessarily prevent LTP induction. Thus, Na+ spikes may facilitate LTP and/or LTD under some conditions, but they are not necessary, a finding consistent with their small size relative to the EPSP in many parts of pyramidal cell dendrites. The nature of the dendritic depolarizing events that control bidirectional plasticity is of central importance to understanding neural function. There are several candidates, including backpropagating action potentials, but also dendritic Ca2+ spikes, the AMPA receptor-mediated EPSP, and NMDA receptor-mediated EPSPs or spikes. These often appear to be more important than the Na+ spike in providing the depolarization necessary for plasticity. We thus feel that it is premature to accept STDP-like processes as the major determinant of LTP/LTD.

  3. Calcium-dependent calcium decay explains STDP in a dynamic model of hippocampal synapses.

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    Dominic Standage

    Full Text Available It is widely accepted that the direction and magnitude of synaptic plasticity depends on post-synaptic calcium flux, where high levels of calcium lead to long-term potentiation and moderate levels lead to long-term depression. At synapses onto neurons in region CA1 of the hippocampus (and many other synapses, NMDA receptors provide the relevant source of calcium. In this regard, post-synaptic calcium captures the coincidence of pre- and post-synaptic activity, due to the blockage of these receptors at low voltage. Previous studies show that under spike timing dependent plasticity (STDP protocols, potentiation at CA1 synapses requires post-synaptic bursting and an inter-pairing frequency in the range of the hippocampal theta rhythm. We hypothesize that these requirements reflect the saturation of the mechanisms of calcium extrusion from the post-synaptic spine. We test this hypothesis with a minimal model of NMDA receptor-dependent plasticity, simulating slow extrusion with a calcium-dependent calcium time constant. In simulations of STDP experiments, the model accounts for latency-dependent depression with either post-synaptic bursting or theta-frequency pairing (or neither and accounts for latency-dependent potentiation when both of these requirements are met. The model makes testable predictions for STDP experiments and our simple implementation is tractable at the network level, demonstrating associative learning in a biophysical network model with realistic synaptic dynamics.

  4. Network-timing-dependent plasticity

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    Vincent eDelattre

    2015-06-01

    Full Text Available Bursts of activity in networks of neurons are thought to convey salient information and drive synaptic plasticity. Here we report that network bursts also exert a profound effect on Spike-Timing-Dependent Plasticity (STDP. In acute slices of juvenile rat somatosensory cortex we paired a network burst, which alone induced long-term depression (LTD, with STDP-induced long-term potentiation and depression (LTP and LTD. We observed that STDP-induced LTP was either unaffected, blocked or flipped into LTD by the network burst, and that STDP-induced LTD was either saturated or flipped into LTP, depending on the relative timing of the network burst with respect to spike coincidences of the STDP event. We hypothesized that network bursts flip STDP-induced LTP to LTD by depleting resources needed for LTP and therefore developed a resource-dependent STDP learning rule. In a model neural network under the influence of the proposed resource-dependent STDP rule, we found that excitatory synaptic coupling was homeostatically regulated to produce power law distributed burst amplitudes reflecting self-organized criticality, a state that ensures optimal information coding.

  5. Network-timing-dependent plasticity.

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    Delattre, Vincent; Keller, Daniel; Perich, Matthew; Markram, Henry; Muller, Eilif B

    2015-01-01

    Bursts of activity in networks of neurons are thought to convey salient information and drive synaptic plasticity. Here we report that network bursts also exert a profound effect on Spike-Timing-Dependent Plasticity (STDP). In acute slices of juvenile rat somatosensory cortex we paired a network burst, which alone induced long-term depression (LTD), with STDP-induced long-term potentiation (LTP) and LTD. We observed that STDP-induced LTP was either unaffected, blocked or flipped into LTD by the network burst, and that STDP-induced LTD was either saturated or flipped into LTP, depending on the relative timing of the network burst with respect to spike coincidences of the STDP event. We hypothesized that network bursts flip STDP-induced LTP to LTD by depleting resources needed for LTP and therefore developed a resource-dependent STDP learning rule. In a model neural network under the influence of the proposed resource-dependent STDP rule, we found that excitatory synaptic coupling was homeostatically regulated to produce power law distributed burst amplitudes reflecting self-organized criticality, a state that ensures optimal information coding.

  6. Cerebellum to motor cortex paired associative stimulation induces bidirectional STDP-like plasticity in human motor cortex

    OpenAIRE

    Lu, Ming-Kuei; Tsai, Chon-Haw; Ziemann, Ulf

    2012-01-01

    The cerebellum is crucially important for motor control and adaptation. Recent non-invasive brain stimulation studies have indicated the possibility to alter the excitability of the cerebellum and its projections to the contralateral motor cortex, with behavioral consequences on motor control and adaptation. Here we sought to induce bidirectional spike-timing dependent plasticity (STDP)-like modifications of motor cortex (M1) excitability by application of paired associative stimulation (PAS)...

  7. STDP in the developing sensory neocortex

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    Rylan S Larsen

    2010-06-01

    Full Text Available Spike timing-dependent plasticity (STDP has been proposed as a mechanism for optimizing the tuning of neurons to sensory inputs, a process that underlies the formation of receptive field properties and associative memories. The properties of STDP must adjust during development to enable neurons to optimally tune their selectivity for environmental stimuli, but these changes are poorly understood. Here we review the properties of STDP and how these may change during development in primary sensory cortical layers 2/3 and 4, initial sites for intracortical processing. We provide a primer discussing postnatal developmental changes in synaptic proteins and neuromodulators that are thought to influence STDP induction and expression. We propose that STDP is shaped by, but also modifies, synapses to produce refinements in neuronal responses to sensory inputs.

  8. Self-organization in Balanced State Networks by STDP and Homeostatic Plasticity.

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    Felix Effenberger

    2015-09-01

    Full Text Available Structural inhomogeneities in synaptic efficacies have a strong impact on population response dynamics of cortical networks and are believed to play an important role in their functioning. However, little is known about how such inhomogeneities could evolve by means of synaptic plasticity. Here we present an adaptive model of a balanced neuronal network that combines two different types of plasticity, STDP and synaptic scaling. The plasticity rules yield both long-tailed distributions of synaptic weights and firing rates. Simultaneously, a highly connected subnetwork of driver neurons with strong synapses emerges. Coincident spiking activity of several driver cells can evoke population bursts and driver cells have similar dynamical properties as leader neurons found experimentally. Our model allows us to observe the delicate interplay between structural and dynamical properties of the emergent inhomogeneities. It is simple, robust to parameter changes and able to explain a multitude of different experimental findings in one basic network.

  9. Cerebellum to motor cortex paired associative stimulation induces bidirectional STDP-like plasticity in human motor cortex.

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    Lu, Ming-Kuei; Tsai, Chon-Haw; Ziemann, Ulf

    2012-01-01

    The cerebellum is crucially important for motor control and adaptation. Recent non-invasive brain stimulation studies have indicated the possibility to alter the excitability of the cerebellum and its projections to the contralateral motor cortex, with behavioral consequences on motor control and adaptation. Here we sought to induce bidirectional spike-timing dependent plasticity (STDP)-like modifications of motor cortex (M1) excitability by application of paired associative stimulation (PAS) in healthy subjects. Conditioning stimulation over the right lateral cerebellum (CB) preceded focal transcranial magnetic stimulation (TMS) of the left M1 hand area at an interstimulus interval of 2 ms (CB→M1 PAS(2 ms)), 6 ms (CB→M1 PAS(6 ms)) or 10 ms (CB→M1 PAS(10 ms)) or randomly alternating intervals of 2 and 10 ms (CB→M1 PAS(Control)). Effects of PAS on M1 excitability were assessed by the motor-evoked potential (MEP) amplitude, short-interval intracortical inhibition (SICI), intracortical facilitation (ICF) and cerebellar-motor cortex inhibition (CBI) in the first dorsal interosseous muscle of the right hand. CB→M1 PAS(2 ms) resulted in MEP potentiation, CB→M1 PAS(6 ms) and CB→M1 PAS(10 ms) in MEP depression, and CB→M1 PAS(Control) in no change. The MEP changes lasted for 30-60 min after PAS. SICI and CBI decreased non-specifically after all PAS protocols, while ICF remained unaltered. The physiological mechanisms underlying these MEP changes are carefully discussed. Findings support the notion of bidirectional STDP-like plasticity in M1 mediated by associative stimulation of the cerebello-dentato-thalamo-cortical pathway and M1. Future studies may investigate the behavioral significance of this plasticity.

  10. STDP in recurrent neuronal networks

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    Matthieu Gilson

    2010-09-01

    Full Text Available Recent results about spike-timing-dependent plasticity (STDP in recurrently connected neurons are reviewed, with a focus on the relationship between the weight dynamics and the emergence of network structure. In particular, the evolution of synaptic weights in the two cases of incoming connections for a single neuron and recurrent connections are compared and contrasted. A theoretical framework is used that is based upon Poisson neurons with a temporally inhomogeneous firing rate and the asymptotic distribution of weights generated by the learning dynamics. Different network configurations examined in recent studies are discussed and an overview of the current understanding of STDP in recurrently connected neuronal networks is presented.

  11. Two Coincidence Detectors for Spike Timing-Dependent Plasticity in Somatosensory Cortex

    OpenAIRE

    2006-01-01

    Many cortical synapses exhibit spike timing-dependent plasticity (STDP) in which the precise timing of presynaptic and postsynaptic spikes induces synaptic strengthening [long-term potentiation (LTP)] or weakening [long-term depression (LTD)]. Standard models posit a single, postsynaptic, NMDA receptor-based coincidence detector for LTP and LTD components of STDP. We show instead that STDP at layer 4 to layer 2/3 synapses in somatosensory (S1) cortex involves separate calcium sources and coin...

  12. Emergence of slow collective oscillations in neural networks with spike-timing dependent plasticity

    DEFF Research Database (Denmark)

    Mikkelsen, Kaare; Imparato, Alberto; Torcini, Alessandro

    2013-01-01

    The collective dynamics of excitatory pulse coupled neurons with spike timing dependent plasticity (STDP) is studied. The introduction of STDP induces persistent irregular oscillations between strongly and weakly synchronized states, reminiscent of brain activity during slow-wave sleep. We explain...

  13. Timing is not everything: neuromodulation opens the STDP gate

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    Verena Pawlak

    2010-10-01

    Full Text Available Spike timing dependent plasticity (STDP is a temporally specific extension of Hebbian associative plasticity that has tied together the timing of presynaptic inputs relative to the postsynaptic single spike. However, it is difficult to translate this mechanism to in vivo conditions where there is an abundance of presynaptic activity constantly impinging upon the dendritic tree as well as ongoing postsynaptic spiking activity that backpropagates along the dendrite. Theoretical studies have proposed that, in addition to this pre- and postsynaptic activity, a ‘third factor’ would enable the association of specific inputs to specific outputs. Experimentally, the picture that is beginning to emerge, is that in addition to the precise timing of pre- and postsynaptic spikes, this third factor involves neuromodulators that have a distinctive influence on STDP rules. Specifically, neuromodulatory systems can influence STDP rules by acting via dopaminergic, noradrenergic, muscarinic and nicotinic receptors. Neuromodulator actions can enable STDP induction or - by increasing or decreasing the threshold - can change the conditions for plasticity induction. Because some of the neuromodulators are also involved in reward, a link between STDP and reward-mediated learning is emerging. However, many outstanding questions concerning the relationship between neuromodulatory systems and STDP rules remain, that once solved, will help make the crucial link from timing-based synaptic plasticity rules to behaviorally-based learning.

  14. The effect of STDP temporal kernel structure on the learning dynamics of single excitatory and inhibitory synapses.

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    Yotam Luz

    Full Text Available Spike-Timing Dependent Plasticity (STDP is characterized by a wide range of temporal kernels. However, much of the theoretical work has focused on a specific kernel - the "temporally asymmetric Hebbian" learning rules. Previous studies linked excitatory STDP to positive feedback that can account for the emergence of response selectivity. Inhibitory plasticity was associated with negative feedback that can balance the excitatory and inhibitory inputs. Here we study the possible computational role of the temporal structure of the STDP. We represent the STDP as a superposition of two processes: potentiation and depression. This allows us to model a wide range of experimentally observed STDP kernels, from Hebbian to anti-Hebbian, by varying a single parameter. We investigate STDP dynamics of a single excitatory or inhibitory synapse in purely feed-forward architecture. We derive a mean-field-Fokker-Planck dynamics for the synaptic weight and analyze the effect of STDP structure on the fixed points of the mean field dynamics. We find a phase transition along the Hebbian to anti-Hebbian parameter from a phase that is characterized by a unimodal distribution of the synaptic weight, in which the STDP dynamics is governed by negative feedback, to a phase with positive feedback characterized by a bimodal distribution. The critical point of this transition depends on general properties of the STDP dynamics and not on the fine details. Namely, the dynamics is affected by the pre-post correlations only via a single number that quantifies its overlap with the STDP kernel. We find that by manipulating the STDP temporal kernel, negative feedback can be induced in excitatory synapses and positive feedback in inhibitory. Moreover, there is an exact symmetry between inhibitory and excitatory plasticity, i.e., for every STDP rule of inhibitory synapse there exists an STDP rule for excitatory synapse, such that their dynamics is identical.

  15. Effect of spike-timing-dependent plasticity on coherence resonance and synchronization transitions by time delay in adaptive neuronal networks

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    Xie, Huijuan; Gong, Yubing; Wang, Qi

    2016-06-01

    In this paper, we numerically study how time delay induces multiple coherence resonance (MCR) and synchronization transitions (ST) in adaptive Hodgkin-Huxley neuronal networks with spike-timing dependent plasticity (STDP). It is found that MCR induced by time delay STDP can be either enhanced or suppressed as the adjusting rate Ap of STDP changes, and ST by time delay varies with the increase of Ap, and there is optimal Ap by which the ST becomes strongest. It is also found that there are optimal network randomness and network size by which ST by time delay becomes strongest, and when Ap increases, the optimal network randomness and optimal network size increase and related ST is enhanced. These results show that STDP can either enhance or suppress MCR and optimal STDP can enhance ST induced by time delay in the adaptive neuronal networks. These findings provide a new insight into STDP's role for the information processing and transmission in neural systems.

  16. A history of spike-timing-dependent plasticity

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    Henry eMarkram

    2011-08-01

    Full Text Available How learning and memory is achieved in the brain is a central question in neuroscience research. Key to today’s research into information storage in the brain is the concept of synaptic plasticity, a notion that has been heavily influenced by Donald Hebb’s 1949 postulate. Hebb conjectured that repeatedly and persistently coactive cells should increase connective strength among populations of interconnected neurons as a means of storing a memory trace, also known as an engram. Hebb certainly was not the first to make such a conjecture, as we show in this history. Nevertheless, literally thousands of studies into the classical frequency-dependent paradigm of cellular learning rules were directly inspired by the Hebbian postulate. But in more recent years, a novel concept in cellular learning has emerged, where temporal order instead of frequency is emphasized. This new learning paradigm — known as Spike-Timing-Dependent Plasticity, or STDP — has rapidly gained tremendous interest, perhaps because of its combination of elegant simplicity, biological plausibility, and computational power. But what are the roots of today’s STDP concept? Here, we discuss several centuries of diverse thinking, beginning with philosophers such as Aristotle, Locke and Ribot, traversing e.g. Lugaro’s plasticità and Rosenblatt’s Perceptron, and culminating with the discovery of STDP. We highlight interactions between theoretical and experimental fields, showing how discoveries sometimes occurred in parallel, seemingly without much knowledge of the other field, and sometimes via concrete back-and-forth communication. We point out where the future directions may lie, which includes interneuron STDP, the functional impact of STDP, its mechanisms and its neuromodulatory regulation, and the linking of STDP to the developmental formation and continuous plasticity of neuronal networks.

  17. STDP in adaptive neurons gives close-to-optimal information transmission

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    Guillaume Hennequin

    2010-12-01

    Full Text Available Spike-frequency adaptation is known to enhance the transmission of information in sensory spiking neurons, by rescaling the dynamic range for input processing, matching it to the temporal statistics of the sensory stimulus. Achieving maximal information transmission has also been recently postulated as a role for Spike-Timing Dependent Plasticity (STDP. However, the link between optimal plasticity and STDP in cortex remains loose, and so does the relationship between STDP and adaptation processes. We investigate how STDP, as described by recent minimal models derived from experimental data, influences the quality of information transmission in an adapting neuron. We show that a phenomenological model based on triplets of spikes yields almost the same information rate as an optimal model specially designed to this end. In contrast, the standard pair-based model of STDP does not improve information transmission as much. This result holds not only for additive STDP with hard weight bounds, known to produce bimodal distributions of synaptic weights, but also for weight-dependent STDP in the context of unimodal but skewed weight distributions. We analyze the similarities between the triplet model and the optimal learning rule, and find that the triplet effect is an important feature of the optimal model when the neuron is adaptive. If STDP is optimized for information transmission, it must take into account the dynamical properties of the postsynaptic cell, which might explain the target-cell specificity of STDP. In particular, it accounts for the differences found in vitro between STDP at excitatory synapses onto principal cells and those onto fast-spiking interneurons.

  18. GABAergic synaptic transmission regulates calcium influx during spike-timing dependent plasticity

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    Trevor Balena

    2010-06-01

    Full Text Available Coincident pre- and postsynaptic activity of hippocampal neurons alters the strength of gamma-aminobutyric acid (GABAA-mediated inhibition through a Ca2+-dependent regulation of cation-chloride cotransporters. This long-term synaptic modulation is termed GABAergic spike-timing dependent plasticity (STDP. In the present study, we examined whether the properties of the GABAergic synapses themselves modulate the required postsynaptic Ca2+ influx during GABAergic STDP induction. To do this we first identified GABAergic synapses between cultured hippocampal neurons based on their relatively long decay time constants and their reversal potentials which lay close to the resting membrane potential. GABAergic STDP was then induced by coincidentally (± 1 ms firing the pre- and postsynaptic neurons at 5 Hz for 30 seconds, while postsynaptic Ca2+ was imaged with the Ca2+-sensitive fluorescent dye Fluo4-AM. In all cases, the induction of GABAergic STDP increased postsynaptic Ca2+ above resting levels. We further found that the magnitude of this increase correlated with the amplitude and polarity of the GABAergic postsynaptic current (GPSC; hyperpolarizing GPSCs reduced the Ca2+ influx in comparison to both depolarizing GPSCs, and postsynaptic neurons spiked alone. This relationship was influenced by both the driving force for Cl- and GABAA conductance (which had positive correlations with the Ca2+ influx. The spike-timing order during STDP induction did not influence the correlation between GPSC amplitude and Ca2+ influx, which is likely accounted for by the symmetrical GABAergic STDP window.

  19. Spike-timing dependent plasticity and the cognitive map

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    Daniel eBush

    2010-10-01

    Full Text Available Since the discovery of place cells – single pyramidal neurons that encode spatial location – it has been hypothesised that the hippocampus may act as a cognitive map of known environments. This putative function has been extensively modelled using auto-associative networks, which utilise rate-coded synaptic plasticity rules in order to generate strong bi-directional connections between concurrently active place cells that encode for neighbouring place fields. However, empirical studies using hippocampal cultures have demonstrated that the magnitude and direction of changes in synaptic strength can also be dictated by the relative timing of pre- and post- synaptic firing according to a spike-timing dependent plasticity (STDP rule. Furthermore, electrophysiology studies have identified persistent ‘theta-coded’ temporal correlations in place cell activity in vivo, characterised by phase precession of firing as the corresponding place field is traversed. It is not yet clear if STDP and theta-coded neural dynamics are compatible with cognitive map theory and previous rate-coded models of spatial learning in the hippocampus. Here, we demonstrate that an STDP rule based on empirical data obtained from the hippocampus can mediate rate-coded Hebbian learning when pre- and post- synaptic activity is stochastic and has no persistent sequence bias. We subsequently demonstrate that a spiking recurrent neural network that utilises this STDP rule, alongside theta-coded neural activity, allows the rapid development of a cognitive map during directed or random exploration of an environment of overlapping place fields. Hence, we establish that STDP and phase precession are compatible with rate-coded models of cognitive map development.

  20. Refinement and Pattern Formation in Neural Circuits by the Interaction of Traveling Waves with Spike-Timing Dependent Plasticity

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    Bennett, James E. M.; Bair, Wyeth

    2015-01-01

    Traveling waves in the developing brain are a prominent source of highly correlated spiking activity that may instruct the refinement of neural circuits. A candidate mechanism for mediating such refinement is spike-timing dependent plasticity (STDP), which translates correlated activity patterns into changes in synaptic strength. To assess the potential of these phenomena to build useful structure in developing neural circuits, we examined the interaction of wave activity with STDP rules in simple, biologically plausible models of spiking neurons. We derive an expression for the synaptic strength dynamics showing that, by mapping the time dependence of STDP into spatial interactions, traveling waves can build periodic synaptic connectivity patterns into feedforward circuits with a broad class of experimentally observed STDP rules. The spatial scale of the connectivity patterns increases with wave speed and STDP time constants. We verify these results with simulations and demonstrate their robustness to likely sources of noise. We show how this pattern formation ability, which is analogous to solutions of reaction-diffusion systems that have been widely applied to biological pattern formation, can be harnessed to instruct the refinement of postsynaptic receptive fields. Our results hold for rich, complex wave patterns in two dimensions and over several orders of magnitude in wave speeds and STDP time constants, and they provide predictions that can be tested under existing experimental paradigms. Our model generalizes across brain areas and STDP rules, allowing broad application to the ubiquitous occurrence of traveling waves and to wave-like activity patterns induced by moving stimuli. PMID:26308406

  1. Plasticity resembling spike-timing dependent synaptic plasticity: the evidence in human cortex

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    Florian Müller-Dahlhaus

    2010-07-01

    Full Text Available Spike-timing dependent plasticity (STDP has been studied extensively in a variety of animal models during the past decade but whether it can be studied at the systems level of the human cortex has been a matter of debate. Only recently newly developed non-invasive brain stimulation techniques such as transcranial magnetic stimulation (TMS have made it possible to induce and assess timing dependent plasticity in conscious human subjects. This review will present a critical synopsis of these experiments, which suggest that several of the principal characteristics and molecular mechanisms of TMS-induced plasticity correspond to those of STDP as studied at a cellular level. TMS combined with a second phasic stimulation modality can induce bidirectional long-lasting changes in the excitability of the stimulated cortex, whose polarity depends on the order of the associated stimulus-evoked events within a critical time window of tens of milliseconds. Pharmacological evidence suggests an NMDA receptor mediated form of synaptic plasticity. Studies in human motor cortex demonstrated that motor learning significantly modulates TMS-induced timing dependent plasticity, and, conversely, may be modulated bidirectionally by prior TMS-induced plasticity, providing circumstantial evidence that long-term potentiation-like mechanisms may be involved in motor learning. In summary, convergent evidence is being accumulated for the contention that it is now possible to induce STDP-like changes in the intact human central nervous system by means of TMS to study and interfere with synaptic plasticity in neural circuits in the context of behaviour such as learning and memory.

  2. Generalized Volterra kernel model identification of spike-timing-dependent plasticity from simulated spiking activity.

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    Robinson, Brian S; Song, Dong; Berger, Theodore W

    2014-01-01

    This paper presents a methodology to estimate a learning rule that governs activity-dependent plasticity from behaviorally recorded spiking events. To demonstrate this framework, we simulate a probabilistic spiking neuron with spike-timing-dependent plasticity (STDP) and estimate all model parameters from the simulated spiking data. In the neuron model, output spiking activity is generated by the combination of noise, feedback from the output, and an input-feedforward component whose magnitude is modulated by synaptic weight. The synaptic weight is calculated with STDP with the following features: (1) weight change based on the relative timing of input-output spike pairs, (2) prolonged plasticity induction, and (3) considerations for system stability. Estimation of all model parameters is achieved iteratively by formulating the model as a generalized linear model with Volterra kernels and basis function expansion. Successful estimation of all model parameters in this study demonstrates the feasibility of this approach for in-vivo experimental studies. Furthermore, the consideration of system stability and prolonged plasticity induction enhances the ability to capture how STDP affects a neural population's signal transformation properties over a realistic time course. Plasticity characterization with this estimation method could yield insights into functional implications of STDP and be incorporated into a cortical prosthesis.

  3. Dopamine regulates intrinsic excitability thereby gating successful induction of spike timing-dependent plasticity in CA1 of the hippocampus.

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    Edelmann, Elke; Lessmann, Volkmar

    2013-01-01

    Long-term potentiation (LTP) and long-term depression (LTD) are generally assumed to be cellular correlates for learning and memory. Different types of LTP induction protocols differing in severity of stimulation can be distinguished in CA1 of the hippocampus. To better understand signaling mechanisms and involvement of neuromodulators such as dopamine (DA) in synaptic plasticity, less severe and more physiological low frequency induction protocols should be used. In the study which is reviewed here, critical determinants of spike timing-dependent plasticity (STDP) at hippocampal CA3-CA1 synapses were investigated. We found that DA via D1 receptor signaling, but not adrenergic signaling activated by the β-adrenergic agonist isoproterenol, is important for successful expression of STDP at CA3-CA1 synapses. The DA effect on STDP is paralleled by changes in spike firing properties, thereby changing intrinsic excitability of postsynaptic CA1 neurons, and gating STDP. Whereas β-adrenergic signaling also leads to a similar (but not identical) regulation of firing pattern, it does not enable STDP. In this focused review we will discuss the current literature on dopaminergic modulation of LTP in CA1, with a special focus on timing dependent (t-)LTP, and we will suggest possible reasons for the selective gating of STDP by DA [but not noradrenaline (NA)] in CA1.

  4. Spike-timing-dependent plasticity enhanced synchronization transitions induced by autapses in adaptive Newman-Watts neuronal networks.

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    Gong, Yubing; Wang, Baoying; Xie, Huijuan

    2016-12-01

    In this paper, we numerically study the effect of spike-timing-dependent plasticity (STDP) on synchronization transitions induced by autaptic activity in adaptive Newman-Watts Hodgkin-Huxley neuron networks. It is found that synchronization transitions induced by autaptic delay vary with the adjusting rate Ap of STDP and become strongest at a certain Ap value, and the Ap value increases when network randomness or network size increases. It is also found that the synchronization transitions induced by autaptic delay become strongest at a certain network randomness and network size, and the values increase and related synchronization transitions are enhanced when Ap increases. These results show that there is optimal STDP that can enhance the synchronization transitions induced by autaptic delay in the adaptive neuronal networks. These findings provide a new insight into the roles of STDP and autapses for the information transmission in neural systems. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  5. The Characteristics of Binary Spike-Time-Dependent Plasticity in HfO2-Based RRAM and Applications for Pattern Recognition

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    Zhou, Zheng; Liu, Chen; Shen, Wensheng; Dong, Zhen; Chen, Zhe; Huang, Peng; Liu, Lifeng; Liu, Xiaoyan; Kang, Jinfeng

    2017-04-01

    A binary spike-time-dependent plasticity (STDP) protocol based on one resistive-switching random access memory (RRAM) device was proposed and experimentally demonstrated in the fabricated RRAM array. Based on the STDP protocol, a novel unsupervised online pattern recognition system including RRAM synapses and CMOS neurons is developed. Our simulations show that the system can efficiently compete the handwritten digits recognition task, which indicates the feasibility of using the RRAM-based binary STDP protocol in neuromorphic computing systems to obtain good performance.

  6. Self-Adaptive Spike-Time-Dependent Plasticity of Metal-Oxide Memristors

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    Prezioso, M.; Merrikh Bayat, F.; Hoskins, B.; Likharev, K.; Strukov, D.

    2016-02-01

    Metal-oxide memristors have emerged as promising candidates for hardware implementation of artificial synapses - the key components of high-performance, analog neuromorphic networks - due to their excellent scaling prospects. Since some advanced cognitive tasks require spiking neuromorphic networks, which explicitly model individual neural pulses (“spikes”) in biological neural systems, it is crucial for memristive synapses to support the spike-time-dependent plasticity (STDP). A major challenge for the STDP implementation is that, in contrast to some simplistic models of the plasticity, the elementary change of a synaptic weight in an artificial hardware synapse depends not only on the pre-synaptic and post-synaptic signals, but also on the initial weight (memristor’s conductance) value. Here we experimentally demonstrate, for the first time, an STDP behavior that ensures self-adaptation of the average memristor conductance, making the plasticity stable, i.e. insensitive to the initial state of the devices. The experiments have been carried out with 200-nm Al2O3/TiO2-x memristors integrated into 12 × 12 crossbars. The experimentally observed self-adaptive STDP behavior has been complemented with numerical modeling of weight dynamics in a simple system with a leaky-integrate-and-fire neuron with a random spike-train input, using a compact model of memristor plasticity, fitted for quantitatively correct description of our memristors.

  7. Spike-Timing–Dependent Synaptic Plasticity and Synaptic Democracy in Dendrites

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    Gidon, Albert; Segev, Idan

    2009-01-01

    We explored in a computational study the effect of dendrites on excitatory synapses undergoing spike-timing–dependent plasticity (STDP), using both cylindrical dendritic models and reconstructed dendritic trees. We show that even if the initial strength, gpeak, of distal synapses is augmented in a location independent manner, the efficacy of distal synapses diminishes following STDP and proximal synapses would eventually dominate. Indeed, proximal synapses always win over distal synapses following linear STDP rule, independent of the initial synaptic strength distribution in the dendritic tree. This effect is more pronounced as the dendritic cable length increases but it does not depend on the dendritic branching structure. Adding a small multiplicative component to the linear STDP rule, whereby already strong synapses tend to be less potentiated than depressed (and vice versa for weak synapses) did partially “save” distal synapses from “dying out.” Another successful strategy for balancing the efficacy of distal and proximal synapses following STDP is to increase the upper bound for the synaptic conductance (gmax) with distance from the soma. We conclude by discussing an experiment for assessing which of these possible strategies might actually operate in dendrites. PMID:19357339

  8. Spike-timing-dependent synaptic plasticity and synaptic democracy in dendrites.

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    Gidon, Albert; Segev, Idan

    2009-06-01

    We explored in a computational study the effect of dendrites on excitatory synapses undergoing spike-timing-dependent plasticity (STDP), using both cylindrical dendritic models and reconstructed dendritic trees. We show that even if the initial strength, g(peak), of distal synapses is augmented in a location independent manner, the efficacy of distal synapses diminishes following STDP and proximal synapses would eventually dominate. Indeed, proximal synapses always win over distal synapses following linear STDP rule, independent of the initial synaptic strength distribution in the dendritic tree. This effect is more pronounced as the dendritic cable length increases but it does not depend on the dendritic branching structure. Adding a small multiplicative component to the linear STDP rule, whereby already strong synapses tend to be less potentiated than depressed (and vice versa for weak synapses) did partially "save" distal synapses from "dying out." Another successful strategy for balancing the efficacy of distal and proximal synapses following STDP is to increase the upper bound for the synaptic conductance (g(max)) with distance from the soma. We conclude by discussing an experiment for assessing which of these possible strategies might actually operate in dendrites.

  9. Linking Neuromodulated Spike-Timing Dependent Plasticity with the Free-Energy Principle.

    Science.gov (United States)

    Isomura, Takuya; Sakai, Koji; Kotani, Kiyoshi; Jimbo, Yasuhiko

    2016-09-01

    The free-energy principle is a candidate unified theory for learning and memory in the brain that predicts that neurons, synapses, and neuromodulators work in a manner that minimizes free energy. However, electrophysiological data elucidating the neural and synaptic bases for this theory are lacking. Here, we propose a novel theory bridging the information-theoretical principle with the biological phenomenon of spike-timing dependent plasticity (STDP) regulated by neuromodulators, which we term mSTDP. We propose that by integrating an mSTDP equation, we can obtain a form of Friston's free energy (an information-theoretical function). Then we analytically and numerically show that dopamine (DA) and noradrenaline (NA) influence the accuracy of a principal component analysis (PCA) performed using the mSTDP algorithm. From the perspective of free-energy minimization, these neuromodulatory changes alter the relative weighting or precision of accuracy and prior terms, which induces a switch from pattern completion to separation. These results are consistent with electrophysiological findings and validate the free-energy principle and mSTDP. Moreover, our scheme can potentially be applied in computational psychiatry to build models of the faulty neural networks that underlie the positive symptoms of schizophrenia, which involve abnormal DA levels, as well as models of the NA contribution to memory triage and posttraumatic stress disorder.

  10. A developmental sensitive period for spike timing-dependent plasticity in the retinotectal projection

    Directory of Open Access Journals (Sweden)

    Jennifer Tsui

    2010-06-01

    Full Text Available The retinotectal projection in Xenopus laevis has been shown to exhibit correlation-based refinement of both anatomical and functional connectivity during development. Spike timing-dependent plasticity (STDP is an appealing experimental model for correlation-based synaptic plasticity because, in contrast to plasticity induction paradigms using tetanic stimulation or sustained postsynaptic depolarization, its induction protocol more closely resembles natural physiological activity. In Xenopus tadpoles, where anatomical remodeling has been reported throughout much of the life of the animal, in vivo retinotectal STDP has only been examined under a limited set of experimental conditions. Using perforated patch recordings of retina-evoked EPSCs in tectal neurons, we confirmed that repeatedly driving a retinotectal EPSP 5-10 ms prior to inducing an action potential in the postsynaptic cell, reliably produced timing-dependent long-term potentiation (t-LTP of the retinotectal synapse in young wild type tadpoles (stages 41-44. At these stages, retinotectal timing-dependent long-term depression (t-LTD also could be induced by evoking an EPSP to arrive 5-10 ms after an action potential in the tectal cell. However, retinotectal STDP using this standard protocol was limited to a developmental sensitive period, as we were unable to induce t-LTP or t-LTD after stage 44. Surprisingly, this STDP protocol also failed to induce reliable STDP in albino tadpoles at the early ages when it was effective in wild type pigmented animals. Nonetheless, low-frequency flashes to the eye produced a robust NMDA receptor-dependent retinotectal LTD in stage 47 albino tadpoles, demonstrating that the retinotectal synapse can nonetheless be modified in these animals using different plasticity paradigms.

  11. Effect of Spike-Timing-Dependent Plasticity on Intrinsic Coherence Resonance in Newman-Watts Stochastic Hodgkin-Huxley Neuronal Networks

    Science.gov (United States)

    Xie, Huijuan; Gong, Yubing; Wang, Qi

    2016-07-01

    In this paper, we numerically study the effect of spike-timing-dependent plasticity (STDP) on coherence resonance (CR) induced by channel noise in adaptive Newman-Watts stochastic Hodgkin-Huxley neuron networks. It is found that STDP can either enhance or suppress the intrinsic CR when the adjusting rate of STDP decreases or increases. STDP can alter the effects of network randomness and network size on the intrinsic CR. Under STDP, for electrical coupling there are optimal network randomness and network size by which the intrinsic CR becomes strongest, however, for chemical coupling the intrinsic CR is always enhanced as network randomness or network size increases, which are different from the results for fixed coupling. These results show that the intrinsic CR of the neuronal networks can be either enhanced or suppressed by STDP, and there are optimal network randomness and network size by which the intrinsic CR becomes strongest. These findings could provide a new insight into the role of STDP for the information processing and transmission in neural systems.

  12. Dynamic clamp with StdpC software.

    Science.gov (United States)

    Kemenes, Ildikó; Marra, Vincenzo; Crossley, Michael; Samu, Dávid; Staras, Kevin; Kemenes, György; Nowotny, Thomas

    2011-03-01

    Dynamic clamp is a powerful method that allows the introduction of artificial electrical components into target cells to simulate ionic conductances and synaptic inputs. This method is based on a fast cycle of measuring the membrane potential of a cell, calculating the current of a desired simulated component using an appropriate model and injecting this current into the cell. Here we present a dynamic clamp protocol using free, fully integrated, open-source software (StdpC, for spike timing-dependent plasticity clamp). Use of this protocol does not require specialist hardware, costly commercial software, experience in real-time operating systems or a strong programming background. The software enables the configuration and operation of a wide range of complex and fully automated dynamic clamp experiments through an intuitive and powerful interface with a minimal initial lead time of a few hours. After initial configuration, experimental results can be generated within minutes of establishing cell recording.

  13. Spike timing dependent plasticity: a consequence of more fundamental learning rules

    Directory of Open Access Journals (Sweden)

    Harel Z Shouval

    2010-07-01

    Full Text Available Spike timing dependent plasticity (STDP is a phenomenon in which the precise timing of spikes affects the sign and magnitude of changes in synaptic strength. STDP is often interpreted as the comprehensive learning rule for a synapse - the “first law” of synaptic plasticity. This interpretation is made explicit in theoretical models in which the total plasticity produced by complex spike patterns results from a superposition of the effects of all spike pairs. Although such models are appealing for their simplicity, they can fail dramatically. For example, the measured single-spike learning rule between hippocampal CA3 and CA1 pyramidal neurons does not predict the existence of long-term potentiation. Layers of complexity have been added to the basic STDP model to repair predictive failures, but they have been outstripped by experimental data. We propose an alternate first law: neural activity triggers changes in key biochemical intermediates, which act as a more direct trigger of plasticity mechanisms. One particularly successful model uses intracellular calcium as the intermediate and can account for many observed properties of bidirectional plasticity. In this formulation, STDP is not itself the basis for explaining other forms of plasticity, but is instead a consequence of changes in the biochemical intermediate, calcium. Eventually a mechanism-based framework for learning rules should include other messengers, discrete change at individual synapses, spread of plasticity among neighboring synapses, and priming of hidden processes that change a synapse’s susceptibility to future change. Mechanism-based models provide a rich framework for the computational representation of synaptic plasticity.

  14. Laguerre-Volterra identification of spike-timing-dependent plasticity from spiking activity: a simulation study.

    Science.gov (United States)

    Robinson, Brian S; Song, Dong; Berger, Theodore W

    2013-01-01

    This paper presents a Laguerre-Volterra methodology for identifying a plasticity learning rule from spiking neural data with four components: 1) By analyzing input-output spiking data, the effective contribution of an input on the output firing probability can be quantified with weighted Volterra kernels. 2) The weight of these Volterra kernels can be tracked over time using the stochastic state point processing filtering algorithm (SSPPF) 3) Plasticity system Volterra kernels can be estimated by treating the tracked change in weight over time as the plasticity system output and the spike timing data as the input. 4) Laguerre expansion of all Volterra kernels allows for minimization of open parameters during estimation steps. A single input spiking neuron with Spike-timing-dependent plasticity (STDP) and prolonged STDP induction is simulated. Using the spiking data from this simulation, the amplitude of the STDP learning rule and the time course of the induction is accurately estimated. This framework can be applied to identify plasticity for more complicated plasticity paradigms and is applicable to in vivo data.

  15. STDP and STDP Variations with Memristors for Spiking Neuromorphic Learning Systems

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    Teresa eSerrano-Gotarredona

    2013-02-01

    Full Text Available In this paper we review several ways of realizing asynchronous Spike-Timing Dependent Plasticity (STDP using memristors as synapses. Our focus is on how to use individual memristors to implement synaptic weight multiplications, in a way such that it is not necessary to (a introduce global synchronization and (b to separate memristor learning phases from memristor performing phases. In the approaches described, neurons fire spikes asynchronously when they wish and memristive synapses perform computation and learn at their own pace, as it happens in biological neural systems. We distinguish between two different memristor physics, depending on whether they respond to the original ``moving wall'' or to the ``filament creation and annihilation'' models. Independent of the memristor physics, we discuss two different types of STDP rules that can be implemented with memristors: either the pure timing-based rule that takes into account the arrival time of the spikes from the pre- and the post-synaptic neurons, or a hybrid rule that takes into account only the timing of pre-synaptic spikes and the membrane potential and other state variables of the post-synaptic neuron. We show how to implement these rules in cross-bar architectures that comprise massive arrays of memristors, and we discuss applications for artificial vision.

  16. Comparison and Regulation of Neuronal Synchronization for Various STDP Rules

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    Yanhua Ruan

    2009-01-01

    Full Text Available We discuss effects of various experimentally supported STDP learning rules on frequency synchronization of two unidirectional coupled neurons systematically. First, we show that synchronization windows for all STDP rules cannot be enhanced compared to constant connection under the same model. Then, we explore the influence of learning parameters on synchronization window and find optimal parameters that lead to the widest window. Our findings indicate that synchronization strongly depends on the specific shape and the parameters of the STDP update rules. Thus, we give some explanations by analyzing the synchronization mechanisms for various STDP rules finally.

  17. Inhibitory and Excitatory Spike-Timing-Dependent Plasticity in the Auditory Cortex

    Science.gov (United States)

    D'amour, James A.; Froemke, Robert C.

    2015-01-01

    Summary Synapses are plastic and can be modified by changes of spike timing. While most studies of long-term synaptic plasticity focus on excitation, inhibitory plasticity may be critical for controlling information processing, memory storage, and overall excitability in neural circuits. Here we examine spike-timing-dependent plasticity (STDP) of inhibitory synapses onto layer 5 neurons in slices of mouse auditory cortex, together with concomitant STDP of excitatory synapses. Pairing pre- and postsynaptic spikes potentiated inhibitory inputs irrespective of precise temporal order within ~10 msec. This was in contrast to excitatory inputs, which displayed an asymmetrical STDP time window. These combined synaptic modifications both required NMDA receptor activation, and adjusted the excitatory-inhibitory ratio of events paired together with postsynaptic spiking. Finally, subthreshold events became suprathreshold, and the time window between excitation and inhibition became more precise. These findings demonstrate that cortical inhibitory plasticity requires interactions with co-activated excitatory synapses to properly regulate excitatory-inhibitory balance. PMID:25843405

  18. Oscillation-Driven Spike-Timing Dependent Plasticity Allows Multiple Overlapping Pattern Recognition in Inhibitory Interneuron Networks

    DEFF Research Database (Denmark)

    Garrido, Jesús A.; Luque, Niceto R.; Tolu, Silvia

    2016-01-01

    understood. Here, we have used a simple model of afferent excitatory neurons and interneurons with lateral inhibition, reproducing a network topology found in many brain areas from the cerebellum to cortical columns. When endowed with spike-timing dependent plasticity (STDP) at the excitatory input synapses...... and at the inhibitory interneuron-interneuron synapses, the interneurons rapidly learned complex input patterns. Interestingly, induction of plasticity required that the network be entrained into theta-frequency band oscillations, setting the internal phase-reference required to drive STDP. Inhibitory plasticity...... patterns. The combination of plasticity in lateral inhibitory connections and homeostatic mechanisms in the inhibitory interneurons optimized mutual information (MI) transfer. The storage of multiple complex patterns in plastic interneuron networks could be critical for the generation of sparse...

  19. Spike-timing dependent plasticity in the striatum

    Directory of Open Access Journals (Sweden)

    Elodie Fino

    2010-06-01

    Full Text Available The striatum is the major input nucleus of basal ganglia, an ensemble of interconnected sub-cortical nuclei associated with fundamental processes of action-selection and procedural learning and memory. The striatum receives afferents from the cerebral cortex and the thalamus. In turn, it relays the integrated information towards the basal ganglia output nuclei through which it operates a selected activation of behavioral effectors. The striatal output neurons, the GABAergic medium-sized spiny neurons (MSNs, are in charge of the detection and integration of behaviorally relevant information. This property confers to the striatum the ability to extract relevant information from the background noise and select cognitive-motor sequences adapted to environmental stimuli. As long-term synaptic efficacy changes are believed to underlie learning and memory, the corticostriatal long-term plasticity provides a fundamental mechanism for the function of the basal ganglia in procedural learning. Here, we reviewed the different forms of spike-timing dependent plasticity (STDP occurring at corticostriatal synapses. Most of the studies have focused on MSNs and their ability to develop long-term plasticity. Nevertheless, the striatal interneurons (the fast-spiking GABAergic, the NO synthase and cholinergic interneurons also receive monosynaptic afferents from the cortex and tightly regulated corticostriatal information processing. Therefore, it is important to take into account the variety of striatal neurons to fully understand the ability of striatum to develop long-term plasticity. Corticostriatal STDP with various spike-timing dependence have been observed depending on the neuronal sub-populations and experimental conditions. This complexity highlights the extraordinary potentiality in term of plasticity of the corticostriatal pathway.

  20. Spike timing dependent plasticity finds the start of repeating patterns in continuous spike trains.

    Directory of Open Access Journals (Sweden)

    Timothée Masquelier

    Full Text Available Experimental studies have observed Long Term synaptic Potentiation (LTP when a presynaptic neuron fires shortly before a postsynaptic neuron, and Long Term Depression (LTD when the presynaptic neuron fires shortly after, a phenomenon known as Spike Timing Dependent Plasticity (STDP. When a neuron is presented successively with discrete volleys of input spikes STDP has been shown to learn 'early spike patterns', that is to concentrate synaptic weights on afferents that consistently fire early, with the result that the postsynaptic spike latency decreases, until it reaches a minimal and stable value. Here, we show that these results still stand in a continuous regime where afferents fire continuously with a constant population rate. As such, STDP is able to solve a very difficult computational problem: to localize a repeating spatio-temporal spike pattern embedded in equally dense 'distractor' spike trains. STDP thus enables some form of temporal coding, even in the absence of an explicit time reference. Given that the mechanism exposed here is simple and cheap it is hard to believe that the brain did not evolve to use it.

  1. Mirrored STDP Implements Autoencoder Learning in a Network of Spiking Neurons.

    Science.gov (United States)

    Burbank, Kendra S

    2015-12-01

    The autoencoder algorithm is a simple but powerful unsupervised method for training neural networks. Autoencoder networks can learn sparse distributed codes similar to those seen in cortical sensory areas such as visual area V1, but they can also be stacked to learn increasingly abstract representations. Several computational neuroscience models of sensory areas, including Olshausen & Field's Sparse Coding algorithm, can be seen as autoencoder variants, and autoencoders have seen extensive use in the machine learning community. Despite their power and versatility, autoencoders have been difficult to implement in a biologically realistic fashion. The challenges include their need to calculate differences between two neuronal activities and their requirement for learning rules which lead to identical changes at feedforward and feedback connections. Here, we study a biologically realistic network of integrate-and-fire neurons with anatomical connectivity and synaptic plasticity that closely matches that observed in cortical sensory areas. Our choice of synaptic plasticity rules is inspired by recent experimental and theoretical results suggesting that learning at feedback connections may have a different form from learning at feedforward connections, and our results depend critically on this novel choice of plasticity rules. Specifically, we propose that plasticity rules at feedforward versus feedback connections are temporally opposed versions of spike-timing dependent plasticity (STDP), leading to a symmetric combined rule we call Mirrored STDP (mSTDP). We show that with mSTDP, our network follows a learning rule that approximately minimizes an autoencoder loss function. When trained with whitened natural image patches, the learned synaptic weights resemble the receptive fields seen in V1. Our results use realistic synaptic plasticity rules to show that the powerful autoencoder learning algorithm could be within the reach of real biological networks.

  2. Interaction of inhibition and triplets of excitatory spikes modulates the NMDA-R-mediated synaptic plasticity in a computational model of spike timing-dependent plasticity.

    Science.gov (United States)

    Cutsuridis, Vassilis

    2013-01-01

    Spike timing-dependent plasticity (STDP) experiments have shown that a synapse is strengthened when a presynaptic spike precedes a postsynaptic one and depressed vice versa. The canonical form of STDP has been shown to have an asymmetric shape with the peak long-term potentiation at +6 ms and the peak long-term depression at -5 ms. Experiments in hippocampal cultures with more complex stimuli such as triplets (one presynaptic spike combined with two postsynaptic spikes or one postsynaptic spike with two presynaptic spikes) have shown that pre-post-pre spike triplets result in no change in synaptic strength, whereas post-pre-post spike triplets lead to significant potentiation. The sign and magnitude of STDP have also been experimentally hypothesized to be modulated by inhibition. Recently, a computational study showed that the asymmetrical form of STDP in the CA1 pyramidal cell dendrite when two spikes interact switches to a symmetrical one in the presence of inhibition under certain conditions. In the present study, I investigate computationally how inhibition modulates STDP in the CA1 pyramidal neuron dendrite when it is driven by triplets. The model uses calcium as the postsynaptic signaling agent for STDP and is shown to be consistent with the experimental triplet observations in the absence of inhibition: simulated pre-post-pre spike triplets result in no change in synaptic strength, whereas simulated post-pre-post spike triplets lead to significant potentiation. When inhibition is bounded by the onset and offset of the triplet stimulation, then the strength of the synapse is decreased as the strength of inhibition increases. When inhibition arrives either few milliseconds before or at the onset of the last spike in the pre-post-pre triplet stimulation, then the synapse is potentiated. Variability in the frequency of inhibition (50 vs. 100 Hz) produces no change in synaptic strength. Finally, a 5% variation in model's calcium parameters (calcium thresholds

  3. Oscillations, phase-of-firing coding, and spike timing-dependent plasticity: an efficient learning scheme.

    Science.gov (United States)

    Masquelier, Timothée; Hugues, Etienne; Deco, Gustavo; Thorpe, Simon J

    2009-10-28

    Recent experiments have established that information can be encoded in the spike times of neurons relative to the phase of a background oscillation in the local field potential-a phenomenon referred to as "phase-of-firing coding" (PoFC). These firing phase preferences could result from combining an oscillation in the input current with a stimulus-dependent static component that would produce the variations in preferred phase, but it remains unclear whether these phases are an epiphenomenon or really affect neuronal interactions-only then could they have a functional role. Here we show that PoFC has a major impact on downstream learning and decoding with the now well established spike timing-dependent plasticity (STDP). To be precise, we demonstrate with simulations how a single neuron equipped with STDP robustly detects a pattern of input currents automatically encoded in the phases of a subset of its afferents, and repeating at random intervals. Remarkably, learning is possible even when only a small fraction of the afferents ( approximately 10%) exhibits PoFC. The ability of STDP to detect repeating patterns had been noted before in continuous activity, but it turns out that oscillations greatly facilitate learning. A benchmark with more conventional rate-based codes demonstrates the superiority of oscillations and PoFC for both STDP-based learning and the speed of decoding: the oscillation partially formats the input spike times, so that they mainly depend on the current input currents, and can be efficiently learned by STDP and then recognized in just one oscillation cycle. This suggests a major functional role for oscillatory brain activity that has been widely reported experimentally.

  4. Oscillations via Spike-Timing Dependent Plasticity in a Feed-Forward Model.

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    Yotam Luz

    2016-04-01

    Full Text Available Neuronal oscillatory activity has been reported in relation to a wide range of cognitive processes including the encoding of external stimuli, attention, and learning. Although the specific role of these oscillations has yet to be determined, it is clear that neuronal oscillations are abundant in the central nervous system. This raises the question of the origin of these oscillations: are the mechanisms for generating these oscillations genetically hard-wired or can they be acquired via a learning process? Here, we study the conditions under which oscillatory activity emerges through a process of spike timing dependent plasticity (STDP in a feed-forward architecture. First, we analyze the effect of oscillations on STDP-driven synaptic dynamics of a single synapse, and study how the parameters that characterize the STDP rule and the oscillations affect the resultant synaptic weight. Next, we analyze STDP-driven synaptic dynamics of a pre-synaptic population of neurons onto a single post-synaptic cell. The pre-synaptic neural population is assumed to be oscillating at the same frequency, albeit with different phases, such that the net activity of the pre-synaptic population is constant in time. Thus, in the homogeneous case in which all synapses are equal, the post-synaptic neuron receives constant input and hence does not oscillate. To investigate the transition to oscillatory activity, we develop a mean-field Fokker-Planck approximation of the synaptic dynamics. We analyze the conditions causing the homogeneous solution to lose its stability. The findings show that oscillatory activity appears through a mechanism of spontaneous symmetry breaking. However, in the general case the homogeneous solution is unstable, and the synaptic dynamics does not converge to a different fixed point, but rather to a limit cycle. We show how the temporal structure of the STDP rule determines the stability of the homogeneous solution and the drift velocity of the

  5. Oscillations via Spike-Timing Dependent Plasticity in a Feed-Forward Model.

    Science.gov (United States)

    Luz, Yotam; Shamir, Maoz

    2016-04-01

    Neuronal oscillatory activity has been reported in relation to a wide range of cognitive processes including the encoding of external stimuli, attention, and learning. Although the specific role of these oscillations has yet to be determined, it is clear that neuronal oscillations are abundant in the central nervous system. This raises the question of the origin of these oscillations: are the mechanisms for generating these oscillations genetically hard-wired or can they be acquired via a learning process? Here, we study the conditions under which oscillatory activity emerges through a process of spike timing dependent plasticity (STDP) in a feed-forward architecture. First, we analyze the effect of oscillations on STDP-driven synaptic dynamics of a single synapse, and study how the parameters that characterize the STDP rule and the oscillations affect the resultant synaptic weight. Next, we analyze STDP-driven synaptic dynamics of a pre-synaptic population of neurons onto a single post-synaptic cell. The pre-synaptic neural population is assumed to be oscillating at the same frequency, albeit with different phases, such that the net activity of the pre-synaptic population is constant in time. Thus, in the homogeneous case in which all synapses are equal, the post-synaptic neuron receives constant input and hence does not oscillate. To investigate the transition to oscillatory activity, we develop a mean-field Fokker-Planck approximation of the synaptic dynamics. We analyze the conditions causing the homogeneous solution to lose its stability. The findings show that oscillatory activity appears through a mechanism of spontaneous symmetry breaking. However, in the general case the homogeneous solution is unstable, and the synaptic dynamics does not converge to a different fixed point, but rather to a limit cycle. We show how the temporal structure of the STDP rule determines the stability of the homogeneous solution and the drift velocity of the limit cycle.

  6. STDP and Mental Retardation: Dysregulation of Dendritic Excitability in Fragile X Syndrome.

    Science.gov (United States)

    Meredith, Rhiannon M; Mansvelder, Huibert D

    2010-01-01

    Development of cognitive function requires the formation and refinement of synaptic networks of neurons in the brain. Morphological abnormalities of synaptic spines occur throughout the brain in a wide variety of syndromic and non-syndromic disorders of mental retardation (MR). In both neurons from human post-mortem tissue and mouse models of retardation, the changes observed in synaptic spine and dendritic morphology can be subtle, in the range of 10-20% alterations for spine protrusion length and density. Functionally, synapses in hippocampus and cortex show deficits in long-term potentiation (LTP) and long-term depression (LTD) in an array of neurodevelopmental disorders including Down's, Angelman, Fragile X and Rett syndrome. Recent studies have shown that in principle the machinery for synaptic plasticity is in place in these synapses, but that significant alterations in spike-timing-dependent plasticity (STDP) induction rules exist in cortical synaptic pathways of Fragile X MR syndrome. In this model, the threshold for inducing timing-dependent long-term potentiation (tLTP) is increased in these synapses. Increased postsynaptic activity can overcome this threshold and induce normal levels of tLTP. In this review, we bring together recent studies investigating STDP in neurodevelopmental learning disorders using Fragile X syndrome as a model and we argue that alterations in dendritic excitability underlie deficits seen in STDP. Known and candidate dendritic mechanisms that may underlie the plasticity deficits are discussed. Studying STDP in monogenic MR syndromes with clear deficits in information processing at the cognitive level also provides the field with an opportunity to make direct links between cognition and processing rules at the synapse during development.

  7. Role of AMPA and NMDA receptors and back-propagating action potentials in spike timing-dependent plasticity.

    Science.gov (United States)

    Fuenzalida, Marco; Fernández de Sevilla, David; Couve, Alejandro; Buño, Washington

    2010-01-01

    The cellular mechanisms that mediate spike timing-dependent plasticity (STDP) are largely unknown. We studied in vitro in CA1 pyramidal neurons the contribution of AMPA and N-methyl-d-aspartate (NMDA) components of Schaffer collateral (SC) excitatory postsynaptic potentials (EPSPs; EPSP(AMPA) and EPSP(NMDA)) and of the back-propagating action potential (BAP) to the long-term potentiation (LTP) induced by a STDP protocol that consisted in pairing an EPSP and a BAP. Transient blockade of EPSP(AMPA) with 7-nitro-2,3-dioxo-1,4-dihydroquinoxaline-6-carbonitrile (CNQX) during the STDP protocol prevented LTP. Contrastingly LTP was induced under transient inhibition of EPSP(AMPA) by combining SC stimulation, an imposed EPSP(AMPA)-like depolarization, and BAP or by coupling the EPSP(NMDA) evoked under sustained depolarization (approximately -40 mV) and BAP. In Mg(2+)-free solution EPSP(NMDA) and BAP also produced LTP. Suppression of EPSP(NMDA) or BAP always prevented LTP. Thus activation of NMDA receptors and BAPs are needed but not sufficient because AMPA receptor activation is also obligatory for STDP. However, a transient depolarization of another origin that unblocks NMDA receptors and a BAP may also trigger LTP.

  8. Symmetric spike timing-dependent plasticity at CA3–CA3 synapses optimizes storage and recall in autoassociative networks

    OpenAIRE

    Mishra, Rajiv K; Kim, Sooyun; Guzman, Segundo J.; Jonas, Peter

    2016-01-01

    CA3–CA3 recurrent excitatory synapses are thought to play a key role in memory storage and pattern completion. Whether the plasticity properties of these synapses are consistent with their proposed network functions remains unclear. Here, we examine the properties of spike timing-dependent plasticity (STDP) at CA3–CA3 synapses. Low-frequency pairing of excitatory postsynaptic potentials (EPSPs) and action potentials (APs) induces long-term potentiation (LTP), independent of temporal order....

  9. Cortico-striatal spike-timing dependent plasticity after activation of subcortical pathways

    Directory of Open Access Journals (Sweden)

    Jan M Schulz

    2010-07-01

    Full Text Available Cortico-striatal spike-timing dependent plasticity (STDP is modulated by dopamine in vitro. The present study investigated STDP in vivo using alternative procedures for modulating dopaminergic inputs. Postsynaptic potentials (PSP were evoked in intracellularly recorded spiny neurons by electrical stimulation of the contralateral motor cortex. PSPs often consisted of up to three distinct components, likely representing distinct cortico-striatal pathways. After baseline recording, bicuculline (BIC was ejected into the superior colliculus (SC to disinhibit visual pathways to the dopamine cells and striatum. Repetitive cortical stimulation (~60; 0.2 Hz was then paired with postsynaptic spike discharge induced by an intracellular current pulse, with each pairing followed 250 ms later by a light flash to the contralateral eye (n=13. Changes in PSPs, measured as the maximal slope normalised to 5 min pre, ranged from potentiation (~120% to depression (~80%. The determining factor was the relative timing between PSP components and spike: PSP components coinciding or closely following the spike tended towards potentiation, whereas PSP components preceding the spike were depressed. Importantly, STDP was only seen in experiments with successful BIC-mediated disinhibition (n=10. Cortico-striatal high-frequency stimulation (50 pulses at 100 Hz followed 100 ms later by a light flash did not induce more robust synaptic plasticity (n=9. However, an elevated post-light spike rate correlated with depression across plasticity protocols (R2=0.55, p=0.009, n=11 active neurons. These results confirm that the direction of cortico-striatal plasticity is determined by the timing of pre- and postsynaptic activity and that synaptic modification is dependent on the activation of additional subcortical inputs.

  10. Oscillation-Driven Spike-Timing Dependent Plasticity Allows Multiple Overlapping Pattern Recognition in Inhibitory Interneuron Networks.

    Science.gov (United States)

    Garrido, Jesús A; Luque, Niceto R; Tolu, Silvia; D'Angelo, Egidio

    2016-08-01

    The majority of operations carried out by the brain require learning complex signal patterns for future recognition, retrieval and reuse. Although learning is thought to depend on multiple forms of long-term synaptic plasticity, the way this latter contributes to pattern recognition is still poorly understood. Here, we have used a simple model of afferent excitatory neurons and interneurons with lateral inhibition, reproducing a network topology found in many brain areas from the cerebellum to cortical columns. When endowed with spike-timing dependent plasticity (STDP) at the excitatory input synapses and at the inhibitory interneuron-interneuron synapses, the interneurons rapidly learned complex input patterns. Interestingly, induction of plasticity required that the network be entrained into theta-frequency band oscillations, setting the internal phase-reference required to drive STDP. Inhibitory plasticity effectively distributed multiple patterns among available interneurons, thus allowing the simultaneous detection of multiple overlapping patterns. The addition of plasticity in intrinsic excitability made the system more robust allowing self-adjustment and rescaling in response to a broad range of input patterns. The combination of plasticity in lateral inhibitory connections and homeostatic mechanisms in the inhibitory interneurons optimized mutual information (MI) transfer. The storage of multiple complex patterns in plastic interneuron networks could be critical for the generation of sparse representations of information in excitatory neuron populations falling under their control.

  11. A neuromorphic architecture for object recognition and motion anticipation using burst-STDP.

    Directory of Open Access Journals (Sweden)

    Andrew Nere

    Full Text Available In this work we investigate the possibilities offered by a minimal framework of artificial spiking neurons to be deployed in silico. Here we introduce a hierarchical network architecture of spiking neurons which learns to recognize moving objects in a visual environment and determine the correct motor output for each object. These tasks are learned through both supervised and unsupervised spike timing dependent plasticity (STDP. STDP is responsible for the strengthening (or weakening of synapses in relation to pre- and post-synaptic spike times and has been described as a Hebbian paradigm taking place both in vitro and in vivo. We utilize a variation of STDP learning, called burst-STDP, which is based on the notion that, since spikes are expensive in terms of energy consumption, then strong bursting activity carries more information than single (sparse spikes. Furthermore, this learning algorithm takes advantage of homeostatic renormalization, which has been hypothesized to promote memory consolidation during NREM sleep. Using this learning rule, we design a spiking neural network architecture capable of object recognition, motion detection, attention towards important objects, and motor control outputs. We demonstrate the abilities of our design in a simple environment with distractor objects, multiple objects moving concurrently, and in the presence of noise. Most importantly, we show how this neural network is capable of performing these tasks using a simple leaky-integrate-and-fire (LIF neuron model with binary synapses, making it fully compatible with state-of-the-art digital neuromorphic hardware designs. As such, the building blocks and learning rules presented in this paper appear promising for scalable fully neuromorphic systems to be implemented in hardware chips.

  12. Optimal design for hetero-associative memory: hippocampal CA1 phase response curve and spike-timing-dependent plasticity.

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    Ryota Miyata

    Full Text Available Recently reported experimental findings suggest that the hippocampal CA1 network stores spatio-temporal spike patterns and retrieves temporally reversed and spread-out patterns. In this paper, we explore the idea that the properties of the neural interactions and the synaptic plasticity rule in the CA1 network enable it to function as a hetero-associative memory recalling such reversed and spread-out spike patterns. In line with Lengyel's speculation (Lengyel et al., 2005, we firstly derive optimally designed spike-timing-dependent plasticity (STDP rules that are matched to neural interactions formalized in terms of phase response curves (PRCs for performing the hetero-associative memory function. By maximizing object functions formulated in terms of mutual information for evaluating memory retrieval performance, we search for STDP window functions that are optimal for retrieval of normal and doubly spread-out patterns under the constraint that the PRCs are those of CA1 pyramidal neurons. The system, which can retrieve normal and doubly spread-out patterns, can also retrieve reversed patterns with the same quality. Finally, we demonstrate that purposely designed STDP window functions qualitatively conform to typical ones found in CA1 pyramidal neurons.

  13. A re-examination of Hebbian-covariance rules and spike timing-dependent plasticity in cat visual cortex in vivo

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    Yves Frégnac

    2010-12-01

    Full Text Available Spike-Timing-Dependent Plasticity (STDP is considered as an ubiquitous rule for associative plasticity in cortical networks in vitro. However, limited supporting evidence for its functional role has been provided in vivo. In particular, there are very few studies demonstrating the co-occurence of synaptic efficiency changes and alteration of sensory responses in adult cortex during Hebbian or STDP protocols. We addressed this issue by reviewing and comparing the functional effects of two types of cellular conditioning in cat visual cortex. The first one, referred to as the covariance protocol, obeys a generalized Hebbian framework, by imposing, for different stimuli, supervised positive and negative changes in covariance between postsynaptic and presynaptic activity rates. The second protocol, based on intracellular recordings, replicated in vivo variants of the theta-burst paradigm (TBS, proven successful in inducing long-term potentiation (LTP in vitro. Since it was shown to impose a precise correlation delay between the electrically activated thalamic input and the TBS-induced postsynaptic spike, this protocol can be seen as a probe of causal (pre-before-post STDP. By choosing a thalamic region where the visual field representation was in retinotopic overlap with the intracellularly recorded cortical receptive field as the afferent site for supervised electrical stimulation, this protocol allowed to look for possible correlates between STDP and functional reorganization of the conditioned cortical receptive field. The rate-based covariance protocol induced significant and large amplitude changes in receptive field properties, in both kitten and adult V1 cortex. The TBS STDP-like protocol produced in the adult significant changes in the synaptic gain of the electrically activated thalamic pathway, but the statistical significance of the functional correlates was detectable mostly at the population level. Comparison of our observations with the

  14. Effects of the spike timing-dependent plasticity on the synchronisation in a random Hodgkin-Huxley neuronal network

    Science.gov (United States)

    Borges, R. R.; Borges, F. S.; Lameu, E. L.; Batista, A. M.; Iarosz, K. C.; Caldas, I. L.; Viana, R. L.; Sanjuán, M. A. F.

    2016-05-01

    In this paper, we study the effects of spike timing-dependent plasticity on synchronisation in a network of Hodgkin-Huxley neurons. Neuron plasticity is a flexible property of a neuron and its network to change temporarily or permanently their biochemical, physiological, and morphological characteristics, in order to adapt to the environment. Regarding the plasticity, we consider Hebbian rules, specifically for spike timing-dependent plasticity (STDP), and with regard to network, we consider that the connections are randomly distributed. We analyse the synchronisation and desynchronisation according to an input level and probability of connections. Moreover, we verify that the transition for synchronisation depends on the neuronal network architecture, and the external perturbation level.

  15. Depression-biased reverse plasticity rule is required for stable learning at top-down connections.

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    Kendra S Burbank

    Full Text Available Top-down synapses are ubiquitous throughout neocortex and play a central role in cognition, yet little is known about their development and specificity. During sensory experience, lower neocortical areas are activated before higher ones, causing top-down synapses to experience a preponderance of post-synaptic activity preceding pre-synaptic activity. This timing pattern is the opposite of that experienced by bottom-up synapses, which suggests that different versions of spike-timing dependent synaptic plasticity (STDP rules may be required at top-down synapses. We consider a two-layer neural network model and investigate which STDP rules can lead to a distribution of top-down synaptic weights that is stable, diverse and avoids strong loops. We introduce a temporally reversed rule (rSTDP where top-down synapses are potentiated if post-synaptic activity precedes pre-synaptic activity. Combining analytical work and integrate-and-fire simulations, we show that only depression-biased rSTDP (and not classical STDP produces stable and diverse top-down weights. The conclusions did not change upon addition of homeostatic mechanisms, multiplicative STDP rules or weak external input to the top neurons. Our prediction for rSTDP at top-down synapses, which are distally located, is supported by recent neurophysiological evidence showing the existence of temporally reversed STDP in synapses that are distal to the post-synaptic cell body.

  16. Effects of spike-time-dependent plasticity on the stochastic resonance of small-world neuronal networks

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    Yu, Haitao; Guo, Xinmeng; Wang, Jiang, E-mail: jiangwang@tju.edu.cn; Deng, Bin; Wei, Xile [School of Electrical Engineering and Automation, Tianjin University, Tianjin 300072 (China)

    2014-09-01

    The phenomenon of stochastic resonance in Newman-Watts small-world neuronal networks is investigated when the strength of synaptic connections between neurons is adaptively adjusted by spike-time-dependent plasticity (STDP). It is shown that irrespective of the synaptic connectivity is fixed or adaptive, the phenomenon of stochastic resonance occurs. The efficiency of network stochastic resonance can be largely enhanced by STDP in the coupling process. Particularly, the resonance for adaptive coupling can reach a much larger value than that for fixed one when the noise intensity is small or intermediate. STDP with dominant depression and small temporal window ratio is more efficient for the transmission of weak external signal in small-world neuronal networks. In addition, we demonstrate that the effect of stochastic resonance can be further improved via fine-tuning of the average coupling strength of the adaptive network. Furthermore, the small-world topology can significantly affect stochastic resonance of excitable neuronal networks. It is found that there exists an optimal probability of adding links by which the noise-induced transmission of weak periodic signal peaks.

  17. Effects of spike-time-dependent plasticity on the stochastic resonance of small-world neuronal networks.

    Science.gov (United States)

    Yu, Haitao; Guo, Xinmeng; Wang, Jiang; Deng, Bin; Wei, Xile

    2014-09-01

    The phenomenon of stochastic resonance in Newman-Watts small-world neuronal networks is investigated when the strength of synaptic connections between neurons is adaptively adjusted by spike-time-dependent plasticity (STDP). It is shown that irrespective of the synaptic connectivity is fixed or adaptive, the phenomenon of stochastic resonance occurs. The efficiency of network stochastic resonance can be largely enhanced by STDP in the coupling process. Particularly, the resonance for adaptive coupling can reach a much larger value than that for fixed one when the noise intensity is small or intermediate. STDP with dominant depression and small temporal window ratio is more efficient for the transmission of weak external signal in small-world neuronal networks. In addition, we demonstrate that the effect of stochastic resonance can be further improved via fine-tuning of the average coupling strength of the adaptive network. Furthermore, the small-world topology can significantly affect stochastic resonance of excitable neuronal networks. It is found that there exists an optimal probability of adding links by which the noise-induced transmission of weak periodic signal peaks.

  18. A common framework of signal processing in the induction of cerebellar LTD and cortical STDP.

    Science.gov (United States)

    Honda, Minoru; Urakubo, Hidetoshi; Koumura, Takuya; Kuroda, Shinya

    2013-07-01

    Cerebellar long-term depression (LTD) and cortical spike-timing-dependent synaptic plasticity (STDP) are two well-known and well-characterized types of synaptic plasticity. Induction of both types of synaptic plasticity depends on the spike timing, pairing frequency, and pairing numbers of two different sources of spiking. This implies that the induction of synaptic plasticity may share common frameworks in terms of signal processing regardless of the different signaling pathways involved in the two types of synaptic plasticity. Here we propose that both types share common frameworks of signal processing for spike-timing, pairing-frequency, and pairing-numbers detection. We developed system models of both types of synaptic plasticity and analyzed signal processing in the induction of synaptic plasticity. We found that both systems have upstream subsystems for spike-timing detection and downstream subsystems for pairing-frequency and pairing-numbers detection. The upstream systems used multiplication of signals from the feedback filters and nonlinear functions for spike-timing detection. The downstream subsystems used temporal filters with longer time constants for pairing-frequency detection and nonlinear switch-like functions for pairing-numbers detection, indicating that the downstream subsystems serve as a leaky integrate-and-fire system. Thus, our findings suggest that a common conceptual framework for the induction of synaptic plasticity exists despite the differences in molecular species and pathways.

  19. A model of human motor sequence learning explains facilitation and interference effects based on spike-timing dependent plasticity.

    Science.gov (United States)

    Wang, Quan; Rothkopf, Constantin A; Triesch, Jochen

    2017-08-01

    The ability to learn sequential behaviors is a fundamental property of our brains. Yet a long stream of studies including recent experiments investigating motor sequence learning in adult human subjects have produced a number of puzzling and seemingly contradictory results. In particular, when subjects have to learn multiple action sequences, learning is sometimes impaired by proactive and retroactive interference effects. In other situations, however, learning is accelerated as reflected in facilitation and transfer effects. At present it is unclear what the underlying neural mechanism are that give rise to these diverse findings. Here we show that a recently developed recurrent neural network model readily reproduces this diverse set of findings. The self-organizing recurrent neural network (SORN) model is a network of recurrently connected threshold units that combines a simplified form of spike-timing dependent plasticity (STDP) with homeostatic plasticity mechanisms ensuring network stability, namely intrinsic plasticity (IP) and synaptic normalization (SN). When trained on sequence learning tasks modeled after recent experiments we find that it reproduces the full range of interference, facilitation, and transfer effects. We show how these effects are rooted in the network's changing internal representation of the different sequences across learning and how they depend on an interaction of training schedule and task similarity. Furthermore, since learning in the model is based on fundamental neuronal plasticity mechanisms, the model reveals how these plasticity mechanisms are ultimately responsible for the network's sequence learning abilities. In particular, we find that all three plasticity mechanisms are essential for the network to learn effective internal models of the different training sequences. This ability to form effective internal models is also the basis for the observed interference and facilitation effects. This suggests that STDP, IP, and SN

  20. A compound memristive synapse model for statistical learning through STDP in spiking neural networks

    Directory of Open Access Journals (Sweden)

    Johannes eBill

    2014-12-01

    Full Text Available Memristors have recently emerged as promising circuit elements to mimic the function of biological synapses in neuromorphic computing. The fabrication of reliable nanoscale memristive synapses, that feature continuous conductance changes based on the timing of pre- and postsynaptic spikes, has however turned out to be challenging. In this article, we propose an alternative approach, the compound memristive synapse, that circumvents this problem by the use of memristors with binary memristive states. A compound memristive synapse employs multiple bistable memristors in parallel to jointly form one synapse, thereby providing a spectrum of synaptic efficacies. We investigate the computational implications of synaptic plasticity in the compound synapse by integrating the recently observed phenomenon of stochastic filament formation into an abstract model of stochastic switching. Using this abstract model, we first show how standard pulsing schemes give rise to spike-timing dependent plasticity (STDP with a stabilizing weight dependence in compound synapses. In a next step, we study unsupervised learning with compound synapses in networks of spiking neurons organized in a winner-take-all architecture. Our theoretical analysis reveals that compound-synapse STDP implements generalized Expectation-Maximization in the spiking network. Specifically, the emergent synapse configuration represents the most salient features of the input distribution in a Mixture-of-Gaussians generative model. Furthermore, the network’s spike response to spiking input streams approximates a well-defined Bayesian posterior distribution. We show in computer simulations how such networks learn to represent high-dimensional distributions over images of handwritten digits with high fidelity even in presence of substantial device variations and under severe noise conditions. Therefore, the compound memristive synapse may provide a synaptic design principle for future neuromorphic

  1. A compound memristive synapse model for statistical learning through STDP in spiking neural networks.

    Science.gov (United States)

    Bill, Johannes; Legenstein, Robert

    2014-01-01

    Memristors have recently emerged as promising circuit elements to mimic the function of biological synapses in neuromorphic computing. The fabrication of reliable nanoscale memristive synapses, that feature continuous conductance changes based on the timing of pre- and postsynaptic spikes, has however turned out to be challenging. In this article, we propose an alternative approach, the compound memristive synapse, that circumvents this problem by the use of memristors with binary memristive states. A compound memristive synapse employs multiple bistable memristors in parallel to jointly form one synapse, thereby providing a spectrum of synaptic efficacies. We investigate the computational implications of synaptic plasticity in the compound synapse by integrating the recently observed phenomenon of stochastic filament formation into an abstract model of stochastic switching. Using this abstract model, we first show how standard pulsing schemes give rise to spike-timing dependent plasticity (STDP) with a stabilizing weight dependence in compound synapses. In a next step, we study unsupervised learning with compound synapses in networks of spiking neurons organized in a winner-take-all architecture. Our theoretical analysis reveals that compound-synapse STDP implements generalized Expectation-Maximization in the spiking network. Specifically, the emergent synapse configuration represents the most salient features of the input distribution in a Mixture-of-Gaussians generative model. Furthermore, the network's spike response to spiking input streams approximates a well-defined Bayesian posterior distribution. We show in computer simulations how such networks learn to represent high-dimensional distributions over images of handwritten digits with high fidelity even in presence of substantial device variations and under severe noise conditions. Therefore, the compound memristive synapse may provide a synaptic design principle for future neuromorphic architectures.

  2. On the applicability of STDP-based learning mechanisms to spiking neuron network models

    Science.gov (United States)

    Sboev, A.; Vlasov, D.; Serenko, A.; Rybka, R.; Moloshnikov, I.

    2016-11-01

    The ways to creating practically effective method for spiking neuron networks learning, that would be appropriate for implementing in neuromorphic hardware and at the same time based on the biologically plausible plasticity rules, namely, on STDP, are discussed. The influence of the amount of correlation between input and output spike trains on the learnability by different STDP rules is evaluated. A usability of alternative combined learning schemes, involving artificial and spiking neuron models is demonstrated on the iris benchmark task and on the practical task of gender recognition.

  3. Exploiting pallidal plasticity for stimulation in Parkinson’s disease

    Science.gov (United States)

    Lourens, Marcel A. J.; Schwab, Bettina C.; Nirody, Jasmine A.; Meijer, Hil G. E.; van Gils, Stephan A.

    2015-04-01

    Objective. Continuous application of high-frequency deep brain stimulation (DBS) often effectively reduces motor symptoms of Parkinson’s disease patients. While there is a growing need for more effective and less traumatic stimulation, the exact mechanism of DBS is still unknown. Here, we present a methodology to exploit the plasticity of GABAergic synapses inside the external globus pallidus (GPe) for the optimization of DBS. Approach. Assuming the existence of spike-timing-dependent plasticity (STDP) at GABAergic GPe-GPe synapses, we simulate neural activity in a network model of the subthalamic nucleus and GPe. In particular, we test different DBS protocols in our model and quantify their influence on neural synchrony. Main results. In an exemplary set of biologically plausible model parameters, we show that STDP in the GPe has a direct influence on neural activity and especially the stability of firing patterns. STDP stabilizes both uncorrelated firing in the healthy state and correlated firing in the parkinsonian state. Alternative stimulation protocols such as coordinated reset stimulation can clearly profit from the stabilizing effect of STDP. These results are widely independent of the STDP learning rule. Significance. Once the model settings, e.g., connection architectures, have been described experimentally, our model can be adjusted and directly applied in the development of novel stimulation protocols. More efficient stimulation leads to both minimization of side effects and savings in battery power.

  4. Circuit reactivation dynamically regulates synaptic plasticity in neocortex

    Science.gov (United States)

    Kruskal, Peter B.; Li, Lucy; Maclean, Jason N.

    2013-10-01

    Circuit reactivations involve a stereotyped sequence of neuronal firing and have been behaviourally linked to memory consolidation. Here we use multiphoton imaging and patch-clamp recording, and observe sparse and stereotyped circuit reactivations that correspond to UP states within active neurons. To evaluate the effect of the circuit on synaptic plasticity, we trigger a single spike-timing-dependent plasticity (STDP) pairing once per circuit reactivation. The pairings reliably fall within a particular epoch of the circuit sequence and result in long-term potentiation. During reactivation, the amplitude of plasticity significantly correlates with the preceding 20-25 ms of membrane depolarization rather than the depolarization at the time of pairing. This circuit-dependent plasticity provides a natural constraint on synaptic potentiation, regulating the inherent instability of STDP in an assembly phase-sequence model. Subthreshold voltage during endogenous circuit reactivations provides a critical informative context for plasticity and facilitates the stable consolidation of a spatiotemporal sequence.

  5. Strain rate dependence in plasticized and un-plasticized PVC

    Directory of Open Access Journals (Sweden)

    Siviour C.R.

    2012-08-01

    Full Text Available An experimental and analytical investigation has been made into the mechanical behaviour of two poly (vinyl chloride (PVC polymers – an un-plasticized PVC and a diisononyl phthalate (DINP-plasticized PVC. Measurements of the compressive stress-strain behaviour of the PVCs at strain rates ranging from 10−3 to 103s−1 and temperatures from − 60 to 100∘C are presented. Dynamic Mechanical Analysis was also performed in order to understand the material transitions observed in compression testing as the strain rate is increased. This investigation develops a better understanding of the interplay between the temperature dependence and rate dependence of polymers, with a focus on locating the temperature and rate-dependent material transitions that occur during high rate testing.

  6. Strain rate dependence in plasticized and un-plasticized PVC

    Science.gov (United States)

    Kendall, M. J.; Siviour, C. R.

    2012-08-01

    An experimental and analytical investigation has been made into the mechanical behaviour of two poly (vinyl chloride) (PVC) polymers - an un-plasticized PVC and a diisononyl phthalate (DINP)-plasticized PVC. Measurements of the compressive stress-strain behaviour of the PVCs at strain rates ranging from 10-3 to 103s-1 and temperatures from - 60 to 100∘C are presented. Dynamic Mechanical Analysis was also performed in order to understand the material transitions observed in compression testing as the strain rate is increased. This investigation develops a better understanding of the interplay between the temperature dependence and rate dependence of polymers, with a focus on locating the temperature and rate-dependent material transitions that occur during high rate testing.

  7. Bimodal stimulus timing-dependent plasticity in primary auditory cortex is altered after noise exposure with and without tinnitus.

    Science.gov (United States)

    Basura, Gregory J; Koehler, Seth D; Shore, Susan E

    2015-12-01

    Central auditory circuits are influenced by the somatosensory system, a relationship that may underlie tinnitus generation. In the guinea pig dorsal cochlear nucleus (DCN), pairing spinal trigeminal nucleus (Sp5) stimulation with tones at specific intervals and orders facilitated or suppressed subsequent tone-evoked neural responses, reflecting spike timing-dependent plasticity (STDP). Furthermore, after noise-induced tinnitus, bimodal responses in DCN were shifted from Hebbian to anti-Hebbian timing rules with less discrete temporal windows, suggesting a role for bimodal plasticity in tinnitus. Here, we aimed to determine if multisensory STDP principles like those in DCN also exist in primary auditory cortex (A1), and whether they change following noise-induced tinnitus. Tone-evoked and spontaneous neural responses were recorded before and 15 min after bimodal stimulation in which the intervals and orders of auditory-somatosensory stimuli were randomized. Tone-evoked and spontaneous firing rates were influenced by the interval and order of the bimodal stimuli, and in sham-controls Hebbian-like timing rules predominated as was seen in DCN. In noise-exposed animals with and without tinnitus, timing rules shifted away from those found in sham-controls to more anti-Hebbian rules. Only those animals with evidence of tinnitus showed increased spontaneous firing rates, a purported neurophysiological correlate of tinnitus in A1. Together, these findings suggest that bimodal plasticity is also evident in A1 following noise damage and may have implications for tinnitus generation and therapeutic intervention across the central auditory circuit.

  8. Spike Pattern Structure Influences Synaptic Efficacy Variability under STDP and Synaptic Homeostasis. II: Spike Shuffling Methods on LIF Networks

    Science.gov (United States)

    Bi, Zedong; Zhou, Changsong

    2016-01-01

    Synapses may undergo variable changes during plasticity because of the variability of spike patterns such as temporal stochasticity and spatial randomness. Here, we call the variability of synaptic weight changes during plasticity to be efficacy variability. In this paper, we investigate how four aspects of spike pattern statistics (i.e., synchronous firing, burstiness/regularity, heterogeneity of rates and heterogeneity of cross-correlations) influence the efficacy variability under pair-wise additive spike-timing dependent plasticity (STDP) and synaptic homeostasis (the mean strength of plastic synapses into a neuron is bounded), by implementing spike shuffling methods onto spike patterns self-organized by a network of excitatory and inhibitory leaky integrate-and-fire (LIF) neurons. With the increase of the decay time scale of the inhibitory synaptic currents, the LIF network undergoes a transition from asynchronous state to weak synchronous state and then to synchronous bursting state. We first shuffle these spike patterns using a variety of methods, each designed to evidently change a specific pattern statistics; and then investigate the change of efficacy variability of the synapses under STDP and synaptic homeostasis, when the neurons in the network fire according to the spike patterns before and after being treated by a shuffling method. In this way, we can understand how the change of pattern statistics may cause the change of efficacy variability. Our results are consistent with those of our previous study which implements spike-generating models on converging motifs. We also find that burstiness/regularity is important to determine the efficacy variability under asynchronous states, while heterogeneity of cross-correlations is the main factor to cause efficacy variability when the network moves into synchronous bursting states (the states observed in epilepsy). PMID:27555816

  9. Energy-efficient STDP-based learning circuits with memristor synapses

    Science.gov (United States)

    Wu, Xinyu; Saxena, Vishal; Campbell, Kristy A.

    2014-05-01

    It is now accepted that the traditional von Neumann architecture, with processor and memory separation, is ill suited to process parallel data streams which a mammalian brain can efficiently handle. Moreover, researchers now envision computing architectures which enable cognitive processing of massive amounts of data by identifying spatio-temporal relationships in real-time and solving complex pattern recognition problems. Memristor cross-point arrays, integrated with standard CMOS technology, are expected to result in massively parallel and low-power Neuromorphic computing architectures. Recently, significant progress has been made in spiking neural networks (SNN) which emulate data processing in the cortical brain. These architectures comprise of a dense network of neurons and the synapses formed between the axons and dendrites. Further, unsupervised or supervised competitive learning schemes are being investigated for global training of the network. In contrast to a software implementation, hardware realization of these networks requires massive circuit overhead for addressing and individually updating network weights. Instead, we employ bio-inspired learning rules such as the spike-timing-dependent plasticity (STDP) to efficiently update the network weights locally. To realize SNNs on a chip, we propose to use densely integrating mixed-signal integrate-andfire neurons (IFNs) and cross-point arrays of memristors in back-end-of-the-line (BEOL) of CMOS chips. Novel IFN circuits have been designed to drive memristive synapses in parallel while maintaining overall power efficiency (<1 pJ/spike/synapse), even at spike rate greater than 10 MHz. We present circuit design details and simulation results of the IFN with memristor synapses, its response to incoming spike trains and STDP learning characterization.

  10. Regulation of spike timing-dependent plasticity of olfactory inputs in mitral cells in the rat olfactory bulb.

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    Teng-Fei Ma

    Full Text Available The recent history of activity input onto granule cells (GCs in the main olfactory bulb can affect the strength of lateral inhibition, which functions to generate contrast enhancement. However, at the plasticity level, it is unknown whether and how the prior modification of lateral inhibition modulates the subsequent induction of long-lasting changes of the excitatory olfactory nerve (ON inputs to mitral cells (MCs. Here we found that the repetitive stimulation of two distinct excitatory inputs to the GCs induced a persistent modification of lateral inhibition in MCs in opposing directions. This bidirectional modification of inhibitory inputs differentially regulated the subsequent synaptic plasticity of the excitatory ON inputs to the MCs, which was induced by the repetitive pairing of excitatory postsynaptic potentials (EPSPs with postsynaptic bursts. The regulation of spike timing-dependent plasticity (STDP was achieved by the regulation of the inter-spike-interval (ISI of the postsynaptic bursts. This novel form of inhibition-dependent regulation of plasticity may contribute to the encoding or processing of olfactory information in the olfactory bulb.

  11. Stress Dependence of Transformation Plastic Behavior

    Institute of Scientific and Technical Information of China (English)

    Tatsuo Inoue

    2004-01-01

    Transformation plasticity is known to play an important role in the course of heat treatment processes, and so affect the results of heat treatment simulations, which means that the transformation plasticity coefficient is necessary to be identifies. The authors developed a new method by use of four-point bending system of a beam to identify transformation plasticity coefficient taking advantage of its easiness and high accuracy compared with other conventional methods like tension test, etc., and identified the coefficient for four kinds of steels; plane carbon steel, Cr-steel, Cr-Mo steel and bearing steel. In this paper, further experimental data are presented for the steels if the coefficient Kp during pearlite transformation depend on the applied stress. Obtained results reveals that the stress dependence of Kp is rather trivial except for uncertain tendency detected in plane carbon steel. The relation between the Kp and carbon content included is

  12. Frequency dependent changes in NMDAR-dependent synaptic plasticity

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    Arvind eKumar

    2011-09-01

    Full Text Available The NMDAR-dependent synaptic plasticity is thought to mediate several forms of learning, and can be induced by spike trains containing a small number of spikes occurring with varying rates and timing, as well as with oscillations. We computed the influence of these variables on the plasticity induced at a single NMDAR containing synapse using a reduced model that was analytically tractable, and these findings were confirmed using detailed, multi-compartment model. In addition to explaining diverse experimental results about the rate and timing dependence of synaptic plasticity, the model made several novel and testable predictions. We found that there was a preferred frequency for inducing long-term potentiation (LTP such that higher frequency stimuli induced lesser LTP, decreasing as 1/f when the number of spikes in the stimulus was kept fixed. Among other things, the preferred frequency for inducing LTP varied as a function of the distance of the synapse from the soma. In fact, same stimulation frequencies could induce LTP or LTD depending on the dendritic location of the synapse. Next, we found that rhythmic stimuli induced greater plasticity then irregular stimuli. Furthermore, brief bursts of spikes significantly expanded the timing dependence of plasticity. Finally, we found that in the ~5-15Hz frequency range both rate- and timing-dependent plasticity mechanisms work synergistically to render the synaptic plasticity most sensitive to spike-timing. These findings provide computational evidence that oscillations can have a profound influence on the plasticity of an NMDAR-dependent synapse, and show a novel role for the dendritic morphology in this process.

  13. Single pairing spike-timing dependent plasticity in BiFeO3 memristors with a time window of 25ms to 125µs

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    Nan eDu

    2015-06-01

    Full Text Available Memristive devices are popular among neuromorphic engineers for their ability to emulate forms of spike-driven synaptic plasticity by applying specific voltage and current waveforms at their two terminals. In this paper, we investigate spike-timing dependent plasticity (STDP with a single pairing of one presynaptic voltage spike and one postsynaptic voltage spike in a BiFeO3 memristive device. In most memristive materials the learning window is primarily a function of the material characteristics and not of the applied waveform. In contrast, we show that the analog resistive switching of the developed artificial synapses allows to adjust the learning time constant of the STDP function from 25ms to 125μs via the duration of applied voltage spikes. Also, as the induced weight change may degrade, we investigate the remanence of the resistance change for several hours after analog resistive switching, thus emulating the processes expected in biological synapses. As the power consumption is a major constraint in neuromorphic circuits, we show methods to reduce the consumed energy per setting pulse to only 4.5 pJ in the developed artificial synapses.

  14. Learning Touch Preferences with a Tactile Robot Using Dopamine Modulated STDP in a Model of Insular Cortex

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    Ting-Shuo eChou

    2015-07-01

    Full Text Available Neurorobots enable researchers to study how behaviors are produced by neural mechanisms in an uncertain, noisy, real-world environment. To investigate how the somatosensory system processes noisy, real-world touch inputs, we introduce a neurorobot called CARL-SJR, which has a full-body tactile sensory area. The design of CARL-SJR is such that it encourages people to communicate with it through gentle touch. CARL-SJR provides feedback to users by displaying bright colors on its surface. In the present study, we show that CARL-SJR is capable of learning associations between conditioned stimuli (CS; a color pattern on its surface and unconditioned stimuli (US; a preferred touch pattern by applying a spiking neural network (SNN with neurobiologically inspired plasticity. Specifically, we modeled the primary somatosensory cortex, prefrontal cortex, striatum, and the insular cortex, which is important for hedonic touch, to process noisy data generated directly from CARL-SJR’s tactile sensory area. To facilitate learning, we applied dopamine-modulated Spike Timing Dependent Plasticity (STDP to our simulated prefrontal cortex, striatum and insular cortex. To cope with noisy, varying inputs, the SNN was tuned to produce traveling waves of activity that carried spatiotemporal information. Despite the noisy tactile sensors, spike trains, and variations in subject hand swipes, the learning was quite robust. Further, the plasticity (i.e., STDP in primary somatosensory cortex and insular cortex in the incremental pathway of dopaminergic reward system allowed us to control CARL-SJR’s preference for touch direction without heavily pre-processed inputs. The emerged behaviors we found in this model match animal’s behaviors wherein they prefer touch in particular areas and directions. Thus, the results in this paper could serve as an explanation on the underlying neural mechanisms for developing tactile preferences and hedonic touch.

  15. The evolution of age-dependent plasticity

    NARCIS (Netherlands)

    Fischer, Barbara; van Doorn, G. Sander; Dieckmann, Ulf; Taborsky, Barbara

    2014-01-01

    When organisms encounter environments that are heterogeneous in time, phenotypic plasticity is often favored by selection. The degree of such plasticity can vary during an organism''s lifetime, but the factors promoting differential plastic responses at different ages or life stages remain poorly un

  16. Synaptic plasticity in medial vestibular nucleus neurons: comparison with computational requirements of VOR adaptation.

    Directory of Open Access Journals (Sweden)

    John R W Menzies

    Full Text Available BACKGROUND: Vestibulo-ocular reflex (VOR gain adaptation, a longstanding experimental model of cerebellar learning, utilizes sites of plasticity in both cerebellar cortex and brainstem. However, the mechanisms by which the activity of cortical Purkinje cells may guide synaptic plasticity in brainstem vestibular neurons are unclear. Theoretical analyses indicate that vestibular plasticity should depend upon the correlation between Purkinje cell and vestibular afferent inputs, so that, in gain-down learning for example, increased cortical activity should induce long-term depression (LTD at vestibular synapses. METHODOLOGY/PRINCIPAL FINDINGS: Here we expressed this correlational learning rule in its simplest form, as an anti-Hebbian, heterosynaptic spike-timing dependent plasticity interaction between excitatory (vestibular and inhibitory (floccular inputs converging on medial vestibular nucleus (MVN neurons (input-spike-timing dependent plasticity, iSTDP. To test this rule, we stimulated vestibular afferents to evoke EPSCs in rat MVN neurons in vitro. Control EPSC recordings were followed by an induction protocol where membrane hyperpolarizing pulses, mimicking IPSPs evoked by flocculus inputs, were paired with single vestibular nerve stimuli. A robust LTD developed at vestibular synapses when the afferent EPSPs coincided with membrane hyperpolarization, while EPSPs occurring before or after the simulated IPSPs induced no lasting change. Furthermore, the iSTDP rule also successfully predicted the effects of a complex protocol using EPSP trains designed to mimic classical conditioning. CONCLUSIONS: These results, in strong support of theoretical predictions, suggest that the cerebellum alters the strength of vestibular synapses on MVN neurons through hetero-synaptic, anti-Hebbian iSTDP. Since the iSTDP rule does not depend on post-synaptic firing, it suggests a possible mechanism for VOR adaptation without compromising gaze-holding and VOR

  17. Neuromodulatory influence of norepinephrine during developmental experience-dependent plasticity.

    Science.gov (United States)

    Golovin, Randall M; Ward, Nicholas J

    2016-07-01

    Critical periods represent phases of development during which neuronal circuits and their responses can be readily shaped by stimuli. Experience-dependent plasticity that occurs within these critical periods can be influenced in many ways; however, Shepard et al. (J Neurosci 35: 2432-2437, 2015) recently singled out norepinephrine as an essential driver of this plasticity within the auditory cortex. This work provides novel insight into the mechanisms of critical period plasticity and challenges previous conceptions that a functional redundancy exists between noradrenergic and cholinergic influences on cortical plasticity.

  18. A Theory of Rate-Dependent Plasticity

    Science.gov (United States)

    1984-05-01

    impact conditions, where a considerable amount of plastic work is liberated as heat, this athermal assumption becomes increasingly poor for defining...crystal microplasticity use a variety of parameters, such as mobile dislocation density and velocity, all of which are eventually related in some manner... impact problems and are not generally encountered in structural integrity analyses. Some final observations concerning tests of material at constant

  19. Reaction-diffusion-like formalism for plastic neural networks reveals dissipative solitons at criticality

    Science.gov (United States)

    Grytskyy, Dmytro; Diesmann, Markus; Helias, Moritz

    2016-06-01

    Self-organized structures in networks with spike-timing dependent synaptic plasticity (STDP) are likely to play a central role for information processing in the brain. In the present study we derive a reaction-diffusion-like formalism for plastic feed-forward networks of nonlinear rate-based model neurons with a correlation sensitive learning rule inspired by and being qualitatively similar to STDP. After obtaining equations that describe the change of the spatial shape of the signal from layer to layer, we derive a criterion for the nonlinearity necessary to obtain stable dynamics for arbitrary input. We classify the possible scenarios of signal evolution and find that close to the transition to the unstable regime metastable solutions appear. The form of these dissipative solitons is determined analytically and the evolution and interaction of several such coexistent objects is investigated.

  20. Reaction-diffusion-like formalism for plastic neural networks reveals dissipative solitons at criticality.

    Science.gov (United States)

    Grytskyy, Dmytro; Diesmann, Markus; Helias, Moritz

    2016-06-01

    Self-organized structures in networks with spike-timing dependent synaptic plasticity (STDP) are likely to play a central role for information processing in the brain. In the present study we derive a reaction-diffusion-like formalism for plastic feed-forward networks of nonlinear rate-based model neurons with a correlation sensitive learning rule inspired by and being qualitatively similar to STDP. After obtaining equations that describe the change of the spatial shape of the signal from layer to layer, we derive a criterion for the nonlinearity necessary to obtain stable dynamics for arbitrary input. We classify the possible scenarios of signal evolution and find that close to the transition to the unstable regime metastable solutions appear. The form of these dissipative solitons is determined analytically and the evolution and interaction of several such coexistent objects is investigated.

  1. 动态STDP突触系统模型设计与验证%Design and Verification of Dynamic Synaptic Modeling with Spike-time Dependent Plasticity

    Institute of Scientific and Technical Information of China (English)

    林凌鹏; 林水生; 黄乐天; 刘培龙

    2011-01-01

    神经突触的STDP(Spike Timing Dependent Plasticity)机制被认为是脑神经网络中最重要的机制之一,最有效的模拟STDP神经突触的方法是建立神经突触的离子通道的动力学模型。目前的STDP突触系统建模均存在一定的缺陷,不能很好地解释STDP机制的细胞分子生物反应原理或者得到STDP的时间非对称实验结果。提出一种新型的STDP神经突触系统模型,通过两个重要的输入信号用以验证该模型。仿真和验证结果表明,所提曲的模型不仅反应7STDP神经突触实际的生理学机理,而且还得到STDP神经突融的时阃非对称结果,%STDP (Spike Timing Dependent Plasticity) mechanism of synapses is considered to be one of the most important mechanisms of neural network, and the most effective method of emulated STDP synapse is to establishing the kinetic model of synaptic ion channels. However, most of the existing modeling of STDP synaptic mechanism have some certain defects, they either can't well explained the biomolecular reactions at a cellular level which is responsible for STDP, or acquired asymmetric STDP responses. A new modeling of STDP synaptic system was proposed. Two significant synaptic inputs were designed which were used to make the verification of the system. The simulation and verification results show that the new modeling not only reflects the actual physiological mechanism of STDP synapses, but also asymmetric STDP responses are obtained.

  2. Different propagation speeds of recalled sequences in plastic spiking neural networks

    Science.gov (United States)

    Huang, Xuhui; Zheng, Zhigang; Hu, Gang; Wu, Si; Rasch, Malte J.

    2015-03-01

    Neural networks can generate spatiotemporal patterns of spike activity. Sequential activity learning and retrieval have been observed in many brain areas, and e.g. is crucial for coding of episodic memory in the hippocampus or generating temporal patterns during song production in birds. In a recent study, a sequential activity pattern was directly entrained onto the neural activity of the primary visual cortex (V1) of rats and subsequently successfully recalled by a local and transient trigger. It was observed that the speed of activity propagation in coordinates of the retinotopically organized neural tissue was constant during retrieval regardless how the speed of light stimulation sweeping across the visual field during training was varied. It is well known that spike-timing dependent plasticity (STDP) is a potential mechanism for embedding temporal sequences into neural network activity. How training and retrieval speeds relate to each other and how network and learning parameters influence retrieval speeds, however, is not well described. We here theoretically analyze sequential activity learning and retrieval in a recurrent neural network with realistic synaptic short-term dynamics and STDP. Testing multiple STDP rules, we confirm that sequence learning can be achieved by STDP. However, we found that a multiplicative nearest-neighbor (NN) weight update rule generated weight distributions and recall activities that best matched the experiments in V1. Using network simulations and mean-field analysis, we further investigated the learning mechanisms and the influence of network parameters on recall speeds. Our analysis suggests that a multiplicative STDP rule with dominant NN spike interaction might be implemented in V1 since recall speed was almost constant in an NMDA-dominant regime. Interestingly, in an AMPA-dominant regime, neural circuits might exhibit recall speeds that instead follow the change in stimulus speeds. This prediction could be tested in

  3. Computational anatomy for studying use-dependant brain plasticity

    Directory of Open Access Journals (Sweden)

    Bogdan eDraganski

    2014-06-01

    Full Text Available In this article we provide a comprehensive literature review on the in vivo assessment of use-dependant brain structure changes in humans using magnetic resonance imaging and computational anatomy. We highlight the recent findings in this field that allow the uncovering of the basic principles behind brain plasticity in light of the existing theoretical models at various scales of observation. Given the current lack of in-depth understanding of the neurobiological basis of brain structure changes we emphasize the necessity of a paradigm shift in the investigation and interpretation of use-dependent brain plasticity. Novel quantitative MRI acquisition techniques provide access to brain tissue microstructural properties (e.g. myelin, iron and water content in-vivo, thereby allowing unprecedented specific insights into the mechanisms underlying brain plasticity. These quantitative MRI techniques require novel methods for image processing and analysis of longitudinal data allowing for straightforward interpretation and causality inferences.

  4. A density-dependent endochronic plasticity for powder compaction processes

    Science.gov (United States)

    Bakhshiani, A.; Khoei, A. R.; Mofid, M.

    This paper is concerned with the numerical modeling of powder cold compaction process using a density-dependent endochronic plasticity model. Endochronic plasticity theory is developed based on a large strain plasticity to describe the nonlinear behavior of powder material. The elastic response is stated in terms of hypoelastic model and endochronic plasticity constitutive equations are stated in unrotated frame of reference. A trivially incrementally objective integration scheme for rate constitutive equations is established. Algorithmic modulus consistent with numerical integration algorithm of constitutive equations is extracted. It is shown how the endochronic plasticity describes the behavior of powder material from the initial stage of compaction to final stage, in which material behaves as solid metals. It is also shown that some commonly used plasticity models for powder material can be derived as special cases of the proposed endochronic theory. Finally, the numerical schemes are examined for efficiency in the modeling of a plain bush, a rotational-flanged and a shaped tablet powder compaction component.

  5. Color opponent receptive fields self-organize in a biophysical model of visual cortex via spike-timing dependent plasticity.

    Science.gov (United States)

    Eguchi, Akihiro; Neymotin, Samuel A; Stringer, Simon M

    2014-01-01

    Although many computational models have been proposed to explain orientation maps in primary visual cortex (V1), it is not yet known how similar clusters of color-selective neurons in macaque V1/V2 are connected and develop. In this work, we address the problem of understanding the cortical processing of color information with a possible mechanism of the development of the patchy distribution of color selectivity via computational modeling. Each color input is decomposed into a red, green, and blue representation and transmitted to the visual cortex via a simulated optic nerve in a luminance channel and red-green and blue-yellow opponent color channels. Our model of the early visual system consists of multiple topographically-arranged layers of excitatory and inhibitory neurons, with sparse intra-layer connectivity and feed-forward connectivity between layers. Layers are arranged based on anatomy of early visual pathways, and include a retina, lateral geniculate nucleus, and layered neocortex. Each neuron in the V1 output layer makes synaptic connections to neighboring neurons and receives the three types of signals in the different channels from the corresponding photoreceptor position. Synaptic weights are randomized and learned using spike-timing-dependent plasticity (STDP). After training with natural images, the neurons display heightened sensitivity to specific colors. Information-theoretic analysis reveals mutual information between particular stimuli and responses, and that the information reaches a maximum with fewer neurons in the higher layers, indicating that estimations of the input colors can be done using the output of fewer cells in the later stages of cortical processing. In addition, cells with similar color receptive fields form clusters. Analysis of spiking activity reveals increased firing synchrony between neurons when particular color inputs are presented or removed (ON-cell/OFF-cell).

  6. A neuromorphic implementation of multiple spike-timing synaptic plasticity rules for large-scale neural networks

    Science.gov (United States)

    Wang, Runchun M.; Hamilton, Tara J.; Tapson, Jonathan C.; van Schaik, André

    2015-01-01

    We present a neuromorphic implementation of multiple synaptic plasticity learning rules, which include both Spike Timing Dependent Plasticity (STDP) and Spike Timing Dependent Delay Plasticity (STDDP). We present a fully digital implementation as well as a mixed-signal implementation, both of which use a novel dynamic-assignment time-multiplexing approach and support up to 226 (64M) synaptic plasticity elements. Rather than implementing dedicated synapses for particular types of synaptic plasticity, we implemented a more generic synaptic plasticity adaptor array that is separate from the neurons in the neural network. Each adaptor performs synaptic plasticity according to the arrival times of the pre- and post-synaptic spikes assigned to it, and sends out a weighted or delayed pre-synaptic spike to the post-synaptic neuron in the neural network. This strategy provides great flexibility for building complex large-scale neural networks, as a neural network can be configured for multiple synaptic plasticity rules without changing its structure. We validate the proposed neuromorphic implementations with measurement results and illustrate that the circuits are capable of performing both STDP and STDDP. We argue that it is practical to scale the work presented here up to 236 (64G) synaptic adaptors on a current high-end FPGA platform. PMID:26041985

  7. A neuromorphic implementation of multiple spike-timing synaptic plasticity rules for large-scale neural networks.

    Science.gov (United States)

    Wang, Runchun M; Hamilton, Tara J; Tapson, Jonathan C; van Schaik, André

    2015-01-01

    We present a neuromorphic implementation of multiple synaptic plasticity learning rules, which include both Spike Timing Dependent Plasticity (STDP) and Spike Timing Dependent Delay Plasticity (STDDP). We present a fully digital implementation as well as a mixed-signal implementation, both of which use a novel dynamic-assignment time-multiplexing approach and support up to 2(26) (64M) synaptic plasticity elements. Rather than implementing dedicated synapses for particular types of synaptic plasticity, we implemented a more generic synaptic plasticity adaptor array that is separate from the neurons in the neural network. Each adaptor performs synaptic plasticity according to the arrival times of the pre- and post-synaptic spikes assigned to it, and sends out a weighted or delayed pre-synaptic spike to the post-synaptic neuron in the neural network. This strategy provides great flexibility for building complex large-scale neural networks, as a neural network can be configured for multiple synaptic plasticity rules without changing its structure. We validate the proposed neuromorphic implementations with measurement results and illustrate that the circuits are capable of performing both STDP and STDDP. We argue that it is practical to scale the work presented here up to 2(36) (64G) synaptic adaptors on a current high-end FPGA platform.

  8. A neuromorphic implementation of multiple spike-timing synaptic plasticity rules for large-scale neural networks

    Directory of Open Access Journals (Sweden)

    Runchun Mark Wang

    2015-05-01

    Full Text Available We present a neuromorphic implementation of multiple synaptic plasticity learning rules, which include both Spike Timing Dependent Plasticity (STDP and Spike Timing Dependent Delay Plasticity (STDDP. We present a fully digital implementation as well as a mixed-signal implementation, both of which use a novel dynamic-assignment time-multiplexing approach and support up to 2^26 (64M synaptic plasticity elements. Rather than implementing dedicated synapses for particular types of synaptic plasticity, we implemented a more generic synaptic plasticity adaptor array that is separate from the neurons in the neural network. Each adaptor performs synaptic plasticity according to the arrival times of the pre- and post-synaptic spikes assigned to it, and sends out a weighted and/or delayed pre-synaptic spike to the target synapse in the neural network. This strategy provides great flexibility for building complex large-scale neural networks, as a neural network can be configured for multiple synaptic plasticity rules without changing its structure. We validate the proposed neuromorphic implementations with measurement results and illustrate that the circuits are capable of performing both STDP and STDDP. We argue that it is practical to scale the work presented here up to 2^36 (64G synaptic adaptors on a current high-end FPGA platform.

  9. Single electrode dynamic clamp with StdpC.

    Science.gov (United States)

    Samu, David; Marra, Vincenzo; Kemenes, Ildiko; Crossley, Michael; Kemenes, György; Staras, Kevin; Nowotny, Thomas

    2012-10-15

    Dynamic clamp is a powerful approach for electrophysiological investigations allowing researchers to introduce artificial electrical components into target neurons to simulate ionic conductances, chemical or electrotonic inputs or connections to other cells. Due to the rapidly changing and potentially large current injections during dynamic clamp, problematic voltage artifacts appear on the electrode used to inject dynamic clamp currents into a target neuron. Dynamic clamp experiments, therefore, typically use two separate electrodes in the same cell, one for recording membrane potential and one for injecting currents. The requirement for two independent electrodes has been a limiting factor for the use of dynamic clamp in applications where dual recordings of this kind are difficult or impossible to achieve. The recent development of an active electrode compensation (AEC) method has overcome some of these prior limitations, permitting artifact-free dynamic clamp experimentation with a single electrode. Here we describe an AEC method for the free dynamic clamp software StdpC. The AEC component of StdpC is the first such system implemented for the use of non-expert users and comes with a set of semi-automated configuration and calibration procedures that facilitate its use. We briefly introduce the AEC method and its implementation in StdpC and then validate it with an electronic model cell and in two different biological preparations.

  10. Role of BDNF epigenetics in activity-dependent neuronal plasticity.

    Science.gov (United States)

    Karpova, Nina N

    2014-01-01

    Brain-derived neurotrophic factor (BDNF) is a key mediator of the activity-dependent processes in the brain that have a major impact on neuronal development and plasticity. Impaired control of neuronal activity-induced BDNF expression mediates the pathogenesis of various neurological and psychiatric disorders. Different environmental stimuli, such as the use of pharmacological compounds, physical and learning exercises or stress exposure, lead to activation of specific neuronal networks. These processes entail tight temporal and spatial transcriptional control of numerous BDNF splice variants through epigenetic mechanisms. The present review highlights recent findings on the dynamic and long-term epigenetic programming of BDNF gene expression by the DNA methylation, histone-modifying and microRNA machineries. The review also summarizes the current knowledge on the activity-dependent BDNF mRNA trafficking critical for rapid local regulation of BDNF levels and synaptic plasticity. Current data open novel directions for discovery of new promising therapeutic targets for treatment of neuropsychiatric disorders. This article is part of the Special Issue entitled 'BDNF Regulation of Synaptic Structure, Function, and Plasticity'. Copyright © 2013 Elsevier Ltd. All rights reserved.

  11. Shaping inhibition: activity dependent structural plasticity of GABAergic synapses

    Directory of Open Access Journals (Sweden)

    Carmen E Flores

    2014-10-01

    Full Text Available Inhibitory transmission through the neurotransmitter Ɣ-aminobutyric acid (GABA shapes network activity in the mammalian cerebral cortex by filtering synaptic incoming information and dictating the activity of principal cells. The incredibly diverse population of cortical neurons that use GABA as neurotransmitter shows an equally diverse range of mechanisms that regulate changes in the strength of GABAergic synaptic transmission and allow them to dynamically follow and command the activity of neuronal ensembles. Similarly to glutamatergic synaptic transmission, activity-dependent functional changes in inhibitory neurotransmission are accompanied by alterations in GABAergic synapse structure that range from morphological reorganization of postsynaptic density to de novo formation and elimination of inhibitory contacts. Here we review several aspects of structural plasticity of inhibitory synapses, including its induction by different forms of neuronal activity, behavioral and sensory experience and the molecular mechanisms and signaling pathways involved. We discuss the functional consequences of GABAergic synapse structural plasticity for information processing and memory formation in view of the heterogenous nature of the structural plasticity phenomena affecting inhibitory synapses impinging on somatic and dendritic compartments of cortical and hippocampal neurons.

  12. Activity-dependent plasticity of mouse hippocampal assemblies in vitro

    Directory of Open Access Journals (Sweden)

    Martin eKeller

    2015-05-01

    Full Text Available Memory formation is associated with the generation of transiently stable neuronal assemblies. In hippocampal networks, such groups of functionally coupled neurons express highly ordered spatiotemporal activity patterns which are coordinated by local network oscillations. One of these patterns, sharp wave-ripple complexes (SPW-R, repetitively activates previously established groups of memory-encoding neurons, thereby supporting memory consolidation. This function implies that repetition of specific SPW-R induces plastic changes which render the underlying neuronal assemblies more stable. We modeled this repetitive activation in an in vitro model of SPW-R in mouse hippocampal slices. Weak electrical stimulation upstream of the CA3-CA1 networks reliably induced SPW-R of stereotypic waveform, thus representing re-activation of similar neuronal activity patterns. Frequent repetition of these patterns (100 times reduced the variance of both, evoked and spontaneous SPW-R waveforms, indicating stabilization of pre-existing assemblies. These effects were most pronounced in the CA1 subfield and depended on the timing of stimulation relative to spontaneous SPW-R. Additionally, plasticity of SPW-R was blocked by application of a NMDA receptor antagonist, suggesting a role for associative synaptic plasticity in this process. Thus, repetitive activation of specific patterns of SPW-R causes stabilization of memory-related networks.

  13. Correlation-based model of artificially induced plasticity in motor cortex by a bidirectional brain-computer interface.

    Directory of Open Access Journals (Sweden)

    Guillaume Lajoie

    2017-02-01

    Full Text Available Experiments show that spike-triggered stimulation performed with Bidirectional Brain-Computer-Interfaces (BBCI can artificially strengthen connections between separate neural sites in motor cortex (MC. When spikes from a neuron recorded at one MC site trigger stimuli at a second target site after a fixed delay, the connections between sites eventually strengthen. It was also found that effective spike-stimulus delays are consistent with experimentally derived spike-timing-dependent plasticity (STDP rules, suggesting that STDP is key to drive these changes. However, the impact of STDP at the level of circuits, and the mechanisms governing its modification with neural implants remain poorly understood. The present work describes a recurrent neural network model with probabilistic spiking mechanisms and plastic synapses capable of capturing both neural and synaptic activity statistics relevant to BBCI conditioning protocols. Our model successfully reproduces key experimental results, both established and new, and offers mechanistic insights into spike-triggered conditioning. Using analytical calculations and numerical simulations, we derive optimal operational regimes for BBCIs, and formulate predictions concerning the efficacy of spike-triggered conditioning in different regimes of cortical activity.

  14. Correlation-based model of artificially induced plasticity in motor cortex by a bidirectional brain-computer interface

    Science.gov (United States)

    Lajoie, Guillaume; Kalaska, John F.; Fairhall, Adrienne L.; Fetz, Eberhard E.

    2017-01-01

    Experiments show that spike-triggered stimulation performed with Bidirectional Brain-Computer-Interfaces (BBCI) can artificially strengthen connections between separate neural sites in motor cortex (MC). When spikes from a neuron recorded at one MC site trigger stimuli at a second target site after a fixed delay, the connections between sites eventually strengthen. It was also found that effective spike-stimulus delays are consistent with experimentally derived spike-timing-dependent plasticity (STDP) rules, suggesting that STDP is key to drive these changes. However, the impact of STDP at the level of circuits, and the mechanisms governing its modification with neural implants remain poorly understood. The present work describes a recurrent neural network model with probabilistic spiking mechanisms and plastic synapses capable of capturing both neural and synaptic activity statistics relevant to BBCI conditioning protocols. Our model successfully reproduces key experimental results, both established and new, and offers mechanistic insights into spike-triggered conditioning. Using analytical calculations and numerical simulations, we derive optimal operational regimes for BBCIs, and formulate predictions concerning the efficacy of spike-triggered conditioning in different regimes of cortical activity. PMID:28151957

  15. Origin of the spike-timing-dependent plasticity rule

    Science.gov (United States)

    Cho, Myoung Won; Choi, M. Y.

    2016-08-01

    A biological synapse changes its efficacy depending on the difference between pre- and post-synaptic spike timings. Formulating spike-timing-dependent interactions in terms of the path integral, we establish a neural-network model, which makes it possible to predict relevant quantities rigorously by means of standard methods in statistical mechanics and field theory. In particular, the biological synaptic plasticity rule is shown to emerge as the optimal form for minimizing the free energy. It is further revealed that maximization of the entropy of neural activities gives rise to the competitive behavior of biological learning. This demonstrates that statistical mechanics helps to understand rigorously key characteristic behaviors of a neural network, thus providing the possibility of physics serving as a useful and relevant framework for probing life.

  16. A Calcium-Dependent Plasticity Rule for HCN Channels Maintains Activity Homeostasis and Stable Synaptic Learning

    Science.gov (United States)

    Honnuraiah, Suraj; Narayanan, Rishikesh

    2013-01-01

    Theoretical and computational frameworks for synaptic plasticity and learning have a long and cherished history, with few parallels within the well-established literature for plasticity of voltage-gated ion channels. In this study, we derive rules for plasticity in the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, and assess the synergy between synaptic and HCN channel plasticity in establishing stability during synaptic learning. To do this, we employ a conductance-based model for the hippocampal pyramidal neuron, and incorporate synaptic plasticity through the well-established Bienenstock-Cooper-Munro (BCM)-like rule for synaptic plasticity, wherein the direction and strength of the plasticity is dependent on the concentration of calcium influx. Under this framework, we derive a rule for HCN channel plasticity to establish homeostasis in synaptically-driven firing rate, and incorporate such plasticity into our model. In demonstrating that this rule for HCN channel plasticity helps maintain firing rate homeostasis after bidirectional synaptic plasticity, we observe a linear relationship between synaptic plasticity and HCN channel plasticity for maintaining firing rate homeostasis. Motivated by this linear relationship, we derive a calcium-dependent rule for HCN-channel plasticity, and demonstrate that firing rate homeostasis is maintained in the face of synaptic plasticity when moderate and high levels of cytosolic calcium influx induced depression and potentiation of the HCN-channel conductance, respectively. Additionally, we show that such synergy between synaptic and HCN-channel plasticity enhances the stability of synaptic learning through metaplasticity in the BCM-like synaptic plasticity profile. Finally, we demonstrate that the synergistic interaction between synaptic and HCN-channel plasticity preserves robustness of information transfer across the neuron under a rate-coding schema. Our results establish specific physiological roles

  17. Timing intervals using population synchrony and spike timing dependent plasticity

    Directory of Open Access Journals (Sweden)

    Wei Xu

    2016-12-01

    Full Text Available We present a computational model by which ensembles of regularly spiking neurons can encode different time intervals through synchronous firing. We show that a neuron responding to a large population of convergent inputs has the potential to learn to produce an appropriately-timed output via spike-time dependent plasticity. We explain why temporal variability of this population synchrony increases with increasing time intervals. We also show that the scalar property of timing and its violation at short intervals can be explained by the spike-wise accumulation of jitter in the inter-spike intervals of timing neurons. We explore how the challenge of encoding longer time intervals can be overcome and conclude that this may involve a switch to a different population of neurons with lower firing rate, with the added effect of producing an earlier bias in response. Experimental data on human timing performance show features in agreement with the model’s output.

  18. Spin-orbit torque induced spike-timing dependent plasticity

    Energy Technology Data Exchange (ETDEWEB)

    Sengupta, Abhronil, E-mail: asengup@purdue.edu; Al Azim, Zubair; Fong, Xuanyao; Roy, Kaushik [School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)

    2015-03-02

    Nanoelectronic devices that mimic the functionality of synapses are a crucial requirement for performing cortical simulations of the brain. In this work, we propose a ferromagnet-heavy metal heterostructure that employs spin-orbit torque to implement spike-timing dependent plasticity. The proposed device offers the advantage of decoupled spike transmission and programming current paths, thereby leading to reliable operation during online learning. Possible arrangement of such devices in a crosspoint architecture can pave the way for ultra-dense neural networks. Simulation studies indicate that the device has the potential of achieving pico-Joule level energy consumption (maximum 2 pJ per synaptic event) which is comparable to the energy consumption for synaptic events in biological synapses.

  19. Dual coding with STDP in a spiking recurrent neural network model of the hippocampus.

    Directory of Open Access Journals (Sweden)

    Daniel Bush

    Full Text Available The firing rate of single neurons in the mammalian hippocampus has been demonstrated to encode for a range of spatial and non-spatial stimuli. It has also been demonstrated that phase of firing, with respect to the theta oscillation that dominates the hippocampal EEG during stereotype learning behaviour, correlates with an animal's spatial location. These findings have led to the hypothesis that the hippocampus operates using a dual (rate and temporal coding system. To investigate the phenomenon of dual coding in the hippocampus, we examine a spiking recurrent network model with theta coded neural dynamics and an STDP rule that mediates rate-coded Hebbian learning when pre- and post-synaptic firing is stochastic. We demonstrate that this plasticity rule can generate both symmetric and asymmetric connections between neurons that fire at concurrent or successive theta phase, respectively, and subsequently produce both pattern completion and sequence prediction from partial cues. This unifies previously disparate auto- and hetero-associative network models of hippocampal function and provides them with a firmer basis in modern neurobiology. Furthermore, the encoding and reactivation of activity in mutually exciting Hebbian cell assemblies demonstrated here is believed to represent a fundamental mechanism of cognitive processing in the brain.

  20. A framework for plasticity implementation on the SpiNNaker neural architecture

    Directory of Open Access Journals (Sweden)

    Francesco eGalluppi

    2015-01-01

    Full Text Available Many of the precise biological mechanisms of synaptic plasticity remain elusive, but simulations of neural networks have greatly enhanced our understanding of how specific global functions arise from the massively parallel computation of neurons and local Hebbian or spike-timing dependent plasticity rules. For simulating large portions of neural tissue, this has created an increasingly strong need for large scale simulations of plastic neural networks on special purpose hardware platforms, because synaptic transmissions and updates are badly matched to computing style supported by current architectures. Because of the great diversity of biological plasticity phenomena and the corresponding diversity of models, there is a great need for testing various hypotheses about plasticity before committing to one hardware implementation. Here we present a novel framework for investigating different plasticity approaches on the SpiNNaker distributed digital neural simulation platform.The key innovation of the proposed architecture is to exploit the reconfigurability of the ARM processors inside SpiNNaker, dedicating a subset of them exclusively to process synaptic plasticity updates, while the rest perform the usual neural and synaptic simulations. We demonstrate the flexibility of the proposed approach by showing the implementation of a variety of spike- and rate-based learning rules, including standard Spike-Timing dependent plasticity (STDP, voltage-dependent STDP, and the rate-based BCM rule.We analyze their performance and validate them by running classical learning experiments in real time on a 4-chip SpiNNaker board. The result is an efficient, modular, flexible and scalable framework, which provides a valuable tool for the fast and easy exploration of learning models of very different kinds on the parallel and reconfigurable SpiNNaker system.

  1. A framework for plasticity implementation on the SpiNNaker neural architecture.

    Science.gov (United States)

    Galluppi, Francesco; Lagorce, Xavier; Stromatias, Evangelos; Pfeiffer, Michael; Plana, Luis A; Furber, Steve B; Benosman, Ryad B

    2014-01-01

    Many of the precise biological mechanisms of synaptic plasticity remain elusive, but simulations of neural networks have greatly enhanced our understanding of how specific global functions arise from the massively parallel computation of neurons and local Hebbian or spike-timing dependent plasticity rules. For simulating large portions of neural tissue, this has created an increasingly strong need for large scale simulations of plastic neural networks on special purpose hardware platforms, because synaptic transmissions and updates are badly matched to computing style supported by current architectures. Because of the great diversity of biological plasticity phenomena and the corresponding diversity of models, there is a great need for testing various hypotheses about plasticity before committing to one hardware implementation. Here we present a novel framework for investigating different plasticity approaches on the SpiNNaker distributed digital neural simulation platform. The key innovation of the proposed architecture is to exploit the reconfigurability of the ARM processors inside SpiNNaker, dedicating a subset of them exclusively to process synaptic plasticity updates, while the rest perform the usual neural and synaptic simulations. We demonstrate the flexibility of the proposed approach by showing the implementation of a variety of spike- and rate-based learning rules, including standard Spike-Timing dependent plasticity (STDP), voltage-dependent STDP, and the rate-based BCM rule. We analyze their performance and validate them by running classical learning experiments in real time on a 4-chip SpiNNaker board. The result is an efficient, modular, flexible and scalable framework, which provides a valuable tool for the fast and easy exploration of learning models of very different kinds on the parallel and reconfigurable SpiNNaker system.

  2. Activity-Dependent Plasticity of Astroglial Potassium and Glutamate Clearance

    Science.gov (United States)

    Cheung, Giselle; Sibille, Jérémie; Zapata, Jonathan; Rouach, Nathalie

    2015-01-01

    Recent evidence has shown that astrocytes play essential roles in synaptic transmission and plasticity. Nevertheless, how neuronal activity alters astroglial functional properties and whether such properties also display specific forms of plasticity still remain elusive. Here, we review research findings supporting this aspect of astrocytes, focusing on their roles in the clearance of extracellular potassium and glutamate, two neuroactive substances promptly released during excitatory synaptic transmission. Their subsequent removal, which is primarily carried out by glial potassium channels and glutamate transporters, is essential for proper functioning of the brain. Similar to neurons, different forms of short- and long-term plasticity in astroglial uptake have been reported. In addition, we also present novel findings showing robust potentiation of astrocytic inward currents in response to repetitive stimulations at mild frequencies, as low as 0.75 Hz, in acute hippocampal slices. Interestingly, neurotransmission was hardly affected at this frequency range, suggesting that astrocytes may be more sensitive to low frequency stimulation and may exhibit stronger plasticity than neurons to prevent hyperexcitability. Taken together, these important findings strongly indicate that astrocytes display both short- and long-term plasticity in their clearance of excess neuroactive substances from the extracellular space, thereby regulating neuronal activity and brain homeostasis. PMID:26346563

  3. The discovery of GluA3-dependent synaptic plasticity

    NARCIS (Netherlands)

    Renner, M.C.

    2016-01-01

    AMPA receptors (AMPARs) are responsible for fast excitatory synaptic transmission. GluA1-containing AMPARs have been extensively studied and play a key role in several forms of synaptic plasticity and memory. In contrast, GluA3-containing AMPARs have historically been ignored because they have

  4. Time-dependent permeation of carbon dioxide through a polyimide membrane above the plasticization pressure

    NARCIS (Netherlands)

    Wessling, M.; Huisman, I.; Boomgaard, van den Th.; Smolders, C.A.

    1995-01-01

    The time-dependent permeation behavior of a glassy polyimide is studied above and below the plasticization pressure with carbon dioxide as the permeating gas. The work particularly focuses on the quantification of the slow increase in permeability at feed pressures above the plasticization pressure.

  5. Calcium-dependent phosphorylation regulates neuronal stability and plasticity in a highly precise pacemaker nucleus.

    Science.gov (United States)

    George, Andrew A; Macleod, Gregory T; Zakon, Harold H

    2011-07-01

    Specific types of neurons show stable, predictable excitability properties, while other neurons show transient adaptive plasticity of their excitability. However, little attention has been paid to how the cellular pathways underlying adaptive plasticity interact with those that maintain neuronal stability. We addressed this question in the pacemaker neurons from a weakly electric fish because these neurons show a highly stable spontaneous firing rate as well as an N-methyl-D-aspartate (NMDA) receptor-dependent form of plasticity. We found that basal firing rates were regulated by a serial interaction of conventional and atypical PKC isoforms and that this interaction establishes individual differences within the species. We observed that NMDA receptor-dependent plasticity is achieved by further activation of these kinases. Importantly, the PKC pathway is maintained in an unsaturated baseline state to allow further Ca(2+)-dependent activation during plasticity. On the other hand, the Ca(2+)/calmodulin-dependent phosphatase calcineurin does not regulate baseline firing but is recruited to control the duration of the NMDA receptor-dependent plasticity and return the pacemaker firing rate back to baseline. This work illustrates how neuronal plasticity can be realized by biasing ongoing mechanisms of stability (e.g., PKC) and terminated by recruiting alternative mechanisms (e.g., calcineurin) that constrain excitability. We propose this as a general model for regulating activity-dependent change in neuronal excitability.

  6. Calculation of temperature distribution in adiabatic shear band based on gradient-dependent plasticity

    Institute of Scientific and Technical Information of China (English)

    王学滨

    2004-01-01

    A method for calculation of temperature distribution in adiabatic shear band is proposed in terms of gradient-dependent plasticity where the characteristic length describes the interactions and interplaying among microstructures. First, the increment of the plastic shear strain distribution in adiabatic shear band is obtained based on gradient-dependent plasticity. Then, the plastic work distribution is derived according to the current flow shear stress and the obtained increment of plastic shear strain distribution. In the light of the well-known assumption that 90% of plastic work is converted into the heat resulting in increase in temperature in adiabatic shear band, the increment of the temperature distribution is presented. Next, the average temperature increment in the shear band is calculated to compute the change in flow shear stress due to the thermal softening effect. After the actual flow shear stress considering the thermal softening effect is obtained according to the Johnson-Cook constitutive relation, the increment of the plastic shear strain distribution, the plastic work and the temperature in the next time step are recalculated until the total time is consumed. Summing the temperature distribution leads to rise in the total temperature distribution. The present calculated maximum temperature in adiabatic shear band in titanium agrees with the experimental observations. Moreover, the temperature profiles for different flow shear stresses are qualitatively consistent with experimental and numerical results. Effects of some related parameters on the temperature distribution are also predicted.

  7. Discrete dislocation plasticity analysis of loading rate-dependent static friction

    Science.gov (United States)

    Song, H.; Deshpande, V. S.; Van der Giessen, E.

    2016-08-01

    From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent on the size of the contact, but also on the rate of deformation. Moreover, depending on its physical origin, adhesion can also be size and rate dependent, albeit different from plasticity. We present a two-dimensional model that incorporates both discrete dislocation plasticity inside a face-centred cubic crystal and adhesion in the interface to understand the rate dependence of friction caused by micrometre-size asperities. The friction strength is the outcome of the competition between adhesion and discrete dislocation plasticity. As a function of contact size, the friction strength contains two plateaus: at small contact length (≲0.6 μ m), the onset of sliding is fully controlled by adhesion while for large contact length (≳10 μ m), the friction strength approaches the size-independent plastic shear yield strength. The transition regime at intermediate contact size is a result of partial de-cohesion and size-dependent dislocation plasticity, and is determined by dislocation properties, interfacial properties as well as by the loading rate.

  8. Dosage-dependent effect of dopamine D2 receptor activation on motor cortex plasticity in humans.

    Science.gov (United States)

    Fresnoza, Shane; Stiksrud, Elisabeth; Klinker, Florian; Liebetanz, David; Paulus, Walter; Kuo, Min-Fang; Nitsche, Michael A

    2014-08-06

    The neuromodulator dopamine plays an important role in synaptic plasticity. The effects depend on receptor subtypes, affinity, concentration level, and the kind of neuroplasticity induced. In animal experiments, dopamine D2-like receptor stimulation revealed partially antagonistic effects on plasticity, which might be explained by dosage dependency. In humans, D2 receptor block abolishes plasticity, and the D2/D3, but predominantly D3, receptor agonist ropinirol has a dosage-dependent nonlinear affect on plasticity. Here we aimed to determine the specific affect of D2 receptor activation on neuroplasticity in humans, because physiological effects of D2 and D3 receptors might differ. Therefore, we combined application of the selective D2 receptor agonist bromocriptine (2.5, 10, and 20 mg or placebo medication) with anodal and cathodal transcranial direct current stimulation (tDCS), which induces nonfocal plasticity, and with paired associative stimulation (PAS) generating a more focal kind of plasticity in the motor cortex of healthy humans. Plasticity was monitored by transcranial magnetic stimulation-induced motor-evoked potential amplitudes. For facilitatory tDCS, bromocriptine prevented plasticity induction independent from drug dosage. However, its application resulted in an inverted U-shaped dose-response curve on inhibitory tDCS, excitability-diminishing PAS, and to a minor degree on excitability-enhancing PAS. These data support the assumption that modulation of D2-like receptor activity exerts a nonlinear dose-dependent effect on neuroplasticity in the human motor cortex that differs from predominantly D3 receptor activation and that the kind of plasticity-induction procedure is relevant for its specific impact.

  9. Model for charge/discharge-rate-dependent plastic flow in amorphous battery materials

    Science.gov (United States)

    Khosrownejad, S. M.; Curtin, W. A.

    2016-09-01

    Plastic flow is an important mechanism for relaxing stresses that develop due to swelling/shrinkage during charging/discharging of battery materials. Amorphous high-storage-capacity Li-Si has lower flow stresses than crystalline materials but there is evidence that the plastic flow stress depends on the conditions of charging and discharging, indicating important non-equilibrium aspects to the flow behavior. Here, a mechanistically-based constitutive model for rate-dependent plastic flow in amorphous materials, such as LixSi alloys, during charging and discharging is developed based on two physical concepts: (i) excess energy is stored in the material during electrochemical charging and discharging due to the inability of the amorphous material to fully relax during the charging/discharging process and (ii) this excess energy reduces the barriers for plastic flow processes and thus reduces the applied stresses necessary to cause plastic flow. The plastic flow stress is thus a competition between the time scales of charging/discharging and the time scales of glassy relaxation. The two concepts, as well as other aspects of the model, are validated using molecular simulations on a model Li-Si system. The model is applied to examine the plastic flow behavior of typical specimen geometries due to combined charging/discharging and stress history, and the results generally rationalize experimental observations.

  10. Learning of Precise Spike Times with Homeostatic Membrane Potential Dependent Synaptic Plasticity.

    Directory of Open Access Journals (Sweden)

    Christian Albers

    Full Text Available Precise spatio-temporal patterns of neuronal action potentials underly e.g. sensory representations and control of muscle activities. However, it is not known how the synaptic efficacies in the neuronal networks of the brain adapt such that they can reliably generate spikes at specific points in time. Existing activity-dependent plasticity rules like Spike-Timing-Dependent Plasticity are agnostic to the goal of learning spike times. On the other hand, the existing formal and supervised learning algorithms perform a temporally precise comparison of projected activity with the target, but there is no known biologically plausible implementation of this comparison. Here, we propose a simple and local unsupervised synaptic plasticity mechanism that is derived from the requirement of a balanced membrane potential. Since the relevant signal for synaptic change is the postsynaptic voltage rather than spike times, we call the plasticity rule Membrane Potential Dependent Plasticity (MPDP. Combining our plasticity mechanism with spike after-hyperpolarization causes a sensitivity of synaptic change to pre- and postsynaptic spike times which can reproduce Hebbian spike timing dependent plasticity for inhibitory synapses as was found in experiments. In addition, the sensitivity of MPDP to the time course of the voltage when generating a spike allows MPDP to distinguish between weak (spurious and strong (teacher spikes, which therefore provides a neuronal basis for the comparison of actual and target activity. For spatio-temporal input spike patterns our conceptually simple plasticity rule achieves a surprisingly high storage capacity for spike associations. The sensitivity of the MPDP to the subthreshold membrane potential during training allows robust memory retrieval after learning even in the presence of activity corrupted by noise. We propose that MPDP represents a biophysically plausible mechanism to learn temporal target activity patterns.

  11. Statistical model of rough surface contact accounting for size-dependent plasticity and asperity interaction

    Science.gov (United States)

    Song, H.; Vakis, A. I.; Liu, X.; Van der Giessen, E.

    2017-09-01

    The work by Greenwood and Williamson (GW) has initiated a simple but effective method of contact mechanics: statistical modeling based on the mechanical response of a single asperity. Two main assumptions of the original GW model are that the asperity response is purely elastic and that there is no interaction between asperities. However, as asperities lie on a continuous substrate, the deformation of one asperity will change the height of all other asperities through deformation of the substrate and will thus influence subsequent contact evolution. Moreover, a high asperity contact pressure will result in plasticity, which below tens of microns is size dependent, with smaller being harder. In this paper, the asperity interaction effect is taken into account through substrate deformation, while a size-dependent plasticity model is adopted for individual asperities. The intrinsic length in the strain gradient plasticity (SGP) theory is obtained by fitting to two-dimensional discrete dislocation plasticity simulations of the flattening of a single asperity. By utilizing the single asperity response in three dimensions and taking asperity interaction into account, a statistical calculation of rough surface contact is performed. The effectiveness of the statistical model is addressed by comparison with full-detail finite element simulations of rough surface contact using SGP. Throughout the paper, our focus is on the difference of contact predictions based on size-dependent plasticity as compared to conventional size-independent plasticity.

  12. Vibrational resonance in adaptive small-world neuronal networks with spike-timing-dependent plasticity

    Science.gov (United States)

    Yu, Haitao; Guo, Xinmeng; Wang, Jiang; Deng, Bin; Wei, Xile

    2015-10-01

    The phenomenon of vibrational resonance is investigated in adaptive Newman-Watts small-world neuronal networks, where the strength of synaptic connections between neurons is modulated based on spike-timing-dependent plasticity. Numerical results demonstrate that there exists appropriate amplitude of high-frequency driving which is able to optimize the neural ensemble response to the weak low-frequency periodic signal. The effect of networked vibrational resonance can be significantly affected by spike-timing-dependent plasticity. It is shown that spike-timing-dependent plasticity with dominant depression can always improve the efficiency of vibrational resonance, and a small adjusting rate can promote the transmission of weak external signal in small-world neuronal networks. In addition, the network topology plays an important role in the vibrational resonance in spike-timing-dependent plasticity-induced neural systems, where the system response to the subthreshold signal is maximized by an optimal network structure. Furthermore, it is demonstrated that the introduction of inhibitory synapses can considerably weaken the phenomenon of vibrational resonance in the hybrid small-world neuronal networks with spike-timing-dependent plasticity.

  13. NMDA receptors mediate stimulus-timing-dependent plasticity and neural synchrony in the dorsal cochlear nucleus

    Directory of Open Access Journals (Sweden)

    Roxana A Stefanescu

    2015-11-01

    Full Text Available Auditory information relayed by auditory nerve fibers and somatosensory information relayed by granule cell parallel fibers converge on the fusiform cells (FCs of the dorsal cochlear nucleus, the first brain station of the auditory pathway. In vitro, parallel fiber synapses on FCs exhibit spike-timing-dependent plasticity with Hebbian learning rules, partially mediated by the NMDA receptor (NMDAr. Well-timed bimodal auditory-somatosensory stimulation, in vivo equivalent of spike-timing-dependent plasticity, can induce stimulus-timing-dependent plasticity (StTDP of the FCs spontaneous and tone-evoked firing rates. In healthy guinea pigs, the resulting distribution of StTDP learning rules across a FC neural population is dominated by a Hebbian profile while anti-Hebbian, suppressive and enhancing LRs are less frequent. In this study, we investigate in vivo, the NMDAr contribution to FC baseline activity and long term plasticity. We find that blocking the NMDAr decreases the synchronization of FC- spontaneous activity and mediates differential modulation of FC rate-level functions such that low, and high threshold units are more likely to increase, and decrease, respectively, their maximum amplitudes. Three significant alterations in mean learning-rule profiles were identified: transitions from an initial Hebbian profile towards (1 an anti-Hebbian and (2 a suppressive profile, and (3 transitions from an anti-Hebbian to a Hebbian profile. FC units preserving their learning rules showed instead, NMDAr-dependent plasticity to unimodal acoustic stimulation, with persistent depression of tone-evoked responses changing to persistent enhancement following the NMDAr antagonist. These results reveal a crucial role of the NMDAr in mediating FC baseline activity and long-term plasticity which have important implications for signal processing and auditory pathologies related to maladaptive plasticity of dorsal cochlear nucleus circuitry.

  14. The requirement of BDNF for hippocampal synaptic plasticity is experience‐dependent

    Science.gov (United States)

    Aarse, Janna; Herlitze, Stefan

    2016-01-01

    ABSTRACT Brain‐derived neurotrophic factor (BDNF) supports neuronal survival, growth, and differentiation and has been implicated in forms of hippocampus‐dependent learning. In vitro, a specific role in hippocampal synaptic plasticity has been described, although not all experience‐dependent forms of synaptic plasticity critically depend on BDNF. Synaptic plasticity is likely to enable long‐term synaptic information storage and memory, and the induction of persistent (>24 h) forms, such as long‐term potentiation (LTP) and long‐term depression (LTD) is tightly associated with learning specific aspects of a spatial representation. Whether BDNF is required for persistent (>24 h) forms of LTP and LTD, and how it contributes to synaptic plasticity in the freely behaving rodent has never been explored. We examined LTP, LTD, and related forms of learning in the CA1 region of freely dependent mice that have a partial knockdown of BDNF (BDNF+/−). We show that whereas early‐LTD (BDNF, short‐term depression (BDNF is required for LTP that is induced by mild, but not strong short afferent stimulation protocols. Object‐place learning triggers LTD in the CA1 region of mice. We observed that object‐place memory was impaired and the object‐place exploration failed to induce LTD in BDNF+/− mice. Furthermore, spatial reference memory, that is believed to be enabled by LTP, was also impaired. Taken together, these data indicate that BDNF is required for specific, but not all, forms of hippocampal‐dependent information storage and memory. Thus, very robust forms of synaptic plasticity may circumvent the need for BDNF, rather it may play a specific role in the optimization of weaker forms of plasticity. The finding that both learning‐facilitated LTD and spatial reference memory are both impaired in BDNF+/− mice, suggests moreover, that it is critically required for the physiological encoding of hippocampus‐dependent memory. © 2015 The Authors

  15. A numerical basis for strain-gradient plasticity theory: Rate-independent and rate-dependent formulations

    DEFF Research Database (Denmark)

    Nielsen, Kim Lau; Niordson, Christian Frithiof

    2014-01-01

    of a single plastic zone is analyzed to illustrate the agreement with earlier published results, whereafter examples of (ii) multiple plastic zone interaction, and (iii) elastic–plastic loading/unloading are presented. Here, the simple shear problem of an infinite slab constrained between rigid plates......–plastic loading/unloading and the interaction of multiple plastic zones, is proposed. The predicted model response is compared to the corresponding rate-dependent version of visco-plastic origin, and coinciding results are obtained in the limit of small strain-rate sensitivity. First, (i) the evolution...

  16. State-dependent and timing-dependent bidirectional associative plasticity in the human SMA-M1 network.

    Science.gov (United States)

    Arai, Noritoshi; Müller-Dahlhaus, Florian; Murakami, Takenobu; Bliem, Barbara; Lu, Ming-Kuei; Ugawa, Yoshikazu; Ziemann, Ulf

    2011-10-26

    The supplementary motor area (SMA-proper) plays a key role in the preparation and execution of voluntary movements. Anatomically, SMA-proper is densely reciprocally connected to primary motor cortex (M1), but neuronal coordination within the SMA-M1 network and its modification by external perturbation are not well understood. Here we modulated the SMA-M1 network using MR-navigated multicoil associative transcranial magnetic stimulation in healthy subjects. Changes in corticospinal excitability were assessed by recording motor evoked potential (MEP) amplitude bilaterally in a hand muscle. We found timing-dependent bidirectional Hebbian-like MEP changes during and for at least 30 min after paired associative SMA-M1 stimulation. MEP amplitude increased if SMA stimulation preceded M1 stimulation by 6 ms, but decreased if SMA stimulation lagged M1 stimulation by 15 ms. This associative plasticity in the SMA-M1 network was highly topographically specific because paired associative stimulation of pre-SMA and M1 did not result in any significant MEP change. Furthermore, associative plasticity in the SMA-M1 network was strongly state-dependent because it required priming by near-simultaneous M1 stimulation to occur. We conclude that timing-dependent bidirectional associative plasticity is demonstrated for the first time at the systems level of a human corticocortical neuronal network. The properties of this form of plasticity are fully compatible with spike-timing-dependent plasticity as defined at the cellular level. The necessity of priming may reflect the strong interhemispheric connectivity of the SMA-M1 network. Findings are relevant for better understanding reorganization and potentially therapeutic modification of neuronal coordination in the SMA-M1 network after cerebral lesions such as stroke.

  17. Instrument specific use-dependent plasticity shapes the anatomical properties of the corpus callosum

    DEFF Research Database (Denmark)

    Vollmann, Henning; Ragert, Patrick; Conde, Virginia;

    2014-01-01

    , the amount of IHI in pianists was comparable to that of non-musicians and there was no significant structure-function relationship. Our findings indicate instrument specific use-dependent plasticity in both functional (IHI) and structural (FA) connectivity of motor related brain regions in musicians....

  18. Mechanical and time-dependent behavior of wood-plastic composites subjected to tension and compression

    Science.gov (United States)

    Scott E. Hamel; John C. Hermanson; Steven M. Cramer

    2012-01-01

    The thermoplastics within wood—plastic composites (WPCs) are known to experience significant time-dependent deformation or creep. In some formulations, creep deformation can be twice as much as the initial quasi-static strain in as little as 4 days. While extensive work has been done on the creep behavior of pure polymers, little information is available on the...

  19. Discrete dislocation plasticity analysis of loading rate-dependent static friction

    NARCIS (Netherlands)

    Song, H.; Deshpande, V. S.; van der Giessen, E.

    2016-01-01

    From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent

  20. The effect of synaptic plasticity on orientation selectivity in a balanced model of primary visual cortex

    Directory of Open Access Journals (Sweden)

    Soledad eGonzalo Cogno

    2015-08-01

    Full Text Available Orientation selectivity is ubiquitous in the primary visual cortex (V1 of mammals. In cats and monkeys, V1 displays spatially ordered maps of orientation preference. Instead, in mice, squirrels and rats, orientation selective neurons in V1 are not spatially organized, giving rise to a seemingly random pattern usually referred to as a salt-and-pepper layout. The fact that such different organizations can sharpen orientation tuning leads to question the structural role of the intracortical connections; specifically the influence of plasticity and the generation of functional connectivity. In this work, we analyze the effect of plasticity processes on orientation selectivity for both scenarios. We study a computational model of layer 2/3 and a reduced one-dimensional model of orientation selective neurons, both in the balanced state. We analyze two plasticity mechanisms. The first one involves spike-timing dependent plasticity (STDP, while the second one considers the reconnection of the interactions according to the preferred orientations of the neurons. We find that under certain conditions STDP can indeed improve selectivity but it works in a somehow unexpected way, that is, effectively decreasing the modulated part of the intracortical connectivity as compared to the non-modulated part of it. For the reconnection mechanism we find that increasing functional connectivity leads, in fact, to a decrease in orientation selectivity if the network is in a stable balanced state. Both counterintuitive results are a consequence of the dynamics of the balanced state. We also find that selectivity can increase due to a reconnection process if the resulting connections give rise to an unstable balanced state. We compare these findings with recent experimental results.

  1. A kinetic model of dopamine- and calcium-dependent striatal synaptic plasticity.

    Directory of Open Access Journals (Sweden)

    Takashi Nakano

    2010-02-01

    Full Text Available Corticostriatal synapse plasticity of medium spiny neurons is regulated by glutamate input from the cortex and dopamine input from the substantia nigra. While cortical stimulation alone results in long-term depression (LTD, the combination with dopamine switches LTD to long-term potentiation (LTP, which is known as dopamine-dependent plasticity. LTP is also induced by cortical stimulation in magnesium-free solution, which leads to massive calcium influx through NMDA-type receptors and is regarded as calcium-dependent plasticity. Signaling cascades in the corticostriatal spines are currently under investigation. However, because of the existence of multiple excitatory and inhibitory pathways with loops, the mechanisms regulating the two types of plasticity remain poorly understood. A signaling pathway model of spines that express D1-type dopamine receptors was constructed to analyze the dynamic mechanisms of dopamine- and calcium-dependent plasticity. The model incorporated all major signaling molecules, including dopamine- and cyclic AMP-regulated phosphoprotein with a molecular weight of 32 kDa (DARPP32, as well as AMPA receptor trafficking in the post-synaptic membrane. Simulations with dopamine and calcium inputs reproduced dopamine- and calcium-dependent plasticity. Further in silico experiments revealed that the positive feedback loop consisted of protein kinase A (PKA, protein phosphatase 2A (PP2A, and the phosphorylation site at threonine 75 of DARPP-32 (Thr75 served as the major switch for inducing LTD and LTP. Calcium input modulated this loop through the PP2B (phosphatase 2B-CK1 (casein kinase 1-Cdk5 (cyclin-dependent kinase 5-Thr75 pathway and PP2A, whereas calcium and dopamine input activated the loop via PKA activation by cyclic AMP (cAMP. The positive feedback loop displayed robust bi-stable responses following changes in the reaction parameters. Increased basal dopamine levels disrupted this dopamine-dependent plasticity. The

  2. Self-Organization of Microcircuits in Networks of Spiking Neurons with Plastic Synapses.

    Directory of Open Access Journals (Sweden)

    Gabriel Koch Ocker

    2015-08-01

    Full Text Available The synaptic connectivity of cortical networks features an overrepresentation of certain wiring motifs compared to simple random-network models. This structure is shaped, in part, by synaptic plasticity that promotes or suppresses connections between neurons depending on their joint spiking activity. Frequently, theoretical studies focus on how feedforward inputs drive plasticity to create this network structure. We study the complementary scenario of self-organized structure in a recurrent network, with spike timing-dependent plasticity driven by spontaneous dynamics. We develop a self-consistent theory for the evolution of network structure by combining fast spiking covariance with a slow evolution of synaptic weights. Through a finite-size expansion of network dynamics we obtain a low-dimensional set of nonlinear differential equations for the evolution of two-synapse connectivity motifs. With this theory in hand, we explore how the form of the plasticity rule drives the evolution of microcircuits in cortical networks. When potentiation and depression are in approximate balance, synaptic dynamics depend on weighted divergent, convergent, and chain motifs. For additive, Hebbian STDP these motif interactions create instabilities in synaptic dynamics that either promote or suppress the initial network structure. Our work provides a consistent theoretical framework for studying how spiking activity in recurrent networks interacts with synaptic plasticity to determine network structure.

  3. Self-Organization of Microcircuits in Networks of Spiking Neurons with Plastic Synapses.

    Science.gov (United States)

    Ocker, Gabriel Koch; Litwin-Kumar, Ashok; Doiron, Brent

    2015-08-01

    The synaptic connectivity of cortical networks features an overrepresentation of certain wiring motifs compared to simple random-network models. This structure is shaped, in part, by synaptic plasticity that promotes or suppresses connections between neurons depending on their joint spiking activity. Frequently, theoretical studies focus on how feedforward inputs drive plasticity to create this network structure. We study the complementary scenario of self-organized structure in a recurrent network, with spike timing-dependent plasticity driven by spontaneous dynamics. We develop a self-consistent theory for the evolution of network structure by combining fast spiking covariance with a slow evolution of synaptic weights. Through a finite-size expansion of network dynamics we obtain a low-dimensional set of nonlinear differential equations for the evolution of two-synapse connectivity motifs. With this theory in hand, we explore how the form of the plasticity rule drives the evolution of microcircuits in cortical networks. When potentiation and depression are in approximate balance, synaptic dynamics depend on weighted divergent, convergent, and chain motifs. For additive, Hebbian STDP these motif interactions create instabilities in synaptic dynamics that either promote or suppress the initial network structure. Our work provides a consistent theoretical framework for studying how spiking activity in recurrent networks interacts with synaptic plasticity to determine network structure.

  4. ON PLASTIC ANISOTROPY OF CONSTITUTIVE MODEL FOR RATE-DEPENDENT SINGLE CRYSTAL

    Institute of Scientific and Technical Information of China (English)

    张光; 张克实; 冯露

    2005-01-01

    An algorithm for single crystals was developed and implemented to simulate plastic anisotropy using a rate-dependent slip model. The proposed procedure was a slightly modified form of single crystal constitutive model of Sarma and Zacharia. Modified Euler method, together with Newton-Raphson method was used to integrate this equation which was stable and efficient. The model together with the developed algorithm was used to study three problems. First, plastic anisotropy was examined by simulating the crystal deformation in tension and plane strain compression, respectively. Secondly, the orientation effect of some material parameters in the model and applied strain rate on plastic anisotropy for single crystal also is investigated. Thirdly, the influence of loading direction on the active slip system was discussed.

  5. Adiabatic shear localization evolution for steel based on the Johnson-Cook model and gradient-dependent plasticity

    Institute of Scientific and Technical Information of China (English)

    Xuebin Wang

    2006-01-01

    Gradient-dependent plasticity is introduced into the phenomenological Johnson-Cook model to study the effects of strainhardening, strain rate sensitivity, thermal-softening, and microstructure. The microstructural effect (interactions and interplay among microstructures) due to heterogeneity of texture plays an important role in the process of development or evolution of an adiabatic shear band with a certain thickness depending on the grain diameter. The distributed plastic shear strain and deformation in the shear band are derived and depend on the critical plastic shear strain corresponding to the peak flow shear stress, the coordinate or position, the internal length parameter, and the average plastic shear strain or the flow shear stress. The critical plastic shear strain, the distributed plastic shear strain, and deformation in the shear band are numerically predicted for a kind of steel deformed at a constant shear strain rate.Beyond the peak shear stress, the local plastic shear strain in the shear band is highly nonuniform and the local plastic shear deformation in the band is highly nonlinear. Shear localization is more apparent with the increase of the average plastic shear strain. The calculated distributions of the local plastic shear strain and deformation agree with the previous numerical and experimental results.

  6. Bounds on the Rate Dependent Plastic Flow of Tantalum up to 75 GPa

    Science.gov (United States)

    Reed, Bryan; Patterson, Reed; Kumar, Mukul

    2013-06-01

    We report improvements in a general thermodynamics-based velocimetry analysis method designed to extract strength and plastic-flow information from shock and ramp compression experiments. The method allows extraction of thermodynamic histories, including deviatoric stress and plastic strain, including nonsteady rate-dependent features. The improved method includes free-surface corrections for pullback waves, reduced noise sensitivity, and application to pressures of 75 GPa and higher. Specifically, we show results for shock waves in tantalum, including bounds on the plastic flow behavior at strain rates exceeding 1e7/s.The deviatoric stress appears to be almost entirely dependent on strain rate, with very little pressure dependence.The deviatoric stress in the post-shock plateau state appears to be very small at higher pressures, calling into question the value of considering strength as a steady- state pressure-dependent quantity. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  7. The BDNF Val66Met polymorphism impairs NMDA receptor-dependent synaptic plasticity in the hippocampus.

    Science.gov (United States)

    Ninan, Ipe; Bath, Kevin G; Dagar, Karishma; Perez-Castro, Rosalia; Plummer, Mark R; Lee, Francis S; Chao, Moses V

    2010-06-30

    The Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene results in a defect in regulated release of BDNF and affects episodic memory and affective behaviors. However, the precise role of the BDNF Val66Met polymorphism in hippocampal synaptic transmission and plasticity has not yet been studied. Therefore, we examined synaptic properties in the hippocampal CA3-CA1 synapses of BDNF(Met/Met) mice and matched wild-type mice. Although basal glutamatergic neurotransmission was normal, both young and adult mice showed a significant reduction in NMDA receptor-dependent long-term potentiation. We also found that NMDA receptor-dependent long-term depression was decreased in BDNF(Met/Met) mice. However, mGluR-dependent long-term depression was not affected by the BDNF Val66Met polymorphism. Consistent with the NMDA receptor-dependent synaptic plasticity impairment, we observed a significant decrease in NMDA receptor neurotransmission in the CA1 pyramidal neurons of BDNF(Met/Met) mice. Thus, these results show that the BDNF Val66Met polymorphism has a direct effect on NMDA receptor transmission, which may account for changes in synaptic plasticity in the hippocampus.

  8. INVESTIGATION ON GRADIENT-DEPENDENT NONLOCAL CONSTITUTIVE MODELS FOR ELASTO-PLASTICITY COUPLED WITH DAMAGE

    Institute of Scientific and Technical Information of China (English)

    SHEN Xin-pu; SHEN Guo-xiao; CHEN Li-xin; YANG Lu

    2005-01-01

    Firstly, typical gradient-dependent nonlocal inelastic models were briefly gradient-dependent constitutive model for plasticity coupled with isotropic damage was presented in the framework of continuum thermodynamics. Numerical scheme for calculation of Laplacian term of damage field with the numerical results obtained by FEM calculation was proposed. Equations have been presented on the basis of Taylor series for both 2-dimensional and 3-dimensional cases, respectively. Numerical results have indicated the validity of the proposed gradient-dependent model and corresponding numerical scheme.

  9. A Rate-Dependent Crystal Plasticity Analysis of Orientation Stability in Biaxial Tension of Magnesium

    Institute of Scientific and Technical Information of China (English)

    Donghong Zhang; Saiyi Li

    2011-01-01

    The development of texture during plastic deformation plays an important role in determining the stretch formability of magnesium alloy sheets. In this study, the orientation stability during equibiaxial tension of magnesium was analyzed based on three dimensional lattice rotations calculated by using a rate-dependent crystal plasticity model and assuming five different combinations of slip modes. The results show that no orientations can satisfy the stability criteria with both zero rotation velocity and convergent orientation flow in all dimensions. However, relatively stable orientations with zero rotation velocity and an overall convergence are found. They are featured by characteristic alignments of specific crystallographic directions in the macroscopic axis of contraction, depending on the slip modes involved in the deformation. It is also shown that the orientation stability varies significantly with the deviation of deformation mode from equibiaxial tension. The simulation results are briefly discussed in comparison with pre-existing experiments.

  10. Kalirin-7 is necessary for normal NMDA receptor-dependent synaptic plasticity

    KAUST Repository

    Lemtiri-Chlieh, Fouad

    2011-12-19

    Background: Dendritic spines represent the postsynaptic component of the vast majority of excitatory synapses present in the mammalian forebrain. The ability of spines to rapidly alter their shape, size, number and receptor content in response to stimulation is considered to be of paramount importance during the development of synaptic plasticity. Indeed, long-term potentiation (LTP), widely believed to be a cellular correlate of learning and memory, has been repeatedly shown to induce both spine enlargement and the formation of new dendritic spines. In our studies, we focus on Kalirin-7 (Kal7), a Rho GDP/GTP exchange factor (Rho-GEF) localized to the postsynaptic density that plays a crucial role in the development and maintenance of dendritic spines both in vitro and in vivo. Previous studies have shown that mice lacking Kal7 (Kal7 KO) have decreased dendritic spine density in the hippocampus as well as focal hippocampal-dependent learning impairments.Results: We have performed a detailed electrophysiological characterization of the role of Kal7 in hippocampal synaptic plasticity. We show that loss of Kal7 results in impaired NMDA receptor-dependent LTP and long-term depression, whereas a NMDA receptor-independent form of LTP is shown to be normal in the absence of Kal7.Conclusions: These results indicate that Kal7 is an essential and selective modulator of NMDA receptor-dependent synaptic plasticity in the hippocampus. 2011 Lemtiri-Chlieh et al; licensee BioMed Central Ltd.

  11. Stimulus-timing dependent multisensory plasticity in the guinea pig dorsal cochlear nucleus.

    Directory of Open Access Journals (Sweden)

    Seth D Koehler

    Full Text Available Multisensory neurons in the dorsal cochlear nucleus (DCN show long-lasting enhancement or suppression of sound-evoked responses when stimulated with combined somatosensory-auditory stimulation. By varying the intervals between sound and somatosensory stimuli we show for the first time in vivo that DCN bimodal responses are influenced by stimulus-timing dependent plasticity. The timing rules and time courses of the observed stimulus-timing dependent plasticity closely mimic those of spike-timing dependent plasticity that have been demonstrated in vitro at parallel-fiber synapses onto DCN principal cells. Furthermore, the degree of inhibition in a neuron influences whether that neuron has Hebbian or anti-Hebbian timing rules. As demonstrated in other cerebellar-like circuits, anti-Hebbian timing rules reflect adaptive filtering, which in the DCN would result in suppression of sound-evoked responses that are predicted by activation of somatosensory inputs, leading to the suppression of body-generated signals such as self-vocalization.

  12. Kalirin-7 is necessary for normal NMDA receptor-dependent synaptic plasticity

    Directory of Open Access Journals (Sweden)

    Lemtiri-Chlieh Fouad

    2011-12-01

    Full Text Available Abstract Background Dendritic spines represent the postsynaptic component of the vast majority of excitatory synapses present in the mammalian forebrain. The ability of spines to rapidly alter their shape, size, number and receptor content in response to stimulation is considered to be of paramount importance during the development of synaptic plasticity. Indeed, long-term potentiation (LTP, widely believed to be a cellular correlate of learning and memory, has been repeatedly shown to induce both spine enlargement and the formation of new dendritic spines. In our studies, we focus on Kalirin-7 (Kal7, a Rho GDP/GTP exchange factor (Rho-GEF localized to the postsynaptic density that plays a crucial role in the development and maintenance of dendritic spines both in vitro and in vivo. Previous studies have shown that mice lacking Kal7 (Kal7KO have decreased dendritic spine density in the hippocampus as well as focal hippocampal-dependent learning impairments. Results We have performed a detailed electrophysiological characterization of the role of Kal7 in hippocampal synaptic plasticity. We show that loss of Kal7 results in impaired NMDA receptor-dependent LTP and long-term depression, whereas a NMDA receptor-independent form of LTP is shown to be normal in the absence of Kal7. Conclusions These results indicate that Kal7 is an essential and selective modulator of NMDA receptor-dependent synaptic plasticity in the hippocampus.

  13. Impaired fear memory specificity associated with deficient endocannabinoid-dependent long-term plasticity.

    Science.gov (United States)

    Lovelace, Jonathan W; Vieira, Philip A; Corches, Alex; Mackie, Ken; Korzus, Edward

    2014-06-01

    In addition to its central role in learning and memory, N-methyl D-aspartate receptor (NMDAR)-dependent signaling regulates central glutamatergic synapse maturation and has been implicated in schizophrenia. We have transiently induced NMDAR hypofunction in infant mice during postnatal days 7-11, followed by testing fear memory specificity and presynaptic plasticity in the prefrontal cortex (PFC) in adult mice. We show that transient NMDAR hypofunction during early brain development, coinciding with the maturation of cortical plasticity results in a loss of an endocannabinoid (eCB)-mediated form of long-term depression (eCB-LTD) at adult central glutamatergic synapses, while another form of presynaptic long-term depression mediated by the metabotropic glutamate receptor 2/3 (mGluR2/3-LTD) remains intact. Mice with this selective impairment of presynaptic plasticity also showed deficits in fear memory specificity. The observed deficit in cortical presynaptic plasticity may represent a neural maladaptation contributing to network instability and abnormal cognitive functioning.

  14. Attaining the rate-independent limit of a rate-dependent strain gradient plasticity theory

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2016-01-01

    The existence of characteristic strain rates in rate-dependent material models, corresponding to rate-independent model behavior, is studied within a back stress based rate-dependent higher order strain gradient crystal plasticity model. Such characteristic rates have recently been observed...... for steady-state processes, and the present study aims to demonstrate that the observations in fact unearth a more widespread phenomenon. In this work, two newly proposed back stress formulations are adopted to account for the strain gradient effects in the single slip simple shear case, and characteristic...

  15. Sugar-dependent modulation of neuronal development, regeneration, and plasticity by chondroitin sulfate proteoglycans.

    Science.gov (United States)

    Miller, Gregory M; Hsieh-Wilson, Linda C

    2015-12-01

    Chondroitin sulfate proteoglycans (CSPGs) play important roles in the developing and mature nervous system, where they guide axons, maintain stable connections, restrict synaptic plasticity, and prevent axon regeneration following CNS injury. The chondroitin sulfate glycosaminoglycan (CS GAG) chains that decorate CSPGs are essential for their functions. Through these sugar chains, CSPGs are able to bind and regulate the activity of a diverse range of proteins. CSPGs have been found both to promote and inhibit neuronal growth. They can promote neurite outgrowth by binding to various growth factors such as midkine (MK), pleiotrophin (PTN), brain-derived neurotrophic factor (BDNF) and other neurotrophin family members. CSPGs can also inhibit neuronal growth and limit plasticity by interacting with transmembrane receptors such as protein tyrosine phosphatase σ (PTPσ), leukocyte common antigen-related (LAR) receptor protein tyrosine phosphatase, and the Nogo receptors 1 and 3 (NgR1 and NgR3). These CS-protein interactions depend on specific sulfation patterns within the CS GAG chains, and accordingly, particular CS sulfation motifs are upregulated during development, in the mature nervous system, and in response to CNS injury. Thus, spatiotemporal regulation of CS GAG biosynthesis may provide an important mechanism to control the functions of CSPGs and to modulate intracellular signaling pathways. Here, we will discuss these sulfation-dependent processes and highlight how the CS sugars on CSPGs contribute to neuronal growth, axon guidance, and plasticity in the nervous system. Copyright © 2015 Elsevier Inc. All rights reserved.

  16. Experience-Dependent Plasticity in Accessory Olfactory Bulb Interneurons following Male-Male Social Interaction.

    Science.gov (United States)

    Cansler, Hillary L; Maksimova, Marina A; Meeks, Julian P

    2017-07-26

    Chemosensory information processing in the mouse accessory olfactory system guides the expression of social behavior. After salient chemosensory encounters, the accessory olfactory bulb (AOB) experiences changes in the balance of excitation and inhibition at reciprocal synapses between mitral cells (MCs) and local interneurons. The mechanisms underlying these changes remain controversial. Moreover, it remains unclear whether MC-interneuron plasticity is unique to specific behaviors, such as mating, or whether it is a more general feature of the AOB circuit. Here, we describe targeted electrophysiological studies of AOB inhibitory internal granule cells (IGCs), many of which upregulate the immediate-early gene Arc after male-male social experience. Following the resident-intruder paradigm, Arc-expressing IGCs in acute AOB slices from resident males displayed stronger excitation than nonexpressing neighbors when sensory inputs were stimulated. The increased excitability of Arc-expressing IGCs was not correlated with changes in the strength or number of excitatory synapses with MCs but was instead associated with increased intrinsic excitability and decreased HCN channel-mediated IH currents. Consistent with increased inhibition by IGCs, MCs responded to sensory input stimulation with decreased depolarization and spiking following resident-intruder encounters. These results reveal that nonmating behaviors drive AOB inhibitory plasticity and indicate that increased MC inhibition involves intrinsic excitability changes in Arc-expressing interneurons.SIGNIFICANCE STATEMENT The accessory olfactory bulb (AOB) is a site of experience-dependent plasticity between excitatory mitral cells (MCs) and inhibitory internal granule cells (IGCs), but the physiological mechanisms and behavioral conditions driving this plasticity remain unclear. Here, we report studies of AOB neuronal plasticity following male-male social chemosensory encounters. We show that the plasticity

  17. Metabolic plasticity during mammalian development is directionally dependent on early nutritional status.

    Science.gov (United States)

    Gluckman, Peter D; Lillycrop, Karen A; Vickers, Mark H; Pleasants, Anthony B; Phillips, Emma S; Beedle, Alan S; Burdge, Graham C; Hanson, Mark A

    2007-07-31

    Developmental plasticity in response to environmental cues can take the form of polyphenism, as for the discrete morphs of some insects, or of an apparently continuous spectrum of phenotype, as for most mammalian traits. The metabolic phenotype of adult rats, including the propensity to obesity, hyperinsulinemia, and hyperphagia, shows plasticity in response to prenatal nutrition and to neonatal administration of the adipokine leptin. Here, we report that the effects of neonatal leptin on hepatic gene expression and epigenetic status in adulthood are directionally dependent on the animal's nutritional status in utero. These results demonstrate that, during mammalian development, the direction of the response to one cue can be determined by previous exposure to another, suggesting the potential for a discontinuous distribution of environmentally induced phenotypes, analogous to the phenomenon of polyphenism.

  18. Oxytocin mediates early experience-dependent cross-modal plasticity in the sensory cortices.

    Science.gov (United States)

    Zheng, Jing-Jing; Li, Shu-Jing; Zhang, Xiao-Di; Miao, Wan-Ying; Zhang, Dinghong; Yao, Haishan; Yu, Xiang

    2014-03-01

    Sensory experience is critical to development and plasticity of neural circuits. Here we report a new form of plasticity in neonatal mice, where early sensory experience cross-modally regulates development of all sensory cortices via oxytocin signaling. Unimodal sensory deprivation from birth through whisker deprivation or dark rearing reduced excitatory synaptic transmission in the correspondent sensory cortex and cross-modally in other sensory cortices. Sensory experience regulated synthesis and secretion of the neuropeptide oxytocin as well as its level in the cortex. Both in vivo oxytocin injection and increased sensory experience elevated excitatory synaptic transmission in multiple sensory cortices and significantly rescued the effects of sensory deprivation. Together, these results identify a new function for oxytocin in promoting cross-modal, experience-dependent cortical development. This link between sensory experience and oxytocin is particularly relevant to autism, where hypersensitivity or hyposensitivity to sensory inputs is prevalent and oxytocin is a hotly debated potential therapy.

  19. Developmental experience-dependent plasticity in the first synapse of the Drosophila olfactory circuit.

    Science.gov (United States)

    Golovin, Randall M; Broadie, Kendal

    2016-12-01

    Evidence accumulating over the past 15 years soundly refutes the dogma that the Drosophila nervous system is hardwired. The preponderance of studies reveals activity-dependent neural circuit refinement driving optimization of behavioral outputs. We describe developmental, sensory input-dependent plasticity in the brain olfactory antennal lobe, which we term long-term central adaption (LTCA). LTCA is evoked by prolonged exposure to an odorant during the first week of posteclosion life, resulting in a persistently decreased response to aversive odors and an enhanced response to attractive odors. This limited window of early-use, experience-dependent plasticity represents a critical period of olfactory circuit refinement tuned by initial sensory input. Consequent behavioral adaptations have been associated with changes in the output of olfactory projection neurons to higher brain centers. Recent studies have indicated a central role for local interneuron signaling in LTCA presentation. Genetic and molecular analyses have implicated the mRNA-binding fragile X mental retardation protein and ataxin-2 regulators, Notch trans-synaptic signaling, and cAMP signal transduction as core regulatory steps driving LTCA. In this article, we discuss the structural, functional, and behavioral changes associated with LTCA and review our current understanding of the molecular pathways underlying these developmental, experience-dependent changes in the olfactory circuitry.

  20. Non-swarming grasshoppers exhibit density-dependent phenotypic plasticity reminiscent of swarming locusts.

    Science.gov (United States)

    Gotham, Steven; Song, Hojun

    2013-11-01

    Locusts are well known for exhibiting an extreme form of density-dependent phenotypic plasticity known as locust phase polyphenism. At low density, locust nymphs are cryptically colored and shy, but at high density they transform into conspicuously colored and gregarious individuals. Most of what we know about locust phase polyphenism come from the study of the desert locust Schistocerca gregaria (Forskål), which is a devastating pest species affecting many countries in North Africa and the Middle East. The desert locust belongs to the grasshopper genus Schistocerca Stål, which includes mostly non-swarming, sedentary species. Recent phylogenetic studies suggest that the desert locust is the earliest branching lineage within Schistocerca, which raises a possibility that the presence of density-dependent phenotypic plasticity may be a plesiomorphic trait for the whole genus. In order to test this idea, we have quantified the effect of rearing density in terms of the resulting behavior, color, and morphology in two non-swarming Schistocerca species native to Florida. When reared in both isolated and crowded conditions, the two non-swarming species, Schistocerca americana (Drury) and Schistocerca serialis cubense (Saussure) clearly exhibited plastic reaction norms in all traits measured, which were reminiscent of the desert locust. Specifically, we found that both species were more active and more attracted to each other when reared in a crowded condition than in isolation. They were mainly bright green in color when isolated, but developed strong black patterns and conspicuous background colors when crowded. We found a strong effect of rearing density in terms of size. There were also more mechanoreceptor hairs on the outer face of the hind femora in the crowded nymphs in both species. Although both species responded similarly, there were some clear species-specific differences in terms of color and behavior. Furthermore, we compare and contrast our findings with

  1. Enhancement of signal sensitivity in a heterogeneous neural network refined from synaptic plasticity

    Energy Technology Data Exchange (ETDEWEB)

    Li Xiumin; Small, Michael, E-mail: ensmall@polyu.edu.h, E-mail: 07901216r@eie.polyu.edu.h [Department of Electronic and Information Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon (Hong Kong)

    2010-08-15

    Long-term synaptic plasticity induced by neural activity is of great importance in informing the formation of neural connectivity and the development of the nervous system. It is reasonable to consider self-organized neural networks instead of prior imposition of a specific topology. In this paper, we propose a novel network evolved from two stages of the learning process, which are respectively guided by two experimentally observed synaptic plasticity rules, i.e. the spike-timing-dependent plasticity (STDP) mechanism and the burst-timing-dependent plasticity (BTDP) mechanism. Due to the existence of heterogeneity in neurons that exhibit different degrees of excitability, a two-level hierarchical structure is obtained after the synaptic refinement. This self-organized network shows higher sensitivity to afferent current injection compared with alternative archetypal networks with different neural connectivity. Statistical analysis also demonstrates that it has the small-world properties of small shortest path length and high clustering coefficients. Thus the selectively refined connectivity enhances the ability of neuronal communications and improves the efficiency of signal transmission in the network.

  2. Context-Dependent Plastic Response during Egg-Laying in a Widespread Newt Species.

    Directory of Open Access Journals (Sweden)

    Zoltán Tóth

    Full Text Available Previous research on predator-induced phenotypic plasticity mostly focused on responses in morphology, developmental time and/or behaviour during early life stages, but the potential significance of anticipatory parental responses has been investigated less often. In this study I examined behavioural and maternal responses of gravid female smooth newts, Lissotriton vulgaris, in the presence of chemical cues originating from invertebrate predators, Acilius sulcatus water beetles and Aeshna cyanea dragonfly larvae. More specifically, I tested the extent of oviposition preference, plasticity in egg-wrapping behaviour and plasticity in egg size when females had the possibility to lay eggs at oviposition sites with and without predator cues during overnight trials. I found that individuals did not avoid laying eggs in the environment with predator cues; however, individuals that deposited eggs into both environments adjusted the size of the laid eggs to the perceived environment. Females deposited larger eggs earlier in the season but egg size decreased with time in the absence of predator cues, whereas individuals laid eggs of average size throughout the investigated reproductive period when such cues were present. Also, egg size was found to be positively related to hatching success. Individuals did not adjust their wrapping behaviour to the presence of predator cues, but females differed in the extent of egg-wrapping between ponds. Females' body mass and tail depth were also different between ponds, whereas their body size was positively associated with egg size. According to these results, female smooth newts have the potential to exhibit activational plasticity and invest differently into eggs depending on temporal and environmental factors. Such an anticipatory response may contribute to the success of this caudate species under a wide range of predator regimes at its natural breeding habitats.

  3. A Bounding Surface Plasticity Model for Intact Rock Exhibiting Size-Dependent Behaviour

    Science.gov (United States)

    Masoumi, Hossein; Douglas, Kurt J.; Russell, Adrian R.

    2016-01-01

    A new constitutive model for intact rock is presented recognising that rock strength, stiffness and stress-strain behaviour are affected by the size of the rock being subjected to loading. The model is formulated using bounding surface plasticity theory. It is validated against a new and extensive set of unconfined compression and triaxial compression test results for Gosford sandstone. The samples tested had diameters ranging from 19 to 145 mm and length-to-diameter ratios of 2. The model captures the continuous nonlinear stress-strain behaviour from initial loading, through peak strength to large shear strains, including transition from brittle to ductile behaviour. The size dependency was accounted for through a unified size effect law applied to the unconfined compressive strength—a key model input parameter. The unconfined compressive strength increases with sample size before peaking and then decreasing with further increasing sample size. Inside the constitutive model two hardening laws act simultaneously, each driven by plastic shear strains. The elasticity is stress level dependent. Simple linear loading and bounding surfaces are adopted, defined using the Mohr-Coulomb criterion, along with a non-associated flow rule. The model simulates well the stress-strain behaviour of Gosford sandstone at confining pressures ranging from 0 to 30 MPa for the variety of sample sizes considered.

  4. Brain composition in Heliconius butterflies, posteclosion growth and experience-dependent neuropil plasticity.

    Science.gov (United States)

    Montgomery, Stephen H; Merrill, Richard M; Ott, Swidbert R

    2016-06-15

    Behavioral and sensory adaptations are often reflected in the differential expansion of brain components. These volumetric differences represent changes in cell number, size, and/or connectivity, which may denote changes in the functional and evolutionary relationships between different brain regions, and between brain composition and behavioral ecology. Here we describe the brain composition of two species of Heliconius butterflies, a long-standing study system for investigating ecological adaptation and speciation. We confirm a previous report of a striking volumetric expansion of the mushroom body, and explore patterns of differential posteclosion and experience-dependent plasticity between different brain regions. This analysis uncovers age- and experience-dependent posteclosion mushroom body growth comparable to that in foraging Hymenoptera, but also identifies plasticity in several other neuropils. An interspecific analysis indicates that Heliconius display a remarkably large investment in mushroom bodies for a lepidopteran, and indeed rank highly compared to other insects. Our analyses lay the foundation for future comparative and experimental analyses that will establish Heliconius as a valuable case study in evolutionary neurobiology.

  5. Dynamic analysis of fault rockburst based on gradient-dependent plasticity and energy criterion

    Institute of Scientific and Technical Information of China (English)

    Xuebin Wang; Xiaobin Yang; Zhihui Zhang; Yishan Pan

    2004-01-01

    Fault rockburst is treated as a strain localization problem under dynamic loading condition considering strain gradient and strain rate. As a kind of dynamic fracture phenomena, rockburst has characteristics of strain localization, which is considered as a one-dimensional shear problem subjected to normal compressive stress and tangential shear stress. The constitutive relation of rock material is bilinear (elastic and strain softening) and sensitive to shear strain rate. The solutions proposed based on gradientdependent plasticity show that intense plastic strain is concentrated in fault band and the thickness of the band depends on the characteristic length of rock material. The post-peak stiffness of the fault band was determined according to the constitutive parameters of rock material and shear strain rate. Fault band undergoing strain softening and elastic rock mass outside the band constitute a system and the instability criterion of the system was proposed based on energy theory. The criterion depends on the constitutive relation of rock material, the structural size and the strain rate. The static result regardless of the strain rate is the special case of the present analytical solution. High strain rate can lead to instability of the system.

  6. Functional consequences of experience-dependent plasticity on tactile perception following perceptual learning.

    Science.gov (United States)

    Trzcinski, Natalie K; Gomez-Ramirez, Manuel; Hsiao, Steven S

    2016-09-01

    Continuous training enhances perceptual discrimination and promotes neural changes in areas encoding the experienced stimuli. This type of experience-dependent plasticity has been demonstrated in several sensory and motor systems. Particularly, non-human primates trained to detect consecutive tactile bar indentations across multiple digits showed expanded excitatory receptive fields (RFs) in somatosensory cortex. However, the perceptual implications of these anatomical changes remain undetermined. Here, we trained human participants for 9 days on a tactile task that promoted expansion of multi-digit RFs. Participants were required to detect consecutive indentations of bar stimuli spanning multiple digits. Throughout the training regime we tracked participants' discrimination thresholds on spatial (grating orientation) and temporal tasks on the trained and untrained hands in separate sessions. We hypothesized that training on the multi-digit task would decrease perceptual thresholds on tasks that require stimulus processing across multiple digits, while also increasing thresholds on tasks requiring discrimination on single digits. We observed an increase in orientation thresholds on a single digit. Importantly, this effect was selective for the stimulus orientation and hand used during multi-digit training. We also found that temporal acuity between digits improved across trained digits, suggesting that discriminating the temporal order of multi-digit stimuli can transfer to temporal discrimination of other tactile stimuli. These results suggest that experience-dependent plasticity following perceptual learning improves and interferes with tactile abilities in manners predictive of the task and stimulus features used during training.

  7. Functional consequences of experience-dependent plasticity on tactile perception following perceptual learning

    Science.gov (United States)

    Trzcinski, Natalie K; Gomez-Ramirez, Manuel; Hsiao, Steven S.

    2016-01-01

    Continuous training enhances perceptual discrimination and promotes neural changes in areas encoding the experienced stimuli. This type of experience-dependent plasticity has been demonstrated in several sensory and motor systems. Particularly, non-human primates trained to detect consecutive tactile bar indentations across multiple digits showed expanded excitatory receptive fields (RFs) in somatosensory cortex. However, the perceptual implications of these anatomical changes remain undetermined. Here, we trained human participants for nine days on a tactile task that promoted expansion of multi-digit RFs. Participants were required to detect consecutive indentations of bar stimuli spanning multiple digits. Throughout the training regime we tracked participants’ discrimination thresholds on spatial (grating orientation) and temporal tasks on the trained and untrained hands in separate sessions. We hypothesized that training on the multi-digit task would decrease perceptual thresholds on tasks that require stimulus processing across multiple digits, while also increasing thresholds on tasks requiring discrimination on single digits. We observed an increase in orientation thresholds on a single-digit. Importantly, this effect was selective for the stimulus orientation and hand used during multi-digit training. We also found that temporal acuity between digits improved across trained digits, suggesting that discriminating the temporal order of multi-digit stimuli can transfer to temporal discrimination of other tactile stimuli. These results suggest that experience-dependent plasticity following perceptual learning improves and interferes with tactile abilities in manners predictive of the task and stimulus features used during training. PMID:27422224

  8. Frequency-dependent gating of synaptic transmission and plasticity by dopamine

    Directory of Open Access Journals (Sweden)

    Hiroshi T Ito

    2007-11-01

    Full Text Available The neurotransmitter dopamine (DA plays an important role in learning by enhancing the saliency of behaviorally relevant stimuli. How this stimulus selection is achieved on the cellular level, however, is not known. Here, in recordings from hippocampal slices, we show that DA acts specifically at the direct cortical input to hippocampal area CA1 (the temporoammonic (TA pathway to filter the excitatory drive onto pyramidal neurons based on the input frequency. During low-frequency patterns of stimulation, DA depressed excitatory TA inputs to both CA1 pyramidal neurons and local inhibitory GABAergic interneurons via presynaptic inhibition. In contrast, during high-frequency patterns of stimulation, DA potently facilitated the TA excitatory drive onto CA1 pyramidal neurons, owing to diminished feedforward inhibition. Analysis of DA's effects over a broad range of stimulus frequencies indicates that it acts as a high-pass filter, augmenting the response to high-frequency inputs while diminishing the impact of low-frequency inputs. These modulatory effects of DA exert a profound influence on activity-dependent forms of synaptic plasticity at both TA-CA1 and Schaffer-collateral (SC-CA1 synapses. Taken together, our data demonstrate that DA acts as a gate on the direct cortical input to the hippocampus, modulating information flow and synaptic plasticity in a frequency-dependent manner.

  9. Temperature Dependence of Sound Velocity in High-Strength Fiber-Reinforced Plastics

    Science.gov (United States)

    Nomura, Ryuji; Yoneyama, Keiichi; Ogasawara, Futoshi; Ueno, Masashi; Okuda, Yuichi; Yamanaka, Atsuhiko

    2003-08-01

    Longitudinal sound velocity in unidirectional hybrid composites or high-strength fiber-reinforced plastics (FRPs) was measured along the fiber axis over a wide temperature range (from 77 K to 420 K). We investigated two kinds of high-strength crystalline polymer fibers, polyethylene (Dyneema) and polybenzobisoxazole (Zylon), which are known to have negative thermal expansion coefficients and high thermal conductivities along the fiber axis. Both FRPs had very high sound velocities of about 9000 m/s at low temperatures and their temperature dependences were very strong. Sound velocity monotonically decreased with increasing temperature. The temperature dependence of sound velocity was much stronger in Dyneema-FRP than in Zylon-FRP.

  10. Age- and location-dependent differences in store depletion-induced h-channel plasticity in hippocampal pyramidal neurons.

    Science.gov (United States)

    Clemens, Ann M; Johnston, Daniel

    2014-03-01

    Disruptions of endoplasmic reticulum (ER) Ca(2+) homeostasis are heavily linked to neuronal pathology. Depletion of ER Ca(2+) stores can result in cellular dysfunction and potentially cell death, although adaptive processes exist to aid in survival. We examined the age and region dependence of one postulated, adaptive response to ER store-depletion (SD), hyperpolarization-activated cation-nonspecific (h)-channel plasticity in neurons of the dorsal and ventral hippocampus (DHC and VHC, respectively) from adolescent and adult rats. With the use of whole-cell patch-clamp recordings from the soma and dendrites of CA1 pyramidal neurons, we observed a change in h-sensitive measurements in response to SD, induced by treatment with cyclopiazonic acid, a sarcoplasmic reticulum/ER Ca(2+)-ATPase blocker. We found that whereas DHC and VHC neurons in adolescent animals respond to SD with a perisomatic expression of SD h plasticity, adult animals express SD h plasticity with a dendritic and somatodendritic locus of plasticity in DHC and VHC neurons, respectively. Furthermore, SD h plasticity in adults was dependent on membrane potential and on the activation of L-type voltage-gated Ca(2+) channels. These results suggest that cellular responses to the impairment of ER function, or ER stress, are dependent on brain region and age and that the differential expression of SD h plasticity could provide a neural basis for region- and age-dependent disease vulnerabilities.

  11. BACE1 Is Necessary for Experience-Dependent Homeostatic Synaptic Plasticity in Visual Cortex

    Directory of Open Access Journals (Sweden)

    Emily Petrus

    2014-01-01

    Full Text Available Alzheimer’s disease (AD is the most common form of age-related dementia, which is thought to result from overproduction and/or reduced clearance of amyloid-beta (Aβ peptides. Studies over the past few decades suggest that Aβ is produced in an activity-dependent manner and has physiological relevance to normal brain functions. Similarly, physiological functions for β- and γ-secretases, the two key enzymes that produce Aβ by sequentially processing the amyloid precursor protein (APP, have been discovered over recent years. In particular, activity-dependent production of Aβ has been suggested to play a role in homeostatic regulation of excitatory synaptic function. There is accumulating evidence that activity-dependent immediate early gene Arc is an activity “sensor,” which acts upstream of Aβ production and triggers AMPA receptor endocytosis to homeostatically downregulate the strength of excitatory synaptic transmission. We previously reported that Arc is critical for sensory experience-dependent homeostatic reduction of excitatory synaptic transmission in the superficial layers of visual cortex. Here we demonstrate that mice lacking the major neuronal β-secretase, BACE1, exhibit a similar phenotype: stronger basal excitatory synaptic transmission and failure to adapt to changes in visual experience. Our results indicate that BACE1 plays an essential role in sensory experience-dependent homeostatic synaptic plasticity in the neocortex.

  12. Homeostatic modulation of stimulation-dependent plasticity in human motor cortex.

    Science.gov (United States)

    Ilić, N V; Milanović, S; Krstić, J; Bajec, D D; Grajić, M; Ilić, T V

    2011-01-01

    Since recently, it is possible, using noninvasive cortical stimulation, such as the protocol of paired associative stimulation (PAS), to induce the plastic changes in the motor cortex, in humans that mimic Hebb's model of learning. Application of TMS conjugated with peripheral electrical stimulation at strictly coherent temporal manner lead to convergence of inputs in the sensory-motor cortex, with the consequent synaptic potentiation or weakening, if applied repetitively. However, when optimal interstimulus interval (ISI) for induction of LTP-like effects is applied as a single pair, Motor evoked potential (MEP) amplitude inhibition is observed, the paradigm known as short-latency afferent inhibition (SLAI). Aiming to resolve this paradox, PAS protocols were applied, with 200 repetitions of TMS pulses paired with median nerve electrical stimulation, at ISI equal to individual latencies of evoked response of somatosensory cortex (N(20)) (PAS(LTP)), and at ISI of N(20) shortened for 5 msec (PAS(LTD)) - protocols that mimic LTP-like changes in the human motor cortex. MEP amplitudes before, during and after interventions were measured as an indicator based on output signals originating from the motor system. Post-intervention MEP amplitudes following the TMS protocols of PAS(LTP) and PAS(LTD) were facilitated and depressed, respectively, contrary to MEP amplitudes during intervention. During PAS(LTP) MEP amplitudes were significantly decreased in case of PAS(LTP), while in the case of PAS(LTD) an upward trend was observed. In conclusions, a possible explanation for the seemingly paradoxical effect of PAS can be found in the mechanism of homeostatic modulation of plasticity. Those findings indicate the existence of complex relationships in the development of plasticity induced by stimulation, depending on the level of the previous motor cortex excitability.

  13. Material length scales in gradient-dependent plasticity/damage and size effects: Theory and computation

    Science.gov (United States)

    Abu Al-Rub, Rashid Kamel

    Structural materials display a strong size-dependence when deformed non-uniformly into the inelastic range: smaller is stronger. This effect has important implications for an increasing number of applications in structural failure, electronics, functional coatings, composites, micro-electro-mechanical systems (MEMS), nanostructured materials, micro/nanometer fabrication technologies, etc. The mechanical behavior of these applications cannot be characterized by classical (local) continuum theories because they incorporate no, 'material length scales' and consequently predict no size effects. On the other hand, it is still not possible to perform quantum and atomistic simulations on realistic time and structures. It is therefore necessary to develop a scale-dependent continuum theory bridging the gap between the classical continuum theories and the atomistic simulations in order to be able to design the size-dependent structures of modern technology. Nonlocal rate-dependent and gradient-dependent theories of plasticity and damage are developed in this work for this purpose. We adopt a multi-scale, hierarchical thermodynamic consistent framework to construct the material constitutive relations for the scale-dependent plasticity/damage behavior. Material length scales are implicitly and explicitly introduced into the governing equations through material rate-dependency (viscosity) and coefficients of spatial higher-order gradients of one or more material state variables, respectively. The proposed framework is implemented into the commercially well-known finite element software ABAQUS. The finite element simulations of material instability problems converge to meaningful results upon further refinement of the finite element mesh, since the width of the fracture process zone (shear band) is determined by the intrinsic material length scale; while the classical continuum theories fail to address this problem. It is also shown that the proposed theory is successful for

  14. It's practice, with sleep, that makes perfect: implications of sleep-dependent learning and plasticity for skill performance.

    Science.gov (United States)

    Walker, Matthew P; Stickgold, Robert

    2005-04-01

    Although there is no consensus regarding the functions of sleep, one exciting hypothesis is that sleep contributes importantly to learning and memory. Over the last decade, several studies have provided substantive evidence supporting the role of sleep in memory processing. This article focuses on sleep-dependent learning and brain plasticity in humans, specifically in the development of skill performance that is the foundation of many sports actions. The different forms and stages of human memory are discussed, then evidence of sleep-dependent skill learning and associated sleep-dependent brain plasticity is described. In conclusion, a consideration of the fundamental importance of sleep in real-life skill learning is provided.

  15. Activity- and age-dependent GABAergic synaptic plasticity in the developing rat hippocampus.

    Science.gov (United States)

    Gubellini, P; Ben-Ari, Y; Gaïarsa, J L

    2001-12-01

    Activity-dependent plasticity of GABAergic synaptic transmission was investigated in rat hippocampal slices obtained between postnatal day (P) 0-15 using the whole-cell patch-clamp recording technique. Spontaneous GABA(A) receptor-mediated postsynaptic currents (sGABA(A)-PSCs) were isolated in the presence of ionotropic glutamate receptor antagonists. A conditioning protocol relevant to the physiological condition, consisting of repetitive depolarizing pulses (DPs) at 0.1 Hz, was able to induce long-lasting changes in both frequency and amplitude of sGABA(A)-PSCs between P0 and P8. Starting from P12, DPs were unable to induce any form of synaptic plasticity. The effects of DPs were tightly keyed to the frequency at which they were delivered. When delivered at a lower (0.05 Hz) or higher (1 Hz) frequency, DPs failed to induce any long-lasting change in the frequency or amplitude of sGABA(A)-PSCs. In two cases, DPs were able to activate sGABA(A)-PSCs in previously synaptically silent cells at P0-1. These results show that long-term changes in GABAergic synaptic activity can be induced during a restricted period of development by a conditioning protocol relevant to the physiological condition. It is suggested that such activity-induced modifications may represent a physiological mechanism for the functional maturation of GABAergic synaptic transmission.

  16. Synaptic plasticity in a cerebellum-like structure depends on temporal order

    Science.gov (United States)

    Bell, Curtis C.; Han, Victor Z.; Sugawara, Yoshiko; Grant, Kirsty

    1997-05-01

    Cerebellum-like structures in fish appear to act as adaptive sensory processors, in which learned predictions about sensory input are generated and subtracted from actual sensory input, allowing unpredicted inputs to stand out1-3. Pairing sensory input with centrally originating predictive signals, such as corollary discharge signals linked to motor commands, results in neural responses to the predictive signals alone that are Negative images' of the previously paired sensory responses. Adding these 'negative images' to actual sensory inputs minimizes the neural response to predictable sensory features. At the cellular level, sensory input is relayed to the basal region of Purkinje-like cells, whereas predictive signals are relayed by parallel fibres to the apical dendrites of the same cells4. The generation of negative images could be explained by plasticity at parallel fibre synapses5-7. We show here that such plasticity exists in the electrosensory lobe of mormyrid electric fish and that it has the necessary properties for such a model: it is reversible, anti-hebbian (excitatory postsynaptic potentials (EPSPs) are depressed after pairing with a postsynaptic spike) and tightly dependent on the sequence of pre- and postsynaptic events, with depression occurring only if the postsynaptic spike follows EPSP onset within 60 ms.

  17. Plasticity-dependent, full detonation at hippocampal mossy fiber–CA3 pyramidal neuron synapses

    Science.gov (United States)

    Vyleta, Nicholas P; Borges-Merjane, Carolina; Jonas, Peter

    2016-01-01

    Mossy fiber synapses on CA3 pyramidal cells are 'conditional detonators' that reliably discharge postsynaptic targets. The 'conditional' nature implies that burst activity in dentate gyrus granule cells is required for detonation. Whether single unitary excitatory postsynaptic potentials (EPSPs) trigger spikes in CA3 neurons remains unknown. Mossy fiber synapses exhibit both pronounced short-term facilitation and uniquely large post-tetanic potentiation (PTP). We tested whether PTP could convert mossy fiber synapses from subdetonator into detonator mode, using a recently developed method to selectively and noninvasively stimulate individual presynaptic terminals in rat brain slices. Unitary EPSPs failed to initiate a spike in CA3 neurons under control conditions, but reliably discharged them after induction of presynaptic short-term plasticity. Remarkably, PTP switched mossy fiber synapses into full detonators for tens of seconds. Plasticity-dependent detonation may be critical for efficient coding, storage, and recall of information in the granule cell–CA3 cell network. DOI: http://dx.doi.org/10.7554/eLife.17977.001 PMID:27780032

  18. Novel experience induces persistent sleep-dependent plasticity in the cortex but not in the hippocampus

    Directory of Open Access Journals (Sweden)

    Sidarta Ribeiro

    2007-10-01

    Full Text Available Episodic and spatial memories engage the hippocampus during acquisition but migrate to the cerebral cortex over time. We have recently proposed that the interplay between slow-wave (SWS and rapid eye movement (REM sleep propagates recent synaptic changes from the hippocampus to the cortex. To test this theory, we jointly assessed extracellular neuronal activity, local field potentials (LFP, and expression levels of plasticity-related immediate-early genes (IEG arc and zif-268 in rats exposed to novel spatio-tactile experience. Post-experience firing rate increases were strongest in SWS and lasted much longer in the cortex (hours than in the hippocampus (minutes. During REM sleep, firing rates showed strong temporal dependence across brain areas: cortical activation during experience predicted hippocampal activity in the first post-experience hour, while hippocampal activation during experience predicted cortical activity in the third post-experience hour. Four hours after experience, IEG expression was specifically upregulated during REM sleep in the cortex, but not in the hippocampus. Arc gene expression in the cortex was proportional to LFP amplitude in the spindle-range (10-14 Hz but not to firing rates, as expected from signals more related to dendritic input than to somatic output. The results indicate that hippocampo-cortical activation during waking is followed by multiple waves of cortical plasticity as full sleep cycles recur. The absence of equivalent changes in the hippocampus may explain its mnemonic disengagement over time.

  19. Multiscale modeling and synaptic plasticity.

    Science.gov (United States)

    Bhalla, Upinder S

    2014-01-01

    Synaptic plasticity is a major convergence point for theory and computation, and the process of plasticity engages physiology, cell, and molecular biology. In its many manifestations, plasticity is at the hub of basic neuroscience questions about memory and development, as well as more medically themed questions of neural damage and recovery. As an important cellular locus of memory, synaptic plasticity has received a huge amount of experimental and theoretical attention. If computational models have tended to pick specific aspects of plasticity, such as STDP, and reduce them to an equation, some experimental studies are equally guilty of oversimplification each time they identify a new molecule and declare it to be the last word in plasticity and learning. Multiscale modeling begins with the acknowledgment that synaptic function spans many levels of signaling, and these are so tightly coupled that we risk losing essential features of plasticity if we focus exclusively on any one level. Despite the technical challenges and gaps in data for model specification, an increasing number of multiscale modeling studies have taken on key questions in plasticity. These have provided new insights, but importantly, they have opened new avenues for questioning. This review discusses a wide range of multiscale models in plasticity, including their technical landscape and their implications.

  20. Environment-dependent plasticity and ontogenetic changes in the brain of hatchery-reared Atlantic salmon

    DEFF Research Database (Denmark)

    Näslund, J.; Larsen, Martin Hage; Thomassen, S.T.;

    2017-01-01

    enhancement strategies, like environmental enrichment. Here, we investigated the size of the brain in hatcheryreared Atlantic salmon Salmo salar kept at standard (high) and reduced (low) tank densities. In contrast to our predictions, we found that fish reared at high density had larger dry mass of cerebellum......Lowered rearing density has repeatedly been shown to increase the performance of hatchery-reared salmonids stocked into natural environments. One possible mechanism for this pattern could be that lower densities enhance brain development, which has been shown to be the case in other hatchery...... the opposite pattern was observed for telencephalon. Overall, these results reveal substantial brain plasticity depending on the surrounding environment as well as ontogenetic adaptive changes in the brain of the Atlantic salmon...

  1. The AAA+ ATPase, Thorase Regulates AMPA Receptor-Dependent Synaptic Plasticity and Behavior

    Science.gov (United States)

    Zhang, Jianmin; Wang, Yue; Chi, Zhikai; Keuss, Matthew J.; Pai, Ying-Min Emily; Kang, Ho Chul; Shin, Jooho; Bugayenko, Artem; Wang, Hong; Xiong, Yulan; Pletnikov, Mikhail V.; Mattson, Mark P.; Dawson, Ted M.; Dawson, Valina L.

    2011-01-01

    SUMMARY The synaptic insertion or removal of AMPA receptors (AMPAR) plays critical roles in the regulation of synaptic activity reflected in the expression of long-term potentiation (LTP) and long-term depression (LTD). The cellular events underlying this important process in learning and memory are still being revealed. Here we describe and characterize the AAA+ ATPase, Thorase, that regulates the expression of surface AMPAR. In an ATPase-dependent manner Thorase mediates the internalization of AMPAR by disassembling the AMPAR-GRIP1 complex. Following genetic deletion of Thorase, the internalization of AMPAR is substantially reduced, leading to increased amplitudes of miniature excitatory postsynaptic currents, enhancement of LTP and elimination of LTD. These molecular events are expressed as deficits in learning and memory in Thorase null mice. This study identifies an AAA+ ATPase that plays a critical role in regulating the surface expression of AMPAR and thereby regulates synaptic plasticity and learning and memory. PMID:21496646

  2. Learning and retrieval behavior in recurrent neural networks with pre-synaptic dependent homeostatic plasticity

    Science.gov (United States)

    Mizusaki, Beatriz E. P.; Agnes, Everton J.; Erichsen, Rubem; Brunnet, Leonardo G.

    2017-08-01

    The plastic character of brain synapses is considered to be one of the foundations for the formation of memories. There are numerous kinds of such phenomenon currently described in the literature, but their role in the development of information pathways in neural networks with recurrent architectures is still not completely clear. In this paper we study the role of an activity-based process, called pre-synaptic dependent homeostatic scaling, in the organization of networks that yield precise-timed spiking patterns. It encodes spatio-temporal information in the synaptic weights as it associates a learned input with a specific response. We introduce a correlation measure to evaluate the precision of the spiking patterns and explore the effects of different inhibitory interactions and learning parameters. We find that large learning periods are important in order to improve the network learning capacity and discuss this ability in the presence of distinct inhibitory currents.

  3. Age-Dependent Glutamate Induction of Synaptic Plasticity in Cultured Hippocampal Neurons

    Science.gov (United States)

    Ivenshitz, Miriam; Segal, Menahem; Sapoznik, Stav

    2006-01-01

    A common denominator for the induction of morphological and functional plasticity in cultured hippocampal neurons involves the activation of excitatory synapses. We now demonstrate massive morphological plasticity in mature cultured hippocampal neurons caused by a brief exposure to glutamate. This plasticity involves a slow, 70%-80% increase in…

  4. ANALYSIS OF DEPENDENCE OF THE FLOW TEMPERATURE OF THE PLASTICIZED POLYMER ON THE CHEMICAL STRUCTURE AND CONCENTRATION OF THE POLYMER AND THE PLASTICIZER

    Directory of Open Access Journals (Sweden)

    Askadskiy Andrey Aleksandrovich

    2012-10-01

    Full Text Available Polymeric materials are widely used in construction. The properties of polymeric construction materials vary to a substantial extent; their durability, thermal stability, frost resistance, waterproof and dielectric properties are particularly pronounced. Their properties serve as the drivers of the high market demand for these products. These materials are applied as finishing materials, molded sanitary engineering products and effective thermal insulation and water proofing materials. The authors analyze the influence of the chemical structure and structural features of polymers on their properties. The authors consider flow and vitrification temperatures of polymers. These temperatures determine the parameters of polymeric products, including those important for the construction process. The analysis of influence of concentration of the plasticizer on the vitrification temperature is based on the two basic theories. In accordance with the first one, reduction of the vitrification temperature is proportionate to the molar fraction of the injected plasticizer. According to the second concept, reduction of the vitrification temperature is proportionate to the volume fraction of the injected solvent. Dependencies of the flow temperature on the molecular weight and the molar fraction of the plasticizer are derived for PVC. As an example, two plasticizers were considered, including dibutyl sebacate and dioctylftalatalate. The basic parameters of all mixtures were calculated through the employment of "Cascade" software programme (A.N. Nesmeyanov Institute of Organoelemental Connections, Russian Academy of Sciences.

  5. Functional Relevance of Different Basal Ganglia Pathways Investigated in a Spiking Model with Reward Dependent Plasticity

    Directory of Open Access Journals (Sweden)

    Pierre Berthet

    2016-07-01

    Full Text Available The brain enables animals to behaviourally adapt in order to survive in a complex and dynamic environment, but how reward-oriented behaviours are achieved and computed by its underlying neural circuitry is an open question. To address this concern, we have developed a spiking model of the basal ganglia (BG that learns to dis-inhibit the action leading to a reward despite ongoing changes in the reward schedule. The architecture of the network features the two pathways commonly described in BG, the direct (denoted D1 and the indirect (denoted D2 pathway, as well as a loop involving striatum and the dopaminergic system. The activity of these dopaminergic neurons conveys the reward prediction error (RPE, which determines the magnitude of synaptic plasticity within the different pathways. All plastic connections implement a versatile four-factor learning rule derived from Bayesian inference that depends upon pre- and postsynaptic activity, receptor type and dopamine level. Synaptic weight updates occur in the D1 or D2 pathways depending on the sign of the RPE, and an efference copy informs upstream nuclei about the action selected. We demonstrate successful performance of the system in a multiple-choice learning task with a transiently changing reward schedule. We simulate lesioning of the various pathways and show that a condition without the D2 pathway fares worse than one without D1. Additionally, we simulate the degeneration observed in Parkinson’s disease (PD by decreasing the number of dopaminergic neurons during learning. The results suggest that the D1 pathway impairment in PD might have been overlooked. Furthermore, an analysis of the alterations in the synaptic weights shows that using the absolute reward value instead of the RPE leads to a larger change in D1.

  6. Experimental febrile seizures induce age-dependent structural plasticity and improve memory in mice.

    Science.gov (United States)

    Tao, K; Ichikawa, J; Matsuki, N; Ikegaya, Y; Koyama, R

    2016-03-24

    Population-based studies have demonstrated that children with a history of febrile seizure (FS) perform better than age-matched controls at hippocampus-dependent memory tasks. Here, we report that FSs induce two distinct structural reorganizations in the hippocampus and bidirectionally modify future learning abilities in an age-dependent manner. Compared with age-matched controls, adult mice that had experienced experimental FSs induced by hyperthermia (HT) on postnatal day 14 (P14-HT) performed better in a cognitive task that requires dentate granule cells (DGCs). The enhanced memory performance correlated with an FS-induced persistent increase in the density of large mossy fiber terminals (LMTs) of the DGCs. The memory enhancement was not observed in mice that had experienced HT-induced seizures at P11 which exhibited abnormally located DGCs in addition to the increased LMT density. The ectopic DGCs of the P11-HT mice were abolished by the diuretic bumetanide, and this pharmacological treatment unveiled the masked memory enhancement. Thus, this work provides a novel basis for age-dependent structural plasticity in which FSs influence future brain function. Copyright © 2016 IBRO. Published by Elsevier Ltd. All rights reserved.

  7. Direct current stimulation promotes BDNF-dependent synaptic plasticity: potential implications for motor learning.

    Science.gov (United States)

    Fritsch, Brita; Reis, Janine; Martinowich, Keri; Schambra, Heidi M; Ji, Yuanyuan; Cohen, Leonardo G; Lu, Bai

    2010-04-29

    Despite its increasing use in experimental and clinical settings, the cellular and molecular mechanisms underlying transcranial direct current stimulation (tDCS) remain unknown. Anodal tDCS applied to the human motor cortex (M1) improves motor skill learning. Here, we demonstrate in mouse M1 slices that DCS induces a long-lasting synaptic potentiation (DCS-LTP), which is polarity specific, NMDA receptor dependent, and requires coupling of DCS with repetitive low-frequency synaptic activation (LFS). Combined DCS and LFS enhance BDNF-secretion and TrkB activation, and DCS-LTP is absent in BDNF and TrkB mutant mice, suggesting that BDNF is a key mediator of this phenomenon. Moreover, the BDNF val66met polymorphism known to partially affect activity-dependent BDNF secretion impairs motor skill acquisition in humans and mice. Motor learning is enhanced by anodal tDCS, as long as activity-dependent BDNF secretion is in place. We propose that tDCS may improve motor skill learning through augmentation of synaptic plasticity that requires BDNF secretion and TrkB activation within M1.

  8. The Role of CREB, SRF, and MEF2 in Activity-Dependent Neuronal Plasticity in the Visual Cortex.

    Science.gov (United States)

    Pulimood, Nisha S; Rodrigues, Wandilson Dos Santos; Atkinson, Devon A; Mooney, Sandra M; Medina, Alexandre E

    2017-07-12

    The transcription factors CREB (cAMP response element binding factor), SRF (serum response factor), and MEF2 (myocyte enhancer factor 2) play critical roles in the mechanisms underlying neuronal plasticity. However, the role of the activation of these transcription factors in the different components of plasticity in vivo is not well known. In this study, we tested the role of CREB, SRF, and MEF2 in ocular dominance plasticity (ODP), a paradigm of activity-dependent neuronal plasticity in the visual cortex. These three proteins bind to the synaptic activity response element (SARE), an enhancer sequence found upstream of many plasticity-related genes (Kawashima et al., 2009; Rodríguez-Tornos et al., 2013), and can act cooperatively to express Arc, a gene required for ODP (McCurry et al., 2010). We used viral-mediated gene transfer to block the transcription function of CREB, SRF, and MEF2 in the visual cortex, and measured visually evoked potentials in awake male and female mice before and after a 7 d monocular deprivation, which allowed us to examine both the depression component (Dc-ODP) and potentiation component (Pc-ODP) of plasticity independently. We found that CREB, SRF, and MEF2 are all required for ODP, but have differential effects on Dc-ODP and Pc-ODP. CREB is necessary for both Dc-ODP and Pc-ODP, whereas SRF and MEF2 are only needed for Dc-ODP. This finding supports previous reports implicating SRF and MEF2 in long-term depression (required for Dc-ODP), and CREB in long-term potentiation (required for Pc-ODP).SIGNIFICANCE STATEMENT Activity-dependent neuronal plasticity is the cellular basis for learning and memory, and it is crucial for the refinement of neuronal circuits during development. Identifying the mechanisms of activity-dependent neuronal plasticity is crucial to finding therapeutic interventions in the myriad of disorders where it is disrupted, such as Fragile X syndrome, Rett syndrome, epilepsy, major depressive disorder, and autism

  9. [Independence in Plastic Surgery - Benefit or Barrier? Analysis of the Publication Performance in Academic Plastic Surgery Depending on Varying Organisational Structures].

    Science.gov (United States)

    Schubert, C D; Leitsch, S; Haertnagl, F; Haas, E M; Giunta, R E

    2015-08-01

    Despite its recognition as an independent specialty, at German university hospitals the field of plastic surgery is still underrepresented in terms of independent departments with a dedicated research focus. The aim of this study was to analyse the publication performance within the German academic plastic surgery environment and to compare independent departments and dependent, subordinate organisational structures regarding their publication performance. Organisational structures and number of attending doctors in German university hospitals were examined via a website analysis. A pubmed analysis was applied to assess the publication performance (number of publications, cumulative impact factor, impact factor/publication, number of publications/MD, number of publications/unit) between 2009 and 2013. In a journal analysis the distribution of the cumulative impact factor and number of publications in different journals as well as the development of the impact factor in the top journals were analysed. Out of all 35 university hospitals there exist 12 independent departments for plastic surgery and 8 subordinate organisational structures. In 15 university hospitals there were no designated plastic surgery units. The number of attending doctors differed considerably between independent departments (3.6 attending doctors/unit) and subordinate organisational structures (1.1 attending doctors/unit). The majority of publications (89.0%) and of the cumulative impact factor (91.2%) as well as most of the publications/MD (54 publications/year) and publications/unit (61 publications/year) were created within the independent departments. Only in departments top publications with an impact factor > 5 were published. In general a negative trend regarding the number of publications (- 13.4%) and cumulative impact factor (- 28.9%) was observed. 58.4% of all publications were distributed over the top 10 journals. Within the latter the majority of articles were published in

  10. Hypocretin/orexin neurons contribute to hippocampus-dependent social memory and synaptic plasticity in mice.

    Science.gov (United States)

    Yang, Liya; Zou, Bende; Xiong, Xiaoxing; Pascual, Conrado; Xie, James; Malik, Adam; Xie, Julian; Sakurai, Takeshi; Xie, Xinmin Simon

    2013-03-20

    Hypocretin/orexin (Hcrt)-producing neurons in the lateral hypothalamus project throughout the brain, including to the hippocampus, where Hcrt receptors are widely expressed. Hcrt neurons activate these targets to orchestrate global arousal state, wake-sleep architecture, energy homeostasis, stress adaptation, and reward behaviors. Recently, Hcrt has been implicated in cognitive functions and social interaction. In the present study, we tested the hypothesis that Hcrt neurons are critical to social interaction, particularly social memory, using neurobehavioral assessment and electrophysiological approaches. The validated "two-enclosure homecage test" devices and procedure were used to test sociability, preference for social novelty (social novelty), and recognition memory. A conventional direct contact social test was conducted to corroborate the findings. We found that adult orexin/ataxin-3-transgenic (AT) mice, in which Hcrt neurons degenerate by 3 months of age, displayed normal sociability and social novelty with respect to their wild-type littermates. However, AT mice displayed deficits in long-term social memory. Nasal administration of exogenous Hcrt-1 restored social memory to an extent in AT mice. Hippocampal slices taken from AT mice exhibited decreases in degree of paired-pulse facilitation and magnitude of long-term potentiation, despite displaying normal basal synaptic neurotransmission in the CA1 area compared to wild-type hippocampal slices. AT hippocampi had lower levels of phosphorylated cAMP response element-binding protein (pCREB), an activity-dependent transcription factor important for synaptic plasticity and long-term memory storage. Our studies demonstrate that Hcrt neurons play an important role in the consolidation of social recognition memory, at least in part through enhancements of hippocampal synaptic plasticity and cAMP response element-binding protein phosphorylation.

  11. The dependence of neuronal encoding efficiency on Hebbian plasticity and homeostatic regulation of neurotransmitter release

    Science.gov (United States)

    Faghihi, Faramarz; Moustafa, Ahmed A.

    2015-01-01

    Synapses act as information filters by different molecular mechanisms including retrograde messenger that affect neuronal spiking activity. One of the well-known effects of retrograde messenger in presynaptic neurons is a change of the probability of neurotransmitter release. Hebbian learning describe a strengthening of a synapse between a presynaptic input onto a postsynaptic neuron when both pre- and postsynaptic neurons are coactive. In this work, a theory of homeostatic regulation of neurotransmitter release by retrograde messenger and Hebbian plasticity in neuronal encoding is presented. Encoding efficiency was measured for different synaptic conditions. In order to gain high encoding efficiency, the spiking pattern of a neuron should be dependent on the intensity of the input and show low levels of noise. In this work, we represent spiking trains as zeros and ones (corresponding to non-spike or spike in a time bin, respectively) as words with length equal to three. Then the frequency of each word (here eight words) is measured using spiking trains. These frequencies are used to measure neuronal efficiency in different conditions and for different parameter values. Results show that neurons that have synapses acting as band-pass filters show the highest efficiency to encode their input when both Hebbian mechanism and homeostatic regulation of neurotransmitter release exist in synapses. Specifically, the integration of homeostatic regulation of feedback inhibition with Hebbian mechanism and homeostatic regulation of neurotransmitter release in the synapses leads to even higher efficiency when high stimulus intensity is presented to the neurons. However, neurons with synapses acting as high-pass filters show no remarkable increase in encoding efficiency for all simulated synaptic plasticity mechanisms. This study demonstrates the importance of cooperation of Hebbian mechanism with regulation of neurotransmitter release induced by rapid diffused retrograde

  12. The dependence of neuronal encoding efficiency on Hebbian plasticity and homeostatic regulation of neurotransmitter release

    Directory of Open Access Journals (Sweden)

    Faramarz eFaghihi

    2015-04-01

    Full Text Available Synapses act as information filters by different molecular mechanisms including retrograde messenger that affect neuronal spiking activity. One of the well-known effects of retrograde messenger in presynaptic neurons is a change of the probability of neurotransmitter release. Hebbian learning describe a strengthening of a synapse between a presynaptic input onto a postsynaptic neuron when both pre- and postsynaptic neurons are coactive. In this work, a theory of homeostatic regulation of neurotransmitter release by retrograde messenger and Hebbian plasticity in neuronal encoding is presented. Encoding efficiency was measured for different synaptic conditions. In order to gain high encoding efficiency, the spiking pattern of a neuron should be dependent on the intensity of the input and show low levels of noise. In this work, we represent spiking trains as zeros and ones (corresponding to non-spike or spike in a time bin, respectively as words with length equal to three. Then the frequency of each word (here eight words is measured using spiking trains. These frequencies are used to measure neuronal efficiency in different conditions and for different parameter values. Results show that neurons that have synapses acting as band-pass filters show the highest efficiency to encode their input when both Hebbian mechanism and homeostatic regulation of neurotransmitter release exist in synapses. Specifically, the integration of homeostatic regulation of feedback inhibition with Hebbian mechanism and homeostatic regulation of neurotransmitter release in the synapses leads to even higher efficiency when high stimulus intensity is presented to the neurons. However, neurons with synapses acting as high-pass filters show no remarkable increase in encoding efficiency for all simulated synaptic plasticity mechanisms.

  13. p38 MAPK Inhibition Improves Synaptic Plasticity and Memory in Angiotensin II-dependent Hypertensive Mice

    Science.gov (United States)

    Dai, Hai-long; Hu, Wei-yuan; Jiang, Li-hong; Li, Le; Gaung, Xue-feng; Xiao, Zhi-cheng

    2016-01-01

    The pathogenesis of hypertension-related cognitive impairment has not been sufficiently clarified, new molecular targets are needed. p38 MAPK pathway plays an important role in hypertensive target organ damage. Activated p38 MAPK was seen in AD brain tissue. In this study, we found that long-term potentiation (LTP) of hippocampal CA1 was decreased, the density of the dendritic spines on the CA1 pyramidal cells was reduced, the p-p38 protein expression in hippocampus was elevated, and cognitive function was impaired in angiotensin II-dependent hypertensive C57BL/6 mice. In vivo, using a p38 heterozygous knockdown mice (p38KI/+) model, we showed that knockdown of p38 MAPK in hippocampus leads to the improvement of cognitive function and hippocampal synaptic plasticity in angiotensin II-dependent p38KI/+ hypertensive mice. In vitro, LTP was improved in hippocampal slices from C57BL/6 hypertensive mice by treatment with p38MAPK inhibitor SKF86002. Our data demonstrated that p38 MAPK may be a potential therapeutic target for hypertension-related cognitive dysfunction. PMID:27283322

  14. Evidence for high-fidelity timing-dependent synaptic plasticity of human motor cortex.

    Science.gov (United States)

    Cash, R F H; Mastaglia, F L; Thickbroom, G W

    2013-01-01

    A single transcranial magnetic stimulation (TMS) pulse typically evokes a short series of spikes in corticospinal neurons [known as indirect (I)-waves] which are thought to arise from transynaptic input. Delivering a second pulse at inter-pulse intervals (IPIs) corresponding to the timing of these I-waves leads to a facilitation of the response, and if stimulus pairs are delivered repeatedly, a persistent LTP-like increase in excitability can occur. This has been demonstrated at an IPI of 1.5 ms, which corresponds to the first I-wave interval, in an intervention referred to as ITMS (I-wave TMS), and it has been argued that this may have similarities with timing-dependent plasticity models. Consequently, we hypothesized that if the second stimulus is delivered so as not to coincide with I-wave timing, it should lead to LTD. We performed a crossover study in 10 subjects in which TMS doublets were timed to coincide (1.5-ms IPI, ITMS(1.5)) or not coincide (2-ms IPI, ITMS(2)) with I-wave firing. Single pulse motor-evoked potential (MEP) amplitude, resting motor threshold (RMT), and short-interval cortical inhibition (SICI) were measured from the first dorsal interosseous (FDI) muscle. After ITMS(1.5) corticomotor excitability was increased by ~60% for 15 min (P < 0.05) and returned to baseline by 20 min. Increasing the IPI by just 500 μs to 2 ms reversed the aftereffect, and MEP amplitude was significantly reduced (~35%, P < 0.05) for 15 min before returning to baseline. This reduction was not associated with an increase in SICI, suggesting a reduction in excitatory transmission rather than an increase in inhibitory efficacy. RMT also remained unchanged, suggesting that these changes were not due to changes in membrane excitability. Amplitude-matching ITMS(2) did not modulate excitability. The results are consistent with timing-dependent synaptic LTP/D-like effects and suggest that there are plasticity mechanisms operating in the human motor cortex with a temporal

  15. Size-dependent ion-beam-induced anisotropic plastic deformation at the nanoscale by nonhydrostatic capillary stresses

    NARCIS (Netherlands)

    van Dillen, T.; van der Giessen, E.; Onck, P. R.; Polman, A.

    2006-01-01

    We develop a phenomenological model for size-dependent anisotropic plastic deformation of colloidal nanoparticles under ion irradiation. We show that, at the nanoscale, nonhydrostatic capillary stresses drive radiation-induced Newtonian viscous flow, counteracting the stress state that initiates the

  16. Modeling the time-dependent flexural response of wood-plastic composite materials

    Science.gov (United States)

    Hamel, Scott E.

    Wood-plastic composites (WPCs) are moisture sensitive bimodal anisotropic nonlinear viscoelastic materials, with time and temperature having the greatest effect on mechanical behavior. As WPC producers seek to manufacture structural bending members, such as beams and joists, it is important that the material's time and temperature-dependent mechanical behavior be understood and characterized. The complicated time-dependent behavior means that WPC bending deflections cannot be adequately predicted for even practical design purposes using simple linear-elastic models. Instead, mechanics-based models that incorporate the observed time-dependent and nonlinear responses are necessary. This dissertation presents an experimental and modeling program used to test and characterize the axial and shear behaviors of seven different WPC products (primarily polyethylene and polypropylene) subjected to both quasi-static and creep loading at multiple temperatures. These data were used to develop a mechanics based model that can predict bending deflections of complex sections at any time or temperature. Additionally, a practical design method and standardized test procedures were created for use in typical long-term bending situations. A mechanical model for WPCs must combine time-dependent material characterization with a tool that can simulate mode dependence, temperature dependence, changing neutral axis location, and nonlinear axial stress distributions that vary over the length of a member and evolve with time. Finite-element (FE) modeling was chosen as the most practical way to satisfy these requirements. The model developed in this study uses an FE model with a custom-designed material model. Bending deflection predictions from the model were compared to experimental testing and the model showed some success despite the difficulties created by the material variability. The practical method created for designing WPC structural bending members utilizes four material constants

  17. Protein-kinase C : its role in activity-dependent Purkinje cell dendritic development and plasticity

    NARCIS (Netherlands)

    Metzger, F; Kapfhammer, JP

    2003-01-01

    The cerebellum is a central organ in the control of motor learning and performance. In this respect, the cellular plasticity model systems of multiple climbing fiber elimination and long-term depression have been intensively studied. The signalling pathways involved in these plastic changes are now

  18. Plasticity dependent damage evolution in composites with strain-gradient effects

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2015-01-01

    A unit cell approach is adopted to numerically analyze the effect of reinforcement size on fracture evolution in metal matrix composites. The matrix material shows plastic size-effects and is modeled by an anisotropic version of the single parameter strain-gradient (higher-order) plasticity model...

  19. Elastic stresses and plastic deformations in 'Santa Clara' tomato fruits caused by package dependent compression

    Directory of Open Access Journals (Sweden)

    PEREIRA ADRIANA VARGAS

    2000-01-01

    Full Text Available The objective of this work was to study the fruit compression behavior aiming to develop new tomato packages. Deformations caused by compression forces were observed inside packages and in individual 'Santa Clara' tomato fruit. The forces applied by a transparent acrylic lever to the fruit surface caused pericarp deformation and the flattened area was proportional to the force magnitude. The deformation was associated to the reduction in the gas volume (Vg, caused by expulsion of the air from the loculus cavity and reduction in the intercellular air volume of the pericarp. As ripening advanced, smaller fractions of the Vg reduced by the compressive force were restored after the stress was relieved. The lack of complete Vg restoration was an indication of permanent plastic deformations of the stressed cells. Vg regeneration (elastic recovery was larger in green fruits than in the red ones. The ratio between the applied force and the flattened area (flattening pressure, which depends on cell turgidity, decreased during ripening. Fruit movements associated with its depth in the container were observed during storage in a transparent glass container (495 x 355 x 220 mm. The downward movement of the fruits was larger in the top layers because these movements seem to be driven by a summation of the deformation of many fruits in all layers.

  20. Analysis of progressive failure of pillar and instability criterion based on gradient-dependent plasticity

    Institute of Scientific and Technical Information of China (English)

    王学滨

    2004-01-01

    A mechanical model for strain softening pillar is proposed considering the characteristics of progressive shear failure and strain localization. The pillar undergoes elastic, strain softening and slabbing stages. In the elastic stage, vertical compressive stress and deformation at upper end of pillar are uniform, while in the strain softening stage there appears nonuniform due to occurrence of shear bands, leading to the decrease of load-carrying capacity.In addition, the size of failure zone increases in the strain softening stage and reaches its maximum value when slabbing begins. In the latter two stages, the size of elastic core always decreases. In the slabbing stage, the size of failure zone remains a constant and the pillar becomes thinner. Total deformation of the pillar is derived by linearly elastic Hooke's law and gradient-dependent plasticity where thickness of localization band is determined according to the characteristic length. Post-peak stiffness is proposed according to analytical solution of averaged compressive stressaverage deformation curve. Instability criterion of the pillar and roof strata system is proposed analytically using instability condition given by Salamon. It is found that the constitutive parameters of material of pillar, the geometrical size of pillar and the number of shear bands influence the stability of the system; stress gradient controls the starting time of slabbing, however it has no influence on the post-peak stiffness of the pillar.

  1. Cognitive endophenotypes, gene-environment interactions and experience-dependent plasticity in animal models of schizophrenia.

    Science.gov (United States)

    Burrows, Emma L; Hannan, Anthony J

    2016-04-01

    Schizophrenia is a devastating brain disorder caused by a complex and heterogeneous combination of genetic and environmental factors. In order to develop effective new strategies to prevent and treat schizophrenia, valid animal models are required which accurately model the disorder, and ideally provide construct, face and predictive validity. The cognitive deficits in schizophrenia represent some of the most debilitating symptoms and are also currently the most poorly treated. Therefore it is crucial that animal models are able to capture the cognitive dysfunction that characterizes schizophrenia, as well as the negative and psychotic symptoms. The genomes of mice have, prior to the recent gene-editing revolution, proven the most easily manipulable of mammalian laboratory species, and hence most genetic targeting has been performed using mouse models. Importantly, when key environmental factors of relevance to schizophrenia are experimentally manipulated, dramatic changes in the phenotypes of these animal models are often observed. We will review recent studies in rodent models which provide insight into gene-environment interactions in schizophrenia. We will focus specifically on environmental factors which modulate levels of experience-dependent plasticity, including environmental enrichment, cognitive stimulation, physical activity and stress. The insights provided by this research will not only help refine the establishment of optimally valid animal models which facilitate development of novel therapeutics, but will also provide insight into the pathogenesis of schizophrenia, thus identifying molecular and cellular targets for future preclinical and clinical investigations.

  2. Experience-dependent plasticity in white matter microstructure: Reasoning training alters structural connectivity

    Directory of Open Access Journals (Sweden)

    Allyson P Mackey

    2012-08-01

    Full Text Available Diffusion tensor imaging (DTI techniques have made it possible to investigate white matter plasticity in humans. Changes in DTI measures, principally increases in fractional anisotropy (FA, have been observed following training programs as diverse as juggling, meditation, and working memory. Here, we sought to test whether three months of reasoning training could alter white matter microstructure. We recruited participants (n=23 who were enrolled in a course to prepare for the Law School Admission Test (LSAT, a test that places strong demands on reasoning skills, as well as age- and IQ-matched controls planning to take the LSAT in the future (n=22. DTI data were collected at two scan sessions scheduled three months apart. In trained participants but not controls, we observed decreases in radial diffusivity (RD in white matter connecting frontal cortices, and in mean diffusivity (MD within frontal and parietal lobe white matter. Further, participants exhibiting larger gains on the LSAT exhibited greater decreases in MD in the right internal capsule. In summary, reasoning training altered multiple measures of white matter structure in young adults. While the cellular underpinnings are unknown, these results provide evidence of experience-dependent white matter changes that may not be limited to myelination.

  3. Modeling activity-dependent plasticity in BCM spiking neural networks with application to human behavior recognition.

    Science.gov (United States)

    Meng, Yan; Jin, Yaochu; Yin, Jun

    2011-12-01

    Spiking neural networks (SNNs) are considered to be computationally more powerful than conventional NNs. However, the capability of SNNs in solving complex real-world problems remains to be demonstrated. In this paper, we propose a substantial extension of the Bienenstock, Cooper, and Munro (BCM) SNN model, in which the plasticity parameters are regulated by a gene regulatory network (GRN). Meanwhile, the dynamics of the GRN is dependent on the activation levels of the BCM neurons. We term the whole model "GRN-BCM." To demonstrate its computational power, we first compare the GRN-BCM with a standard BCM, a hidden Markov model, and a reservoir computing model on a complex time series classification problem. Simulation results indicate that the GRN-BCM significantly outperforms the compared models. The GRN-BCM is then applied to two widely used datasets for human behavior recognition. Comparative results on the two datasets suggest that the GRN-BCM is very promising for human behavior recognition, although the current experiments are still limited to the scenarios in which only one object is moving in the considered video sequences.

  4. Phosphorylation of synaptotagmin-1 controls a post-priming step in PKC-dependent presynaptic plasticity.

    Science.gov (United States)

    de Jong, Arthur P H; Meijer, Marieke; Saarloos, Ingrid; Cornelisse, Lennart Niels; Toonen, Ruud F G; Sørensen, Jakob B; Verhage, Matthijs

    2016-05-03

    Presynaptic activation of the diacylglycerol (DAG)/protein kinase C (PKC) pathway is a central event in short-term synaptic plasticity. Two substrates, Munc13-1 and Munc18-1, are essential for DAG-induced potentiation of vesicle priming, but the role of most presynaptic PKC substrates is not understood. Here, we show that a mutation in synaptotagmin-1 (Syt1(T112A)), which prevents its PKC-dependent phosphorylation, abolishes DAG-induced potentiation of synaptic transmission in hippocampal neurons. This mutant also reduces potentiation of spontaneous release, but only if alternative Ca(2+) sensors, Doc2A/B proteins, are absent. However, unlike mutations in Munc13-1 or Munc18-1 that prevent DAG-induced potentiation, the synaptotagmin-1 mutation does not affect paired-pulse facilitation. Furthermore, experiments to probe vesicle priming (recovery after train stimulation and dual application of hypertonic solutions) also reveal no abnormalities. Expression of synaptotagmin-2, which lacks a seven amino acid sequence that contains the phosphorylation site in synaptotagmin-1, or a synaptotagmin-1 variant with these seven residues removed (Syt1(Δ109-116)), supports normal DAG-induced potentiation. These data suggest that this seven residue sequence in synaptotagmin-1 situated in the linker between the transmembrane and C2A domains is inhibitory in the unphosphorylated state and becomes permissive of potentiation upon phosphorylation. We conclude that synaptotagmin-1 phosphorylation is an essential step in PKC-dependent potentiation of synaptic transmission, acting downstream of the two other essential DAG/PKC substrates, Munc13-1 and Munc18-1.

  5. A new macroscopically anisotropic pressure dependent yield function for metal matrix composite based on strain gradient plasticity for the microstructure

    DEFF Research Database (Denmark)

    Azizi, Reza; Legarth, Brian Nyvang; Niordson, Christian Frithiof

    2013-01-01

    Metal matrix composites with long aligned elastic fibers are studied using an energetic rate independent strain gradient plasticity theory with an isotropic pressure independent yield function at the microscale. The material response is homogenized to obtain a conventional macroscopic model...... that exhibits anisotropic yield properties with a pressure dependence. At the microscale free energy includes both elastic strains and plastic strain gradients, and the theory demands higher order boundary conditions in terms of plastic strain or work conjugate higher order tractions. The mechanical response...... of the composite is inclined compared to a standard pressure independent yield surfaces. The evolution of the macroscopic yield surface is investigated by quantifying both anisotropic hardening (expansion) and kinematic hardening (translation), where the coefficients of anisotropy and the Bauschinger stress...

  6. Climate change and temperature-dependent sex determination: can individual plasticity in nesting phenology prevent extreme sex ratios?

    Science.gov (United States)

    Schwanz, Lisa E; Janzen, Fredric J

    2008-01-01

    Under temperature-dependent sex determination (TSD), temperatures experienced by embryos during development determine the sex of the offspring. Consequently, populations of organisms with TSD have the potential to be strongly impacted by climatic warming that could bias offspring sex ratio, a fundamental demographic parameter involved in population dynamics. Moreover, many taxa with TSD are imperiled, so research on this phenomenon, particularly long-term field study, has assumed great urgency. Recently, turtles with TSD have joined the diverse list of taxa that have demonstrated population-level changes in breeding phenology in response to recent climate change. This raises the possibility that any adverse impacts of climate change on populations may be alleviated by individual plasticity in nesting phenology. Here, we examine data from a long-term study on a population of painted turtles (Chrysemys picta) to determine whether changes in phenology are due to individual plasticity and whether individual plasticity in the timing of nesting has the capacity to offset the sex ratio effects of a rise in climatic temperature. We find that individual females show plasticity in the date of first nesting each year, and that this plasticity depends on the climate from the previous winter. First nesting date is not repeatable within individuals, suggesting that it would not respond to selection. Sex ratios of hatchlings within a nest declined nonsignificantly over the nesting season. However, small increases in summer temperature had a much stronger effect on nest sex ratios than did laying nests earlier in the season. For this and other reasons, it seems unlikely that individual plasticity in the timing of nesting will offset the effects of climate change on sex ratios in this population, and we hypothesize that this conclusion applies to other populations with TSD.

  7. Analysis of localized shear deformation of ductile metal based on gradient-dependent plasticity

    Institute of Scientific and Technical Information of China (English)

    王学滨; 代树红; 海龙; 潘一山

    2003-01-01

    Shear localization in linear strain softening heterogeneous material under simple shear was investigated analytically.The closed-form solutions obtained based on gradient plasticity theory considering interactions and interplaying among microstructures due to heterogeneity of metal material show that in the normal direction of shear band,elastic shear displacement is linear; while plastic and total shear displacement are non-linear.Elastic shear strain in the band is uniform and the non-uniformity of total shear displacement stems from localized plastic shear displacement.In the center of the band,plastic and total shear displacement all reach their maximum values.In strain-softening process,elastic displacement decreases as flow shear stress decreases.Contrarily,plastic and total shear displacement increase and manifest shear localization occurs progressively.Under the same shear stress level,plastic and total shear displacement increase as strain softening modulus and elastic shear modulus decrease.The present analytical solutions were compared with many experimental results and the agreement is good.

  8. TrkB/BDNF-dependent striatal plasticity and behavior in a genetic model of epilepsy: modulation by valproic acid.

    Science.gov (United States)

    Ghiglieri, Veronica; Sgobio, Carmelo; Patassini, Stefano; Bagetta, Vincenza; Fejtova, Anna; Giampà, Carmela; Marinucci, Silvia; Heyden, Alexandra; Gundelfinger, Eckart D; Fusco, Francesca R; Calabresi, Paolo; Picconi, Barbara

    2010-06-01

    In mice lacking the central domain of the presynaptic scaffold Bassoon the occurrence of repeated cortical seizures induces cell-type-specific plasticity changes resulting in a general enhancement of the feedforward inhibition within the striatal microcircuit. Early antiepileptic treatment with valproic acid (VPA) reduces epileptic attacks, inhibits the emergence of pathological form of plasticity in fast-spiking (FS) interneurons and restores physiological striatal synaptic plasticity in medium spiny (MS) neurons. Brain-derived neurotrophic factor (BDNF) is a key factor for the induction and maintenance of synaptic plasticity and it is also implicated in the mechanisms underlying epilepsy-induced adaptive changes. In this study, we explore the possibility that the TrkB/BDNF system is involved in the striatal modifications associated with the Bassoon gene (Bsn) mutation. In epileptic mice abnormal striatum-dependent learning was paralleled by higher TrkB levels and an altered distribution of BDNF. Accordingly, subchronic intrastriatal administration of k252a, an inhibitor of TrkB receptor tyrosine kinase activity, reversed behavioral alterations in Bsn mutant mice. In addition, in vitro manipulations of the TrkB/BDNF complex by k252a, prevented the emergence of pathological plasticity in FS interneurons. Chronic treatment with VPA, by reducing seizures, was able to rebalance TrkB to control levels favoring a physiological redistribution of BDNF between MS neurons and FS interneurons with a concomitant recovery of striatal plasticity. Our results provide the first indication that BDNF is involved in determining the striatal alterations occurring in the early-onset epileptic syndrome associated with the absence of presynaptic protein Bassoon.

  9. Strain-dependent variations in spatial learning and in hippocampal synaptic plasticity in the dentate gyrus of freely behaving rats

    Directory of Open Access Journals (Sweden)

    Denise eManahan-Vaughan

    2011-03-01

    Full Text Available Hippocampal synaptic plasticity is believed to comprise the cellular basis for spatial learning. Strain-dependent differences in synaptic plasticity in the CA1 region have been reported. However, it is not known whether these differences extend to other synapses within the trisynaptic circuit, although there is evidence for morphological variations within that path. We investigated whether Wistar and Hooded Lister (HL rat strains express differences in synaptic plasticity in the dentate gyrus in vivo. We also explored whether they exhibit differences in the ability to engage in spatial learning in an 8-arm radial maze. Basal synaptic transmission was stable over a 24h period in both rat strains, and the input-output relationship of both strains was not significantly different. Paired-pulse analysis revealed significantly less paired-pulse facilitation in the Hooded Lister strain when pulses were given 40-100 msec apart. Low frequency stimulation at 1Hz evoked long-term depression (>24h in Wistar and short-term depression (<2h in HL rats; 200Hz stimulation induced long-term potentiation (>24h in Wistar, and a transient, significantly smaller potentiation (<1h in HL rats, suggesting that HL rats have higher thresholds for expression of persistent synaptic plasticity. Training for 10d in an 8-arm radial maze revealed that HL rats master the working memory task faster than Wistar rats, although both strains show an equivalent performance by the end of the trial period. HL rats also perform more efficiently in a double working and reference memory task. On the other hand, Wistar rats show better reference memory performance on the final (8-10 days of training. Wistar rats were less active and more anxious than HL rats.These data suggest that strain-dependent variations in hippocampal synaptic plasticity occur in different hippocampal synapses. A clear correlation with differences in spatial learning is not evident however.

  10. Age- and location-dependent differences in store depletion-induced h-channel plasticity in hippocampal pyramidal neurons

    OpenAIRE

    Clemens, Ann M.; Johnston, Daniel

    2013-01-01

    Disruptions of endoplasmic reticulum (ER) Ca2+ homeostasis are heavily linked to neuronal pathology. Depletion of ER Ca2+ stores can result in cellular dysfunction and potentially cell death, although adaptive processes exist to aid in survival. We examined the age and region dependence of one postulated, adaptive response to ER store-depletion (SD), hyperpolarization-activated cation-nonspecific (h)-channel plasticity in neurons of the dorsal and ventral hippocampus (DHC and VHC, respectivel...

  11. Activity-Dependent NPAS4 Expression and the Regulation of Gene Programs Underlying Plasticity in the Central Nervous System

    Directory of Open Access Journals (Sweden)

    José Fernando Maya-Vetencourt

    2013-01-01

    Full Text Available The capability of the brain to change functionally in response to sensory experience is most active during early stages of development but it decreases later in life when major alterations of neuronal network structures no longer take place in response to experience. This view has been recently challenged by experimental strategies based on the enhancement of environmental stimulation levels, genetic manipulations, and pharmacological treatments, which all have demonstrated that the adult brain retains a degree of plasticity that allows for a rewiring of neuronal circuitries over the entire life course. A hot spot in the field of neuronal plasticity centres on gene programs that underlie plastic phenomena in adulthood. Here, I discuss the role of the recently discovered neuronal-specific and activity-dependent transcription factor NPAS4 as a critical mediator of plasticity in the nervous system. A better understanding of how modifications in the connectivity of neuronal networks occur may shed light on the treatment of pathological conditions such as brain damage or disease in adult life, some of which were once considered untreatable.

  12. Activity-Dependent NPAS4 Expression and the Regulation of Gene Programs Underlying Plasticity in the Central Nervous System

    Science.gov (United States)

    2013-01-01

    The capability of the brain to change functionally in response to sensory experience is most active during early stages of development but it decreases later in life when major alterations of neuronal network structures no longer take place in response to experience. This view has been recently challenged by experimental strategies based on the enhancement of environmental stimulation levels, genetic manipulations, and pharmacological treatments, which all have demonstrated that the adult brain retains a degree of plasticity that allows for a rewiring of neuronal circuitries over the entire life course. A hot spot in the field of neuronal plasticity centres on gene programs that underlie plastic phenomena in adulthood. Here, I discuss the role of the recently discovered neuronal-specific and activity-dependent transcription factor NPAS4 as a critical mediator of plasticity in the nervous system. A better understanding of how modifications in the connectivity of neuronal networks occur may shed light on the treatment of pathological conditions such as brain damage or disease in adult life, some of which were once considered untreatable. PMID:24024041

  13. Enriched environment, nitric oxide production and synaptic plasticity prevent the aging-dependent impairment of spatial cognition.

    Science.gov (United States)

    Arnaiz, Silvia Lores; D'Amico, Gabriela; Paglia, Nora; Arismendi, Mariana; Basso, Nidia; del Rosario Lores Arnaiz, María

    2004-01-01

    In rodents, neuronal plasticity decreases and spatial learning and working memory deficits increase upon aging. Several authors have shown that rats reared in enriched environments have better cognitive performance in association with increased neuronal plasticity than animals reared in standard environments. We hypothesized that enriched environment could preserve animals from the age-associated neurological impairments, mainly through NO-dependent mechanisms of induction of neuronal plasticity. We present evidence that 27 months old rats from an enriched environment show a better performance in spatial working memory than standard reared rats of the same age. Both mtNOS and cytosolic nNOS activities were found significantly increased (73% and 155%, respectively) in female rats from enriched environment as compared with control animals kept in a standard environment. The enzymatic activity of complex I was 80% increased in rats from enriched environment as compared with control rats. We conclude that an extensively enriched environment prevents old rats from the aging-associated impairment of spatial cognition, synaptic plasticity and nitric oxide production.

  14. Extensive enriched environments protect old rats from the aging dependent impairment of spatial cognition, synaptic plasticity and nitric oxide production.

    Science.gov (United States)

    Lores-Arnaiz, S; Bustamante, J; Arismendi, M; Vilas, S; Paglia, N; Basso, N; Capani, F; Coirini, H; Costa, J J López; Arnaiz, M R Lores

    2006-05-15

    In aged rodents, neuronal plasticity decreases while spatial learning and working memory (WM) deficits increase. As it is well known, rats reared in enriched environments (EE) show better cognitive performances and an increased neuronal plasticity than rats reared in standard environments (SE). We hypothesized that EE could preserve the aged animals from cognitive impairment through NO dependent mechanisms of neuronal plasticity. WM performance and plasticity were measured in 27-month-old rats from EE and SE. EE animals showed a better spatial WM performance (66% increase) than SE ones. Cytosolic NOS activity was 128 and 155% higher in EE male and female rats, respectively. Mitochondrial NOS activity and expression were also significantly higher in EE male and female rats. Mitochondrial NOS protein expression was higher in brain submitochondrial membranes from EE reared rats. Complex I activity was 70-80% increased in EE as compared to SE rats. A significant increase in the area of NADPH-d reactive neurons was observed in the parietotemporal cortex and CA1 hippocampal region of EE animals.

  15. Learning Structure of Sensory Inputs with Synaptic Plasticity Leads to Interference

    Directory of Open Access Journals (Sweden)

    Joseph eChrol-Cannon

    2015-08-01

    Full Text Available Synaptic plasticity is often explored as a form of unsupervised adaptationin cortical microcircuits to learn the structure of complex sensoryinputs and thereby improve performance of classification and prediction. The question of whether the specific structure of the input patterns is encoded in the structure of neural networks has been largely neglected. Existing studies that have analyzed input-specific structural adaptation have used simplified, synthetic inputs in contrast to complex and noisy patterns found in real-world sensory data.In this work, input-specific structural changes are analyzed forthree empirically derived models of plasticity applied to three temporal sensory classification tasks that include complex, real-world visual and auditory data. Two forms of spike-timing dependent plasticity (STDP and the Bienenstock-Cooper-Munro (BCM plasticity rule are used to adapt the recurrent network structure during the training process before performance is tested on the pattern recognition tasks.It is shown that synaptic adaptation is highly sensitive to specific classes of input pattern. However, plasticity does not improve the performance on sensory pattern recognition tasks, partly due to synaptic interference between consecutively presented input samples. The changes in synaptic strength produced by one stimulus are reversed by thepresentation of another, thus largely preventing input-specific synaptic changes from being retained in the structure of the network.To solve the problem of interference, we suggest that models of plasticitybe extended to restrict neural activity and synaptic modification to a subset of the neural circuit, which is increasingly found to be the casein experimental neuroscience.

  16. Anodal tDCS over the Primary Motor Cortex Facilitates Long-Term Memory Formation Reflecting Use-Dependent Plasticity.

    Directory of Open Access Journals (Sweden)

    Orjon Rroji

    Full Text Available Previous research suggests that anodal transcranial direct current stimulation (tDCS over the primary motor cortex (M1 modulates NMDA receptor dependent processes that mediate synaptic plasticity. Here we test this proposal by applying anodal versus sham tDCS while subjects practiced to flex the thumb as fast as possible (ballistic movements. Repetitive practice of this task has been shown to result in performance improvements that reflect use-dependent plasticity resulting from NMDA receptor mediated, long-term potentiation (LTP-like processes. Using a double-blind within-subject cross-over design, subjects (n=14 participated either in an anodal or a sham tDCS session which were at least 3 months apart. Sham or anodal tDCS (1 mA was applied for 20 min during motor practice and retention was tested 30 min, 24 hours and one week later. All subjects improved performance during each of the two sessions (p < 0.001 and learning gains were similar. Our main result is that long term retention performance (i.e. 1 week after practice was significantly better when practice was performed with anodal tDCS than with sham tDCS (p < 0.001. This effect was large (Cohen's d=1.01 and all but one subject followed the group trend. Our data strongly suggest that anodal tDCS facilitates long-term memory formation reflecting use-dependent plasticity. Our results support the notion that anodal tDCS facilitates synaptic plasticity mediated by an LTP-like mechanism, which is in accordance with previous research.

  17. Phosphorylation of synaptotagmin-1 controls a post-priming step in PKC-dependent presynaptic plasticity

    DEFF Research Database (Denmark)

    de Jong, Arthur P H; Meijer, Marieke; Saarloos, Ingrid

    2016-01-01

    Presynaptic activation of the diacylglycerol (DAG)/protein kinase C (PKC) pathway is a central event in short-term synaptic plasticity. Two substrates, Munc13-1 and Munc18-1, are essential for DAG-induced potentiation of vesicle priming, but the role of most presynaptic PKC substrates is not unde...

  18. A Presynaptic Role for FMRP during Protein Synthesis-Dependent Long-Term Plasticity in "Aplysia"

    Science.gov (United States)

    Till, Sally M.; Li, Hsiu-Ling; Miniaci, Maria Concetta; Kandel, Eric R.; Choi, Yun-Beom

    2011-01-01

    Loss of the Fragile X mental retardation protein (FMRP) is associated with presumed postsynaptic deficits in mouse models of Fragile X syndrome. However, the possible presynaptic roles of FMRP in learning-related plasticity have received little attention. As a result, the mechanisms whereby FMRP influences synaptic function remain poorly…

  19. Protein Phosphatase 1-Dependent Transcriptional Programs for Long-Term Memory and Plasticity

    Science.gov (United States)

    Graff, Johannes; Koshibu, Kyoko; Jouvenceau, Anne; Dutar, Patrick; Mansuy, Isabelle M.

    2010-01-01

    Gene transcription is essential for the establishment and the maintenance of long-term memory (LTM) and for long-lasting forms of synaptic plasticity. The molecular mechanisms that control gene transcription in neuronal cells are complex and recruit multiple signaling pathways in the cytoplasm and the nucleus. Protein kinases (PKs) and…

  20. A Presynaptic Role for FMRP during Protein Synthesis-Dependent Long-Term Plasticity in "Aplysia"

    Science.gov (United States)

    Till, Sally M.; Li, Hsiu-Ling; Miniaci, Maria Concetta; Kandel, Eric R.; Choi, Yun-Beom

    2011-01-01

    Loss of the Fragile X mental retardation protein (FMRP) is associated with presumed postsynaptic deficits in mouse models of Fragile X syndrome. However, the possible presynaptic roles of FMRP in learning-related plasticity have received little attention. As a result, the mechanisms whereby FMRP influences synaptic function remain poorly…

  1. CX3CR1 deficiency alters hippocampal-dependent plasticity phenomena blunting the effects of enriched environment

    Directory of Open Access Journals (Sweden)

    Laura eMaggi

    2011-10-01

    Full Text Available In recent years several evidence demonstrated that some features of hippocampal biology, like neurogenesis, synaptic transmission, learning and memory performances are deeply modulated by social, motor and sensorial experiences. Fractalkine/CX3CL1 is a transmembrane chemokine abundantly expressed in the brain by neurons, where it modulates glutamatergic transmission and long-term plasticity processes regulating the intercellular communication between glia and neurons, being its specific receptor CX3CR1 expressed by microglia. In this paper we investigated the role of CX3CL1/CX3CR1 signaling on experience-dependent hippocampal plasticity processes. At this aim wt and CX3CR1GFP/GFP mice were exposed to long-lasting-enriched environment (EE and the effects on hippocampal functions were studied by electrophysiological recordings of long-term potentiation (LTP of synaptic activity, behavioral tests of learning and memory in the Morris water maze paradigm and analysis of neurogenesis in the subgranular zone of the dentate gyrus (DG.We found that CX3CR1 deficiency increases hippocampal plasticity and spatial memory blunting the potentiating effects of EE. In contrast, exposure to EE increased the number and migration of neural progenitors in the DG of both wt and CX3CR1GFP/GFP mice. These data indicate that CX3CL1/CX3CR1-mediated signaling is crucial for a normal experience-dependent modulation of hippocampal functions.

  2. The BDNF Val66Met polymorphism enhances glutamatergic transmission but diminishes activity-dependent synaptic plasticity in the dorsolateral striatum.

    Science.gov (United States)

    Jing, Deqiang; Lee, Francis S; Ninan, Ipe

    2017-01-01

    The Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene disrupts the activity-dependent release of BDNF, which might underlie its involvement in several neuropsychiatric disorders. Consistent with the potential role of regulated release of BDNF in synaptic functions, earlier studies have demonstrated that the BDNF Val66Met polymorphism impairs NMDA receptor-mediated synaptic transmission and plasticity in the hippocampus, the medial prefrontal cortex and the central amygdala. However, it is unknown whether the BDNF Val66Met polymorphism affects synapses in the dorsal striatum, which depends on cortical afferents for BDNF. Electrophysiological experiments revealed an enhanced glutamatergic transmission in the dorsolateral striatum (DLS) of knock-in mice containing the variant polymorphism (BDNF(Met/Met)) compared to the wild-type (BDNF(Val/Val)) mice. This increase in glutamatergic transmission is mediated by a potentiation in glutamate release and NMDA receptor transmission in the medium spiny neurons without any alterations in non-NMDA receptor-mediated transmission. We also observed an impairment of synaptic plasticity, both long-term potentiation and depression in the DLS neurons, in BDNF(Met/Met) mice. Thus, the BDNF Val66Met polymorphism exerts an increase in glutamatergic transmission but impairs synaptic plasticity in the dorsal striatum, which might play a role in its effect on neuropsychiatric symptoms. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.

  3. An exploration of plastic deformation dependence of cell viability and adhesion in metallic implant materials.

    Science.gov (United States)

    Uzer, B; Toker, S M; Cingoz, A; Bagci-Onder, T; Gerstein, G; Maier, H J; Canadinc, D

    2016-07-01

    The relationship between cell viability and adhesion behavior, and micro-deformation mechanisms was investigated on austenitic 316L stainless steel samples, which were subjected to different amounts of plastic strains (5%, 15%, 25%, 35% and 60%) to promote a variety in the slip and twin activities in the microstructure. Confocal laser scanning microscopy (CLSM) and field emission scanning electron microscopy (FESEM) revealed that cells most favored the samples with the largest plastic deformation, such that they spread more and formed significant filopodial extensions. Specifically, brain tumor cells seeded on the 35% deformed samples exhibited the best adhesion performance, where a significant slip activity was prevalent, accompanied by considerable slip-twin interactions. Furthermore, maximum viability was exhibited by the cells seeded on the 60% deformed samples, which were particularly designed in a specific geometry that could endure greater strain values. Overall, the current findings open a new venue for the production of metallic implants with enhanced biocompatibility, such that the adhesion and viability of the cells surrounding an implant can be optimized by tailoring the surface relief of the material, which is dictated by the micro-deformation mechanism activities facilitated by plastic deformation imposed by machining.

  4. Deprivation-related and use-dependent plasticity go hand in hand.

    Science.gov (United States)

    Makin, Tamar R; Cramer, Alona O; Scholz, Jan; Hahamy, Avital; Henderson Slater, David; Tracey, Irene; Johansen-Berg, Heidi

    2013-11-12

    Arm-amputation involves two powerful drivers for brain plasticity-sensory deprivation and altered use. However, research has largely focused on sensory deprivation and maladaptive change. Here we show that adaptive patterns of limb usage after amputation drive cortical plasticity. We report that individuals with congenital or acquired limb-absence vary in whether they preferentially use their intact hand or residual arm in daily activities. Using fMRI, we show that the deprived sensorimotor cortex is employed by whichever limb individuals are over-using. Individuals from either group that rely more on their intact hands (and report less frequent residual arm usage) showed increased intact hand representation in the deprived cortex, and increased white matter fractional anisotropy underlying the deprived cortex, irrespective of the age at which deprivation occurred. Our results demonstrate how experience-driven plasticity in the human brain can transcend boundaries that have been thought to limit reorganisation after sensory deprivation in adults. DOI: http://dx.doi.org/10.7554/eLife.01273.001.

  5. Environment- and activity-dependent dopamine neurotransmitter plasticity in the adult substantia nigra.

    Science.gov (United States)

    Aumann, Tim D

    2016-04-01

    The ability of neurons to change the amount or type of neurotransmitter they use, or 'neurotransmitter plasticity', is an emerging new form of adult brain plasticity. For example, it has recently been shown that neurons in the adult rat hypothalamus up- or down-regulate dopamine (DA) neurotransmission in response to the amount of light the animal receives (photoperiod), and that this in turn affects anxiety- and depressive-like behaviors (Dulcis et al., 2013). In this Chapter I consolidate recent evidence from my laboratory suggesting neurons in the adult mouse substantia nigra pars compacta (SNc) also undergo DA neurotransmitter plasticity in response to persistent changes in their electrical activity, including that driven by the mouse's environment or behavior. Specifically, we have shown that the amounts of tyrosine hydroxylase (TH, the rate-limiting enzyme in DA synthesis) gene promoter activity, TH mRNA and TH protein in SNc neurons increases or decreases after ∼20h of altered electrical activity. Also, infusion of ion-channel agonists or antagonists into the midbrain for 2 weeks results in ∼10% (∼500 neurons) more or fewer TH immunoreactive (TH+) SNc neurons, with no change in the total number of SNc neurons (TH+ and TH-). Targeting ion-channels mediating cell-autonomous pacemaker activity in, or synaptic input and afferent pathways to, SNc neurons are equally effective in this regard. In addition, exposing mice to different environments (sex pairing or environment enrichment) for 1-2 weeks induces ∼10% more or fewer TH+ SNc (and ventral tegmental area or VTA) neurons and this is abolished by concurrent blockade of synaptic transmission in midbrain. Although further research is required to establish SNc (and VTA) DA neurotransmitter plasticity, and to determine whether it alters brain function and behavior, it is an exciting prospect because: (1) It may play important roles in movement, motor learning, reward, motivation, memory and cognition; and (2

  6. 基于神经元突触可塑性机制图像边缘检测方法%Image edge detection method based on synaptic plasticity mechanism

    Institute of Scientific and Technical Information of China (English)

    方芳; 范影乐; 廖进文; 张梦楠

    2015-01-01

    To extract the image edge information effectively,a new method of image edge detection based on spike time dependent plasticity (STDP)and other visual mechanism was proposed.Firstly, the color opponent-process characteristic was realized by image intensity and chromaticity coding mechanism.Secondly,Log-Gabor filter was adopted to realize the orientation selectivity of visual sys-tem.Then,a neuronal population network with the characteristic of STDP was proposed,which used the relevance of the asynchronous pulse spiking between neurons and visual contour to strengthen the edge information.Finally,spiking times were recorded for the first spiking time decoding to obtain the edge information.Taking the micrograph for example,the result shows the new method is effec-tive in extracting edge information distinctly and completely and can retain more small details,which proposes a new way for synaptic plasticity to be applied into image processing.%针对图像边缘信息的有效提取问题,提出了基于脉冲时间相关突触可塑性(STDP)机制的边缘检测新方法。首先通过亮度和色度编码实现颜色拮抗特性;利用 Log-Gabor 滤波器提取符合人类视觉特性的特定方向图像信息;接着建立了一种具有突触 STDP 特性的神经元网络模型,利用神经元之间非同步放电与视觉轮廓的关联性强化边缘信息;最后通过首次放电时间解码获取边缘信息。以微生物显微图像为例进行实验研究,结果表明:所提方法获取的图像边缘信息清晰完整,并且保留了更多的微弱细节;为突触可塑性机制在图像处理中的应用提供新思路。

  7. Distinct target cell-dependent forms of short-term plasticity of the central visceral afferent synapses of the rat

    Directory of Open Access Journals (Sweden)

    Watabe Ayako M

    2010-10-01

    Full Text Available Abstract Background The visceral afferents from various cervico-abdominal sensory receptors project to the dorsal vagal complex (DVC, which is composed of the nucleus of the solitary tract (NTS, the area postrema and the dorsal motor nucleus of the vagus nerve (DMX, via the vagus and glossopharyngeal nerves and then the solitary tract (TS in the brainstem. While the excitatory transmission at the TS-NTS synapses shows strong frequency-dependent suppression in response to repeated stimulation of the afferents, the frequency dependence and short-term plasticity at the TS-DMX synapses, which also transmit monosynaptic information from the visceral afferents to the DVC neurons, remain largely unknown. Results Recording of the EPSCs activated by paired or repeated TS stimulation in the brainstem slices of rats revealed that, unlike NTS neurons whose paired-pulse ratio (PPR is consistently below 0.6, the distribution of the PPR of DMX neurons shows bimodal peaks that are composed of type I (PPR, 0.6-1.5; 53% of 120 neurons recorded and type II (PPR, Conclusions These two general types of short-term plasticity might contribute to the differential activation of distinct vago-vagal reflex circuits, depending on the firing frequency and type of visceral afferents.

  8. Probing the Elastic-Plastic, Time-Dependant Response of Test Fasteners using Finite Element Analysis (FEA)

    Energy Technology Data Exchange (ETDEWEB)

    ML Renauld; H Lien

    2004-12-13

    The evolution of global and local stress/strain conditions in test fasteners under test conditions is investigated using elastic-plastic, time-dependent finite element analyses (FEA). For elastic-plastic response, tensile data from multiple specimens, material heats and test temperatures are integrated into a single, normalized flow curve from which temperature dependency is extracted. A primary creep model is calibrated with specimen- and fastener-based thermal relaxation data generated under a range of times, temperatures, stress levels and environments. These material inputs are used in analytical simulations of experimental test conditions for several types of fasteners. These fastener models are constructed with automated routines and contact conditions prescribed at all potentially mating surfaces. Thermal or mechanical room temperature pre-loading, as appropriate for a given fastener, is followed by a temperature ramp and a dwell time at constant temperature. While the amount of thermal stress relaxation is limited for the conditions modeled, local stress states are highly dependent upon geometry (thread root radius, for example), pre-loading history and thermal expansion differences between the test fastener and test fixture. Benefits of this FE approach over an elastic methodology for stress calculation will be illustrated with correlations of Stress Corrosion Cracking (SCC) initiation time and crack orientations in stress concentrations.

  9. Finite deformation analysis of continuum structures with time dependent anisotropic elastic plastic material behavior (LWBR/AWBA Development Program)

    Energy Technology Data Exchange (ETDEWEB)

    Hutula, D.N.

    1980-03-01

    A finite element procedure is presented for finite deformation analysis of continuum structures with time-dependent anisotropic elastic-plastic material behavior. An updated Lagrangian formulation is used to describe the kinematics of deformation. Anisotropic constitutive relations are referred, at each material point, to a set of three mutually orthogonal axes which rotate as a unit with an angular velocity equal to the spin at the point. The time-history of the solution is generated by using a linear incremental procedure with residual force correction, along with an automatic time step control algorithm which chooses time step sizes to control the accuracy and numerical stability of the solution.

  10. Activity-dependent structural plasticity after aversive experiences in amygdala and auditory cortex pyramidal neurons.

    Science.gov (United States)

    Gruene, Tina; Flick, Katelyn; Rendall, Sam; Cho, Jin Hyung; Gray, Jesse; Shansky, Rebecca

    2016-07-22

    The brain is highly plastic and undergoes changes in response to many experiences. Learning especially can induce structural remodeling of dendritic spines, which is thought to relate to memory formation. Classical Pavlovian fear conditioning (FC) traditionally pairs an auditory cue with an aversive footshock, and has been widely used to study neural processes underlying associative learning and memory. Past research has found dendritic spine changes after FC in several structures. But, due to heterogeneity of cells within brain structures and limitations of traditional neuroanatomical techniques, it is unclear if all cells included in analyses were actually active during learning processes, even if known circuits are isolated. In this study, we employed a novel approach to analyze structural plasticity explicitly in neurons activated by exposure to either cued or uncued footshocks. We used male and female Arc-dVenus transgenic mice, which express the Venus fluorophore driven by the activity-related Arc promoter, to identify neurons that were active during either scenario. We then targeted fluorescent microinjections to Arc+ and neighboring Arc- neurons in the basolateral area of the amygdala (BLA) and auditory association cortex (TeA). In both BLA and TeA, Arc+ neurons had reduced thin and mushroom spine densities compared to Arc- neurons. This effect was present in males and females alike and also in both cued and uncued shock groups. Overall, this study adds to our understanding of how neuronal activity affects structural plasticity, and represents a methodological advance in the ways we can directly relate structural changes to experience-related neural activity.

  11. Orientation-dependent recrystallization in an oxide dispersion strengthened steel after dynamic plastic deformation

    DEFF Research Database (Denmark)

    Zhang, Zhenbo; Tao, N.R.; Mishin, Oleg V.

    2015-01-01

    dynamic plastic deformation. Different boundary spacings and different stored energy densities for regions belonging to either of the two fibre texture components result in a quite heterogeneous deformation microstructure. Upon annealing, preferential recovery and preferential nucleation...... of recrystallization are found in the 〈111〉- oriented lamellae, which had a higher stored energy density in the as-deformed condition. In the course of recrystallization, the initial duplex fibre texture is replaced by a strong 〈111〉 fibre recrystallization texture....

  12. Orientation dependence of the plastic slip near notches in ductile FCC single crystals

    Science.gov (United States)

    Crone, W. C.; Shield, T. W.; Creuziger, A.; Henneman, B.

    2004-01-01

    Results from experiments conducted on copper FCC single crystals are reported. Two symmetric crystallographic orientations and four nonsymmetric crystallographic orientations were tested. The slip line fields that form near a pre-existing notch in these specimens were observed. The changes in these patterns as the orientation of the notch in the crystal is rotated in an {101} plane are discussed. Sectors of similar slip line patterns are identified and the type of boundaries between these sectors are discussed. A type of sector boundary called mixed kink is identified. Specimen orientations that differ by 90° are found to have different slip line patterns, contrary to the predictions of perfectly plastic slip line theory. The locations of the first slip lines to form are compared to the predictions obtained using anisotropic linear elastic stress field solutions and the initial plane-strain yield surfaces. It is found that comparison of these surface slip line fields to plane strain crack tip solutions in the annular region between 350 and 750 μm is justified. The differences in anisotropic elastic solutions for orientations that are 90° apart explain the lack of agreement with perfectly plastic slip line theory.

  13. Mind Bomb-2 Regulates Hippocampus-dependent Memory Formation and Synaptic Plasticity.

    Science.gov (United States)

    Kim, Somi; Kim, TaeHyun; Lee, Hye-Ryeon; Kong, Young-Yun; Kaang, Bong-Kiun

    2015-11-01

    Notch signaling is a key regulator of neuronal fate during embryonic development, but its function in the adult brain is still largely unknown. Mind bomb-2 (Mib2) is an essential positive regulator of the Notch pathway, which acts in the Notch signal-sending cells. Therefore, genetic deletion of Mib2 in the mouse brain might help understand Notch signaling-mediated cell-cell interactions between neurons and their physiological function. Here we show that deletion of Mib2 in the mouse brain results in impaired hippocampal spatial memory and contextual fear memory. Accordingly, we found impaired hippocampal synaptic plasticity in Mib2 knock-out (KO) mice; however, basal synaptic transmission did not change at the Schaffer collateral-CA1 synapses. Using western blot analysis, we found that the level of cleaved Notch1 was lower in Mib2 KO mice than in wild type (WT) littermates after mild foot shock. Taken together, these data suggest that Mib2 plays a critical role in synaptic plasticity and spatial memory through the Notch signaling pathway.

  14. The regenerative plasticity of isolated urodele myofibers and its dependence on MSX1.

    Directory of Open Access Journals (Sweden)

    Anoop Kumar

    2004-08-01

    Full Text Available The conversion of multinucleate postmitotic muscle fibers to dividing mononucleate progeny cells (cellularisation occurs during limb regeneration in salamanders, but the cellular events and molecular regulation underlying this remarkable process are not understood. The homeobox gene Msx1 has been studied as an antagonist of muscle differentiation, and its expression in cultured mouse myotubes induces about 5% of the cells to undergo cellularisation and viable fragmentation, but its relevance for the endogenous programme of salamander regeneration is unknown. We dissociated muscle fibers from the limb of larval salamanders and plated them in culture. Most of the fibers were activated by dissociation to mobilise their nuclei and undergo cellularisation or breakage into viable multinucleate fragments. This was followed by microinjection of a lineage tracer into single fibers and analysis of the labelled progeny cells, as well as by time-lapse microscopy. The fibers showing morphological plasticity selectively expressed Msx1 mRNA and protein. The uptake of morpholino antisense oligonucleotides directed to Msx1 led to a specific decrease in expression of Msx1 protein in myonuclei and marked inhibition of cellularisation and fragmentation. Myofibers of the salamander respond to dissociation by activation of an endogenous programme of cellularisation and fragmentation. Lineage tracing demonstrates that cycling mononucleate progeny cells are derived from a single myofiber. The induction of Msx1 expression is required to activate this programme. Our understanding of the regulation of plasticity in postmitotic salamander cells should inform strategies to promote regeneration in other contexts.

  15. The brain-tumor related protein podoplanin regulates synaptic plasticity and hippocampus-dependent learning and memory.

    Science.gov (United States)

    Cicvaric, Ana; Yang, Jiaye; Krieger, Sigurd; Khan, Deeba; Kim, Eun-Jung; Dominguez-Rodriguez, Manuel; Cabatic, Maureen; Molz, Barbara; Acevedo Aguilar, Juan Pablo; Milicevic, Radoslav; Smani, Tarik; Breuss, Johannes M; Kerjaschki, Dontscho; Pollak, Daniela D; Uhrin, Pavel; Monje, Francisco J

    2016-12-01

    Podoplanin is a cell-surface glycoprotein constitutively expressed in the brain and implicated in human brain tumorigenesis. The intrinsic function of podoplanin in brain neurons remains however uncharacterized. Using an established podoplanin-knockout mouse model and electrophysiological, biochemical, and behavioral approaches, we investigated the brain neuronal role of podoplanin. Ex-vivo electrophysiology showed that podoplanin deletion impairs dentate gyrus synaptic strengthening. In vivo, podoplanin deletion selectively impaired hippocampus-dependent spatial learning and memory without affecting amygdala-dependent cued fear conditioning. In vitro, neuronal overexpression of podoplanin promoted synaptic activity and neuritic outgrowth whereas podoplanin-deficient neurons exhibited stunted outgrowth and lower levels of p-Ezrin, TrkA, and CREB in response to nerve growth factor (NGF). Surface Plasmon Resonance data further indicated a physical interaction between podoplanin and NGF. This work proposes podoplanin as a novel component of the neuronal machinery underlying neuritogenesis, synaptic plasticity, and hippocampus-dependent memory functions. The existence of a relevant cross-talk between podoplanin and the NGF/TrkA signaling pathway is also for the first time proposed here, thus providing a novel molecular complex as a target for future multidisciplinary studies of the brain function in the physiology and the pathology. Key messages Podoplanin, a protein linked to the promotion of human brain tumors, is required in vivo for proper hippocampus-dependent learning and memory functions. Deletion of podoplanin selectively impairs activity-dependent synaptic strengthening at the neurogenic dentate-gyrus and hampers neuritogenesis and phospho Ezrin, TrkA and CREB protein levels upon NGF stimulation. Surface plasmon resonance data indicates a physical interaction between podoplanin and NGF. On these grounds, a relevant cross-talk between podoplanin and NGF as well

  16. Direct-current-dependent shift of theta-burst-induced plasticity in the human motor cortex.

    Science.gov (United States)

    Hasan, Alkomiet; Hamada, Masashi; Nitsche, Michael A; Ruge, Diane; Galea, Joseph M; Wobrock, Thomas; Rothwell, John C

    2012-03-01

    Animal studies using polarising currents have shown that induction of synaptic long-term potentiation (LTP) and long-term depression (LTD) by bursts of patterned stimulation is affected by the membrane potential of the postsynaptic neurone. The aim of the present experiments was to test whether it is possible to observe similar phenomena in humans with the aim of improving present protocols of inducing synaptic plasticity for therapeutic purposes. We tested whether the LTP/LTD-like after effects of transcranial theta-burst stimulation (TBS) of human motor cortex, an analogue of patterned electrical stimulation in animals, were affected by simultaneous transcranial direct-current stimulation (tDCS), a non-invasive method of polarising cortical neurones in humans. Nine healthy volunteers were investigated in a single-blind, balanced cross-over study; continuous TBS (cTBS) was used to introduce LTD-like after effects, whereas intermittent TBS (iTBS) produced LTP-like effects. Each pattern was coupled with concurrent application of tDCS (motor thresholds and intracortical inhibitory/facilitatory networks were not altered by any of the stimulation protocols. We conclude that the after effects of TBS can be modulated by concurrent tDCS. We hypothesise that tDCS changes the membrane potential of the apical dendrites of cortical pyramidal neurones and that this changes the response to patterned synaptic input evoked by TBS. The data show that it may be possible to enhance LTP-like plasticity after TBS in the human cortex.

  17. Chronic alcohol exposure alters behavioral and synaptic plasticity of the rodent prefrontal cortex.

    Directory of Open Access Journals (Sweden)

    Sven Kroener

    Full Text Available In the present study, we used a mouse model of chronic intermittent ethanol (CIE exposure to examine how CIE alters the plasticity of the medial prefrontal cortex (mPFC. In acute slices obtained either immediately or 1-week after the last episode of alcohol exposure, voltage-clamp recording of excitatory post-synaptic currents (EPSCs in mPFC layer V pyramidal neurons revealed that CIE exposure resulted in an increase in the NMDA/AMPA current ratio. This increase appeared to result from a selective increase in the NMDA component of the EPSC. Consistent with this, Western blot analysis of the postsynaptic density fraction showed that while there was no change in expression of the AMPA GluR1 subunit, NMDA NR1 and NRB subunits were significantly increased in CIE exposed mice when examined immediately after the last episode of alcohol exposure. Unexpectedly, this increase in NR1 and NR2B was no longer observed after 1-week of withdrawal in spite of a persistent increase in synaptic NMDA currents. Analysis of spines on the basal dendrites of layer V neurons revealed that while the total density of spines was not altered, there was a selective increase in the density of mushroom-type spines following CIE exposure. Examination of NMDA-receptor mediated spike-timing-dependent plasticity (STDP showed that CIE exposure was associated with altered expression of long-term potentiation (LTP. Lastly, behavioral studies using an attentional set-shifting task that depends upon the mPFC for optimal performance revealed deficits in cognitive flexibility in CIE exposed mice when tested up to 1-week after the last episode of alcohol exposure. Taken together, these observations are consistent with those in human alcoholics showing protracted deficits in executive function, and suggest these deficits may be associated with alterations in synaptic plasticity in the mPFC.

  18. A transcription-dependent increase in miniature EPSC frequency accompanies late-phase plasticity in cultured hippocampal neurons

    Directory of Open Access Journals (Sweden)

    Hofmann Frank

    2009-09-01

    Full Text Available Abstract Background The magnitude and longevity of synaptic activity-induced changes in synaptic efficacy is quantified by measuring evoked responses whose potentiation requires gene transcription to persist for more than 2-3 hours. While miniature EPSCs (mEPSCs are also increased in amplitude and/or frequency during long-term potentiation (LTP, it is not known how long such changes persist or whether gene transcription is required. Results We use whole-cell patch clamp recordings from dissociated hippocampal cultures to characterise for the first time the persistence and transcription dependency of mEPSC upregulation during synaptic potentiation. The persistence of recurrent action potential bursting in these cultures is transcription-, translation- and NMDA receptor-dependent thus providing an accessible model for long-lasting plasticity. Blockade of GABAA-receptors with bicuculline for 15 minutes induced action potential bursting in all neurons and was maintained in 50-60% of neurons for more than 6 hours. Throughout this period, the frequency but neither the amplitude of mEPSCs nor whole-cell AMPA currents was markedly increased. The transcription blocker actinomycin D abrogated, within 2 hours of burst induction, both action potential bursting and the increase in mEPSCs. Reversible blockade of action potentials during, but not after this 2 hour transcription period suppressed the increase in mEPSC frequency and the recovery of burst activity at a time point 6 hours after induction. Conclusion These results indicate that increased mEPSC frequency persists well beyond the 2 hour transcription-independent phase of plasticity in this model. This long-lasting mEPSC upregulation is transcription-dependent and requires ongoing action potential activity during the initial 2 hour period but not thereafter. Thus mEPSC upregulation may underlie the long term, transcription-dependent persistence of action potential bursting. This provides mechanistic

  19. Quantitative calculation for the dissipated energy of fault rock burst based on gradient-dependent plasticity

    Institute of Scientific and Technical Information of China (English)

    Xuebin Wang; Shuhong Dai; Long Hai

    2004-01-01

    The capacity of energy absorption by fault bands after rock burst was calculated quantitatively according to shear stressshear deformation curves considering the interactions and interplaying among microstructures due to the heterogeneity of strain softening rock materials. The post-peak stiffness of rock specimens subjected to direct shear was derived strictly based on gradientdependent plasticity, which can not be obtained from the classical elastoplastic theory. Analytical solutions for the dissipated energy of rock burst were proposed whether the slope of the post-peak shear stress-shear deformation curve is positive or not. The analytical solutions show that shear stress level, confining pressure, shear strength, brittleness, strain rate and heterogeneity of rock materials have important influence on the dissipated energy. The larger value of the dissipated energy means that the capacity of energy dissipation in the form of shear bands is superior and a lower magnitude of rock burst is expected under the condition of the same work done by external shear force. The possibility of rock burst is reduced for a lower softening modulus or a larger thickness of shear bands.

  20. Dependence of Microelastic-plastic Nonlinearity of Martensitic Stainless Steel on Fatigue Damage Accumulation

    Science.gov (United States)

    Cantrell, John H.

    2006-01-01

    Self-organized substructural arrangements of dislocations formed in wavy slip metals during cyclic stress-induced fatigue produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter Beta extracted from acoustic harmonic generation measurements. The contributions to Beta from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell model as a function of percent full fatigue life to fracture. A wave interaction factor f(sub WI) is introduced into the model to account experimentally for the relative volume of material fatigue damage included in the volume of material swept out by an interrogating acoustic wave. For cyclic stress-controlled loading at 551 MPa and f(sub WI) = 0.013 the model predicts a monotonic increase in Beta from dislocation substructures of almost 100 percent from the virgin state to roughly 95 percent full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, over the last five percent of fatigue life the model predicts a rapid monotonic increase of Beta by several thousand percent that is dominated by crack growth. The theoretical predictions are in good agreement with experimental measurements of 410Cb stainless steel samples fatigued in uniaxial, stress-controlled cyclic loading at 551 MPa from zero to full tensile load with a measured f(sub WI) of 0.013.

  1. Dependence of bending losses on cladding thickness in plastic optical fibers.

    Science.gov (United States)

    Durana, Gaizka; Zubia, Joseba; Arrue, Jon; Aldabaldetreku, Gotzon; Mateo, Javier

    2003-02-20

    Our main goal is to provide a comprehensive explanation of the existing differences in bending losses arising from having step-index multimode plastic optical fibers with different cladding thickness and under different types of conditions, namely, the variable bend radius R, the number of fiber turns, or the fiber diameter. For this purpose, both experimental and numerical result of bending losses are presented for different cladding thicknesses and conditions. For the measurements, two cladding thicknesses have been considered: one finite and another infinite. A fiber in air has a finite cladding thickness, and rays are reflected at the cladding-air interface, whereas a fiber covered by oil is equivalent to having an infinite cladding, since the very similar refractive index of oil prevents reflections from occurring at the cladding-oil interface. For the sake of comparison, numerical simulations based on ray tracing have been performed for finite-cladding step-index multimode waveguides. The numerical results reinforce the experimental data, and both the experimental measurements and the computational simulations turn out to be very useful to explain the behavior of refracting and tunneling rays along bent multimode waveguides and along finite-cladding fibers.

  2. Modulation of Hippocampus-Dependent Learning and Synaptic Plasticity by Nicotine

    OpenAIRE

    Kenney, Justin W.; Gould, Thomas J.

    2008-01-01

    A long-standing relationship between nicotinic acetylcholine receptors (nAChRs) and cognition exists. Drugs that act at nAChRs can have cognitive-enhancing effects and diseases that disrupt cognition such as Alzheimer’s disease and schizophrenia are associated with altered nAChR function. Specifically, hippocampus-dependent learning is particularly sensitive to the effects of nicotine. However, the effects of nicotine on hippocampus-dependent learning vary not only with the doses of nicotine ...

  3. Cyanobacterial carbon metabolism: Fluxome plasticity and oxygen dependence: Cyanobacterial Carbon Metabolism

    Energy Technology Data Exchange (ETDEWEB)

    Wan, Ni [Washington Univ., St. Louis, MO (United States); DeLorenzo, Drew M. [Washington Univ., St. Louis, MO (United States); He, Lian [Washington Univ., St. Louis, MO (United States); You, Le [Washington Univ., St. Louis, MO (United States); Immethun, Cheryl M. [Washington Univ., St. Louis, MO (United States); Wang, George [Joint BioEnergy Inst. (JBEI), Emeryville, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Baidoo, Edward E. K. [Joint BioEnergy Inst. (JBEI), Emeryville, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Hollinshead, Whitney [Washington Univ., St. Louis, MO (United States); Keasling, Jay D. [Joint BioEnergy Inst. (JBEI), Emeryville, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); Technical Univ. of Denmark, Lyngby (Denmark); Moon, Tae Seok [Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis Missouri 63130; Tang, Yinjie J. [Washington Univ., St. Louis, MO (United States)

    2017-03-30

    Synechocystis sp. strain PCC 6803 has been widely used as a photo-biorefinery chassis. Based on its genome annotation, this species contains a complete TCA cycle, an Embden-Meyerhof-Parnas pathway (EMPP), an oxidative pentose phosphate pathway (OPPP), and an Entner–Doudoroff pathway (EDP). To evaluate how Synechocystis 6803 catabolizes glucose under heterotrophic conditions, we performed 13C metabolic flux analysis, metabolite pool size analysis, gene knockouts, and heterologous expressions. The results revealed a cyclic mode of flux through the OPPP. Small, but non-zero, fluxes were observed through the TCA cycle and the malic shunt. Independent knockouts of 6-phosphogluconate dehydrogenase (gnd) and malic enzyme (me) corroborated these results, as neither mutant could grow under dark heterotrophic conditions. Our data also indicate that Synechocystis 6803 metabolism relies upon oxidative phosphorylation to generate ATP from NADPH under dark or insufficient light conditions. The pool sizes of intermediates in the TCA cycle, particularly acetyl-CoA, were found to be several fold lower in Synechocystis 6803 (compared to E. coli metabolite pool sizes), while its sugar phosphate intermediates were several-fold higher. Moreover, negligible flux was detected through the native, or heterologous, EDP in the wild type or Δgnd strains under heterotrophic conditions. Comparing photoautotrophic, photomixotrophic, and heterotrophic conditions, the Calvin cycle, OPPP, and EMPP in Synechocystis 6803 possess the ability to regulate their fluxes under various growth conditions (plastic), whereas its TCA cycle always maintains at low levels (rigid). This work also demonstrates how genetic profiles do not always reflect actual metabolic flux through native or heterologous pathways. Biotechnol. Bioeng. 2017;114: 1593–1602. © 2017 Wiley Periodicals, Inc.

  4. A VLSI array of low-power spiking neurons and bistable synapses with spike-timing dependent plasticity.

    Science.gov (United States)

    Indiveri, Giacomo; Chicca, Elisabetta; Douglas, Rodney

    2006-01-01

    We present a mixed-mode analog/digital VLSI device comprising an array of leaky integrate-and-fire (I&F) neurons, adaptive synapses with spike-timing dependent plasticity, and an asynchronous event based communication infrastructure that allows the user to (re)configure networks of spiking neurons with arbitrary topologies. The asynchronous communication protocol used by the silicon neurons to transmit spikes (events) off-chip and the silicon synapses to receive spikes from the outside is based on the "address-event representation" (AER). We describe the analog circuits designed to implement the silicon neurons and synapses and present experimental data showing the neuron's response properties and the synapses characteristics, in response to AER input spike trains. Our results indicate that these circuits can be used in massively parallel VLSI networks of I&F neurons to simulate real-time complex spike-based learning algorithms.

  5. Memory suppression trades prolonged fear and sleep-dependent fear plasticity for the avoidance of current fear

    Science.gov (United States)

    Kuriyama, Kenichi; Honma, Motoyasu; Yoshiike, Takuya; Kim, Yoshiharu

    2013-07-01

    Sleep deprivation immediately following an aversive event reduces fear by preventing memory consolidation during homeostatic sleep. This suggests that acute insomnia might act prophylactically against the development of posttraumatic stress disorder (PTSD) even though it is also a possible risk factor for PTSD. We examined total sleep deprivation and memory suppression to evaluate the effects of these interventions on subsequent aversive memory formation and fear conditioning. Active suppression of aversive memory impaired retention of event memory. However, although the remembered fear was more reduced in sleep-deprived than sleep-control subjects, suppressed fear increased, and seemed to abandon the sleep-dependent plasticity of fear. Active memory suppression, which provides a psychological model for Freud's ego defense mechanism, enhances fear and casts doubt on the potential of acute insomnia as a prophylactic measure against PTSD. Our findings bring into question the role of sleep in aversive-memory consolidation in clinical PTSD pathophysiology.

  6. Long-term social recognition memory is mediated by oxytocin-dependent synaptic plasticity in the medial amygdala.

    Science.gov (United States)

    Gur, Rotem; Tendler, Alex; Wagner, Shlomo

    2014-09-01

    Recognition of specific individuals is fundamental to mammalian social behavior and is mediated in most mammals by the main and accessory olfactory systems. Both these systems innervate the medial amygdala (MeA), where activity of the neuropeptide oxytocin is thought to mediate social recognition memory (SRM). The specific contribution of the MeA to SRM formation and the specific actions of oxytocin in the MeA are unknown. We used the social discrimination test to evaluate short-term and long-term SRM in adult Sprague-Dawley male rats (n = 38). The role of protein synthesis in the MeA was investigated by local application of the protein synthesis blocker anisomycin (n = 11). Synaptic plasticity was assessed in vivo by recording the MeA evoked field potential responses to stimulation of the main (n = 21) and accessory (n = 56) olfactory bulbs before and after theta burst stimulation. Intracerebroventricular administration of saline, oxytocin, or oxytocin receptor antagonist was used to measure the effect of oxytocin on synaptic plasticity. Anisomycin application to the MeA prevented the formation of long-term SRM. In addition, the responses of MeA neurons underwent long-term depression (LTD) after theta burst stimulation of the accessory olfactory bulb, but not the main accessory bulb, in an oxytocin-dependent manner. No LTD was found in socially isolated rats, which are known to lack long-term SRM. Finally, accessory olfactory bulb stimulation before SRM acquisition blocked long-term SRM, supporting the involvement of LTD in the MeA in formation of long-term SRM. Our results indicate that long-term SRM in rats involves protein synthesis and oxytocin-dependent LTD in the MeA. Copyright © 2014 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

  7. A neuromorphic VLSI design for spike timing and rate based synaptic plasticity.

    Science.gov (United States)

    Rahimi Azghadi, Mostafa; Al-Sarawi, Said; Abbott, Derek; Iannella, Nicolangelo

    2013-09-01

    Triplet-based Spike Timing Dependent Plasticity (TSTDP) is a powerful synaptic plasticity rule that acts beyond conventional pair-based STDP (PSTDP). Here, the TSTDP is capable of reproducing the outcomes from a variety of biological experiments, while the PSTDP rule fails to reproduce them. Additionally, it has been shown that the behaviour inherent to the spike rate-based Bienenstock-Cooper-Munro (BCM) synaptic plasticity rule can also emerge from the TSTDP rule. This paper proposes an analogue implementation of the TSTDP rule. The proposed VLSI circuit has been designed using the AMS 0.35 μm CMOS process and has been simulated using design kits for Synopsys and Cadence tools. Simulation results demonstrate how well the proposed circuit can alter synaptic weights according to the timing difference amongst a set of different patterns of spikes. Furthermore, the circuit is shown to give rise to a BCM-like learning rule, which is a rate-based rule. To mimic an implementation environment, a 1000 run Monte Carlo (MC) analysis was conducted on the proposed circuit. The presented MC simulation analysis and the simulation result from fine-tuned circuits show that it is possible to mitigate the effect of process variations in the proof of concept circuit; however, a practical variation aware design technique is required to promise a high circuit performance in a large scale neural network. We believe that the proposed design can play a significant role in future VLSI implementations of both spike timing and rate based neuromorphic learning systems.

  8. p53-Dependent Nestin Regulation Links Tumor Suppression to Cellular Plasticity in Liver Cancer

    DEFF Research Database (Denmark)

    Tschaharganeh, Darjus F; Xue, Wen; Calvisi, Diego F

    2014-01-01

    nestin in an Sp1/3 transcription-factor-dependent manner and that Nestin is required for tumor initiation in vivo. Moreover, loss of p53 facilitates dedifferentiation of mature hepatocytes into nestin-positive progenitor-like cells, which are poised to differentiate into hepatocellular carcinomas (HCCs...

  9. Role of motor cortex NMDA receptors in learning-dependent synaptic plasticity of behaving mice

    OpenAIRE

    Mazahir T Hasan; Hernández-González, Samuel; Dogbevia, Godwin; Treviño, Mario; Bertocchi, Ilaria; Gruart, Agnès; Delgado-García, José M.

    2013-01-01

    The primary motor cortex has an important role in the precise execution of learned motor responses. During motor learning, synaptic efficacy between sensory and primary motor cortical neurons is enhanced, possibly involving long-term potentiation and N-methyl-D-aspartate (NMDA)-specific glutamate receptor function. To investigate whether NMDA receptor in the primary motor cortex can act as a coincidence detector for activity-dependent changes in synaptic strength and associative learning, her...

  10. Modelling the time dependent movements of the La Saxe Rockslide by a dynamic visco-plastic model

    Science.gov (United States)

    Battista Crosta, Giovanni; di Prisco, Claudio; Castellanza, Riccardo; Frattini, Paolo; Agliardi, Federico; Frigerio, Gabriele

    2013-04-01

    A challenging issue in geological and geotechnical problems associated with slope stability concerns the analysis of sliding masses subject to continuous slow movements and intermittent stages of slowing and accelerating motion. In this work an attempt for simulating and forecasting the movement of the La Saxe rockslide (Aosta valley; Italian Western Alps; volume: about 8*10e6 m3) will be shown. The La Saxe rockslide movement could be interpreted as the result of two specific behaviours: i) a continuous creep-like movement occurring independently on groundwater conditions, even under dry-winter conditions, when the water table is mainly below or close to the failure surface; ii) a superimposed acceleration-exhaustion trend, occurring during the snow melting period (late spring-early summer) and directly related to the associated water table fluctuations, which disappears when the water inputs are reduced (late summer and winter conditions). A reliable, monitoring-driven approach to model such rockslide behaviour should account for: a) the time-dependent behaviour by means of a viscous-plastic constitutive law reproducing the creep behaviour; b) the water table fluctuation as main input to reproduce the late spring - early summer acceleration; c) 3D rockslide behaviour maintaining at the same time an high level of simplicity so to allow implementation within EWS (Early Warning System) for risk management. To this purpose a 1D pseudo-dynamic visco-plastic Newmark approach, based on Perzyna's theory (Secondi et. al 2011) has been applied. Newmark's approach considers the slope as a rigid block placed in the centre of mass of the rock slide, where the active forces are: the landslide weight, the inertial forces and the seepage force deriving from the water table level which is a function of time. All the non-linearities are condensed in an interface thin layer between the rigid block and the bedrock, whose mechanical response is assumed to be visco-plastic. In order to

  11. Optical Dissection of Experience-Dependent Pre- and Postsynaptic Plasticity in the Drosophila Brain

    Directory of Open Access Journals (Sweden)

    Ulrike Pech

    2015-03-01

    Full Text Available Drosophila represents a key model organism for dissecting neuronal circuits that underlie innate and adaptive behavior. However, this task is limited by a lack of tools to monitor physiological parameters of spatially distributed, central synapses in identified neurons. We generated transgenic fly strains that express functional fluorescent reporters targeted to either pre- or postsynaptic compartments. Presynaptic Ca2+ dynamics are monitored using synaptophysin-coupled GCaMP3, synaptic transmission is monitored using red fluorescent synaptophysin-pHTomato, and postsynaptic Ca2+ dynamics are visualized using GCaMP3 fused with the postsynaptic matrix protein, dHomer. Using two-photon in vivo imaging of olfactory projection neurons, odor-evoked activity across populations of synapses is visualized in the antennal lobe and the mushroom body calyx. Prolonged odor exposure causes odor-specific and differential experience-dependent changes in pre- and postsynaptic activity at both levels of olfactory processing. The approach advances the physiological analysis of synaptic connections across defined groups of neurons in intact Drosophila.

  12. Intermittent Hypoxia-Induced Spinal Inflammation Impairs Respiratory Motor Plasticity by a Spinal p38 MAP Kinase-Dependent Mechanism.

    Science.gov (United States)

    Huxtable, Adrianne G; Smith, Stephanie M C; Peterson, Timothy J; Watters, Jyoti J; Mitchell, Gordon S

    2015-04-29

    Inflammation is characteristic of most clinical disorders that challenge the neural control of breathing. Since inflammation modulates neuroplasticity, we studied the impact of inflammation caused by prolonged intermittent hypoxia on an important form of respiratory plasticity, acute intermittent hypoxia (three, 5 min hypoxic episodes, 5 min normoxic intervals) induced phrenic long-term facilitation (pLTF). Because chronic intermittent hypoxia elicits neuroinflammation and pLTF is undermined by lipopolysaccharide-induced systemic inflammation, we hypothesized that one night of intermittent hypoxia (IH-1) elicits spinal inflammation, thereby impairing pLTF by a p38 MAP kinase-dependent mechanism. pLTF and spinal inflammation were assessed in anesthetized rats pretreated with IH-1 (2 min hypoxia, 2 min normoxia; 8 h) or sham normoxia and allowed 16 h for recovery. IH-1 (1) transiently increased IL-6 (1.5 ± 0.2-fold; p = 0.02) and inducible nitric oxide synthase (iNOS) (2.4 ± 0.4-fold; p = 0.01) mRNA in cervical spinal homogenates, (2) elicited a sustained increase in IL-1β mRNA (2.4 ± 0.2-fold; p < 0.001) in isolated cervical spinal microglia, and (3) abolished pLTF (-1 ± 5% vs 56 ± 10% in controls; p < 0.001). pLTF was restored after IH-1 by systemic NSAID administration (ketoprofen; 55 ± 9%; p < 0.001) or spinal p38 MAP kinase inhibition (58 ± 2%; p < 0.001). IH-1 increased phosphorylated (activated) p38 MAP kinase immunofluorescence in identified phrenic motoneurons and adjacent microglia. In conclusion, IH-1 elicits spinal inflammation and impairs pLTF by a spinal p38 MAP kinase-dependent mechanism. By targeting inflammation, we may develop strategies to manipulate respiratory motor plasticity for therapeutic advantage when the respiratory control system is compromised (e.g., sleep apnea, apnea of prematurity, spinal injury, or motor neuron disease).

  13. GluA1 and its PDZ-interaction: a role in experience-dependent behavioral plasticity in the forced swim test

    NARCIS (Netherlands)

    Freudenberg, F.; Marx, V.; Mack, V.; Layer, L.E.; Klugmann, M.; Seeburg, P.H.; Sprengel, R.; Celikel, T.

    2013-01-01

    Glutamate receptor dependent synaptic plasticity plays an important role in the pathophysiology of depression. Hippocampal samples from clinically depressed patients display reduced mRNA levels for GluA1, a major subunit of AMPA receptors. Moreover, activation and synaptic incorporation of GluA1-con

  14. Presynaptic Spike Timing-Dependent Long-Term Depression in the Mouse Hippocampus

    Science.gov (United States)

    Andrade-Talavera, Yuniesky; Duque-Feria, Paloma; Paulsen, Ole; Rodríguez-Moreno, Antonio

    2016-01-01

    Spike timing-dependent plasticity (STDP) is a Hebbian learning rule important for synaptic refinement during development and for learning and memory in the adult. Given the importance of the hippocampus in memory, surprisingly little is known about the mechanisms and functions of hippocampal STDP. In the present work, we investigated the requirements for induction of hippocampal spike timing-dependent long-term potentiation (t-LTP) and spike timing-dependent long-term depression (t-LTD) and the mechanisms of these 2 forms of plasticity at CA3-CA1 synapses in young (P12–P18) mouse hippocampus. We found that both t-LTP and t-LTD can be induced at hippocampal CA3-CA1 synapses by pairing presynaptic activity with single postsynaptic action potentials at low stimulation frequency (0.2 Hz). Both t-LTP and t-LTD require NMDA-type glutamate receptors for their induction, but the location and properties of these receptors are different: While t-LTP requires postsynaptic ionotropic NMDA receptor function, t-LTD does not, and whereas t-LTP is blocked by antagonists at GluN2A and GluN2B subunit-containing NMDA receptors, t-LTD is blocked by GluN2C or GluN2D subunit-preferring NMDA receptor antagonists. Both t-LTP and t-LTD require postsynaptic Ca2+ for their induction. Induction of t-LTD also requires metabotropic glutamate receptor activation, phospholipase C activation, postsynaptic IP3 receptor-mediated Ca2+ release from internal stores, postsynaptic endocannabinoid (eCB) synthesis, activation of CB1 receptors and astrocytic signaling, possibly via release of the gliotransmitter d-serine. We furthermore found that presynaptic calcineurin is required for t-LTD induction. t-LTD is expressed presynaptically as indicated by fluctuation analysis, paired-pulse ratio, and rate of use-dependent depression of postsynaptic NMDA receptor currents by MK801. The results show that CA3-CA1 synapses display both NMDA receptor-dependent t-LTP and t-LTD during development and identify a

  15. Is a 4-bit synaptic weight resolution enough? - constraints on enabling spike-timing dependent plasticity in neuromorphic hardware.

    Science.gov (United States)

    Pfeil, Thomas; Potjans, Tobias C; Schrader, Sven; Potjans, Wiebke; Schemmel, Johannes; Diesmann, Markus; Meier, Karlheinz

    2012-01-01

    Large-scale neuromorphic hardware systems typically bear the trade-off between detail level and required chip resources. Especially when implementing spike-timing dependent plasticity, reduction in resources leads to limitations as compared to floating point precision. By design, a natural modification that saves resources would be reducing synaptic weight resolution. In this study, we give an estimate for the impact of synaptic weight discretization on different levels, ranging from random walks of individual weights to computer simulations of spiking neural networks. The FACETS wafer-scale hardware system offers a 4-bit resolution of synaptic weights, which is shown to be sufficient within the scope of our network benchmark. Our findings indicate that increasing the resolution may not even be useful in light of further restrictions of customized mixed-signal synapses. In addition, variations due to production imperfections are investigated and shown to be uncritical in the context of the presented study. Our results represent a general framework for setting up and configuring hardware-constrained synapses. We suggest how weight discretization could be considered for other backends dedicated to large-scale simulations. Thus, our proposition of a good hardware verification practice may rise synergy effects between hardware developers and neuroscientists.

  16. Plastic Surgery

    Science.gov (United States)

    ... Surgery? A Week of Healthy Breakfasts Shyness Plastic Surgery KidsHealth > For Teens > Plastic Surgery Print A A ... forehead lightened with a laser? What Is Plastic Surgery? Just because the name includes the word "plastic" ...

  17. Vascular endothelial growth factor-dependent angiogenesis and dynamic vascular plasticity in the sensory circumventricular organs of adult mouse brain.

    Science.gov (United States)

    Morita, Shoko; Furube, Eriko; Mannari, Tetsuya; Okuda, Hiroaki; Tatsumi, Kouko; Wanaka, Akio; Miyata, Seiji

    2015-03-01

    The sensory circumventricular organs (CVOs), which comprise the organum vasculosum of the lamina terminalis (OVLT), the subfornical organ (SFO) and the area postrema (AP), lack a typical blood-brain barrier (BBB) and monitor directly blood-derived information to regulate body fluid homeostasis, inflammation, feeding and vomiting. Until now, almost nothing has been documented about vascular features of the sensory CVOs except fenestration of vascular endothelial cells. We therefore examine whether continuous angiogenesis occurs in the sensory CVOs of adult mouse. The angiogenesis-inducing factor vascular endothelial growth factor-A (VEGF-A) and the VEGF-A-regulating transcription factor hypoxia-inducible factor-1α were highly expressed in neurons of the OVLT and SFO and in both neurons and astrocytes of the AP. Expression of the pericyte-regulating factor platelet-derived growth factor B was high in astrocytes of the sensory CVOs. Immunohistochemistry of bromodeoxyuridine and Ki-67, a nuclear protein that is associated with cellular proliferation, revealed active proliferation of endothelial cells. Moreover, immunohistochemistry of caspase-3 and the basement membrane marker laminin showed the presence of apoptosis and sprouting of endothelial cells, respectively. Treatment with the VEGF receptor-associated tyrosine kinase inhibitor AZD2171 significantly reduced proliferation and filopodia sprouting of endothelial cells, as well as the area and diameter of microvessels. The mitotic inhibitor cytosine-b-D-arabinofuranoside reduced proliferation of endothelial cells and the vascular permeability of blood-derived low-molecular-weight molecules without changing vascular area and microvessel diameter. Thus, our data indicate that continuous angiogenesis is dependent on VEGF signaling and responsible for the dynamic plasticity of vascular structure and permeability.

  18. A Small Motor Cortex Lesion Abolished Ocular Dominance Plasticity in the Adult Mouse Primary Visual Cortex and Impaired Experience-Dependent Visual Improvements.

    Science.gov (United States)

    Pielecka-Fortuna, Justyna; Kalogeraki, Evgenia; Greifzu, Franziska; Löwel, Siegrid

    2015-01-01

    It was previously shown that a small lesion in the primary somatosensory cortex (S1) prevented both cortical plasticity and sensory learning in the adult mouse visual system: While 3-month-old control mice continued to show ocular dominance (OD) plasticity in their primary visual cortex (V1) after monocular deprivation (MD), age-matched mice with a small photothrombotically induced (PT) stroke lesion in S1, positioned at least 1 mm anterior to the anterior border of V1, no longer expressed OD-plasticity. In addition, in the S1-lesioned mice, neither the experience-dependent increase of the spatial frequency threshold ("visual acuity") nor of the contrast threshold ("contrast sensitivity") of the optomotor reflex through the open eye was present. To assess whether these plasticity impairments can also occur if a lesion is placed more distant from V1, we tested the effect of a PT-lesion in the secondary motor cortex (M2). We observed that mice with a small M2-lesion restricted to the superficial cortical layers no longer expressed an OD-shift towards the open eye after 7 days of MD in V1 of the lesioned hemisphere. Consistent with previous findings about the consequences of an S1-lesion, OD-plasticity in V1 of the nonlesioned hemisphere of the M2-lesioned mice was still present. In addition, the experience-dependent improvements of both visual acuity and contrast sensitivity of the open eye were severely reduced. In contrast, sham-lesioned mice displayed both an OD-shift and improvements of visual capabilities of their open eye. To summarize, our data indicate that even a very small lesion restricted to the superficial cortical layers and more than 3mm anterior to the anterior border of V1 compromised V1-plasticity and impaired learning-induced visual improvements in adult mice. Thus both plasticity phenomena cannot only depend on modality-specific and local nerve cell networks but are clearly influenced by long-range interactions even from distant brain regions.

  19. A Small Motor Cortex Lesion Abolished Ocular Dominance Plasticity in the Adult Mouse Primary Visual Cortex and Impaired Experience-Dependent Visual Improvements

    Science.gov (United States)

    Pielecka-Fortuna, Justyna; Kalogeraki, Evgenia; Greifzu, Franziska; Löwel, Siegrid

    2015-01-01

    It was previously shown that a small lesion in the primary somatosensory cortex (S1) prevented both cortical plasticity and sensory learning in the adult mouse visual system: While 3-month-old control mice continued to show ocular dominance (OD) plasticity in their primary visual cortex (V1) after monocular deprivation (MD), age-matched mice with a small photothrombotically induced (PT) stroke lesion in S1, positioned at least 1 mm anterior to the anterior border of V1, no longer expressed OD-plasticity. In addition, in the S1-lesioned mice, neither the experience-dependent increase of the spatial frequency threshold (“visual acuity”) nor of the contrast threshold (“contrast sensitivity”) of the optomotor reflex through the open eye was present. To assess whether these plasticity impairments can also occur if a lesion is placed more distant from V1, we tested the effect of a PT-lesion in the secondary motor cortex (M2). We observed that mice with a small M2-lesion restricted to the superficial cortical layers no longer expressed an OD-shift towards the open eye after 7 days of MD in V1 of the lesioned hemisphere. Consistent with previous findings about the consequences of an S1-lesion, OD-plasticity in V1 of the nonlesioned hemisphere of the M2-lesioned mice was still present. In addition, the experience-dependent improvements of both visual acuity and contrast sensitivity of the open eye were severely reduced. In contrast, sham-lesioned mice displayed both an OD-shift and improvements of visual capabilities of their open eye. To summarize, our data indicate that even a very small lesion restricted to the superficial cortical layers and more than 3mm anterior to the anterior border of V1 compromised V1-plasticity and impaired learning-induced visual improvements in adult mice. Thus both plasticity phenomena cannot only depend on modality-specific and local nerve cell networks but are clearly influenced by long-range interactions even from distant brain

  20. Genetic deletion of melanin-concentrating hormone neurons impairs hippocampal short-term synaptic plasticity and hippocampal-dependent forms of short-term memory.

    Science.gov (United States)

    Le Barillier, Léa; Léger, Lucienne; Luppi, Pierre-Hervé; Fort, Patrice; Malleret, Gaël; Salin, Paul-Antoine

    2015-11-01

    The cognitive role of melanin-concentrating hormone (MCH) neurons, a neuronal population located in the mammalian postero-lateral hypothalamus sending projections to all cortical areas, remains poorly understood. Mainly activated during paradoxical sleep (PS), MCH neurons have been implicated in sleep regulation. The genetic deletion of the only known MCH receptor in rodent leads to an impairment of hippocampal dependent forms of memory and to an alteration of hippocampal long-term synaptic plasticity. By using MCH/ataxin3 mice, a genetic model characterized by a selective deletion of MCH neurons in the adult, we investigated the role of MCH neurons in hippocampal synaptic plasticity and hippocampal-dependent forms of memory. MCH/ataxin3 mice exhibited a deficit in the early part of both long-term potentiation and depression in the CA1 area of the hippocampus. Post-tetanic potentiation (PTP) was diminished while synaptic depression induced by repetitive stimulation was enhanced suggesting an alteration of pre-synaptic forms of short-term plasticity in these mice. Behaviorally, MCH/ataxin3 mice spent more time and showed a higher level of hesitation as compared to their controls in performing a short-term memory T-maze task, displayed retardation in acquiring a reference memory task in a Morris water maze, and showed a habituation deficit in an open field task. Deletion of MCH neurons could thus alter spatial short-term memory by impairing short-term plasticity in the hippocampus. Altogether, these findings could provide a cellular mechanism by which PS may facilitate memory encoding. Via MCH neuron activation, PS could prepare the day's learning by increasing and modulating short-term synaptic plasticity in the hippocampus. © 2015 Wiley Periodicals, Inc.

  1. Homeostatic role of heterosynaptic plasticity: Models and experiments

    Directory of Open Access Journals (Sweden)

    Marina eChistiakova

    2015-07-01

    Full Text Available Homosynaptic Hebbian-type plasticity provides a cellular mechanism of learning and refinement of connectivity during development in a variety of biological systems. In this review we argue that a complimentary form of plasticity - heterosynaptic plasticity - represents a necessary cellular component for homeostatic regulation of synaptic weights and neuronal activity. The required properties of a homeostatic mechanism which acutely constrains the runaway dynamics imposed by Hebbian associative plasticity have been well-articulated by theoretical and modeling studies. Such mechanism(s should robustly support the stability of operation of neuronal networks and synaptic competition, include changes at non-active synapses, and operate on a similar time scale to Hebbian-type plasticity. The experimentally observed properties of heterosynaptic plasticity have introduced it as a strong candidate to fulfill this homeostatic role. Subsequent modeling studies which incorporate heterosynaptic plasticity into model neurons with Hebbian synapses (utilizing an STDP learning rule have confirmed its ability to robustly provide stability and competition. In contrast, properties of homeostatic synaptic scaling, which is triggered by extreme and long lasting (hours and days changes of neuronal activity, do not fit two crucial requirements for a hypothetical homeostatic mechanism needed to provide stability of operation in the face of on-going synaptic changes driven by Hebbian-type learning rules. Both the trigger and the time scale of homeostatic synaptic scaling are fundamentally different from those of the Hebbian-type plasticity. We conclude that heterosynaptic plasticity, which is triggered by the same episodes of strong postsynaptic activity and operates on the same time scale as Hebbian-type associative plasticity, is ideally suited to serve homeostatic role during on-going synaptic plasticity.

  2. Adaptation of short-term plasticity parameters via error-driven learning may explain the correlation between activity-dependent synaptic properties, connectivity motifs and target specificity.

    Science.gov (United States)

    Esposito, Umberto; Giugliano, Michele; Vasilaki, Eleni

    2014-01-01

    The anatomical connectivity among neurons has been experimentally found to be largely non-random across brain areas. This means that certain connectivity motifs occur at a higher frequency than would be expected by chance. Of particular interest, short-term synaptic plasticity properties were found to colocalize with specific motifs: an over-expression of bidirectional motifs has been found in neuronal pairs where short-term facilitation dominates synaptic transmission among the neurons, whereas an over-expression of unidirectional motifs has been observed in neuronal pairs where short-term depression dominates. In previous work we found that, given a network with fixed short-term properties, the interaction between short- and long-term plasticity of synaptic transmission is sufficient for the emergence of specific motifs. Here, we introduce an error-driven learning mechanism for short-term plasticity that may explain how such observed correspondences develop from randomly initialized dynamic synapses. By allowing synapses to change their properties, neurons are able to adapt their own activity depending on an error signal. This results in more rich dynamics and also, provided that the learning mechanism is target-specific, leads to specialized groups of synapses projecting onto functionally different targets, qualitatively replicating the experimental results of Wang and collaborators.

  3. Effects of Augmenting N-Methyl-D-Aspartate Receptor Signaling on Working Memory and Experience-Dependent Plasticity in Schizophrenia: An Exploratory Study Using Acute d-cycloserine.

    Science.gov (United States)

    Forsyth, Jennifer K; Bachman, Peter; Mathalon, Daniel H; Roach, Brian J; Ye, Elissa; Asarnow, Robert F

    2017-09-01

    Cognitive deficits in schizophrenia have been hypothesized to reflect N-methyl-D-aspartate receptor (NMDAR) dysfunction. However, the mechanisms through which the NMDAR contributes to individual cognitive functions differ. To explore how NMDAR signaling relates to specific cognitive deficits in schizophrenia, we tested the effects of enhancing NMDAR signaling on working memory and experience-dependent plasticity using d-cycloserine (DCS). Plasticity was assessed using an EEG paradigm that utilizes high-frequency visual stimulation (HFvS) to induce neural potentiation, and 2 learning tasks, the information integration (IIT) and weather prediction (WPT) tasks. Working memory was assessed using an N-back task. Forty-five schizophrenia patients were randomized to receive a single 100 mg DCS dose (SZ-DCS; n = 24) or placebo (SZ-PLC; n = 21) in a double-blind, between-groups design. Testing occurred on a single day after placebo or DCS administration; baseline values were not obtained. DCS did not affect plasticity, as indicated by similar neural potentiation, and similar IIT and WPT learning between groups. However, among patients who successfully engaged in the working memory task (ie, performed above chance), SZ-DCS (n = 17) showed superior 2-back performance compared to SZ-PLC (n = 16). Interestingly, SZ-DCS also showed larger pre-HFvS neural responses during the LTP task. Notably, this pattern of DCS effects is the opposite of those found in our prior study of healthy adults. Results are consistent with target engagement of the NMDAR by DCS, but suggest that NMDAR signaling was not translated into synaptic plasticity changes in schizophrenia. Results highlight the importance of considering how distinct NMDAR-associated processes contribute to individual cognitive deficits in schizophrenia. © The Author 2017. Published by Oxford University Press on behalf of the Maryland Psychiatric Research Center. All rights reserved. For permissions, please email: journals.permissions@oup.com.

  4. On the exploitation of Armstrong-Frederik type nonlinear kinematic hardening in the numerical integration and finite-element implementation of pressure dependent plasticity models

    Science.gov (United States)

    Metzger, Mario; Seifert, Thomas

    2013-09-01

    In this paper, an unconditionally stable algorithm for the numerical integration and finite-element implementation of a class of pressure dependent plasticity models with nonlinear isotropic and kinematic hardening is presented. Existing algorithms are improved in the sense that the number of equations to be solved iteratively is significantly reduced. This is achieved by exploitation of the structure of Armstrong-Frederik-type kinematic hardening laws. The consistent material tangent is derived analytically and compared to the numerically computed tangent in order to validate the implementation. The performance of the new algorithm is compared to an existing one that does not consider the possibility of reducing the number of unknowns to be iterated. The algorithm is used to implement a time and temperature dependent cast iron plasticity model, which is based on the pressure dependent Gurson model, in the finite-element program ABAQUS. The implementation is applied to compute stresses and strains in a large-scale finite-element model of a three cylinder engine block. This computation proofs the applicability of the algorithm in industrial practice that is of interest in applied sciences.

  5. Evolution of Dislocation Subsystem Components During Plastic Deformation Depending on Parameters of Strengthening Phase with L12 Superstructure

    Science.gov (United States)

    Daneyko, O. I.; Kovalevskaya, T. A.; Kulaeva, N. A.; Kolupaeva, S. N.; Shalygina, T. A.

    2017-09-01

    The paper presents results of mathematical modelling of plastic deformation in dispersion-hardened materials with FCC crystal system and L12 superstructure particles. Research results show that the size and the distance between particles of the strengthening phase affect the strain hardening and the evolution of the dislocation subsystem of the FCC alloy hardened with coherent L12 superstructure particles. It is found that increased size of ordered particles or decreased distance between them enhances the abnormal growth in the flow stress and the density of the dislocation subsystem components. Investigations show that prismatic dislocation loops predominate in the dislocation subsystem of materials having a nano-dispersion strengthening phase.

  6. Persistent deficits in hippocampal synaptic plasticity accompany losses of hippocampus-dependent memory in a rodent model of psychosis

    Directory of Open Access Journals (Sweden)

    Valentina eWiescholleck

    2013-03-01

    Full Text Available Irreversible N-methyl-D-aspartate receptor (NMDAR antagonism is known to provoke symptoms of psychosis and schizophrenia in healthy humans. NMDAR hypofunction is believed to play a central role in the pathophysiology of both disorders and in an animal model of psychosis, that is based on irreversible antagonism of NMDARs, pronounced deficits in hippocampal synaptic plasticity have been reported shortly after antagonist treatment. Here, we examined the long-term consequences for long-term potentiation (LTP of a single acute treatment with an irreversible antagonist and investigated whether deficits are associated with memory impairments.The ability to express long-term potentiation (LTP at the perforant pathway – dentate gyrus synapse, as well as object recognition memory was assessed 1, 2, 3 and 4 weeks after a single -treatment of the antagonist, MK801. Here, LTP in freely behaving rats was significantly impaired at all time-points compared to control LTP before treatment. Object recognition memory was also significantly poorer in MK801-treated compared to vehicle-treated animals for several weeks after treatment. Histological analysis revealed no changes in brain tissue.Taken together, these data support that acute treatment with an irreversible NMDAR antagonist persistently impairs hippocampal functioning on behavioral, as well as synaptic levels. The long-term deficits in synaptic plasticity may underlie the cognitive impairments that are associated with schizophrenia-spectrum disorders.

  7. Insulin- and Warts-Dependent Regulation of Tracheal Plasticity Modulates Systemic Larval Growth during Hypoxia in Drosophila melanogaster

    Science.gov (United States)

    Wong, Daniel M.; Shen, Zhouyang; Owyang, Kristin E.; Martinez-Agosto, Julian A.

    2014-01-01

    Adaptation to dynamic environmental cues during organismal development requires coordination of tissue growth with available resources. More specifically, the effects of oxygen availability on body size have been well-documented, but the mechanisms through which hypoxia restricts systemic growth have not been fully elucidated. Here, we characterize the larval growth and metabolic defects in Drosophila that result from hypoxia. Hypoxic conditions reduced fat body opacity and increased lipid droplet accumulation in this tissue, without eliciting lipid aggregation in hepatocyte-like cells called oenocytes. Additionally, hypoxia increased the retention of Dilp2 in the insulin-producing cells of the larval brain, associated with a reduction of insulin signaling in peripheral tissues. Overexpression of the wildtype form of the insulin receptor ubiquitously and in the larval trachea rendered larvae resistant to hypoxia-induced growth restriction. Furthermore, Warts downregulation in the trachea was similar to increased insulin receptor signaling during oxygen deprivation, which both rescued hypoxia-induced growth restriction, inhibition of tracheal molting, and developmental delay. Insulin signaling and loss of Warts function increased tracheal growth and augmented tracheal plasticity under hypoxic conditions, enhancing oxygen delivery during periods of oxygen deprivation. Our findings demonstrate a mechanism that coordinates oxygen availability with systemic growth in which hypoxia-induced reduction of insulin receptor signaling decreases plasticity of the larval trachea that is required for the maintenance of systemic growth during times of limiting oxygen availability. PMID:25541690

  8. Instability criterion for the system composed of elastic beam and strain-softening pillar based on gradient-dependent plasticity

    Institute of Scientific and Technical Information of China (English)

    Xuebin Wang

    2005-01-01

    A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear slips of multiple shear bands, the pillar is divided into several narrow slices where compressive deformation is treated as uniformity. In the light of the compatibility condition of deformation, the total compressive displacement of the pillar is equal to the displacement of the beam in the middle span. An insta bility criterion is derived analytically based on the energy principle using a known size of localization band according to gradientdependent plasticity. The main advantage of the present model is that the effects of the constitutive parameters of rock and the geometrical size of structure are reflected in the criterion. The condition that the derivative of distributed load with respect to the deflection of the beam in the middle span is less than zero is not only equivalent to, but also even more concise in form than the instability criterion. To study the influences of constitutive parameters and geometrical size on stability, some examples are presented.

  9. Insulin- and warts-dependent regulation of tracheal plasticity modulates systemic larval growth during hypoxia in Drosophila melanogaster.

    Directory of Open Access Journals (Sweden)

    Daniel M Wong

    Full Text Available Adaptation to dynamic environmental cues during organismal development requires coordination of tissue growth with available resources. More specifically, the effects of oxygen availability on body size have been well-documented, but the mechanisms through which hypoxia restricts systemic growth have not been fully elucidated. Here, we characterize the larval growth and metabolic defects in Drosophila that result from hypoxia. Hypoxic conditions reduced fat body opacity and increased lipid droplet accumulation in this tissue, without eliciting lipid aggregation in hepatocyte-like cells called oenocytes. Additionally, hypoxia increased the retention of Dilp2 in the insulin-producing cells of the larval brain, associated with a reduction of insulin signaling in peripheral tissues. Overexpression of the wildtype form of the insulin receptor ubiquitously and in the larval trachea rendered larvae resistant to hypoxia-induced growth restriction. Furthermore, Warts downregulation in the trachea was similar to increased insulin receptor signaling during oxygen deprivation, which both rescued hypoxia-induced growth restriction, inhibition of tracheal molting, and developmental delay. Insulin signaling and loss of Warts function increased tracheal growth and augmented tracheal plasticity under hypoxic conditions, enhancing oxygen delivery during periods of oxygen deprivation. Our findings demonstrate a mechanism that coordinates oxygen availability with systemic growth in which hypoxia-induced reduction of insulin receptor signaling decreases plasticity of the larval trachea that is required for the maintenance of systemic growth during times of limiting oxygen availability.

  10. Composition dependence of the synergistic effect of nucleating agent and plasticizer in poly(lactic acid: A Mixture Design study

    Directory of Open Access Journals (Sweden)

    M. K. Fehri

    2016-04-01

    Full Text Available Blends consisting of commercial poly(lactic acid (PLA, poly(lactic acid oligomer (OLA8 as plasticizer and a sulfonic salt of a phthalic ester and poly(D-lactic acid as nucleating agents were prepared by melt extrusion, following a Mixture Design approach, in order to systematically study mechanical and thermal properties as a function of composition. The full investigation was carried out by differential scanning calorimetry (DSC, dynamic mechanical thermal analysis (DMTA and tensile tests. The crystallization half-time was also studied at 105 °C as a function of the blends composition. A range of compositions in which the plasticizer and the nucleation agent minimized the crystallization half-time in a synergistic way was clearly identified thanks to the application of the Mixture Design approach. The results allowed also the identification of a composition range to maximize the crystallinity developed during the rapid cooling below glass transition temperature in injection moulding, thus allowing an easier processing of PLA based materials. Moreover the mechanical properties were discussed by correlating them to the chemical structural features and thermal behaviour of blends.

  11. Plasticity theory

    CERN Document Server

    Lubliner, Jacob

    2008-01-01

    The aim of Plasticity Theory is to provide a comprehensive introduction to the contemporary state of knowledge in basic plasticity theory and to its applications. It treats several areas not commonly found between the covers of a single book: the physics of plasticity, constitutive theory, dynamic plasticity, large-deformation plasticity, and numerical methods, in addition to a representative survey of problems treated by classical methods, such as elastic-plastic problems, plane plastic flow, and limit analysis; the problem discussed come from areas of interest to mechanical, structural, and

  12. Late-Life Environmental Enrichment Induces Acetylation Events and Nuclear Factor κB-Dependent Regulations in the Hippocampus of Aged Rats Showing Improved Plasticity and Learning.

    Science.gov (United States)

    Neidl, Romain; Schneider, Anne; Bousiges, Olivier; Majchrzak, Monique; Barbelivien, Alexandra; de Vasconcelos, Anne Pereira; Dorgans, Kevin; Doussau, Frédéric; Loeffler, Jean-Philippe; Cassel, Jean-Christophe; Boutillier, Anne-Laurence

    2016-04-13

    Aging weakens memory functions. Exposing healthy rodents or pathological rodent models to environmental enrichment (EE) housing improves their cognitive functions by changing neuronal levels of excitation, cellular signaling, and plasticity, notably in the hippocampus. At the molecular level, brain derived-neurotrophic factor (BDNF) represents an important player that supports EE-associated changes. EE facilitation of learning was also shown to correlate with chromatin acetylation in the hippocampus. It is not known, however, whether such mechanisms are still into play during aging. In this study, we exposed a cohort of aged rats (18-month-old) to either a 6 month period of EE or standard housing conditions and investigated chromatin acetylation-associated events [histone acetyltranferase activity, gene expression, and histone 3 (H3) acetylation] and epigenetic modulation of the Bdnf gene under rest conditions and during learning. We show that EE leads to upregulation of acetylation-dependent mechanisms in aged rats, whether at rest or following a learning challenge. We found an increased expression of Bdnf through Exon-I-dependent transcription, associated with an enrichment of acetylated H3 at several sites of Bdnf promoter I, more particularly on a proximal nuclear factor κB (NF-κB) site under learning conditions. We further evidenced p65/NF-κB binding to chromatin at promoters of genes important for plasticity and hippocampus-dependent learning (e.g., Bdnf, CamK2D). Altogether, our findings demonstrate that aged rats respond to a belated period of EE by increasing hippocampal plasticity, together with activating sustained acetylation-associated mechanisms recruiting NF-κB and promoting related gene transcription. These responses are likely to trigger beneficial effects associated with EE during aging. Aging weakens memory functions. Optimizing the neuronal circuitry required for normal brain function can be achieved by increasing sensory, motor, and

  13. Homeostatic role of heterosynaptic plasticity: models and experiments

    Science.gov (United States)

    Chistiakova, Marina; Bannon, Nicholas M.; Chen, Jen-Yung; Bazhenov, Maxim; Volgushev, Maxim

    2015-01-01

    Homosynaptic Hebbian-type plasticity provides a cellular mechanism of learning and refinement of connectivity during development in a variety of biological systems. In this review we argue that a complimentary form of plasticity—heterosynaptic plasticity—represents a necessary cellular component for homeostatic regulation of synaptic weights and neuronal activity. The required properties of a homeostatic mechanism which acutely constrains the runaway dynamics imposed by Hebbian associative plasticity have been well-articulated by theoretical and modeling studies. Such mechanism(s) should robustly support the stability of operation of neuronal networks and synaptic competition, include changes at non-active synapses, and operate on a similar time scale to Hebbian-type plasticity. The experimentally observed properties of heterosynaptic plasticity have introduced it as a strong candidate to fulfill this homeostatic role. Subsequent modeling studies which incorporate heterosynaptic plasticity into model neurons with Hebbian synapses (utilizing an STDP learning rule) have confirmed its ability to robustly provide stability and competition. In contrast, properties of homeostatic synaptic scaling, which is triggered by extreme and long lasting (hours and days) changes of neuronal activity, do not fit two crucial requirements for a hypothetical homeostatic mechanism needed to provide stability of operation in the face of on-going synaptic changes driven by Hebbian-type learning rules. Both the trigger and the time scale of homeostatic synaptic scaling are fundamentally different from those of the Hebbian-type plasticity. We conclude that heterosynaptic plasticity, which is triggered by the same episodes of strong postsynaptic activity and operates on the same time scale as Hebbian-type associative plasticity, is ideally suited to serve a homeostatic role during on-going synaptic plasticity. PMID:26217218

  14. Instrument specific use-dependent plasticity shapes the anatomical properties of the corpus callosum: A comparison between musicians and non-musicians

    Directory of Open Access Journals (Sweden)

    Henning eVollmann

    2014-07-01

    Full Text Available Long-term musical expertise has been shown to be associated with a number of functional and structural brain changes, making it an attractive model for investigating use-dependent plasticity in humans. Physiological interhemispheric inhibition (IHI as examined by transcranial magnetic stimulation has been shown to be correlated with anatomical properties of the corpus callosum as indexed by fractional anisotropy (FA. However, whether or not IHI or the relationship between IHI and FA in the corpus callosum can be modified by different musical training regimes remains largely unknown. We investigated this question in musicians with different requirements for bimanual finger movements (piano and string players and non-expert controls. IHI values were generally higher in musicians, but differed significantly from non-musicians only in string players. IHI was correlated with FA in the posterior midbody of the corpus callosum across all participants. Interestingly, subsequent analyses revealed that this relationship may indeed be modulated by different musical training regimes. Crucially, while string players had greater IHI than non-musicians and showed a positive structure-function relationship, the amount of IHI in pianists was comparable to that of non-musicians and there was no significant structure-function relationship. Our findings indicate instrument specific use-dependent plasticity in both functional (IHI and structural (FA connectivity of motor related brain regions in musicians.

  15. Natural convection in Bingham plastic fluids from an isothermal spheroid: Effects of fluid yield stress, viscous dissipation and temperature-dependent viscosity

    Science.gov (United States)

    Gupta, Anoop Kumar; Gupta, Sanjay; Chhabra, Rajendra Prasad

    2017-08-01

    In this work, the buoyancy-induced convection from an isothermal spheroid is studied in a Bingham plastic fluid. Extensive results on the morphology of approximate yield surfaces, temperature profiles, and the local and average Nusselt numbers are reported to elucidate the effects of the pertinent dimensionless parameters: Rayleigh number, 102 ≤ Ra ≤ 106; Prandtl number, 20 ≤ Pr ≤ 100; Bingham number, 0 ≤ Bn ≤ 103, and aspect ratio, 0.2 ≤ e ≤ 5. Due to the fluid yield stress, fluid-like (yielded) and solid-like (unyielded) regions coexist in the flow domain depending upon the prevailing stress levels vis-a-vis the value of the fluid yield stress. The yielded parts progressively grow in size with the rising Rayleigh number while this tendency is countered by the increasing Bingham and Prandtl numbers. Due to these two competing effects, a limiting value of the Bingham number ( Bn max) is observed beyond which heat transfer occurs solely by conduction due to the solid-like behaviour of the fluid everywhere in the domain. Such limiting values bear a positive dependence on the Rayleigh number ( Ra) and aspect ratio ( e). In addition to this, oblate shapes ( e 1) impede it. Finally, simple predictive expressions for the maximum Bingham number and the average Nusselt number are developed which can be used to predict a priori the overall heat transfer coefficient in a new application. Also, a criterion is developed in terms of the composite parameter Bn• Gr-1/2 which predicts the onset of convection in such fluids. Similarly, another criterion is developed which delineates the conditions for the onset of settling due to buoyancy effects. The paper is concluded by presenting limited results to delineate the effects of viscous dissipation and the temperature-dependent viscosity on the Nusselt number. Both these effects are seen to be rather small in Bingham plastic fluids.

  16. Target-cell-dependent plasticity within the mossy fibre-CA3 circuit reveals compartmentalized regulation of presynaptic function at divergent release sites.

    Science.gov (United States)

    Pelkey, Kenneth A; McBain, Chris J

    2008-03-15

    Individual axons of central neurons innervate a large number of distinct postsynaptic targets belonging to divergent functional categories such as glutamatergic principal cells and inhibitory interneurons. While each bouton along a common axon should experience the same activity pattern in response to action potential firing within the parent presynaptic neuron, accumulating evidence suggests that neighbouring boutons contacting functionally distinct postsynaptic targets regulate their release properties independently, despite being separated by only a few microns. This target-cell-specific autonomy of presynaptic function can greatly expand the computational prowess of central axons to allow for precise coordination of large neuronal ensembles within a given circuit. An excellent example of target-cell-specific presynaptic mechanisms occurs in the CA3 hippocampus where mossy fibre (MF) axons of dentate gyrus granule cells target both principal cells and local circuit inhibitory interneurons via both anatomically and functionally specialized terminals. Of particular interest, mechanisms of both short- and long-term plasticity remain autonomous at these divergent release sites due to an anatomical and biochemical segregation of discrete molecular signalling cascades. Here we review roughly a decades worth of research on the MF-CA3 pathway to showcase the target-cell dependence of presynaptically expressed NMDA receptor-independent synaptic plasticity.

  17. Plastic Jellyfish.

    Science.gov (United States)

    Moseley, Christine

    2000-01-01

    Presents an environmental science activity designed to enhance students' awareness of the hazards of plastic waste for wildlife in aquatic environments. Discusses how students can take steps to reduce the effects of plastic waste. (WRM)

  18. Path Dependency and Path Plasticity: the Co-evolution of Institutions and Innovation - the German Customized Business Software Industry

    OpenAIRE

    Strambach, Simone (Prof. Dr.)

    2008-01-01

    Path dependence and the co-evolution of technology and institutions is a key concept to understand the dynamics of structural change at the level of firms, sectors and multi-level spatial scales. The concept of path dependency is often used in economic geography to explain the economic specialisation and long-standing success as well as crises and economically unfavourable development of regions. The understanding of the institutional dynamics within a well-established technological and insti...

  19. Variability in State-Dependent Plasticity of Intrinsic Properties during Cell-Autonomous Self-Regulation of Calcium Homeostasis in Hippocampal Model Neurons1,2,3

    Science.gov (United States)

    Srikanth, Sunandha

    2015-01-01

    Abstract How do neurons reconcile the maintenance of calcium homeostasis with perpetual switches in patterns of afferent activity? Here, we assessed state-dependent evolution of calcium homeostasis in a population of hippocampal pyramidal neuron models, through an adaptation of a recent study on stomatogastric ganglion neurons. Calcium homeostasis was set to emerge through cell-autonomous updates to 12 ionic conductances, responding to different types of synaptically driven afferent activity. We first assessed the impact of theta-frequency inputs on the evolution of ionic conductances toward maintenance of calcium homeostasis. Although calcium homeostasis emerged efficaciously across all models in the population, disparate changes in ionic conductances that mediated this emergence resulted in variable plasticity to several intrinsic properties, also manifesting as significant differences in firing responses across models. Assessing the sensitivity of this form of plasticity, we noted that intrinsic neuronal properties and the firing response were sensitive to the target calcium concentration and to the strength and frequency of afferent activity. Next, we studied the evolution of calcium homeostasis when afferent activity was switched, in different temporal sequences, between two behaviorally distinct types of activity: theta-frequency inputs and sharp-wave ripples riding on largely silent periods. We found that the conductance values, intrinsic properties, and firing response of neurons exhibited differential robustness to an intervening switch in the type of afferent activity. These results unveil critical dissociations between different forms of homeostasis, and call for a systematic evaluation of the impact of state-dependent switches in afferent activity on neuronal intrinsic properties during neural coding and homeostasis. PMID:26464994

  20. Steroid-dependent auditory plasticity for the enhancement of acoustic communication: recent insights from a vocal teleost fish

    OpenAIRE

    Joseph A Sisneros

    2009-01-01

    The vocal plainfin midshipman fish (Porichthys notatus) has become an excellent model for identifying neural mechanisms of auditory perception that may be shared by all vertebrates. Recent neuroethological studies of the midshipman fish have yielded strong evidence for the steroid-dependent modulation of hearing sensitivity that leads to enhanced coupling of sender and receiver in this vocal-acoustic communication system. Previous work shows that non-reproductive females treated with either t...

  1. Neuromodulation and Synaptic Plasticity for the Control of Fast Periodic Movement: Energy Efficiency in Coupled Compliant Joints via PCA.

    Science.gov (United States)

    Stratmann, Philipp; Lakatos, Dominic; Albu-Schäffer, Alin

    2016-01-01

    There are multiple indications that the nervous system of animals tunes muscle output to exploit natural dynamics of the elastic locomotor system and the environment. This is an advantageous strategy especially in fast periodic movements, since the elastic elements store energy and increase energy efficiency and movement speed. Experimental evidence suggests that coordination among joints involves proprioceptive input and neuromodulatory influence originating in the brain stem. However, the neural strategies underlying the coordination of fast periodic movements remain poorly understood. Based on robotics control theory, we suggest that the nervous system implements a mechanism to accomplish coordination between joints by a linear coordinate transformation from the multi-dimensional space representing proprioceptive input at the joint level into a one-dimensional controller space. In this one-dimensional subspace, the movements of a whole limb can be driven by a single oscillating unit as simple as a reflex interneuron. The output of the oscillating unit is transformed back to joint space via the same transformation. The transformation weights correspond to the dominant principal component of the movement. In this study, we propose a biologically plausible neural network to exemplify that the central nervous system (CNS) may encode our controller design. Using theoretical considerations and computer simulations, we demonstrate that spike-timing-dependent plasticity (STDP) for the input mapping and serotonergic neuromodulation for the output mapping can extract the dominant principal component of sensory signals. Our simulations show that our network can reliably control mechanical systems of different complexity and increase the energy efficiency of ongoing cyclic movements. The proposed network is simple and consistent with previous biologic experiments. Thus, our controller could serve as a candidate to describe the neural control of fast, energy

  2. Sensory deprivation unmasks a PKA-dependent synaptic plasticity mechanism that operates in parallel with CaMKII.

    Science.gov (United States)

    Hardingham, Neil; Wright, Nick; Dachtler, James; Fox, Kevin

    2008-12-10

    Calcium/calmodulin kinase II (CaMKII) is required for LTP and experience-dependent potentiation in the barrel cortex. Here, we find that whisker deprivation increases LTP in the layer IV to II/III pathway and that PKA antagonists block the additional LTP. No LTP was seen in undeprived CaMKII-T286A mice, but whisker deprivation again unmasked PKA-sensitive LTP. Infusion of a PKA agonist potentiated EPSPs in deprived wild-types and deprived CaMKII-T286A point mutants but not in undeprived animals of either genotype. The PKA-dependent potentiation mechanism was not present in GluR1 knockouts. Infusion of a PKA antagonist caused depression of EPSPs in undeprived but not deprived cortex. LTD was occluded by whisker deprivation and blocked by PKA manipulation, but not blocked by cannabinoid antagonists. NMDA receptor currents were unaffected by sensory deprivation. These results suggest that sensory deprivation causes synaptic depression by reversing a PKA-dependent process that may act via GluR1.

  3. Constitutive modeling of rate dependence and microinertia effects in porous-plastic materials with multi-sized voids (MSVs)

    KAUST Repository

    Liu, Jinxing

    2012-11-27

    Micro-voids of varying sizes exist in most metals and alloys. Both experiments and numerical studies have demonstrated the critical influence of initial void sizes on void growth. The classical Gurson-Tvergaard-Needleman model summarizes the influence of voids with a single parameter, namely the void-volume fraction, excluding any possible effects of the void-size distribution. We extend our newly proposed model including the multi-sized void (MSV) effect and the void-interaction effect for the capability of working for both moderate and high loading rate cases, where either rate dependence or microinertia becomes considerable or even dominant. Parametric studies show that the MSV-related competitive mechanism among void growth leads to the dependence of the void growth rate on void size, which directly influences the void\\'s contribution to the total energy composition. We finally show that the stress-strain constitutive behavior is also affected by this MSV-related competitive mechanism. The stabilizing effect due to rate sensitivity and microinertia is emphasized. © 2013 IOP Publishing Ltd.

  4. Constitutive modeling of rate dependence and microinertia effects in porous-plastic materials with multi-sized voids (MSVs)

    Science.gov (United States)

    Liu, J. X.; El Sayed, T.

    2013-01-01

    Micro-voids of varying sizes exist in most metals and alloys. Both experiments and numerical studies have demonstrated the critical influence of initial void sizes on void growth. The classical Gurson-Tvergaard-Needleman model summarizes the influence of voids with a single parameter, namely the void-volume fraction, excluding any possible effects of the void-size distribution. We extend our newly proposed model including the multi-sized void (MSV) effect and the void-interaction effect for the capability of working for both moderate and high loading rate cases, where either rate dependence or microinertia becomes considerable or even dominant. Parametric studies show that the MSV-related competitive mechanism among void growth leads to the dependence of the void growth rate on void size, which directly influences the void's contribution to the total energy composition. We finally show that the stress-strain constitutive behavior is also affected by this MSV-related competitive mechanism. The stabilizing effect due to rate sensitivity and microinertia is emphasized.

  5. Magnetic field response of NaCl:Eu crystal plasticity due to spin-dependent Eu2+ aggregation

    Science.gov (United States)

    Morgunov, R. B.; Buchachenko, A. L.

    2010-07-01

    Magnetic field impulse (7 T amplitude 10 ms duration) was found to affect microhardness of NaCl:Eu crystals at room temperature. Dimers (pairs of Eu2+ paramagnetic ions) were shown to be responsible for the crystal softening induced by magnetic field. Theoretical treatment of the magnetoplastic effect based on the spin dependence of processes resulting in transformation of the dimers in crystals is developed and applied to the description of the long-term magnetic memory. Activation energies of the dimer formation, E1=0.23±0.04eV and decomposition, E2=0.33±0.06eV were extracted from thermoactivation analysis of magnetic field controlled Eu2+ aggregation in 77-473 K temperature range.

  6. Evolution of phenotypic plasticity in colonizing species.

    Science.gov (United States)

    Lande, Russell

    2015-05-01

    I elaborate an hypothesis to explain inconsistent empirical findings comparing phenotypic plasticity in colonizing populations or species with plasticity from their native or ancestral range. Quantitative genetic theory on the evolution of plasticity reveals that colonization of a novel environment can cause a transient increase in plasticity: a rapid initial increase in plasticity accelerates evolution of a new optimal phenotype, followed by slow genetic assimilation of the new phenotype and reduction of plasticity. An association of colonization with increased plasticity depends on the difference in the optimal phenotype between ancestral and colonized environments, the difference in mean, variance and predictability of the environment, the cost of plasticity, and the time elapsed since colonization. The relative importance of these parameters depends on whether a phenotypic character develops by one-shot plasticity to a constant adult phenotype or by labile plasticity involving continuous and reversible development throughout adult life. © 2014 John Wiley & Sons Ltd.

  7. At immature mossy-fiber-CA3 synapses, correlated presynaptic and postsynaptic activity persistently enhances GABA release and network excitability via BDNF and cAMP-dependent PKA.

    Science.gov (United States)

    Sivakumaran, Sudhir; Mohajerani, Majid H; Cherubini, Enrico

    2009-02-25

    In the adult rat hippocampus, the axons of granule cells in the dentate gyrus, the mossy fibers (MF), form excitatory glutamatergic synapses with CA3 principal cells. In neonates, MF release into their targets mainly GABA, which at this developmental stage is depolarizing. Here we tested the hypothesis that, at immature MF-CA3 synapses, correlated presynaptic [single fiber-evoked GABA(A)-mediated postsynaptic potentials (GPSPs)] and postsynaptic activity (back propagating action potentials) may exert a critical control on synaptic efficacy. This form of plasticity, called spike-timing-dependent plasticity (STDP), is a Hebbian type form of learning extensively studied at the level of glutamatergic synapses. Depending on the relative timing, pairing postsynaptic spiking and single MF-GPSPs induced bidirectional changes in synaptic efficacy. In case of positive pairing, spike-timing-dependent-long-term potentiation (STD-LTP) was associated with a persistent increase in GPSP slope and in the probability of cell firing. The transduction pathway involved a rise of calcium in the postsynaptic cell and the combined activity of cAMP-dependent PKA (protein kinase A) and brain-derived neurotrophic factor (BDNF). Retrograde signaling via BDNF and presynaptic TrkB receptors led to a persistent increase in GABA release. In "presynaptically" silent neurons, the enhanced probability of GABA release induced by the pairing protocol, unsilenced these synapses. Shifting E(GABA) from the depolarizing to the hyperpolarizing direction with bumetanide failed to modify synaptic strength. Thus, STD-LTP of GPSPs provides a reliable way to convey information from granule cells to the CA3 associative network at a time when glutamatergic synapses are still poorly developed.

  8. Microplastic interactions with freshwater microalgae: Hetero-aggregation and changes in plastic density appear strongly dependent on polymer type.

    Science.gov (United States)

    Lagarde, Fabienne; Olivier, Ophélie; Zanella, Marie; Daniel, Philippe; Hiard, Sophie; Caruso, Aurore

    2016-08-01

    In this study, the interactions between microplastics, chosen among the most widely used in industry such as polypropylene (PP) and high-density polyethylene (HDPE), and a model freshwater microalgae, Chlamydomas reinhardtii, were investigated. It was shown that the presence of high concentrations of microplastics with size >400 μm did not directly impact the growth of microalgae in the first days of contact and that the expression of three genes involved in the stress response was not modified after 78 days. In parallel, a similar colonization was observed for the two polymers. However, after 20 days of contact, in the case of PP only, hetero-aggregates constituted of microalgae, microplastics and exopolysaccharides were formed. An estimation of the hetero-aggregates composition was approximately 50% of PP fragments and 50% of microalgae, which led to a final density close to 1.2. Such hetero-aggregates appear as an important pathway for the vertical transport of PP microplastics from the water surface to sediment. Moreover, after more than 70 days of contact with microplastics, the microalgae genes involved in the sugar biosynthesis pathways were strongly over-expressed compared to control conditions. The levels of over-expression were higher in the case of HDPE than in PP condition. This work presents the first evidence that depending on their chemical nature, microplastics will follow different fates in the environment. Copyright © 2016 Elsevier Ltd. All rights reserved.

  9. Optical implementation of neural learning algorithms based on cross-gain modulation in a semiconductor optical amplifier

    Science.gov (United States)

    Li, Qiang; Wang, Zhi; Le, Yansi; Sun, Chonghui; Song, Xiaojia; Wu, Chongqing

    2016-10-01

    Neuromorphic engineering has a wide range of applications in the fields of machine learning, pattern recognition, adaptive control, etc. Photonics, characterized by its high speed, wide bandwidth, low power consumption and massive parallelism, is an ideal way to realize ultrafast spiking neural networks (SNNs). Synaptic plasticity is believed to be critical for learning, memory and development in neural circuits. Experimental results have shown that changes of synapse are highly dependent on the relative timing of pre- and postsynaptic spikes. Synaptic plasticity in which presynaptic spikes preceding postsynaptic spikes results in strengthening, while the opposite timing results in weakening is called antisymmetric spike-timing-dependent plasticity (STDP) learning rule. And synaptic plasticity has the opposite effect under the same conditions is called antisymmetric anti-STDP learning rule. We proposed and experimentally demonstrated an optical implementation of neural learning algorithms, which can achieve both of antisymmetric STDP and anti-STDP learning rule, based on the cross-gain modulation (XGM) within a single semiconductor optical amplifier (SOA). The weight and height of the potentitation and depression window can be controlled by adjusting the injection current of the SOA, to mimic the biological antisymmetric STDP and anti-STDP learning rule more realistically. As the injection current increases, the width of depression and potentitation window decreases and height increases, due to the decreasing of recovery time and increasing of gain under a stronger injection current. Based on the demonstrated optical STDP circuit, ultrafast learning in optical SNNs can be realized.

  10. Ethanol up-regulates nucleus accumbens neuronal activity dependent pentraxin (Narp): implications for alcohol-induced behavioral plasticity.

    Science.gov (United States)

    Ary, Alexis W; Cozzoli, Debra K; Finn, Deborah A; Crabbe, John C; Dehoff, Marlin H; Worley, Paul F; Szumlinski, Karen K

    2012-06-01

    Neuronal activity dependent pentraxin (Narp) interacts with α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) glutamate receptors to facilitate excitatory synapse formation by aggregating them at established synapses. Alcohol is well-characterized to influence central glutamatergic transmission, including AMPA receptor function. Herein, we examined the influence of injected and ingested alcohol upon Narp protein expression, as well as basal Narp expression in mouse lines selectively bred for high blood alcohol concentrations under limited access conditions. Alcohol up-regulated accumbens Narp levels, concomitant with increases in levels of the GluR1 AMPA receptor subunit. However, accumbens Narp or GluR1 levels did not vary as a function of selectively bred genotype. We next employed a Narp knock-out (KO) strategy to begin to understand the behavioral relevance of alcohol-induced changes in protein expression in several assays of alcohol reward. Compared to wild-type mice, Narp KO animals: fail to escalate daily intake of high alcohol concentrations under free-access conditions; shift their preference away from high alcohol concentrations with repeated alcohol experience; exhibit a conditioned place-aversion in response to the repeated pairing of 3 g/kg alcohol with a distinct environment and fail to exhibit alcohol-induced locomotor hyperactivity following repeated alcohol treatment. Narp deletion did not influence the daily intake of either food or water, nor did it alter any aspect of spontaneous or alcohol-induced motor activity, including the development of tolerance to its motor-impairing effects with repeated treatment. Taken together, these data indicate that Narp induction, and presumably subsequent aggregation of AMPA receptors, may be important for neuroplasticity within limbic subcircuits mediating or maintaining the rewarding properties of alcohol.

  11. Plastics Technology.

    Science.gov (United States)

    Barker, Tommy G.

    This curriculum guide is designed to assist junior high schools industrial arts teachers in planning new courses and revising existing courses in plastics technology. Addressed in the individual units of the guide are the following topics: introduction to production technology; history and development of plastics; safety; youth leadership,…

  12. User’s Manual for SAC-3: A Three-Dimensional Nonlinear, Time Dependent Soil Analysis Code Using the Bounding Surface Plasticity Model.

    Science.gov (United States)

    1983-12-01

    by the fact that two distinct processes are involved, i.e. water flow and soil plasticity . 35 %. ........ - w 2 A L4 bL’ ,- - P7 Thus a certain amount...for *• MODCAL-Bounding Surface Soil Plasticity Model Calibration and Prediction -. *.Code (Volume II)," Civil Engineering Laboratory, Naval

  13. User’s Manual for SAC-2. A Two-Dimensional Nonlinear, Time Dependent Soil Analysis Code Using the Bounding Surface Plasticity Model.

    Science.gov (United States)

    1983-12-01

    of appropriate time step lengths is complicated by the fact that two distinct processes are involved, i.e. water flow and soil plasticity . Thus a...1981. 9. DeNatale, 3.S., L.R. Herrmann, and Y.F. Dafalias, "User’s Manual for MODCAL-Bounding Surface Soil Plasticity Model Calibration and Prediction

  14. Hydrogenation induced deviation of temperature and concentration dependences of polymer-solvent interactions in poly(vinyl chloride) and a new eco-friendly plasticizer

    Science.gov (United States)

    Liu, Yang; Zhang, Rongchun; Wang, Xiaoliang; Sun, Pingchuan; Chen, Wei; Shen, Jianyi; Xue, Gi

    2015-06-01

    As a substitute for di-2-ethylhexyl phthalate (DOP), a new eco-friendly plasticizer, di(2-ethylhexyl) cyclohexane-1,2-dicarboxylate (DEHHP), was systematically studied in this work, mainly focusing on its interaction with poly(vinyl chloride) (PVC). The temperature and concentration dependences of polymer-solvent interactions in PVC/DEHHP were systematically investigated by rheology, low-field NMR and molecular dynamics simulations, and the results were quite different from those in PVC/DOP. With temperature increasing or PVC concentration decreasing, rheology experiments revealed that polymer-solvent interactions in PVC/DEHHP were weaker than that in PVC/DOP. Low-field 1H NMR results showed that the number of polymer-solvent complexes decreased as temperature increased. A faster decreasing rate of this number made the polymer-solvent interactions weaker in PVC/DEHHP than in PVC/DOP. Molecular dynamics simulations were further performed to study the role of polymer-solvent hydrogen bonding interactions in the systems. The radial distribution function showed that heating and dilution both resulted in faster molecular motions, and disassociation of the hydrogen bonds in the simplex hydrogen bonding system. Therefore, heating and dilution had an equivalent effect on the polymer-solvent interactions.

  15. Effects of bursting dynamic features on the generation of multi-clustered structure of neural network with symmetric spike-timing-dependent plasticity learning rule

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Hui; Song, Yongduan; Xue, Fangzheng; Li, Xiumin, E-mail: xmli@cqu.edu.cn [Key Laboratory of Dependable Service Computing in Cyber Physical Society of Ministry of Education, Chongqing University, Chongqing 400044 (China); College of Automation, Chongqing University, Chongqing 400044 (China)

    2015-11-15

    In this paper, the generation of multi-clustered structure of self-organized neural network with different neuronal firing patterns, i.e., bursting or spiking, has been investigated. The initially all-to-all-connected spiking neural network or bursting neural network can be self-organized into clustered structure through the symmetric spike-timing-dependent plasticity learning for both bursting and spiking neurons. However, the time consumption of this clustering procedure of the burst-based self-organized neural network (BSON) is much shorter than the spike-based self-organized neural network (SSON). Our results show that the BSON network has more obvious small-world properties, i.e., higher clustering coefficient and smaller shortest path length than the SSON network. Also, the results of larger structure entropy and activity entropy of the BSON network demonstrate that this network has higher topological complexity and dynamical diversity, which benefits for enhancing information transmission of neural circuits. Hence, we conclude that the burst firing can significantly enhance the efficiency of clustering procedure and the emergent clustered structure renders the whole network more synchronous and therefore more sensitive to weak input. This result is further confirmed from its improved performance on stochastic resonance. Therefore, we believe that the multi-clustered neural network which self-organized from the bursting dynamics has high efficiency in information processing.

  16. Effects of bursting dynamic features on the generation of multi-clustered structure of neural network with symmetric spike-timing-dependent plasticity learning rule

    Science.gov (United States)

    Liu, Hui; Song, Yongduan; Xue, Fangzheng; Li, Xiumin

    2015-11-01

    In this paper, the generation of multi-clustered structure of self-organized neural network with different neuronal firing patterns, i.e., bursting or spiking, has been investigated. The initially all-to-all-connected spiking neural network or bursting neural network can be self-organized into clustered structure through the symmetric spike-timing-dependent plasticity learning for both bursting and spiking neurons. However, the time consumption of this clustering procedure of the burst-based self-organized neural network (BSON) is much shorter than the spike-based self-organized neural network (SSON). Our results show that the BSON network has more obvious small-world properties, i.e., higher clustering coefficient and smaller shortest path length than the SSON network. Also, the results of larger structure entropy and activity entropy of the BSON network demonstrate that this network has higher topological complexity and dynamical diversity, which benefits for enhancing information transmission of neural circuits. Hence, we conclude that the burst firing can significantly enhance the efficiency of clustering procedure and the emergent clustered structure renders the whole network more synchronous and therefore more sensitive to weak input. This result is further confirmed from its improved performance on stochastic resonance. Therefore, we believe that the multi-clustered neural network which self-organized from the bursting dynamics has high efficiency in information processing.

  17. The dependence on pressure of the plastic flow of rocksalt in the temperature range 25-250° C: implications for the rate controlling mechanism

    Science.gov (United States)

    Muhammad, Nawaz; Spiers, Chris; De Bresser, Hans; Peach, Colin

    2014-05-01

    Despite the large body of data that already exists, the question what microphysical mechanisms govern plastic flow of natural rocksalt at in situ conditions has not yet been answered to full satisfaction. In particular, the exact mechanism controlling dislocation motion at relatively low temperature is still insufficiently understood. As a result, uncertainties exist regarding the appropriate mechanism-based flow-law for low temperature, hampering reliable extrapolation of lab creep data to in situ strain rates. Such extrapolation is required for the modelling of the long term behaviour of salt for geomechanical purposes (e.g. subsidence prognosis). Several dislocation models have been proposed to control plastic flow of rocksalt, such as dislocation climb, cross-slip and (impurity-controlled) glide, but none of these have been rigorously verified. One way to test which model is appropriate is by investigating the pressure dependence of flow of rocksalt. Dislocation glide is expected to be hardly affected by pressure, cross slip (controlled by constriction of partial dislocations) will become easier with increasing pressure, and dislocation climb will become more difficult. We performed conventional axi-symmetric compression tests on synthetic polycrystalline salt samples with an average grain size of 300 μm. The samples were dry, in order to eliminate the possible influence of pressure solution creep. The experiments were carried out at temperatures in the range 25-250° C, i.e. 0.28-0.48Tm, and at pressure ranging 50-600 MPa, which is a range not previously covered for polycrystalline rocksalt. Argon gas was used as the pressure medium. With confining pressure increasing from 50 to 600 MPa, the rocksalt remained of the same strength at RT, but became about 60% stronger at 125oC and about 80% stronger at 250oC at strain rate 10-6 s-1 (at 15% strain). Using a conventional (Dorn-type) power law to describe the mechanical behaviour, stress exponents (n) were found

  18. Storage of phase-coded patterns via STDP in fully-connected and sparse network: a study of the network capacity

    Directory of Open Access Journals (Sweden)

    Silvia Scarpetta

    2010-08-01

    Full Text Available We study the storage and retrieval of phase-coded patterns as stable dynamical attractors in recurrent neural networks, for both an analog and a integrate-and-fire spiking model. The synaptic strength is determined by a learning rule based on spike-time-dependent plasticity, with an asymmetric time window depending on the relative timing between pre- and post-synaptic activity. We store multiple patterns and study the network capacity. For the analog model, we find that the network capacity scales linearly with the network size, and that both capacity and the oscillation frequency of the retrieval state depend on the asymmetry of the learning time window. In addition to fully-connected networks, we study sparse networks, where each neuron is connected only to a small number $zll N$ of other neurons. Connections can be short range, between neighboring neurons placed on a regular lattice, or long range, between randomly chosen pairs of neurons. We find that a small fraction of long range connections is able to amplify the capacity of the network. This imply that a small-world-network topology is optimal, as a compromise between the cost of long range connections and the capacity increase. Also in the spiking integrate and fire model the crucial result of storing and retrieval of multiple phase-coded patterns is observed. The capacity of the fully-connected spiking network is investigated, together with the relation between oscillation frequency of retrieval state and window asymmetry.

  19. Plastic bronchitis

    National Research Council Canada - National Science Library

    Singhi, Anil Kumar; Vinoth, Bharathi; Kuruvilla, Sarah; Sivakumar, Kothandam

    2015-01-01

    Plastic bronchitis, a rare but serious clinical condition, commonly seen after Fontan surgeries in children, may be a manifestation of suboptimal adaptation to the cavopulmonary circulation with unfavorable hemodynamics...

  20. Plastic Fishes

    CERN Multimedia

    Trettnak, Wolfgang

    2015-01-01

    In terms of weight, the plastic pollution in the world’s oceans is estimated to be around 300,000 tonnes. This plastic comes from both land-based and ocean-based sources. A lecture at CERN by chemist Wolfgang Trettnak addressed this issue and highlighted the role of art in raising people’s awareness. The slideshow below gives you a taste of the artworks by Wolfgang Trettnak and Margarita Cimadevila.

  1. Plastic Bridge

    Institute of Scientific and Technical Information of China (English)

    履之

    1994-01-01

    Already ubiquitous in homes and cars, plastic is now appearing inbridges. An academic-industrial consortium based at the University ofCalifornia in San Diego is launching a three-year research program aimed atdeveloping the world’s first plastic highway bridge, a 450-foot span madeentirely from glass-,carbon,and polymer-fiber-reinforced composite mate-rials, the stuff of military aircraft. It will cross Interstate 5 to connect thetwo sides of the school’s campus.

  2. Discrete dislocation plasticity

    NARCIS (Netherlands)

    van der Giessen, E.; Finel, A; Maziere, D; Veron, M

    2003-01-01

    Conventional continuum mechanics models of inelastic deformation processes axe size scale independent. In contrast, there is considerable experimental evidence that plastic flow in crystalline materials is size dependent over length scales of the order of tens of microns and smaller. At present ther

  3. 基于梯度塑性理论的断层活化机理%Faults activation mechanism based on gradient-dependent plasticity

    Institute of Scientific and Technical Information of China (English)

    林远东; 涂敏; 刘文震; 吴建强

    2012-01-01

    Analyzed the strain softening and consequent strain localization behavior for fault based on gradient-dependent plasticity.Regarded fault as continuous geological bodies with thickness.The gradient-dependent plasticity was introduced into the fault model.The theoretical expression of fault band displacement in direction of fault azimuth was presented,and ‘the equivalent shear stiffness of the fault band’ was defined.The displacement of fault hanging wall in direction of fault azimuth was presented and ‘the equivalent shear stiffness of the fault hanging-foot-wall’ was defined considering the stress conditions of element body in interface at the lower edge of fault hanging wall.The fault activation criterion was obtained according to comparing ‘the equivalent shear stiffness of the fault hanging-foot-wall’ with ‘the equivalent shear stiffness of the fault band’.The results show that fault activation is determined with the factors which not only include the material properties(such as brittleness,the internal structure size of geo-materials in fault),but also include fault hanging-foot-wall characteristic parameters(such as shear elastic modulus,Poisson’s ratio).Besides,fault activation is determined with the minimum width of the rock mass which include the integral fault.It is found that the lower internal parameter or ‘the shear equivalent stiffness of fault hanging-foot-wall’,and the higher brittleness of fault geo-materials or the minimum width of the rock mass which include the integral fault lead to increasing the possibility of fault activation.%基于梯度塑性理论,将断层视为内部连续、有厚度的地质体,分析断层带应变软化及其应变局部化问题。将梯度塑性理论引入断层带模型,得到了断层带沿倾向相对错动位移的理论表达式,定义了"断层带等效剪切刚度";通过对上盘岩体的下边缘界面处单元体应力分析,得到上盘岩体沿断层倾向的相对错动位

  4. Structural and Functional Plasticity within the Nucleus Accumbens and Prefrontal Cortex Associated with Time-Dependent Increases in Food Cue Seeking Behavior.

    Science.gov (United States)

    Dingess, Paige M; Darling, Rebecca A; Derman, Rifka C; Wulff, Shaun S; Hunter, Melissa L; Ferrario, Carrie R; Brown, Travis E

    2017-03-15

    Urges to consume food can be driven by stimuli in the environment that are associated with previous food experience. Identifying adaptations within brain reward circuits that facilitate cue-induced food seeking is critical for understanding and preventing the overconsumption of food and subsequent weight gain. Utilizing electrophysiological, biochemical, and DiI labeling we examined functional and structural changes in the nucleus accumbens (NAc) and prefrontal cortex (PFC) associated with time-dependent increases in food craving ('incubation of craving'). Rats self-administered 60% high-fat or chow 45 mg pellets and were then tested for incubation of craving either 1 or 30 days after training (1d, 30d). High-fat was chosen for comparison to determine if palatability differentially affected incubation and/or plasticity. Rats showed robust incubation of craving for both food rewards, although responding for cues previously associated with high-fat was greater than chow at both 1d and 30d. In addition, previous experience with high-fat consumption reduced dendritic spine density in the PFC at both time points. In contrast, incubation was associated with an increase in NAc spine density and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated transmission at 30d in both groups. Finally, incubation of craving for chow and high-fat was accompanied by an increase in calcium-permeable and calcium-impermeable AMPARs, respectively. Our results suggest that incubation of food craving alters brain reward circuitry and macronutrient composition specifically induces cortical changes in a way that may facilitate maladaptive food seeking behaviors.Neuropsychopharmacology accepted article preview online, 15 March 2017. doi:10.1038/npp.2017.57.

  5. Steady-state dynamics and experience-dependent plasticity of dendritic spines of layer 4/5a pyramidal neurons in somatosensory cortex

    Directory of Open Access Journals (Sweden)

    Amaya Miquelajauregui

    2014-04-01

    Full Text Available The steady state dynamics and experience-dependent plasticity of dendritic spines of layer (L 2/3 and L5B cortical pyramidal neurons have recently been assessed using in vivo two-photon microscopy (Trachtenberg et al., 2002; Zuo et al., 2005; Holtmaat et al., 2006. In contrast, not much is known about spine dynamics in L4/5a neurons, regarded as direct recipients of thalamocortical input (Constantinople and Bruno, 2013. In the adult mouse somatosensory cortex (SCx, the transcription factor Ebf2 is enriched in excitatory neurons of L4/5a, including pyramidal neurons. We assessed the molecular and electrophysiological properties of these neurons as well as the morphology of their apical tufts (Scholl analysis and cortical outputs (optogenetics within the SCx. To test the hypothesis that L4/5a pyramidal neurons play an important role in sensory processing (given their key laminar position; soma depth ~450-480 µm, we successfully labeled them in Ebf2-Cre mice with EGFP by expressing recombinant rAAV vectors in utero. Using longitudinal in vivo two-photon microscopy through a craniotomy (Mostany and Portera-Cailliau, 2008, we repeatedly imaged spines in apical dendritic tufts of L4/5a neurons under basal conditions and after sensory deprivation. Under steady-state conditions in adults, the morphology of the apical tufts and the mean spine density were stable at 0.39 ± 0.05 spines/μm (comparable to L5B, Mostany et al., 2011. Interestingly, spine elimination increases 4-8 days after sensory deprivation, probably due to input loss. This suggests that Ebf2+ L4/5a neurons could be involved in early steps of processing of thalamocortical information.

  6. GREEN PLASTIC: A NEW PLASTIC FOR PACKAGING

    OpenAIRE

    Mr. Pankaj Kumar*, Sonia

    2016-01-01

    This paper gives a brief idea about a new type of plastic called as bio-plastic or green plastic. Plastic is used as a packaging material for various products, but this plastic is made up of non renewable raw materials. There are various disadvantages of using conventional plastic like littering, CO2 production, non-degradable in nature etc. To overcome these problems a new type of plastic is discovered called bio-plastic or green plastic. Bio-plastic is made from renewable resources and also...

  7. Progress in neural plasticity

    Institute of Scientific and Technical Information of China (English)

    POO; Mu-Ming

    2010-01-01

    One of the properties of the nervous system is the use-dependent plasticity of neural circuits.The structure and function of neural circuits are susceptible to changes induced by prior neuronal activity,as reflected by short-and long-term modifications of synaptic efficacy and neuronal excitability.Regarded as the most attractive cellular mechanism underlying higher cognitive functions such as learning and memory,activity-dependent synaptic plasticity has been in the spotlight of modern neuroscience since 1973 when activity-induced long-term potentiation(LTP) of hippocampal synapses was first discovered.Over the last 10 years,Chinese neuroscientists have made notable contributions to the study of the cellular and molecular mechanisms of synaptic plasticity,as well as of the plasticity beyond synapses,including activity-dependent changes in intrinsic neuronal excitability,dendritic integration functions,neuron-glia signaling,and neural network activity.This work highlight some of these significant findings.

  8. Dopamine D1/D5, But not D2/D3, Receptor Dependency of Synaptic Plasticity at Hippocampal Mossy Fiber Synapses that Is Enabled by Patterned Afferent Stimulation, or Spatial Learning

    Science.gov (United States)

    Hagena, Hardy; Manahan-Vaughan, Denise

    2016-01-01

    important role for DA acting on D1/D5 receptors in the support of long-lasting and learning-related forms of synaptic plasticity at MF-CA3 synapses and provide further evidence for an important neuromodulatory role for this receptor in experience-dependent synaptic encoding in the hippocampal subfields. PMID:27721791

  9. Dopamine D1/D5, but not D2/D3, receptor dependency of synaptic plasticity at hippocampal mossy fiber synapses that is enabled by patterned afferent stimulation, or spatial learning

    Directory of Open Access Journals (Sweden)

    Hardy Hagena

    2016-09-01

    indicate an important role for dopamine acting on D1/D5 receptors in the support of long-lasting and learning-related forms of synaptic plasticity at MF-CA3 synapses and provide further evidence for an important neuromodulatory role for this receptor in experience-dependent synaptic encoding in the hippocampal subfields.

  10. Plastic condoms.

    Science.gov (United States)

    1968-01-01

    Only simple equipment, simple technology and low initial capital investment are needed in their manufacture. The condoms can be made by people who were previously unskilled or only semi-skilled workers. Plastic condoms differ from those made of latex rubber in that the nature of the plastic film allows unlimited shelf-life. Also, the plastic has a higher degree of lubricity than latex rubber; if there is a demand for extra lubrication in a particular market, this can be provided. Because the plastic is inert, these condoms need not be packaged in hermetically sealed containers. All these attributes make it possible to put these condoms on the distributors' shelves in developing countries competitively with rubber condoms. The shape of the plastic condom is based on that of the lamb caecum, which has long been used as luxury-type condom. The plastic condom is made from plastic film (ethylene ethyl acrilate) of 0.001 inch (0.0254 mm.) thickness. In addition, a rubber ring is provided and sealed into the base of the condom for retention during coitus. The advantage of the plastic condom design and the equipment on which it is made is that production can be carried out either in labour-intensive economy or with varying degrees of mechanization and automation. The uniform, finished condom if made using previously untrained workers. Training of workers can be done in a matter of hours on the two machines which are needed to produce and test the condoms. The plastic film is provided on a double wound roll, and condom blanks are prepared by means of a heat-sealing die on the stamping machine. The rubber rings are united to the condom blanks on an assembly machine, which consists of a mandrel and heat-sealing equipment to seal the rubber ring to the base of the condom. Built into the assembly machine is a simple air-testing apparatus that can detect the smallest pinhole flaw in a condom. The manufacturing process is completed by unravelling the condom from the assembly

  11. Plastic Bronchitis.

    Science.gov (United States)

    Rubin, Bruce K

    2016-09-01

    Plastic bronchitis is an uncommon and probably underrecognized disorder, diagnosed by the expectoration or bronchoscopic removal of firm, cohesive, branching casts. It should not be confused with purulent mucous plugging of the airway as seen in patients with cystic fibrosis or bronchiectasis. Few medications have been shown to be effective and some are now recognized as potentially harmful. Current research directions in plastic bronchitis research include understanding the genetics of lymphatic development and maldevelopment, determining how abnormal lymphatic malformations contribute to cast formation, and developing new treatments. Copyright © 2016 Elsevier Inc. All rights reserved.

  12. Mixed plastics recycling technology

    CERN Document Server

    Hegberg, Bruce

    1995-01-01

    Presents an overview of mixed plastics recycling technology. In addition, it characterizes mixed plastics wastes and describes collection methods, costs, and markets for reprocessed plastics products.

  13. Plastic food packaging and health

    Directory of Open Access Journals (Sweden)

    Raika Durusoy

    2011-02-01

    Full Text Available Plastics have a wide usage in our daily lives. One of their uses is for food packaging and food containers. The aim of this review is to introduce different types of chemicals that can leach from food packaging plastics into foods and cause human exposure and to mention their effects on health. The types of plastics were reviewed under the 13 headings in Turkish Codex Alimentarius and plastics recycling symbols were provided to enable the recognition of the type of plastic when applicable. Chemicals used during the production and that can cause health risks are investigated under the heading of the relevant type of plastic. The most important chemicals from plastic food packaging that can cause toxicity are styrene, 1,3-butadiene, melamine, formaldehyde, acrylamide, di-2-ethylhexyl phthalate, di-2-ethylhexyl adipate, vinyl chloride and bisphenol A. These chemicals have endocrine disrupting, carcinogenic and/or development disrupting effects. These chemicals may leach into foods depending on the chemical properties of the plastic or food, temperature during packaging, processing and storage, exposure to UV and duration of storage. Contact with fatty/oily or acidic foods, heating of the food inside the container, or drinking hot drinks from plastic cups, use of old and scratched plastics and some detergents increase the risk of leaching. The use of plastic containers and packaging for food and beveradges should be avoided whenever possible and when necessary, less harmful types of plastic should be preferred. [TAF Prev Med Bull 2011; 10(1.000: 87-96

  14. Plastic fish

    CERN Multimedia

    Antonella Del Rosso

    2015-01-01

    In terms of weight, the plastic pollution in the world’s oceans is estimated to be around 300,000 tonnes. This plastic comes from both land-based and ocean-based sources. A lecture at CERN by chemist Wolfgang Trettnak addressed this issue and highlighted the role of art in raising people’s awareness.   Artwork by Wolfgang Trettnak. Packaging materials, consumer goods (shoes, kids’ toys, etc.), leftovers from fishing and aquaculture activities… our oceans and beaches are full of plastic litter. Most of the debris from beaches is plastic bottles. “PET bottles have high durability and stability,” explains Wolfgang Trettnak, a chemist by education and artist from Austria, who gave a lecture on this topic organised by the Staff Association at CERN on 26 May. “PET degrades very slowly and the estimated lifetime of a bottle is 450 years.” In addition to the beach litter accumulated from human use, rivers bring several ki...

  15. Plastic zonnecellen

    NARCIS (Netherlands)

    Roggen, Marjolein

    1998-01-01

    De zonnecel van de toekomst is in de maak. Onderzoekers van uiteenlopend pluimage werken eendrachtig aan een plastic zonnecel. De basis is technisch gelegd met een optimale, door invallend licht veroorzaakte, vorming van ladingdragers binnen een composiet van polymeren en buckyballs. Nu is het zaak

  16. Age-dependent modulation of synaptic plasticity and insulin mimetic effect of lipoic acid on a mouse model of Alzheimer's disease.

    Directory of Open Access Journals (Sweden)

    Harsh Sancheti

    Full Text Available Alzheimer's disease is a progressive neurodegenerative disease that entails impairments of memory, thinking and behavior and culminates into brain atrophy. Impaired glucose uptake (accumulating into energy deficits and synaptic plasticity have been shown to be affected in the early stages of Alzheimer's disease. This study examines the ability of lipoic acid to increase brain glucose uptake and lead to improvements in synaptic plasticity on a triple transgenic mouse model of Alzheimer's disease (3xTg-AD that shows progression of pathology as a function of age; two age groups: 6 months (young and 12 months (old were used in this study. 3xTg-AD mice fed 0.23% w/v lipoic acid in drinking water for 4 weeks showed an insulin mimetic effect that consisted of increased brain glucose uptake, activation of the insulin receptor substrate and of the PI3K/Akt signaling pathway. Lipoic acid supplementation led to important changes in synaptic function as shown by increased input/output (I/O and long term potentiation (LTP (measured by electrophysiology. Lipoic acid was more effective in stimulating an insulin-like effect and reversing the impaired synaptic plasticity in the old mice, wherein the impairment of insulin signaling and synaptic plasticity was more pronounced than those in young mice.

  17. Age-dependent modulation of synaptic plasticity and insulin mimetic effect of lipoic acid on a mouse model of Alzheimer's disease.

    Science.gov (United States)

    Sancheti, Harsh; Akopian, Garnik; Yin, Fei; Brinton, Roberta D; Walsh, John P; Cadenas, Enrique

    2013-01-01

    Alzheimer's disease is a progressive neurodegenerative disease that entails impairments of memory, thinking and behavior and culminates into brain atrophy. Impaired glucose uptake (accumulating into energy deficits) and synaptic plasticity have been shown to be affected in the early stages of Alzheimer's disease. This study examines the ability of lipoic acid to increase brain glucose uptake and lead to improvements in synaptic plasticity on a triple transgenic mouse model of Alzheimer's disease (3xTg-AD) that shows progression of pathology as a function of age; two age groups: 6 months (young) and 12 months (old) were used in this study. 3xTg-AD mice fed 0.23% w/v lipoic acid in drinking water for 4 weeks showed an insulin mimetic effect that consisted of increased brain glucose uptake, activation of the insulin receptor substrate and of the PI3K/Akt signaling pathway. Lipoic acid supplementation led to important changes in synaptic function as shown by increased input/output (I/O) and long term potentiation (LTP) (measured by electrophysiology). Lipoic acid was more effective in stimulating an insulin-like effect and reversing the impaired synaptic plasticity in the old mice, wherein the impairment of insulin signaling and synaptic plasticity was more pronounced than those in young mice.

  18. Features of plastic deformation and fracture of dispersion-strengthened V–Cr–Zr–W alloy depending on temperature of tension

    Energy Technology Data Exchange (ETDEWEB)

    Ditenberg, Ivan A.; Grinyaev, Konstantin V.; Tyumentsev, Alexander N. [National Research Tomsk State University, Tomsk, 634050 (Russian Federation); Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Siberian Physical-Technical Institute, Tomsk, 634050 (Russian Federation); Smirnov, Ivan V., E-mail: smirnov-iv@bk.ru [National Research Tomsk State University, Tomsk, 634050 (Russian Federation); Siberian Physical-Technical Institute, Tomsk, 634050 (Russian Federation); Pinzhin, Yury P. [National Research Tomsk State University, Tomsk, 634050 (Russian Federation); Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Tsverova, Anastasiya S. [National Research Tomsk State University, Tomsk, 634050 (Russian Federation); Chernov, Vyacheslav M. [A.A. Bochvar High Technology Research Institute of Inorganic Materials, Moscow, 123098 (Russian Federation)

    2015-10-27

    Influence of tension temperature on features of plastic deformation and fracture of V–4.23Cr–1.69Zr–7.56W alloy was investigated by scanning and transmission electron microscopy. It is shown that temperature increase leads to activation of the recovery processes, which manifests in the coarsening of microstructure elements, reducing the dislocation density, relaxation of continuous misorientations.

  19. Plastic Surgery Statistics

    Science.gov (United States)

    ... PSN PSEN GRAFT Contact Us News Plastic Surgery Statistics Plastic surgery procedural statistics from the American Society of Plastic Surgeons. Statistics by Year Print 2016 Plastic Surgery Statistics 2015 ...

  20. Plastic bronchitis

    Directory of Open Access Journals (Sweden)

    Anil Kumar Singhi

    2015-01-01

    Full Text Available Plastic bronchitis, a rare but serious clinical condition, commonly seen after Fontan surgeries in children, may be a manifestation of suboptimal adaptation to the cavopulmonary circulation with unfavorable hemodynamics. They are ominous with poor prognosis. Sometimes, infection or airway reactivity may provoke cast bronchitis as a two-step insult on a vulnerable vascular bed. In such instances, aggressive management leads to longer survival. This report of cast bronchitis discusses its current understanding.

  1. Critical role of promoter IV-driven BDNF transcription in GABAergic transmission and synaptic plasticity in the prefrontal cortex.

    Science.gov (United States)

    Sakata, Kazuko; Woo, Newton H; Martinowich, Keri; Greene, Joshua S; Schloesser, Robert J; Shen, Liya; Lu, Bai

    2009-04-07

    Transcription of Bdnf is controlled by multiple promoters, which drive expression of multiple transcripts encoding for the same protein. Promoter IV contributes significantly to activity-dependent brain-derived neurotrophic factor (BDNF) transcription. We have generated promoter IV mutant mice (BDNF-KIV) by inserting a GFP-STOP cassette within the Bdnf exon IV locus. This genetic manipulation results in disruption of promoter IV-mediated Bdnf expression. BDNF-KIV animals exhibited significant deficits in GABAergic interneurons in the prefrontal cortex (PFC), particularly those expressing parvalbumin, a subtype implicated in executive function and schizophrenia. Moreover, disruption of promoter IV-driven Bdnf transcription impaired inhibitory but not excitatory synaptic transmission recorded from layer V pyramidal neurons in the PFC. The attenuation of GABAergic inputs resulted in an aberrant appearance of spike-timing-dependent synaptic potentiation (STDP) in PFC slices derived from BDNF-KIV, but not wild-type littermates. These results demonstrate the importance of promoter IV-dependent Bdnf transcription in GABAergic function and reveal an unexpected regulation of STDP in the PFC by BDNF.

  2. 大脑皮层内活动依赖的神经环路结构可塑性研究进展%Progress in activity-dependent structural plasticity of neural circuits in cortex

    Institute of Scientific and Technical Information of China (English)

    饶小平; 许智祥; 徐富强

    2012-01-01

    哺乳动物大脑皮层内的神经环路在神经发育、学习记忆、神经和精神疾病过程中表现出令人惊异的结构和功能可塑性.随着新的成像技术及分子生物学方法的应用,在细胞和突触水平上观察活体皮层内神经环路的动态结构变化成为可能,因此近十年来有关活动依赖的神经环路结构可塑性方面的研究进展迅速.该文综述了该方面的部分实验结果,重点阐述个体生长发育、丰富环境、感觉剥夺、病理状态以及学习和记忆等过程和条件下树突的结构可塑性特点,尤其是树突棘的形态和数量变化特征;并简单介绍轴突的结构可塑性,以及结构可塑性相关的分子和细胞机制,最后提出未来该领域内亟待解决的问题.%Neural circuits of mammalian cerebral cortex have exhibited amazing abilities of structural and functional plasticity in development, learning and memory, neurological and psychiatric diseases. With the new imaging techniques and the application of molecular biology methods, observation neural circuits' structural dynamics within the cortex in vivo at the cellular and synaptic level was possible, so there were many great progresses in the field of the activity-dependent structural plasticity over the past decade. This paper reviewed some of the aspects of the experimental results, focused on the characteristics of dendritic structural plasticity in individual growth and development, rich environment, sensory deprivation, and pathological conditions, as well as learning and memory, especially the dynamics of dendritic spines on morphology and quantity; after that, we introduced axonal structural plasticity, the molecular and cellular mechanisms of structural plasticity, and proposed some future problems to be solved at last.

  3. Overcoming maladaptive plasticity through plastic compensation

    Directory of Open Access Journals (Sweden)

    Matthew R.J. MORRIS, Sean M. ROGERS

    2013-08-01

    Full Text Available Most species evolve within fluctuating environments, and have developed adaptations to meet the challenges posed by environmental heterogeneity. One such adaptation is phenotypic plasticity, or the ability of a single genotype to produce multiple environmentally-induced phenotypes. Yet, not all plasticity is adaptive. Despite the renewed interest in adaptive phenotypic plasticity and its consequences for evolution, much less is known about maladaptive plasticity. However, maladaptive plasticity is likely an important driver of phenotypic similarity among populations living in different environments. This paper traces four strategies for overcoming maladaptive plasticity that result in phenotypic similarity, two of which involve genetic changes (standing genetic variation, genetic compensation and two of which do not (standing epigenetic variation, plastic compensation. Plastic compensation is defined as adaptive plasticity overcoming maladaptive plasticity. In particular, plastic compensation may increase the likelihood of genetic compensation by facilitating population persistence. We provide key terms to disentangle these aspects of phenotypic plasticity and introduce examples to reinforce the potential importance of plastic compensation for understanding evolutionary change [Current Zoology 59 (4: 526–536, 2013].

  4. Overcoming maladaptive plasticity through plastic compensation

    Institute of Scientific and Technical Information of China (English)

    Matthew R.J.MORRIS; Sean M.ROGERS

    2013-01-01

    Most species evolve within fluctuating environments,and have developed adaptations to meet the challenges posed by environmental heterogeneity.One such adaptation is phenotypic plasticity,or the ability of a single genotype to produce multiple environmentally-induced phenotypes.Yet,not all plasticity is adaptive.Despite the renewed interest in adaptive phenotypic plasticity and its consequences for evolution,much less is known about maladaptive plasticity.However,maladaptive plasticity is likely an important driver of phenotypic similarity among populations living in different environments.This paper traces four strategies for overcoming maladaptive plasticity that result in phenotypic similarity,two of which involve genetic changes (standing genetic variation,genetic compensation) and two of which do not (standing epigenetic variation,plastic compensation).Plastic compensation is defined as adaptive plasticity overcoming maladaptive plasticity.In particular,plastic compensation may increase the likelihood of genetic compensation by facilitating population persistence.We provide key terms to disentangle these aspects of phenotypic plasticity and introduce examples to reinforce the potential importance of plastic compensation for understanding evolutionary change.

  5. Constraints on the evolution of phenotypic plasticity: limits and costs of phenotype and plasticity.

    Science.gov (United States)

    Murren, C J; Auld, J R; Callahan, H; Ghalambor, C K; Handelsman, C A; Heskel, M A; Kingsolver, J G; Maclean, H J; Masel, J; Maughan, H; Pfennig, D W; Relyea, R A; Seiter, S; Snell-Rood, E; Steiner, U K; Schlichting, C D

    2015-10-01

    Phenotypic plasticity is ubiquitous and generally regarded as a key mechanism for enabling organisms to survive in the face of environmental change. Because no organism is infinitely or ideally plastic, theory suggests that there must be limits (for example, the lack of ability to produce an optimal trait) to the evolution of phenotypic plasticity, or that plasticity may have inherent significant costs. Yet numerous experimental studies have not detected widespread costs. Explicitly differentiating plasticity costs from phenotype costs, we re-evaluate fundamental questions of the limits to the evolution of plasticity and of generalists vs specialists. We advocate for the view that relaxed selection and variable selection intensities are likely more important constraints to the evolution of plasticity than the costs of plasticity. Some forms of plasticity, such as learning, may be inherently costly. In addition, we examine opportunities to offset costs of phenotypes through ontogeny, amelioration of phenotypic costs across environments, and the condition-dependent hypothesis. We propose avenues of further inquiry in the limits of plasticity using new and classic methods of ecological parameterization, phylogenetics and omics in the context of answering questions on the constraints of plasticity. Given plasticity's key role in coping with environmental change, approaches spanning the spectrum from applied to basic will greatly enrich our understanding of the evolution of plasticity and resolve our understanding of limits.

  6. Recycling of Plastic

    DEFF Research Database (Denmark)

    Christensen, Thomas Højlund; Fruergaard, Thilde

    2011-01-01

    Plastic is produced from fossil oil. Plastic is used for many different products. Some plastic products like, for example, wrapping foil, bags and disposable containers for food and beverage have very short lifetimes and thus constitute a major fraction of most waste. Other plastic products like......, good strength and long durability. Recycling of plastic waste from production is well-established, while recycling of postconsumer plastic waste still is in its infancy. This chapter describes briefly how plastic is produced and how waste plastic is recycled in the industry. Quality requirements...

  7. Disrupted in schizophrenia 1 (DISC1) L100P mutants have impaired activity-dependent plasticity in vivo and in vitro

    Science.gov (United States)

    Tropea, D; Molinos, I; Petit, E; Bellini, S; Nagakura, I; O'Tuathaigh, C; Schorova, L; Mitchell, K J; Waddington, J; Sur, M; Gill, M; Corvin, A P

    2016-01-01

    Major neuropsychiatric disorders are genetically complex but share overlapping etiology. Mice mutant for rare, highly penetrant risk variants can be useful in dissecting the molecular mechanisms involved. The gene disrupted in schizophrenia 1 (DISC1) has been associated with increased risk for neuropsychiatric conditions. Mice mutant for Disc1 display morphological, functional and behavioral deficits that are consistent with impairments observed across these disorders. Here we report that Disc1 L100P mutants are less able to reorganize cortical circuitry in response to stimulation in vivo. Molecular analysis reveals that the mutants have a reduced expression of PSD95 and pCREB in visual cortex and fail to adjust expression of such markers in response to altered stimulation. In vitro analysis shows that mutants have impaired functional reorganization of cortical neurons in response to selected forms of neuronal stimulation, but there is no altered basal expression of synaptic markers. These findings suggest that DISC1 has a critical role in the reorganization of cortical plasticity and that this phenotype becomes evident only under challenge, even at early postnatal stages. This result may represent an important etiological mechanism in the emergence of neuropsychiatric disorders. PMID:26756905

  8. Candidate genes in ocular dominance plasticity

    NARCIS (Netherlands)

    M.L. Rietman; J.-P. Sommeijer; C.N. Levelt; J.A. Heimel; A.B. Brussaard; J.G.G. Borst; Y. Elgersma; N. Galjart; G.T. van der Horst; C.M. Pennartz; A.B. Smit; B.M. Spruijt; M. Verhage; C.I. de Zeeuw

    2012-01-01

    Many studies have been devoted to the identification of genes involved in experience-dependent plasticity in the visual cortex. To discover new candidate genes, we have reexamined data from one such study on ocular dominance (OD) plasticity in recombinant inbred BXD mouse strains. We have correlated

  9. The genetics of phenotypic plasticity. XI. Joint evolution of plasticity and dispersal rate.

    Science.gov (United States)

    Scheiner, Samuel M; Barfield, Michael; Holt, Robert D

    2012-08-01

    In a spatially heterogeneous environment, the rate at which individuals move among habitats affects whether selection favors phenotypic plasticity or genetic differentiation, with high dispersal rates favoring trait plasticity. Until now, in theoretical explorations of plasticity evolution, dispersal rate has been treated as a fixed, albeit probabilistic, characteristic of a population, raising the question of what happens when the propensity to disperse and trait plasticity are allowed to evolve jointly. We examined the effects of their joint evolution on selection for plasticity using an individual-based computer simulation model. In the model, the environment consisted of a linear gradient of 50 demes with dispersal occurring either before or after selection. Individuals consisted of loci whose phenotypic expression either are affected by the environment (plastic) or are not affected (nonplastic), plus a locus determining the propensity to disperse. When dispersal rate and trait plasticity evolve jointly, the system tends to dichotomous outcomes of either high trait plasticity and high dispersal, or low trait plasticity and low dispersal. The outcome strongly depended on starting conditions, with high trait plasticity and dispersal favored when the system started at high values for either trait plasticity or dispersal rate (or both). Adding a cost of plasticity tended to drive the system to genetic differentiation, although this effect also depended on initial conditions. Genetic linkage between trait plasticity loci and dispersal loci further enhanced this strong dichotomy in evolutionary outcomes. All of these effects depended on organismal life history pattern, and in particular whether selection occurred before or after dispersal. These results can explain why adaptive trait plasticity is less common than might be expected.

  10. Field based plastic contamination sensing

    Science.gov (United States)

    The United States has a long-held reputation of being a dependable source of high quality, contaminant-free cotton. Recently, increased incidence of plastic contamination from sources such as shopping bags, vegetable mulch, surface irrigation tubing, and module covers has threatened the reputation o...

  11. Memristive Neural Networks Based on STDP Rules and Its Applications in Image Storage%基于STDP规则的忆阻神经网络在图像存储中的应用

    Institute of Scientific and Technical Information of China (English)

    王丽丹; 段美涛; 段书凯

    2013-01-01

    忆阻器是具有记忆和类突触特性的非线性电路元件,将忆阻器与STDP学习规则相结合,提出了基于STDP学习规则的忆阻神经网络,并将它应用于二值图像的叠加和灰度图像的存储与输出。首先将忆阻器作突触,通过实验证实在特定形状动作电位下,可实现STDP学习规则;构建了4×4的忆阻交叉阵列神经网络;用16×16的忆阻交叉阵列神经网络实现二值图像的叠加。最后用N×N的忆阻神经网络实现了灰度图像的存储与输出。通过MATLAB仿真实验证实了该方案的有效性,该忆阻神经网络具有仿生特性,有望解决模式识别、人工智能中出现的复杂问题。%Memristor is a nonlinear circuit element which has property of memory and the similar synapse characteristic. In this paper, a memristive neural network based on STDP learning rule is proposed and used in the binary image overlay and the storage and output of gray and color images. Firstly, the memristor is used as the synapse, and the specific shape action potentials realizing STDP learning rules are demonstrated. Secondly, 4×4 memristive crossbar array neural networks are realized. And then the binary image overlay is obtained by the neural network of 16×16 memristive crossbar array neural networks. Finally, the storage and output of gray and color images are achieved by the N×N memristive neural network. The feasibility of the proposed method is proved by MATLAB simulation experiments. This neural network has more bionic feasibility, which could be applied to solve the complex problems in pattern recognition and artificial intelligence.

  12. Target-cell specificity of kainate autoreceptor and Ca2+-store-dependent short-term plasticity at hippocampal mossy fiber synapses.

    Science.gov (United States)

    Scott, Ricardo; Lalic, Tatjana; Kullmann, Dimitri M; Capogna, Marco; Rusakov, Dmitri A

    2008-12-03

    Presynaptic kainate receptors (KARs) modulate transmission between dentate granule cells and CA3 pyramidal neurons. Whether presynaptic KARs affect other synapses made by granule cell axons [mossy fibers (MFs)], on hilar mossy cells or interneurons, is not known. Nor is it known whether glutamate release from a single MF is sufficient to activate these receptors. Here, we monitor Ca(2+) in identified MF boutons traced from granule cell bodies. We show that a single action potential in a single MF activates both presynaptic KARs and Ca(2+) stores, contributing to use-dependent facilitation at MF-CA3 pyramidal cell synapses. Rapid local application of kainate to the giant MF bouton has no detectable effect on the resting Ca(2+) but facilitates action-potential-evoked Ca(2+) entry through a Ca(2+) store-dependent mechanism. Localized two-photon uncaging of the Ca(2+) store receptor ligand IP(3) directly confirms the presence of functional Ca(2+) stores at these boutons. In contrast, presynaptic Ca(2+) kinetics at MF synapses on interneurons or mossy cells are insensitive to KAR blockade, to local kainate application or to photolytic release of IP(3). Consistent with this, postsynaptic responses evoked by activation of a single MF show KAR-dependent paired-pulse facilitation in CA3 pyramidal cells, but not in interneurons or mossy cells. Thus, KAR-Ca(2+) store coupling acts as a synapse-specific, short-range autoreceptor mechanism.

  13. Recycling of Plastic

    DEFF Research Database (Denmark)

    Christensen, Thomas Højlund; Fruergaard, Thilde

    2011-01-01

    Plastic is produced from fossil oil. Plastic is used for many different products. Some plastic products like, for example, wrapping foil, bags and disposable containers for food and beverage have very short lifetimes and thus constitute a major fraction of most waste. Other plastic products like......, for example, gutters, window frames, car parts and transportation boxes have long lifetimes and thus appear as waste only many years after they have been introduced on the market. Plastic is constantly being used for new products because of its attractive material properties: relatively cheap, easy to form......, good strength and long durability. Recycling of plastic waste from production is well-established, while recycling of postconsumer plastic waste still is in its infancy. This chapter describes briefly how plastic is produced and how waste plastic is recycled in the industry. Quality requirements...

  14. Effects of drugs of abuse on hippocampal plasticity and hippocampus-dependent learning and memory: contributions to development and maintenance of addiction.

    Science.gov (United States)

    Kutlu, Munir Gunes; Gould, Thomas J

    2016-10-01

    It has long been hypothesized that conditioning mechanisms play major roles in addiction. Specifically, the associations between rewarding properties of drugs of abuse and the drug context can contribute to future use and facilitate the transition from initial drug use into drug dependency. On the other hand, the self-medication hypothesis of drug abuse suggests that negative consequences of drug withdrawal result in relapse to drug use as an attempt to alleviate the negative symptoms. In this review, we explored these hypotheses and the involvement of the hippocampus in the development and maintenance of addiction to widely abused drugs such as cocaine, amphetamine, nicotine, alcohol, opiates, and cannabis. Studies suggest that initial exposure to stimulants (i.e., cocaine, nicotine, and amphetamine) and alcohol may enhance hippocampal function and, therefore, the formation of augmented drug-context associations that contribute to the development of addiction. In line with the self-medication hypothesis, withdrawal from stimulants, ethanol, and cannabis results in hippocampus-dependent learning and memory deficits, which suggest that an attempt to alleviate these deficits may contribute to relapse to drug use and maintenance of addiction. Interestingly, opiate withdrawal leads to enhancement of hippocampus-dependent learning and memory. Given that a conditioned aversion to drug context develops during opiate withdrawal, the cognitive enhancement in this case may result in the formation of an augmented association between withdrawal-induced aversion and withdrawal context. Therefore, individuals with opiate addiction may return to opiate use to avoid aversive symptoms triggered by the withdrawal context. Overall, the systematic examination of the role of the hippocampus in drug addiction may help to formulate a better understanding of addiction and underlying neural substrates.

  15. An Semi-implicit Integration Scheme for Rate Dependent Crystal Plasticity%一种适用于率相关晶体塑性模型的准隐式积分算法

    Institute of Scientific and Technical Information of China (English)

    章海明; 董湘怀

    2011-01-01

    A semi-implicit integration scheme for rate dependent crystal plasticity is proposed in this paper. The algorithm is similar to the tangent modulus method. A modified hyperelastic frame is adopted to circumvent the troublesome incremental objectivity encountered by the hypoelastic crystal plasticity models, especially when Green-Naghdi material co-rotational coordi- nate system (MCCS) is used, e.g. in many commercial explicit FEM software. The algorithm combines the advantages of the tangent modulus method and the hyperelastic frame. This algorithm is implemented into ABAQUS/Explicit to simulate deep drawing of aluminum alloy sheets with initial different textures. The predication of the earing profiles shows good agreement with the experimental results, and it is also found that the proposed model is computationally efficient.%参考经典的切线系数法,采用向前梯度法对修正的超弹性晶体塑性模型进行本构方程积分,提出了一种新的准隐式积分算法。该算法采用基于中间构型的超弹性晶体塑性模型,无需更新晶粒取向相关的状态变量;采用修正的超弹性框架,无需进行由Green-Naghdi材料共旋引起的旋转变换。这种准隐式积分算法兼有超弹性模型和切线系数法的优点。通过对铝合金筒形件拉深的模拟表明,该晶体塑性模型能有效地预测不同初始织构产生的不同制耳现象,同时具有很高的计算效率。

  16. 77 FR 54930 - Carlyle Plastics and Resins, Formerly Known as Fortis Plastics, A Subsidiary of Plastics...

    Science.gov (United States)

    2012-09-06

    ... Employment and Training Administration Carlyle Plastics and Resins, Formerly Known as Fortis Plastics, A... plastic parts. New information shows that Fortis Plastics is now called Carlyle Plastics and Resins. In... of Carlyle Plastics and Resins, formerly known as Fortis Plastics, a subsidiary of...

  17. ANALYSIS ON INCLINATION ANGLE OF SHEAR BAND UNDER LOW CONFINING PRESSURE BASED ON GRADIENT-DEPENDENT PLASTICITY%围压对剪切带倾角影响的梯度塑性理论分析

    Institute of Scientific and Technical Information of China (English)

    王学滨; 姚再兴; 潘一山

    2004-01-01

    The inclination angle of shear band is analyzed considering heterogeneity of rock material when a single shear band is formed in the center of specimen under triaxial compression. The analytical solution of post-peak axial stress-axial strain curve is deduced using the assumption that the total post-peak deformation is composed of entire uniform elastic deformation and localized shear plastic deformation dependent on the thickness of shear band. The obtained solution shows that the post-peak stiffness is related to the inclination angle of shear band,confining pressure,thickness of shear band and elastic modulus,etc. Using the solution,the expression for the inclination angle of shear band can be presented easily and it is dependent on constitutive parameters of rock material and geometry parameters of rock specimen. Larger dilation angle or loading rate leads to increment of the inclination angle. In addition,the inclination angle increases with the thickness of the shear band,which cannot be explained or forecasted by other existing solutions,such as Coulomb inclination,Roscoe inclination and Arthur inclination,etc.

  18. Axonal accumulation of synaptic markers in APP transgenic Drosophila depends on the NPTY motif and is paralleled by defects in synaptic plasticity

    DEFF Research Database (Denmark)

    Rusu, Patricia; Jansen, Anna; Soba, Peter;

    2007-01-01

    Alzheimer's disease (AD) is characterized by neurofibrillary tangles and extracellular plaques, which consist mainly of beta-amyloid derived from the beta-amyloid precursor protein (APP). An additional feature of AD is axonopathy, which might contribute to impairment of cognitive functions....... Specifically, axonal transport defects have been reported in AD animal models, including mice and flies that overexpress APP and tau. Here we demonstrate that the APP-induced traffic jam of vesicles in peripheral nerves of Drosophila melanogaster larvae depends on the four residues NPTY motif in the APP...... intracellular domain. Furthermore, heterologous expression of Fe65 and JIP1b, scaffolding proteins interacting with the NPTY motif, also perturb axonal transport. Together, these data indicate that JIP1b or Fe65 may be involved in the APP-induced axonal transport defect. Moreover, we have characterized...

  19. Our plastic age

    National Research Council Canada - National Science Library

    Richard C. Thompson; Shanna H. Swan; Charles J. Moore; Frederick S. vom Saal

    2009-01-01

    Within the last few decades, plastics have revolutionized our daily lives. Globally we use in excess of 260 million tonnes of plastic per annum, accounting for approximately 8 per cent of world oil production...

  20. Weinig plastic in vissenmaag

    NARCIS (Netherlands)

    Foekema, E.M.

    2012-01-01

    Waar de magen van sommige zeevogels vol plastic zitten, lijken vissen in de Noordzee nauwelijks last te hebben van kunststofafval. Onderzoekers die plastic resten zochten in vissenmagen vonden ze in elk geval nauwelijks.

  1. Ear Plastic Surgery

    Science.gov (United States)

    ... ENTCareers Marketplace Find an ENT Doctor Near You Ear Plastic Surgery Ear Plastic Surgery Patient Health Information ... they may improve appearance and self-confidence. Can Ear Deformities Be Corrected? Formation of the ear during ...

  2. Biodegradability of Plastics

    OpenAIRE

    Yutaka Tokiwa; Calabia, Buenaventurada P.; Charles U. Ugwu; Seiichi Aiba

    2009-01-01

    Plastic is a broad name given to different polymers with high molecular weight, which can be degraded by various processes. However, considering their abundance in the environment and their specificity in attacking plastics, biodegradation of plastics by microorganisms and enzymes seems to be the most effective process. When plastics are used as substrates for microorganisms, evaluation of their biodegradability should not only be based on their chemical structure, but also on their physical ...

  3. MODULATING EXCITATION THROUGH PLASTICITY AT INHIBITORY SYNAPSES

    Directory of Open Access Journals (Sweden)

    Vivien eChevaleyre

    2014-03-01

    Full Text Available Learning is believed to depend on lasting changes in synaptic efficacy such as long-term potentiation and long-term depression. As a result, a profusion of studies has tried to elucidate the mechanisms underlying these forms of plasticity. Traditionally, experience-dependent changes at excitatory synapses were assumed to underlie learning and memory formation. However, with the relatively more recent investigation of inhibitory transmission, it had become evident that inhibitory synapses are not only plastic, but also provide an additional way to modulate excitatory transmission and the induction of plasticity at excitatory synapses.Thanks to recent technological advances, progress has been made in understanding synaptic transmission and plasticity from particular interneuron subtypes. In this review article, we will describe various forms of synaptic plasticity that have been ascribed to two fairly well characterized populations of interneurons in the hippocampus, those expressing cholecystokinin (CCK and parvalbumin (PV. We will discuss the resulting changes in the strength and plasticity of excitatory transmission that occur in the local circuit as a result of the modulation of inhibitory transmission. We will focus on the hippocampus because this region has a relatively well-understood circuitry, numerous forms of activity-dependent plasticity and a multitude of identified interneuron subclasses.

  4. [Features of adhesion of anaerobic periodontopathogenic bacteria and Candida albicans fungi to experimental samples of basis dental plastic depending on surface roughness and polishing method].

    Science.gov (United States)

    Tsarev, V N; Ippolitov, E V; Trefilov, A G; Arutiunov, S D; Pivovarov, A A

    2014-01-01

    Study the main surface parameters of milled polyacrylic materials using atomic force microscopy and primary microbial adhesion of periodontopathogenic group bacteria and Candida albicans fungi taking into consideration the method of sample polishing. Studied samples: mill-treated without polishing (control); ergobox polished; polished in dental laboratory conditions; polished by a rubber brush in dentists' office. Microbial strains belonging to periodontopathogenic species (clinical isolates) that had been isolated from periodontal pockets of periodontitis patients: Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus sanguis, C. albicans fungi were used for modelling experiments of primary adhesion of microbes to the material samples. S. sanguis had the highest degree of adhesion to polymer after milling, P. gingivalis, C. albicans--medium, F. nucleatum--low. A significant reduction of adhesion is observed during polishing in dental laboratory conditions or ergobox, less significant--during polishing in dental office. The data obtained allow to make a conclusion that the samples from polymer materials for preparation of prosthesis basis have varying degree of intensity of microbial adhesion of members of periodontopathogenic microflora and C. albicans fungi that depends on the polishing method, that accordingly determined the differences in colonization resistance against formation of microbial biofilm during polymer use in clinical conditions. . ,

  5. Chemical Recycle of Plastics

    Directory of Open Access Journals (Sweden)

    Sara Fatima

    2014-11-01

    Full Text Available Various chemical processes currently prevalent in the chemical industry for plastics recycling have been discussed. Possible future scenarios in chemical recycling have also been discussed. Also analyzed are the effects on the environment, the risks, costs and benefits of PVC recycling. Also listed are the various types of plastics and which plastics are safe to use and which not after rcycle

  6. Plastic value chains

    DEFF Research Database (Denmark)

    Baxter, John; Wahlstrom, Margareta; Zu Castell-Rüdenhausen, Malin

    2014-01-01

    Optimizing plastic value chains is regarded as an important measure in order to increase recycling of plastics in an efficient way. This can also lead to improved awareness of the hazardous substances contained in plastic waste, and how to avoid that these substances are recycled. As an example...

  7. Phyllosphere yeasts rapidly break down biodegradable plastics.

    Science.gov (United States)

    Kitamoto, Hiroko K; Shinozaki, Yukiko; Cao, Xiao-Hong; Morita, Tomotake; Konishi, Masaaki; Tago, Kanako; Kajiwara, Hideyuki; Koitabashi, Motoo; Yoshida, Shigenobu; Watanabe, Takashi; Sameshima-Yamashita, Yuka; Nakajima-Kambe, Toshiaki; Tsushima, Seiya

    2011-11-29

    The use of biodegradable plastics can reduce the accumulation of environmentally persistent plastic wastes. The rate of degradation of biodegradable plastics depends on environmental conditions and is highly variable. Techniques for achieving more consistent degradation are needed. However, only a few microorganisms involved in the degradation process have been isolated so far from the environment. Here, we show that Pseudozyma spp. yeasts, which are common in the phyllosphere and are easily isolated from plant surfaces, displayed strong degradation activity on films made from poly-butylene succinate or poly-butylene succinate-co-adipate. Strains of P. antarctica isolated from leaves and husks of paddy rice displayed strong degradation activity on these films at 30°C. The type strain, P. antarctica JCM 10317, and Pseudozyma spp. strains from phyllosphere secreted a biodegradable plastic-degrading enzyme with a molecular mass of about 22 kDa. Reliable source of biodegradable plastic-degrading microorganisms are now in our hands.

  8. Biodegradability of plastics.

    Science.gov (United States)

    Tokiwa, Yutaka; Calabia, Buenaventurada P; Ugwu, Charles U; Aiba, Seiichi

    2009-08-26

    Plastic is a broad name given to different polymers with high molecular weight, which can be degraded by various processes. However, considering their abundance in the environment and their specificity in attacking plastics, biodegradation of plastics by microorganisms and enzymes seems to be the most effective process. When plastics are used as substrates for microorganisms, evaluation of their biodegradability should not only be based on their chemical structure, but also on their physical properties (melting point, glass transition temperature, crystallinity, storage modulus etc.). In this review, microbial and enzymatic biodegradation of plastics and some factors that affect their biodegradability are discussed.

  9. Plastic value chains

    DEFF Research Database (Denmark)

    Baxter, John; Wahlstrom, Margareta; Zu Castell-Rüdenhausen, Malin

    2014-01-01

    Optimizing plastic value chains is regarded as an important measure in order to increase recycling of plastics in an efficient way. This can also lead to improved awareness of the hazardous substances contained in plastic waste, and how to avoid that these substances are recycled. As an example......, plastics from WEEE is chosen as a Nordic case study. The project aims to propose a number of improvements for this value chain together with representatives from Nordic stakeholders. Based on the experiences made, a guide for other plastic value chains shall be developed....

  10. Biodegradability of Plastics

    Directory of Open Access Journals (Sweden)

    Yutaka Tokiwa

    2009-08-01

    Full Text Available Plastic is a broad name given to different polymers with high molecular weight, which can be degraded by various processes. However, considering their abundance in the environment and their specificity in attacking plastics, biodegradation of plastics by microorganisms and enzymes seems to be the most effective process. When plastics are used as substrates for microorganisms, evaluation of their biodegradability should not only be based on their chemical structure, but also on their physical properties (melting point, glass transition temperature, crystallinity, storage modulus etc.. In this review, microbial and enzymatic biodegradation of plastics and some factors that affect their biodegradability are discussed.

  11. Journal of CHINA PLASTICS

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    Journal of CHINA PLASTICS was authorized and approved by The State Committee of Science and Technology of China and The Bureau of News Press of China, and published by The China Plastics Processing Industry Association,Beijing Technology and Business University and The Institute of Plastics Processing and Application of Light Industry, distributed worldwide. Since its birth in 1987, CHINA PLASTICS has become a leading magazine in plastics industry in China, a national Chinese core journal and journal of Chinese scientific and technological article statistics. It is covered by CA.

  12. Motor cortical plasticity in Parkinson's disease.

    Science.gov (United States)

    Udupa, Kaviraja; Chen, Robert

    2013-09-04

    In Parkinson's disease (PD), there are alterations of the basal ganglia (BG) thalamocortical networks, primarily due to degeneration of nigrostriatal dopaminergic neurons. These changes in subcortical networks lead to plastic changes in primary motor cortex (M1), which mediates cortical motor output and is a potential target for treatment of PD. Studies investigating the motor cortical plasticity using non-invasive transcranial magnetic stimulation (TMS) have found altered plasticity in PD, but there are inconsistencies among these studies. This is likely because plasticity depends on many factors such as the extent of dopaminergic loss and disease severity, response to dopaminergic replacement therapies, development of l-DOPA-induced dyskinesias (LID), the plasticity protocol used, medication, and stimulation status in patients treated with deep brain stimulation (DBS). The influences of LID and DBS on BG and M1 plasticity have been explored in animal models and in PD patients. In addition, many other factors such age, genetic factors (e.g., brain derived neurotropic factor and other neurotransmitters or receptors polymorphism), emotional state, time of the day, physical fitness have been documented to play role in the extent of plasticity induced by TMS in human studies. In this review, we summarize the studies that investigated M1 plasticity in PD and demonstrate how these afore-mentioned factors affect motor cortical plasticity in PD. We conclude that it is important to consider the clinical, demographic, and technical factors that influence various plasticity protocols while developing these protocols as diagnostic or prognostic tools in PD. We also discuss how the modulation of cortical excitability and the plasticity with these non-invasive brain stimulation techniques facilitate the understanding of the pathophysiology of PD and help design potential therapeutic possibilities in this disorder.

  13. Magnetic Tunnel Junction Based Long-Term Short-Term Stochastic Synapse for a Spiking Neural Network with On-Chip STDP Learning

    Science.gov (United States)

    Srinivasan, Gopalakrishnan; Sengupta, Abhronil; Roy, Kaushik

    2016-01-01

    Spiking Neural Networks (SNNs) have emerged as a powerful neuromorphic computing paradigm to carry out classification and recognition tasks. Nevertheless, the general purpose computing platforms and the custom hardware architectures implemented using standard CMOS technology, have been unable to rival the power efficiency of the human brain. Hence, there is a need for novel nanoelectronic devices that can efficiently model the neurons and synapses constituting an SNN. In this work, we propose a heterostructure composed of a Magnetic Tunnel Junction (MTJ) and a heavy metal as a stochastic binary synapse. Synaptic plasticity is achieved by the stochastic switching of the MTJ conductance states, based on the temporal correlation between the spiking activities of the interconnecting neurons. Additionally, we present a significance driven long-term short-term stochastic synapse comprising two unique binary synaptic elements, in order to improve the synaptic learning efficiency. We demonstrate the efficacy of the proposed synaptic configurations and the stochastic learning algorithm on an SNN trained to classify handwritten digits from the MNIST dataset, using a device to system-level simulation framework. The power efficiency of the proposed neuromorphic system stems from the ultra-low programming energy of the spintronic synapses. PMID:27405788

  14. Magnetic Tunnel Junction Based Long-Term Short-Term Stochastic Synapse for a Spiking Neural Network with On-Chip STDP Learning

    Science.gov (United States)

    Srinivasan, Gopalakrishnan; Sengupta, Abhronil; Roy, Kaushik

    2016-07-01

    Spiking Neural Networks (SNNs) have emerged as a powerful neuromorphic computing paradigm to carry out classification and recognition tasks. Nevertheless, the general purpose computing platforms and the custom hardware architectures implemented using standard CMOS technology, have been unable to rival the power efficiency of the human brain. Hence, there is a need for novel nanoelectronic devices that can efficiently model the neurons and synapses constituting an SNN. In this work, we propose a heterostructure composed of a Magnetic Tunnel Junction (MTJ) and a heavy metal as a stochastic binary synapse. Synaptic plasticity is achieved by the stochastic switching of the MTJ conductance states, based on the temporal correlation between the spiking activities of the interconnecting neurons. Additionally, we present a significance driven long-term short-term stochastic synapse comprising two unique binary synaptic elements, in order to improve the synaptic learning efficiency. We demonstrate the efficacy of the proposed synaptic configurations and the stochastic learning algorithm on an SNN trained to classify handwritten digits from the MNIST dataset, using a device to system-level simulation framework. The power efficiency of the proposed neuromorphic system stems from the ultra-low programming energy of the spintronic synapses.

  15. Challenges in plastics recycling

    DEFF Research Database (Denmark)

    Pivnenko, Kostyantyn; Jakobsen, L. G.; Eriksen, Marie Kampmann

    2015-01-01

    Recycling of waste plastics still remains a challenging area in the waste management sector. The current and potential goals proposed on EU or regional levels are difficult to achieve, and even to partially fullfil them the improvements in collection and sorting should be considerable. A study...... was undertaken to investigate the factors affecting quality in plastics recycling. The preliminary results showed factors primarily influencing quality of plastics recycling to be polymer cross contamination, presence of additives, non-polymer impurities, and polymer degradation. Deprivation of plastics quality......, with respect to recycling, has been shown to happen throughout the plastics value chain, but steps where improvements may happen have been preliminary identified. Example of Cr in plastic samples analysed showed potential spreading and accumulation of chemicals ending up in the waste plastics. In order...

  16. Glassy metallic plastics

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    This paper reports a class of bulk metallic glass including Ce-, LaCe-, CaLi-, Yb-, and Sr-based metallic glasses, which are regarded as glassy metallic plastics because they combine some unique properties of both plastics and metallic alloys. These glassy metallic plastics have very low glass transition temperature (Tg~25oC to 150oC) and low Young’s modulus (~20 GPa to 35 GPa). Similar to glassy plastics, these metallic plastics show excellent plastic-like deformability on macro-, micro- and even nano-scale in their supercooled liquid range and can be processed, such as elongated, compressed, bent, and imprinted at low temperatures, in hot water for instance. Under ambient conditions, they display such metallic properties as high thermal and electric conductivities and excellent mechanical properties and other unique properties. The metallic plastics have potential applications and are also a model system for studying issues in glass physics.

  17. Strain gradient plasticity analysis of elasto-plastic contact between rough surfaces

    Science.gov (United States)

    Song, H.; Van der Giessen, E.; Liu, X.

    2016-11-01

    From a microscopic point of view, the real contact area between two rough surfaces is the sum of the areas of contact between facing asperities. Since the real contact area is a fraction of the nominal contact area, the real contact pressure is much higher than the nominal contact pressure, which results in plastic deformation of asperities. As plasticity is size dependent at size scales below tens of micrometers, with the general trend of smaller being harder, macroscopic plasticity is not suitable to describe plastic deformation of small asperities and thus fails to capture the real contact area and pressure accurately. Here we adopt conventional mechanism-based strain gradient plasticity (CMSGP) to analyze the contact between a rigid platen and an elasto-plastic solid with a rough surface. Flattening of a single sinusoidal asperity is analyzed first to highlight the difference between CMSGP and J2 isotropic plasticity. For the rough surface contact, besides CMSGP, pure elastic and J2 isotropic plasticity analysis is also carried out for comparison. In all cases, the contact area A rises linearly with the applied load, but with a different slope which implies that the mean contact pressures are different. CMSGP produces qualitative changes in the distributions of local contact pressures compared with pure elastic and J2 isotropic plasticity analysis, furthermore, bounded by the two.

  18. Plastic Pollution from Ships

    OpenAIRE

    Čulin, Jelena; Bielić, Toni

    2016-01-01

    The environmental impact of shipping on marine environment includes discharge of garbage. Plastic litter is of particular concern due to abundance, resistance to degradation and detrimental effect on marine biota. According to recently published studies, a further research is required to assess human health risk. Monitoring data indicate that despite banning plastic disposal at sea, shipping is still a source of plastic pollution. Some of the measures to combat the problem are discussed.

  19. Handbook of Plastic Welding

    DEFF Research Database (Denmark)

    Islam, Aminul

    The purpose of this document is to summarize the information about the laser welding of plastic. Laser welding is a matured process nevertheless laser welding of micro dimensional plastic parts is still a big challenge. This report collects the latest information about the laser welding of plasti...... as a knowledge handbook for laser welding of plastic components. This document should provide the information for all aspects of plastic laser welding and help the design engineers to take all critical issues into consideration from the very beginning of the design phase....

  20. Plastics and health risks.

    Science.gov (United States)

    Halden, Rolf U

    2010-01-01

    By 2010, the worldwide annual production of plastics will surpass 300 million tons. Plastics are indispensable materials in modern society, and many products manufactured from plastics are a boon to public health (e.g., disposable syringes, intravenous bags). However, plastics also pose health risks. Of principal concern are endocrine-disrupting properties, as triggered for example by bisphenol A and di-(2-ethylhexyl) phthalate (DEHP). Opinions on the safety of plastics vary widely, and despite more than five decades of research, scientific consensus on product safety is still elusive. This literature review summarizes information from more than 120 peer-reviewed publications on health effects of plastics and plasticizers in lab animals and humans. It examines problematic exposures of susceptible populations and also briefly summarizes adverse environmental impacts from plastic pollution. Ongoing efforts to steer human society toward resource conservation and sustainable consumption are discussed, including the concept of the 5 Rs--i.e., reduce, reuse, recycle, rethink, restrain--for minimizing pre- and postnatal exposures to potentially harmful components of plastics.

  1. Synaptic Plasticity and Nociception

    Institute of Scientific and Technical Information of China (English)

    ChenJianguo

    2004-01-01

    Synaptic plasticity is one of the fields that progresses rapidly and has a lot of success in neuroscience. The two major types of synaptie plasticity: long-term potentiation ( LTP and long-term depression (LTD are thought to be the cellular mochanisms of learning and memory. Recently, accumulating evidence suggests that, besides serving as a cellular model for learning and memory, the synaptic plasticity involves in other physiological or pathophysiological processes, such as the perception of pain and the regulation of cardiovascular system. This minireview will focus on the relationship between synaptic plasticity and nociception.

  2. Genetic Regulation of Phenotypic Plasticity and Canalisation in Yeast Growth.

    Science.gov (United States)

    Yadav, Anupama; Dhole, Kaustubh; Sinha, Himanshu

    2016-01-01

    The ability of a genotype to show diverse phenotypes in different environments is called phenotypic plasticity. Phenotypic plasticity helps populations to evade extinctions in novel environments, facilitates adaptation and fuels evolution. However, most studies focus on understanding the genetic basis of phenotypic regulation in specific environments. As a result, while it's evolutionary relevance is well established, genetic mechanisms regulating phenotypic plasticity and their overlap with the environment specific regulators is not well understood. Saccharomyces cerevisiae is highly sensitive to the environment, which acts as not just external stimulus but also as signalling cue for this unicellular, sessile organism. We used a previously published dataset of a biparental yeast population grown in 34 diverse environments and mapped genetic loci regulating variation in phenotypic plasticity, plasticity QTL, and compared them with environment-specific QTL. Plasticity QTL is one whose one allele exhibits high plasticity whereas the other shows a relatively canalised behaviour. We mapped phenotypic plasticity using two parameters-environmental variance, an environmental order-independent parameter and reaction norm (slope), an environmental order-dependent parameter. Our results show a partial overlap between pleiotropic QTL and plasticity QTL such that while some plasticity QTL are also pleiotropic, others have a significant effect on phenotypic plasticity without being significant in any environment independently. Furthermore, while some plasticity QTL are revealed only in specific environmental orders, we identify large effect plasticity QTL, which are order-independent such that whatever the order of the environments, one allele is always plastic and the other is canalised. Finally, we show that the environments can be divided into two categories based on the phenotypic diversity of the population within them and the two categories have differential regulators of

  3. Exercise and plasticize the brain

    DEFF Research Database (Denmark)

    Mala, Hana; Wilms, Inge

    Neuroscientific studies continue to shed light on brain’s plasticity and its innate mechanisms to recover. The recovery process includes re-wiring of the existing circuitry, establishment of new connections, and recruitment of peri-lesional and homologous areas in the opposite hemisphere. The pla......Neuroscientific studies continue to shed light on brain’s plasticity and its innate mechanisms to recover. The recovery process includes re-wiring of the existing circuitry, establishment of new connections, and recruitment of peri-lesional and homologous areas in the opposite hemisphere...... potential through available training methods. Furthermore, research into neurorehabilitation is dependent on input from a number of fields (such as neuropsychology, neurology, physiotherapy, speech and language therapy, special education, and social work) and requires a close collaboration between...

  4. Neural plasticity and implications for hand rehabilitation after neurological insult.

    Science.gov (United States)

    Westlake, Kelly P; Byl, Nancy N

    2013-01-01

    Experience dependent plasticity refers to ability of the brain to adapt to new experiences by changing its structure and function. The purpose of this paper is to provide a brief review the neurophysiological and structural correlates of neural plasticity that occur during and following motor learning. We also consider that the extent of plastic reorganization is dependent upon several key principals and that the resulting behavioral consequences can be adaptive or maladaptive. In light of this research, we conclude that an increased understanding of the complexities of brain plasticity will translate into enhanced treatment opportunities for the clinician to optimize hand function.

  5. Equivalent Plastic Strain Gradient Plasticity with Grain Boundary Hardening and Comparison to Discrete Dislocation Dynamics

    CERN Document Server

    Bayerschen, E; Wulfinghoff, S; Weygand, D; Böhlke, T

    2015-01-01

    The gradient crystal plasticity framework of Wulfinghoff et al. [53] incorporating an equivalent plastic strain and grain boundary yielding, is extended with additional grain boundary hardening. By comparison to averaged results from many discrete dislocation dynamics (DDD) simulations of an aluminum type tricrystal under tensile loading, the new hardening parameter in the continuum model is calibrated. It is shown that although the grain boundaries (GBs) in the discrete simulations are impenetrable, an infinite GB yield strength corresponding to microhard GB conditions, is not applicable in the continuum model. A combination of a finite GB yield strength with an isotropic bulk Voce hardening relation alone also fails to model the plastic strain profiles obtained by DDD. Instead, a finite GB yield strength in combination with GB hardening depending on the equivalent plastic strain at the GBs is shown to give a better agreement to DDD results. The differences in the plastic strain profiles obtained in DDD simu...

  6. Can previous learning alter future plasticity mechanisms?

    Science.gov (United States)

    Crestani, Ana Paula; Quillfeldt, Jorge Alberto

    2016-02-01

    The dynamic processes related to mnemonic plasticity have been extensively researched in the last decades. More recently, studies have attracted attention because they show an unusual plasticity mechanism that is independent of the receptor most usually related to first-time learning--that is, memory acquisition-the NMDA receptor. An interesting feature of this type of learning is that a previous experience may cause modifications in the plasticity mechanism of a subsequent learning, suggesting that prior experience in a very similar task triggers a memory acquisition process that does not depend on NMDARs. The intracellular molecular cascades necessary to assist the learning process seem to depend on the activation of hippocampal CP-AMPARs. Moreover, most of these studies were performed on hippocampus-dependent tasks, even though other brain areas, such as the basolateral amygdala, also display NMDAR-independent learning.

  7. Pathological Plasticity in Fragile X Syndrome

    Directory of Open Access Journals (Sweden)

    Brandon S. Martin

    2012-01-01

    Full Text Available Deficits in neuronal plasticity are common hallmarks of many neurodevelopmental disorders. In the case of fragile-X syndrome (FXS, disruption in the function of a single gene, FMR1, results in a variety of neurological consequences directly related to problems with the development, maintenance, and capacity of plastic neuronal networks. In this paper, we discuss current research illustrating the mechanisms underlying plasticity deficits in FXS. These processes include synaptic, cell intrinsic, and homeostatic mechanisms both dependent on and independent of abnormal metabotropic glutamate receptor transmission. We place particular emphasis on how identified deficits may play a role in developmental critical periods to produce neuronal networks with permanently decreased capacity to dynamically respond to changes in activity central to learning, memory, and cognition in patients with FXS. Characterizing early developmental deficits in plasticity is fundamental to develop therapies that not only treat symptoms but also minimize the developmental pathology of the disease.

  8. Halos of Plastic

    Institute of Scientific and Technical Information of China (English)

    Maya Reid

    2012-01-01

    The halos that span South Africa's coastline are anything but angelic. Fanning out around four major urban centers-Cape Town, Port Elizabeth, East London and Durban-they are made up of innumerable bits and pieces of plastic. As a form of pollution, their shelflife is unfathomable. Plastic is essentially chemically inactive. It's designed to never break down.

  9. Biodegradation of plastics.

    Science.gov (United States)

    Shimao, M

    2001-06-01

    Widespread studies on the biodegradation of plastics have been carried out in order to overcome the environmental problems associated with synthetic plastic waste. Recent work has included studies of the distribution of synthetic polymer-degrading microorganisms in the environment, the isolation of new microorganisms for biodegradation, the discovery of new degradation enzymes, and the cloning of genes for synthetic polymer-degrading enzymes.

  10. DESIGNERS’ KNOWLEDGE IN PLASTICS

    DEFF Research Database (Denmark)

    Eriksen, Kaare

    2013-01-01

    The Industrial designers’ knowledge in plastics materials and manufacturing principles of polymer products is very important for the innovative strength of the industry, according to a group of Danish plastics manufacturers, design students and practicing industrial designers. These three groups...... answered the first Danish national survey, PD13[1], investigating the importance of industrial designers’ knowledge in plastics and the collaboration between designers and the polymer industry. The plastics industry and the industrial designers collaborate well, but both groups frequently experience...... that the designers’ lack of knowledge concerning polymer materials and manufacturing methods can be problematic or annoying, and design students from most Danish design universities express the need for more contact with the industry and more competencies and tools to handle even simple topics when designing plastic...

  11. Consciousness and neural plasticity

    DEFF Research Database (Denmark)

    In contemporary consciousness studies the phenomenon of neural plasticity has received little attention despite the fact that neural plasticity is of still increased interest in neuroscience. We will, however, argue that neural plasticity could be of great importance to consciousness studies....... If consciousness is related to neural processes it seems, at least prima facie, that the ability of the neural structures to change should be reflected in a theory of this relationship "Neural plasticity" refers to the fact that the brain can change due to its own activity. The brain is not static but rather...... the relation between consciousness and brain functions. If consciousness is connected to specific brain structures (as a function or in identity) what happens to consciousness when those specific underlying structures change? It is therefore possible that the understanding and theories of neural plasticity can...

  12. Opposing Effects of Neuronal Activity on Structural Plasticity.

    Science.gov (United States)

    Fauth, Michael; Tetzlaff, Christian

    2016-01-01

    The connectivity of the brain is continuously adjusted to new environmental influences by several activity-dependent adaptive processes. The most investigated adaptive mechanism is activity-dependent functional or synaptic plasticity regulating the transmission efficacy of existing synapses. Another important but less prominently discussed adaptive process is structural plasticity, which changes the connectivity by the formation and deletion of synapses. In this review, we show, based on experimental evidence, that structural plasticity can be classified similar to synaptic plasticity into two categories: (i) Hebbian structural plasticity, which leads to an increase (decrease) of the number of synapses during phases of high (low) neuronal activity and (ii) homeostatic structural plasticity, which balances these changes by removing and adding synapses. Furthermore, based on experimental and theoretical insights, we argue that each type of structural plasticity fulfills a different function. While Hebbian structural changes enhance memory lifetime, storage capacity, and memory robustness, homeostatic structural plasticity self-organizes the connectivity of the neural network to assure stability. However, the link between functional synaptic and structural plasticity as well as the detailed interactions between Hebbian and homeostatic structural plasticity are more complex. This implies even richer dynamics requiring further experimental and theoretical investigations.

  13. Astrocyte and Neuronal Plasticity in the Somatosensory System

    OpenAIRE

    Sims, Robert E.; Butcher, John B.; Parri, H. Rheinallt; Glazewski, Stanislaw

    2015-01-01

    Changing the whisker complement on a rodent's snout can lead to two forms of experience-dependent plasticity (EDP) in the neurons of the barrel cortex, where whiskers are somatotopically represented. One form, termed coding plasticity, concerns changes in synaptic transmission and connectivity between neurons. This is thought to underlie learning and memory processes and so adaptation to a changing environment. The second, called homeostatic plasticity, serves to maintain a restricted dynamic...

  14. The genetics of phenotypic plasticity. XIII. Interactions with developmental instability.

    Science.gov (United States)

    Scheiner, Samuel M

    2014-04-01

    In a heterogeneous environment, natural selection on a trait can lead to a variety of outcomes, including phenotypic plasticity and bet-hedging through developmental instability. These outcomes depend on the magnitude and pattern of that heterogeneity and the spatial and temporal distribution of individuals. However, we do not know if and how those two outcomes might interact with each other. I examined the joint evolution of plasticity and instability through the use of an individual-based simulation in which each could be genetically independent or pleiotropically linked. When plasticity and instability were determined by different loci, the only effect on the evolution of plasticity was the elimination of plasticity as a bet-hedging strategy. In contrast, the effects on the evolution of instability were more substantial. If conditions were such that the population was likely to evolve to the optimal reaction norm, then instability was disfavored. Instability was favored only when the lack of a reliable environmental cue disfavored plasticity. When plasticity and instability were determined by the same loci, instability acted as a strong limitation on the evolution of plasticity. Under some conditions, selection for instability resulted in maladaptive plasticity. Therefore, before testing any models of plasticity or instability evolution, or interpreting empirical patterns, it is important to know the ecological, life history, developmental, and genetic contexts of trait phenotypic plasticity and developmental instability.

  15. Plastic deformation modelling of tempered martensite steel block structure by a nonlocal crystal plasticity model

    Directory of Open Access Journals (Sweden)

    Martin Boeff

    2014-01-01

    Full Text Available The plastic deformations of tempered martensite steel representative volume elements with different martensite block structures have been investigated by using a nonlocal crystal plasticity model which considers isotropic and kinematic hardening produced by plastic strain gradients. It was found that pronounced strain gradients occur in the grain boundary region even under homogeneous loading. The isotropic hardening of strain gradients strongly influences the global stress–strain diagram while the kinematic hardening of strain gradients influences the local deformation behaviour. It is found that the additional strain gradient hardening is not only dependent on the block width but also on the misorientations or the deformation incompatibilities in adjacent blocks.

  16. RM-SORN: a reward-modulated self-organizing recurrent neural network.

    Science.gov (United States)

    Aswolinskiy, Witali; Pipa, Gordon

    2015-01-01

    Neural plasticity plays an important role in learning and memory. Reward-modulation of plasticity offers an explanation for the ability of the brain to adapt its neural activity to achieve a rewarded goal. Here, we define a neural network model that learns through the interaction of Intrinsic Plasticity (IP) and reward-modulated Spike-Timing-Dependent Plasticity (STDP). IP enables the network to explore possible output sequences and STDP, modulated by reward, reinforces the creation of the rewarded output sequences. The model is tested on tasks for prediction, recall, non-linear computation, pattern recognition, and sequence generation. It achieves performance comparable to networks trained with supervised learning, while using simple, biologically motivated plasticity rules, and rewarding strategies. The results confirm the importance of investigating the interaction of several plasticity rules in the context of reward-modulated learning and whether reward-modulated self-organization can explain the amazing capabilities of the brain.

  17. Glassy features of crystal plasticity

    Science.gov (United States)

    Lehtinen, Arttu; Costantini, Giulio; Alava, Mikko J.; Zapperi, Stefano; Laurson, Lasse

    2016-08-01

    Crystal plasticity occurs by deformation bursts due to the avalanchelike motion of dislocations. Here we perform extensive numerical simulations of a three-dimensional dislocation dynamics model under quasistatic stress-controlled loading. Our results show that avalanches are power-law distributed and display peculiar stress and sample size dependence: The average avalanche size grows exponentially with the applied stress, and the amount of slip increases with the system size. These results suggest that intermittent deformation processes in crystalline materials exhibit an extended critical-like phase in analogy to glassy systems instead of originating from a nonequilibrium phase transition critical point.

  18. The Size Spectrum as Tool for Analyzing Marine Plastic Pollution

    KAUST Repository

    Martí, E.

    2016-12-02

    Marine plastic debris spans over six orders of magnitude in lineal size, from microns to meters. The broad range of plastic sizes mainly arises from the continuous photodegradation and fragmentation affecting the plastic objects. Interestingly, this time-dependent process links, to some degree, the size to the age of the debris. The variety of plastic sizes gives the possibility to marine biota to interact and possible take up microplastics through numerous pathways. Physical processes such as sinking and wind-induced transport or the chemical adsorption of contaminants are also closely related to the size and shape of the plastic items. Likewise, available sampling techniques should be considered as partial views of the marine plastic size range. This being so and given that the size is one of the most easily measurable plastic traits, the size spectrum appears as an ideal frame to arrange, integrate, and analyze plastic data of diverse nature. In this work, we examined tens of thousands of plastic items sampled from across the world with the aim of (1) developing and standardizing the size-spectrum tool to study marine plastics, and (2) assembling a global plastic size spectrum (GPSS) database, relating individual size measurements to abundance, color (129 tons), polymer type, and category (rigid fragments, films, threads, foam, pellets, and microbeads). Using GPSS database, we show for instance the dependence of plastic composition on the item size, with high diversity of categories for items larger than 1 cm and a clear dominance (~90%) of hard fragments below, except for the size interval corresponding to microbeads (around 0.5 mm). GPSS database depicts a comprehensive size-based framework for analyzing the marine plastic pollution, enabling the comparison of size-related studies or the testing of hypothesis.

  19. Neural Plasticity: For Good and Bad

    Science.gov (United States)

    Møller, A. R.

    The brain's ability to change its organization and function is necessary for normal development of the nervous system and it makes it possible to adapt to changing demands but it can also cause disorders when going awry. This property, known as neural plasticity, is only evident when induced, very much like genes. Plastic changes may be programmed and providing a ``midcourse correction" during childhood development. If that is not executed in the normal way severe developmental disorders such as autism may results. Normal development of functions and anatomical organization of the brain and the spinal cord depend on appropriate sensory stimulation and motor activations. So-called enriched sensory environments have been shown to be beneficial for cognitive development and enriched acoustic environment may even slow the progression of age-related hearing loss. It is possible that the beneficial effect of physical exercise is achieved through activation of neural plasticity. The beneficial effect of training after trauma to the brain or spinal cord is mainly achieved through shifting functions from damaged brain area to other parts of the central nervous system and adapting these parts to take over the functions that are lost. This is accomplished through activation of neural plasticity. Plastic changes can also be harmful and cause symptoms and signs of disorders such as some forms of chronic pain (central neuropathic pain) and severe tinnitus. We will call such disorders ``plasticity disorders".

  20. Informative document waste plastics

    NARCIS (Netherlands)

    Nagelhout D; Sein AA; Duvoort GL

    1989-01-01

    This "Informative document waste plastics" forms part of a series of "informative documents waste materials". These documents are conducted by RIVM on the indstruction of the Directorate General for the Environment, Waste Materials Directorate, in behalf of the program of

  1. A Plastic Menagerie

    Science.gov (United States)

    Hadley, Mary Jane

    2010-01-01

    Bobble heads had become quite popular, depicting all sorts of sports figures, animals, and even presidents. In this article, the author describes how her fourth graders made bobble head sculptures out of empty plastic drink bottles. (Contains 1 online resource.)

  2. Cortical plasticity and rehabilitation.

    Science.gov (United States)

    Moucha, Raluca; Kilgard, Michael P

    2006-01-01

    The brain is constantly adapting to environmental and endogenous changes (including injury) that occur at every stage of life. The mechanisms that regulate neural plasticity have been refined over millions of years. Motivation and sensory experience directly shape the rewiring that makes learning and neurological recovery possible. Guiding neural reorganization in a manner that facilitates recovery of function is a primary goal of neurological rehabilitation. As the rules that govern neural plasticity become better understood, it will be possible to manipulate the sensory and motor experience of patients to induce specific forms of plasticity. This review summarizes our current knowledge regarding factors that regulate cortical plasticity, illustrates specific forms of reorganization induced by control of each factor, and suggests how to exploit these factors for clinical benefit.

  3. Mechanical plasticity of cells

    Science.gov (United States)

    Bonakdar, Navid; Gerum, Richard; Kuhn, Michael; Spörrer, Marina; Lippert, Anna; Schneider, Werner; Aifantis, Katerina E.; Fabry, Ben

    2016-10-01

    Under mechanical loading, most living cells show a viscoelastic deformation that follows a power law in time. After removal of the mechanical load, the cell shape recovers only incompletely to its original undeformed configuration. Here, we show that incomplete shape recovery is due to an additive plastic deformation that displays the same power-law dynamics as the fully reversible viscoelastic deformation response. Moreover, the plastic deformation is a constant fraction of the total cell deformation and originates from bond ruptures within the cytoskeleton. A simple extension of the prevailing viscoelastic power-law response theory with a plastic element correctly predicts the cell behaviour under cyclic loading. Our findings show that plastic energy dissipation during cell deformation is tightly linked to elastic cytoskeletal stresses, which suggests the existence of an adaptive mechanism that protects the cell against mechanical damage.

  4. Targeting tumour Cell Plasticity

    Institute of Scientific and Technical Information of China (English)

    Elizabeth D. WILLIAMS

    2009-01-01

    @@ Her research is focused on understanding the mechanisms of tumour progression and metastasis, particularly in uro-logical carcinomas (bladder and prostate). Tumour cell plasticity, including epithelial-mesenchymal transition, is a cen-tral theme in Dr Williams' work.

  5. Laser cutting plastic materials

    Energy Technology Data Exchange (ETDEWEB)

    Van Cleave, R.A.

    1980-08-01

    A 1000-watt CO/sub 2/ laser has been demonstrated as a reliable production machine tool for cutting of plastics, high strength reinforced composites, and other nonmetals. More than 40 different plastics have been laser cut, and the results are tabulated. Applications for laser cutting described include fiberglass-reinforced laminates, Kevlar/epoxy composites, fiberglass-reinforced phenolics, nylon/epoxy laminates, ceramics, and disposable tooling made from acrylic.

  6. Localization of plastic deformation

    Energy Technology Data Exchange (ETDEWEB)

    Rice, J R

    1976-04-01

    The localization of plastic deformation into a shear band is discussed as an instability of plastic flow and a precursor to rupture. Experimental observations are reviewed, a general theoretical framework is presented, and specific calculations of critical conditions are carried out for a variety of material models. The interplay between features of inelastic constitutive description, especially deviations from normality and vertex-like yielding, and the onset of localization is emphasized.

  7. Production of Methane and Water from Crew Plastic Waste

    Science.gov (United States)

    Captain, Janine; Santiago, Eddie; Parrish, Clyde; Strayer, Richard F.; Garland, Jay L.

    2008-01-01

    Recycling is a technology that will be key to creating a self sustaining lunar outpost. The plastics used for food packaging provide a source of material that could be recycled to produce water and methane. The recycling of these plastics will require some additional resources that will affect the initial estimate of starting materials that will have to be transported from earth, mainly oxygen, energy and mass. These requirements will vary depending on the recycling conditions. The degredation products of these plastics will vary under different atmospheric conditions. An estimate of the the production rate of methane and water using typical ISRU processes along with the plastic recycling will be presented.

  8. Development of plastic surgery

    Directory of Open Access Journals (Sweden)

    Pećanac Marija Đ.

    2015-01-01

    Full Text Available Introduction. Plastic surgery is a medical specialty dealing with corrections of defects, improvements in appearance and restoration of lost function. Ancient Times. The first recorded account of reconstructive plastic surgery was found in ancient Indian Sanskrit texts, which described reconstructive surgeries of the nose and ears. In ancient Greece and Rome, many medicine men performed simple plastic cosmetic surgeries to repair damaged parts of the body caused by war mutilation, punishment or humiliation. In the Middle Ages, the development of all medical braches, including plastic surgery was hindered. New age. The interest in surgical reconstruction of mutilated body parts was renewed in the XVIII century by a great number of enthusiastic and charismatic surgeons, who mastered surgical disciplines and became true artists that created new forms. Modern Era. In the XX century, plastic surgery developed as a modern branch in medicine including many types of reconstructive surgery, hand, head and neck surgery, microsurgery and replantation, treatment of burns and their sequelae, and esthetic surgery. Contemporary and future plastic surgery will continue to evolve and improve with regenerative medicine and tissue engineering resulting in a lot of benefits to be gained by patients in reconstruction after body trauma, oncology amputation, and for congenital disfigurement and dysfunction.

  9. Oscillation, Conduction Delays, and Learning Cooperate to Establish Neural Competition in Recurrent Networks.

    Science.gov (United States)

    Kato, Hideyuki; Ikeguchi, Tohru

    2016-01-01

    Specific memory might be stored in a subnetwork consisting of a small population of neurons. To select neurons involved in memory formation, neural competition might be essential. In this paper, we show that excitable neurons are competitive and organize into two assemblies in a recurrent network with spike timing-dependent synaptic plasticity (STDP) and axonal conduction delays. Neural competition is established by the cooperation of spontaneously induced neural oscillation, axonal conduction delays, and STDP. We also suggest that the competition mechanism in this paper is one of the basic functions required to organize memory-storing subnetworks into fine-scale cortical networks.

  10. Sorting Plastic Waste in Hydrocyclone

    Directory of Open Access Journals (Sweden)

    Ernestas Šutinys

    2011-02-01

    Full Text Available The article presents material about sorting plastic waste in hydrocyclone. The tests on sorting plastic waste were carried out. Also, the findings received from the performed experiment on the technology of sorting plastic waste are interpreted applying an experimental model of the equipment used for sorting plastics of different density.Article in Lithuanian

  11. Epigenetic Basis of Neuronal and Synaptic Plasticity.

    Science.gov (United States)

    Karpova, Nina N; Sales, Amanda J; Joca, Samia R

    2017-01-01

    Neuronal network and plasticity change as a function of experience. Altered neural connectivity leads to distinct transcriptional programs of neuronal plasticity-related genes. The environmental challenges throughout life may promote long-lasting reprogramming of gene expression and the development of brain disorders. The modifications in neuronal epigenome mediate gene-environmental interactions and are required for activity-dependent regulation of neuronal differentiation, maturation and plasticity. Here, we highlight the latest advances in understanding the role of the main players of epigenetic machinery (DNA methylation and demethylation, histone modifications, chromatin-remodeling enzymes, transposons, and non-coding RNAs) in activity-dependent and long- term neural and synaptic plasticity. The review focuses on both the transcriptional and post-transcriptional regulation of gene expression levels, including the processes of promoter activation, alternative splicing, regulation of stability of gene transcripts by natural antisense RNAs, and alternative polyadenylation. Further, we discuss the epigenetic aspects of impaired neuronal plasticity and the pathogenesis of neurodevelopmental (Rett syndrome, Fragile X Syndrome, genomic imprinting disorders, schizophrenia, and others), stressrelated (mood disorders) and neurodegenerative Alzheimer's, Parkinson's and Huntington's disorders. The review also highlights the pharmacological compounds that modulate epigenetic programming of gene expression, the potential treatment strategies of discussed brain disorders, and the questions that should be addressed during the development of effective and safe approaches for the treatment of brain disorders.

  12. Candidate genes in ocular dominance plasticity

    Directory of Open Access Journals (Sweden)

    M. Liset Rietman

    2012-02-01

    Full Text Available The objective of this study was to identify new candidate genes involved in experience-dependent plasticity. To this aim, we combined previously obtained data from recombinant inbred BXD strains on ocular dominance (OD plasticity and gene expression levels in the neocortex. We validated our approach using a list of genes which alter OD plasticity when inactivated. The expression levels of one fifth of these genes correlated with the amount of OD plasticity. Moreover, the two genes with the highest relative inter-strain differences were among the correlated genes. This suggests that correlation between gene expression levels and OD plasticity is indeed likely to point to genes with a causal role in modulating or generating plasticity in the visual cortex. After this validation on known plasticity genes, we identified new candidate genes by a multi-step approach. First, a list was compiled of all genes of which the expression level in BXD strains correlate with the amount of OD plasticity. To narrow this list to the more promising candidates, we took its cross-section with a list of genes co-regulated with the sensitive period for OD plasticity and a list of genes associated with pathways implicated in OD plasticity. This analysis resulted in a list of 32 candidate genes. The list contained unproven, but not surprising, candidates, such as the genes for IGF-1, NCAM1, NOGO-A, the gamma2 subunit of the GABA(A receptor, acetylcholine esterase and the catalytic subunit of cAMP-dependent protein kinase A. This was indicative of the viability of our approach, but more interesting were the novel candidate genes: Akap7, Akt1, Camk2d, Cckbr, Cd44, Crim1, Ctdsp2, Dnajc5, Gnai1, Itpka, Mapk8, Nbea, Nfatc3, Nlk, Npy5r, Phf21a, Phip, Ppm1l, Ppp1r1b, Rbbp4, Slc1a3, Slit2, Socs2, Spock3, St8sia1, Zfp207. The possible role of some of these candidates is discussed in the article.

  13. 4. pi. physics with the plastic ball

    Energy Technology Data Exchange (ETDEWEB)

    Gutbrod, H.H.; Loehner, H.; Poskanzer, A.M.; Renner, T.; Riedesel, H.; Ritter, H.G.; Warwick, A.; Weik, F.; Wieman, H.

    1982-10-01

    4 ..pi.. data taken with the Plastic Ball show that cluster production in relativistic nuclear collisions depends on both the size of the participant volume and the finite size of the cluster. The measurement of the degree of thermalization and the search for collective flow will permit the study of the applicability of macroscopic concepts such as temperature and density.

  14. Underappreciated Consequences of Phenotypic Plasticity for Ecological Speciation

    Directory of Open Access Journals (Sweden)

    Benjamin M. Fitzpatrick

    2012-01-01

    Full Text Available Phenotypic plasticity was once seen primarily as a constraint on adaptive evolution or merely a nuisance by geneticists. However, some biologists promote plasticity as a source of novelty and a factor in evolution on par with mutation, drift, gene flow, and selection. These claims are controversial and largely untested, but progress has been made on more modest questions about effects of plasticity on local adaptation (the first component of ecological speciation. Adaptive phenotypic plasticity can be a buffer against divergent selection. It can also facilitate colonization of new niches and rapid divergent evolution. The influence of non-adaptive plasticity has been underappreciated. Non-adaptive plasticity, too can interact with selection to promote or inhibit genetic differentiation. Finally, phenotypic plasticity of reproductive characters might directly influence evolution of reproductive isolation (the second component of ecological speciation. Plasticity can cause assortative mating, but its influence on gene flow ultimately depends on maintenance of environmental similarity between parents and offspring. Examples of plasticity influencing mating and habitat choice suggest that this, too, might be an underappreciated factor in speciation. Plasticity is an important consideration for studies of speciation in nature, and this topic promises fertile ground for integrating developmental biology with ecology and evolution.

  15. Thermal Viscoelastic Analysis of Plastic Components Considering Residual Stress

    Science.gov (United States)

    Choi, Chel Woo; Jeoung, Kab Sik; Moon, Hyung-Il; Kim, Heon Young

    Plastics is commonly used in consumer electronics because of it is high strength per unit mass and good productivity, but plastic components may often become distorted after injection molding due to residual stress after the filling, packing, and cooling processes. In addition, plastic deteriorates depending on various temperature conditions and the operating time, which can be characterized by stress relaxation and creep. The viscoelastic behavior of plastic materials in the time domain can be expressed by the Prony series using the ABAQUS commercial software package. This paper suggests a process for predicting post-production deformation under cyclic thermal loading. The process was applied to real plastic panels, and the deformation predicted by the analysis was compared to that measured in actual testing, showing the possibility of using this process for predicting the post-production deformation of plastic products under thermal loading.

  16. A mathematical basis for strain-gradient plasticity theory. Part II: Tensorial plastic multiplier

    Science.gov (United States)

    Fleck, N. A.; Willis, J. R.

    2009-07-01

    A phenomenological, flow theory version of gradient plasticity for isotropic and anisotropic solids is constructed along the lines of Gudmundson [Gudmundson, P., 2004. A unified treatment of strain-gradient plasticity. J. Mech. Phys. Solids 52, 1379-1406]. Both energetic and dissipative stresses are considered in order to develop a kinematic hardening theory, which in the absence of gradient terms reduces to conventional J 2 flow theory with kinematic hardening. The dissipative stress measures, work-conjugate to plastic strain and its gradient, satisfy a yield condition with associated plastic flow. The theory includes interfacial terms: elastic energy is stored and plastic work is dissipated at internal interfaces, and a yield surface is postulated for the work-conjugate stress quantities at the interface. Uniqueness and extremum principles are constructed for the solution of boundary value problems, for both the rate-dependent and the rate-independent cases. In the absence of strain gradient and interface effects, the minimum principles reduce to the classical extremum principles for a kinematically hardening elasto-plastic solid. A rigid-hardening version of the theory is also stated and the resulting theory gives rise to an extension to the classical limit load theorems. This has particular appeal as previous trial fields for limit load analysis can be used to generate immediately size-dependent bounds on limit loads.

  17. Neuronal plasticity and neurotrophic factors in drug responses.

    Science.gov (United States)

    Castrén, E; Antila, H

    2017-08-01

    Neurotrophic factors, particularly brain-derived neurotrophic factor (BDNF) and other members of the neurotrophin family, are central mediators of the activity-dependent plasticity through which environmental experiences, such as sensory information are translated into the structure and function of neuronal networks. Synthesis, release and action of BDNF is regulated by neuronal activity and BDNF in turn leads to trophic effects such as formation, stabilization and potentiation of synapses through its high-affinity TrkB receptors. Several clinically available drugs activate neurotrophin signaling and neuronal plasticity. In particular, antidepressant drugs rapidly activate TrkB signaling and gradually increase BDNF expression, and the behavioral effects of antidepressants are mediated by and dependent on BDNF signaling through TrkB at least in rodents. These findings indicate that antidepressants, widely used drugs, effectively act as TrkB activators. They further imply that neuronal plasticity is a central mechanism in the action of antidepressant drugs. Indeed, it was recently discovered that antidepressants reactivate a state of plasticity in the adult cerebral cortex that closely resembles the enhanced plasticity normally observed during postnatal critical periods. This state of induced plasticity, known as iPlasticity, allows environmental stimuli to beneficially reorganize networks abnormally wired during early life. iPlasticity has been observed in cortical as well as subcortical networks and is induced by several pharmacological and non-pharmacological treatments. iPlasticity is a new pharmacological principle where drug treatment and rehabilitation cooperate; the drug acts permissively to enhance plasticity and rehabilitation provides activity to guide the appropriate wiring of the plastic network. Optimization of iPlastic drug treatment with novel means of rehabilitation may help improve the efficacy of available drug treatments and expand the use of

  18. Precise synaptic efficacy alignment suggests potentiation dominated learning

    Directory of Open Access Journals (Sweden)

    Christoph eHartmann

    2016-01-01

    Full Text Available Recent evidence suggests that parallel synapses from the same axonal branch onto the same dendritic branch have almost identical strength. It has been proposed that this alignment is only possible through learning rules that integrate activity over long time spans. However, learning mechanisms such as spike-timing-dependent plasticity (STDP are commonly assumed to be temporally local. Here, we propose that the combination of temporally local STDP and a multiplicative synaptic normalization mechanism is sufficient to explain the alignment of parallel synapses.To address this issue, we introduce three increasingly complex models: First, we model the idealized interaction of STDP and synaptic normalization in a single neuron as a simple stochastic process and derive analytically that the alignment effect can be described by a so-called Kesten process. From this we can derive that synaptic efficacy alignment requires potentiation-dominated learning regimes. We verify these conditions in a single-neuron model with independent spiking activities but more realistic synapses. As expected, we only observe synaptic efficacy alignment for long-term potentiation-biased STDP. Finally, we explore how well the findings transfer to recurrent neural networks where the learning mechanisms interact with the correlated activity of the network. We find that due to the self-reinforcing correlations in recurrent circuits under STDP, alignment occurs for both long-term potentiation- and depression-biased STDP, because the learning will be potentiation dominated in both cases due to the potentiating events induced by correlated activity. This is in line with recent results demonstrating a dominance of potentiation over depression during waking and normalization during sleep. This leads us to predict that individual spine pairs will be more similar in the morning than they are after sleep depriviation.In conclusion, we show that synaptic normalization in conjunction with

  19. and minimum plastic zone radius (MPZR) for four point bend ...

    African Journals Online (AJOL)

    user

    LEFM) approach. ... where the radius of plastic zone takes either a local or global minimum depending on the ..... facilities provided by the Research Centre, B V B College of Engineering & ... American institute of physics conference proceedings.

  20. A Semi-Persistent Adult Ocular Dominance Plasticity in Visual Cortex Is Stabilized by Activated CREB

    Science.gov (United States)

    Barco, Angel; Kandel, Eric R.; Gordon, Barbara; Lickey, Marvin E.; Suzuki, Seigo; Pham, Tony A.; Graham, Sarah J.

    2004-01-01

    The adult cerebral cortex can adapt to environmental change. Using monocular deprivation as a paradigm, we find that rapid experience-dependent plasticity exists even in the mature primary visual cortex. However, adult cortical plasticity differs from developmental plasticity in two important ways. First, the effect of adult, but not juvenile…

  1. Molecular kinesis in cellular function and plasticity.

    Science.gov (United States)

    Tiedge, H; Bloom, F E; Richter, D

    2001-06-19

    Intracellular transport and localization of cellular components are essential for the functional organization and plasticity of eukaryotic cells. Although the elucidation of protein transport mechanisms has made impressive progress in recent years, intracellular transport of RNA remains less well understood. The National Academy of Sciences Colloquium on Molecular Kinesis in Cellular Function and Plasticity therefore was devised as an interdisciplinary platform for participants to discuss intracellular molecular transport from a variety of different perspectives. Topics covered at the meeting included RNA metabolism and transport, mechanisms of protein synthesis and localization, the formation of complex interactive protein ensembles, and the relevance of such mechanisms for activity-dependent regulation and synaptic plasticity in neurons. It was the overall objective of the colloquium to generate momentum and cohesion for the emerging research field of molecular kinesis.

  2. Magnetar Field Evolution and Crustal Plasticity

    Science.gov (United States)

    Lander, S. K.

    2016-06-01

    The activity of magnetars is believed to be powered by colossal magnetic energy reservoirs. We sketch an evolutionary picture in which internal field evolution in magnetars generates a twisted corona, from which energy may be released suddenly in a single giant flare, or more gradually through smaller outbursts and persistent emission. Given the ages of magnetars and the energy of their giant flares, we suggest that their evolution is driven by a novel mechanism: magnetic flux transport/decay due to persistent plastic flow in the crust, which would invalidate the common assumption that the crustal lattice is static and evolves only under Hall drift and Ohmic decay. We estimate the field strength required to induce plastic flow as a function of crustal depth, and the viscosity of the plastic phase. The star’s superconducting core may also play a role in magnetar field evolution, depending on the star’s spindown history and how rotational vortices and magnetic fluxtubes interact.

  3. 基于应变梯度塑性理论的直接剪切试验尺寸效应、剪切变形及扩容分析%ANALYSIS OF SIZE EFFECT,SHEAR DEFORMATION AND DILATION IN DIRECT SHEAR TEST BASED ON GRADIENT DEPENDENT PLASTICITY

    Institute of Scientific and Technical Information of China (English)

    王学滨; 唐巨鹏; 张智慧

    2004-01-01

    The paper concerns the issue of size law, localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band, and based on gradient-dependent plasticity, an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen, the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain, the dilation and compaction within shear band are analyzed.Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.

  4. Structural plasticity mechanisms and developmental psychiatric disorders

    Directory of Open Access Journals (Sweden)

    Dominique eMuller

    2014-11-01

    Full Text Available Synaptic plasticity mechanisms are usually discussed in terms of changes in synaptic strength. The capacity of excitatory synapses to rapidly modify the membrane expression of glutamate receptors in an activity-dependent manner plays a critical role in learning and memory processes by re-distributing activity within neuronal networks. Recent work has however also shown that functional plasticity properties are associated with a rewiring of synaptic connections and a selective stabilization of activated synapses. These structural aspects of plasticity have the potential to continuously modify the organization of synaptic networks and thereby introduce specificity in the wiring diagram of cortical circuits. Recent work has started to unravel some of the molecular mechanisms that underlie these properties of structural plasticity, highlighting an important role of signaling pathways that are also major candidates for contributing to developmental psychiatric disorders. We review here some of these recent advances and discuss the hypothesis that alterations of structural plasticity could represent a common mechanism contributing to the cognitive and functional defects observed in diseases such as intellectual disability, autism spectrum disorders and schizophrenia.

  5. A two-speed model for finite-strain elasto-plasticity

    OpenAIRE

    Rindler, Filip

    2015-01-01

    This work presents a new modeling approach to macroscopic, polycrystalline elasto-plasticity starting from first principles and a few well-defined structural assumptions, incorporating the mildly rate-dependent (viscous) nature of plastic flow and the microscopic origins of plastic deformations. For the global dynamics, we start from a two-stage time-stepping scheme, expressing the fact that in most real materials plastic flow is much slower than elastic deformations, and then perform a detai...

  6. Astrocyte and Neuronal Plasticity in the Somatosensory System.

    Science.gov (United States)

    Sims, Robert E; Butcher, John B; Parri, H Rheinallt; Glazewski, Stanislaw

    2015-01-01

    Changing the whisker complement on a rodent's snout can lead to two forms of experience-dependent plasticity (EDP) in the neurons of the barrel cortex, where whiskers are somatotopically represented. One form, termed coding plasticity, concerns changes in synaptic transmission and connectivity between neurons. This is thought to underlie learning and memory processes and so adaptation to a changing environment. The second, called homeostatic plasticity, serves to maintain a restricted dynamic range of neuronal activity thus preventing its saturation or total downregulation. Current explanatory models of cortical EDP are almost exclusively neurocentric. However, in recent years, increasing evidence has emerged on the role of astrocytes in brain function, including plasticity. Indeed, astrocytes appear as necessary partners of neurons at the core of the mechanisms of coding and homeostatic plasticity recorded in neurons. In addition to neuronal plasticity, several different forms of astrocytic plasticity have recently been discovered. They extend from changes in receptor expression and dynamic changes in morphology to alteration in gliotransmitter release. It is however unclear how astrocytic plasticity contributes to the neuronal EDP. Here, we review the known and possible roles for astrocytes in the barrel cortex, including its plasticity.

  7. SABIC Innovative Plastics: Be the World Best Plastic Resin Manufacturer

    Institute of Scientific and Technical Information of China (English)

    Jenny Du

    2007-01-01

    @@ "SABIC Innovative Plastics is a global supplier of plastic resins, manufacturing and compounding polycarbonate, ABS, SAN, ASA, PPE, PC/ABS, PBT and PEI resins, as well as the LNP* line of high performance specialty compounds," said Hiroshi Yoshida, the Global Market Director for Electronics of SABIC Innovative Plastics based in Tokyo at the press conference held by SABIC Innovative Plastics, November 8th 2007, Shanghai.

  8. [Galactorrhea after mammary plastic surgery].

    Science.gov (United States)

    Inguenault, C; Capon-Degardin, N; Martinot-Duquennoy, V; Pellerin, P

    2005-04-01

    Galactorrhoea is a complication rarely observed after mammary plastic surgery. Our experience in the domain extends to three clinical cases - two after prosthetic insertion and one after breast reduction - wich will be presented here. The origin of this complication is uncertain. Nevertheless, it is likely to be multifocal, as surgery alone is not the only cause. Postsurgical galactorrhoea often follows a benign course culminating in spontaneous resolution. However, it may reveal the presence of o prolactin secreting adenoma, as was the case with one of our patients. A detailed history, exploring antecedent factors, is an essential step in guiding subsequent management. When faced with postsurgical galactorrhoea, serum prolactin levels should be measured. If serum prolactin levels exceed 150 ng/ml further investigation by way of an MRI of the sella turcica is advisable to rule out pituitary adenoma. Depending on symptom severity, treatment may be medical with the prescription of dopaminergic agonists, and/or surgical with drainage or removal of prostheses. Increased awareness of galactorrhea as a possible complication of plastic surgery to the breast will improve management.

  9. Preserving in Plastic.

    Science.gov (United States)

    Wahla, James

    1985-01-01

    Outlines steps for casting insects in permanent molds prepared from commercially available liquid plastic. Also describes dry mountings in glass, acrylic, and petri dishes. The rationale for specimen use, hints for producing quality results, purchasing information, and safety precautions are considered. (DH)

  10. Informative document waste plastics

    NARCIS (Netherlands)

    Nagelhout D; Sein AA; Duvoort GL

    1989-01-01

    This "Informative document waste plastics" forms part of a series of "informative documents waste materials". These documents are conducted by RIVM on the indstruction of the Directorate General for the Environment, Waste Materials Directorate, in behalf of the program of acti

  11. New plastic recycling technology

    Science.gov (United States)

    Greater than 60% of the total plastic content of municipal solid waste is comprised of polyolefins (high-density, low-density, and linear polyethylene and polypropylene. Polyethylene (PE) is the largest-volume component but presents a challenge due to the absence of low-energy de...

  12. Persisting Plastic Addiction

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    The policy on curbing plastic shopping bag use implemented three years ago has produced mixed results In a bustling farmers’market tucked in a narrow street in Xisanqi residential community in north Beijing,stalls selling vegetables,fruits and other foods line the sidewalk.

  13. Regulating critical period plasticity: insight from the visual system to fear circuitry for therapeutic interventions.

    Science.gov (United States)

    Nabel, Elisa M; Morishita, Hirofumi

    2013-01-01

    Early temporary windows of heightened brain plasticity called critical periods developmentally sculpt neural circuits and contribute to adult behavior. Regulatory mechanisms of visual cortex development - the preeminent model of experience-dependent critical period plasticity-actively limit adult plasticity and have proved fruitful therapeutic targets to reopen plasticity and rewire faulty visual system connections later in life. Interestingly, these molecular mechanisms have been implicated in the regulation of plasticity in other functions beyond vision. Applying mechanistic understandings of critical period plasticity in the visual cortex to fear circuitry may provide a conceptual framework for developing novel therapeutic tools to mitigate aberrant fear responses in post traumatic stress disorder. In this review, we turn to the model of experience-dependent visual plasticity to provide novel insights for the mechanisms regulating plasticity in the fear system. Fear circuitry, particularly fear memory erasure, also undergoes age-related changes in experience-dependent plasticity. We consider the contributions of molecular brakes that halt visual critical period plasticity to circuitry underlying fear memory erasure. A major molecular brake in the visual cortex, perineuronal net formation, recently has been identified in the development of fear systems that are resilient to fear memory erasure. The roles of other molecular brakes, myelin-related Nogo receptor signaling and Lynx family proteins - endogenous inhibitors for nicotinic acetylcholine receptor, are explored in the context of fear memory plasticity. Such fear plasticity regulators, including epigenetic effects, provide promising targets for therapeutic interventions.

  14. Regulating Critical Period Plasticity: Insight from the Visual System to Fear Circuitry for Therapeutic Interventions

    Directory of Open Access Journals (Sweden)

    Elisa M. Nabel

    2013-11-01

    Full Text Available Early temporary windows of heightened brain plasticity called critical periods developmentally sculpt neural circuits and contribute to adult behavior. Regulatory mechanisms of visual cortex development –the preeminent model of experience-dependent critical period plasticity- actively limit adult plasticity and have proved fruitful therapeutic targets to reopen plasticity and rewire faulty visual system connections later in life. Interestingly, these molecular mechanisms have been implicated in the regulation of plasticity in other functions beyond vision. Applying mechanistic understandings of critical period plasticity in the visual cortex to fear circuitry may provide a conceptual framework for developing novel therapeutic tools to mitigate aberrant fear responses in post traumatic stress disorder. In this review, we turn to the model of experience-dependent visual plasticity to provide novel insights for the mechanisms regulating plasticity in the fear system. Fear circuitry, particularly fear memory erasure, also undergoes age-related changes in experience-dependent plasticity. We consider the contributions of molecular brakes that halt visual critical period plasticity to circuitry underlying fear memory erasure. A major molecular brake in the visual cortex, perineuronal net formation, recently has been identified in the development of fear systems that are resilient to fear memory erasure. The roles of other molecular brakes, myelin-related Nogo receptor signaling and Lynx family proteins– endogenous inhibitors for nicotinic acetylcholine receptor, are explored in the context of fear memory plasticity. Such fear plasticity regulators, including epigenetic effects, provide promising targets for therapeutic interventions.

  15. How plastic can phenotypic plasticity be? The branching coral Stylophora pistillata as a model system.

    Directory of Open Access Journals (Sweden)

    Lee Shaish

    Full Text Available Phenotypic plasticity enables multicellular organisms to adjust morphologies and various life history traits to variable environmental challenges. Here, we elucidate fixed and plastic architectural rules for colony astogeny in multiple types of colonial ramets, propagated by cutting from genets of the branching coral Stylophora pistillata from Eilat, the Red Sea. We examined 16 morphometric parameters on 136 one-year old S. pistillata colonies (of seven genotypes, originating from small fragments belonging, each, to one of three single-branch types (single tips, start-up, and advanced bifurcating tips or to structural preparative manipulations (representing a single or two growth axes. Experiments were guided by the rationale that in colonial forms, complexity of evolving phenotypic plasticity can be associated with a degree of structural modularity, where shapes are approached by erecting iterative growth patterns at different levels of coral-colony organization. Analyses revealed plastic morphometric characters at branch level, and predetermined morphometric traits at colony level (only single trait exhibited plasticity under extreme manipulation state. Therefore, under the experimental manipulations of this study, phenotypic plasticity in S. pistillata appears to be related to branch level of organization, whereas colony traits are controlled by predetermined genetic architectural rules. Each level of organization undergoes its own mode of astogeny. However, depending on the original ramet structure, the spherical 3-D colonial architecture in this species is orchestrated and assembled by both developmental trajectories at the branch level, and traits at the colony level of organization. In nature, branching colonial forms are often subjected to harsh environmental conditions that cause fragmentation of colony into ramets of different sizes and structures. Developmental traits that are plastic, responding to fragment structure and are not

  16. Adaptive tuning of elasto-plastic damper

    DEFF Research Database (Denmark)

    Høgsberg, Jan Riess; Krenk, Steen

    2007-01-01

    Hysteretic dampers are frequency independent, and thereby otentially effective for several structural vibration modes, provided that the inherent amplitude dependence can be controlled. An adaptive tuning procedure is proposed, aiming at elimination of the amplitude dependence by adjusting...... the damper parameter(s) with respect to the magnitude of the damper motion. The procedure is demonstrated in terms of the bilinear elasto-plastic damper model, and optimality corresponds to maximum modal damping. A parametric solution for the damping ratio is obtained by a two-component system reduction...... in controlling the amplitude dependence, resulting in equal damping for the first vibration modes....

  17. A QSPR for the plasticization efficiency of polyvinylchloride plasticizers.

    Science.gov (United States)

    Chandola, Mridula; Marathe, Sujata

    2008-01-01

    A simple quantitative structure property relationship (QSPR) for correlating the plasticization efficiency of 25 polyvinylchloride (PVC) plasticizers was obtained using molecular modeling. The plasticizers studied were-aromatic esters (phthalate, terephthalate, benzoate, trimellitate), aliphatic esters (adipate, sebacate, azelate), citrates and a phosphate. The low temperature flex point, Tf, of plasticized polyvinylchloride resins was considered as an indicator of plasticization efficiency. Initially, we attempted to predict plasticization efficiency of PVC plasticizers from physical and structural descriptors derived from the plasticizer molecule alone. However, the correlation of these descriptors with Tf was not very good with R=0.78 and r2=0.613. This implied that the selected descriptors were unable to predict all the interactions between PVC and plasticizer. Hence, to account for these interactions, a model containing two polyvinylchloride (PVC) chain segments along with a plasticizer molecule in a simulation box was constructed, using molecular mechanics. A good QSPR equation correlating physical and structural descriptors derived from the model to Tf of the plasticized resins was obtained with R=0.954 and r2=0.909.

  18. Synaptic plasticity functions in an organic electrochemical transistor

    Science.gov (United States)

    Gkoupidenis, Paschalis; Schaefer, Nathan; Strakosas, Xenofon; Fairfield, Jessamyn A.; Malliaras, George G.

    2015-12-01

    Synaptic plasticity functions play a crucial role in the transmission of neural signals in the brain. Short-term plasticity is required for the transmission, encoding, and filtering of the neural signal, whereas long-term plasticity establishes more permanent changes in neural microcircuitry and thus underlies memory and learning. The realization of bioinspired circuits that can actually mimic signal processing in the brain demands the reproduction of both short- and long-term aspects of synaptic plasticity in a single device. Here, we demonstrate the implementation of neuromorphic functions similar to biological memory, such as short- to long-term memory transition, in non-volatile organic electrochemical transistors (OECTs). Depending on the training of the OECT, the device displays either short- or long-term plasticity, therefore, exhibiting non von Neumann characteristics with merged processing and storing functionalities. These results are a first step towards the implementation of organic-based neuromorphic circuits.

  19. Synaptic Plasticity onto Dopamine Neurons Shapes Fear Learning.

    Science.gov (United States)

    Pignatelli, Marco; Umanah, George Kwabena Essien; Ribeiro, Sissi Palma; Chen, Rong; Karuppagounder, Senthilkumar Senthil; Yau, Hau-Jie; Eacker, Stephen; Dawson, Valina Lynn; Dawson, Ted Murray; Bonci, Antonello

    2017-01-18

    Fear learning is a fundamental behavioral process that requires dopamine (DA) release. Experience-dependent synaptic plasticity occurs on DA neurons while an organism is engaged in aversive experiences. However, whether synaptic plasticity onto DA neurons is causally involved in aversion learning is unknown. Here, we show that a stress priming procedure enhances fear learning by engaging VTA synaptic plasticity. Moreover, we took advantage of the ability of the ATPase Thorase to regulate the internalization of AMPA receptors (AMPARs) in order to selectively manipulate glutamatergic synaptic plasticity on DA neurons. Genetic ablation of Thorase in DAT(+) neurons produced increased AMPAR surface expression and function that lead to impaired induction of both long-term depression (LTD) and long-term potentiation (LTP). Strikingly, animals lacking Thorase in DAT(+) neurons expressed greater associative learning in a fear conditioning paradigm. In conclusion, our data provide a novel, causal link between synaptic plasticity onto DA neurons and fear learning. Published by Elsevier Inc.

  20. Cross-modal synaptic plasticity in adult primary sensory cortices.

    Science.gov (United States)

    Lee, Hey-Kyoung; Whitt, Jessica L

    2015-12-01

    Sensory loss leads to widespread adaptation of brain circuits to allow an organism to navigate its environment with its remaining senses, which is broadly referred to as cross-modal plasticity. Such adaptation can be observed even in the primary sensory cortices, and falls into two distinct categories: recruitment of the deprived sensory cortex for processing the remaining senses, which we term 'cross-modal recruitment', and experience-dependent refinement of the spared sensory cortices referred to as 'compensatory plasticity.' Here we will review recent studies demonstrating that cortical adaptation to sensory loss involves LTP/LTD and homeostatic synaptic plasticity. Cross-modal synaptic plasticity is observed in adults, hence cross-modal sensory deprivation may be an effective way to promote plasticity in adult primary sensory cortices.

  1. Sustainable reverse logistics for household plastic waste

    OpenAIRE

    Bing, X

    2014-01-01

    Summary of the thesis titled “Sustainable Reverse Logistics for Household Plastic Waste” PhD Candidate: Xiaoyun Bing Recycled plastic can be used in the manufacturing of plastic products to reduce the use of virgin plastics material. The cost of recycled plastics is usually lower than that of virgin plastics. Therefore, it is environmentally and economically beneficial to improve the plastic recycling system to ensure more plastic waste from households is properly collected and pr...

  2. Effects of constitutive parameters on adiabatic shear localization for ductile metal based on JOHNSON-COOK and gradient plasticity models

    Institute of Scientific and Technical Information of China (English)

    WANG Xue-bin

    2006-01-01

    By using the widely used JOHNSON-COOK model and the gradient-dependent plasticity to consider microstmctural effect beyond the occurrence of shear strain localization, the distributions of local plastic shear strain and deformation in adiabatic shear band(ASB) were analyzed. The peak local plastic shear strain is proportional to the average plastic shear strain, while it is inversely proportional to the critical plastic shear strain corresponding to the peak flow shear stress. The relative plastic shear deformation between the top and base of ASB depends on the thickness of ASB and the average plastic shear strain. A parametric study was carried out to study the influence of constitutive parameters on shear strain localization. Higher values of static shear strength and work to heat conversion factor lead to lower critical plastic shear strain so that the shear localization is more apparent at the same average plastic shear strain. Higher values of strain-hardening exponent, strain rate sensitive coefficient, melting point,thermal capacity and mass density result in higher critical plastic shear strain, leading to less apparent shear localization at the same average plastic shear strain. The strain rate sensitive coefficient has a minor influence on the critical plastic shear strain, the distributions of local plastic shear strain and deformation in ASB. The effect of strain-hardening modulus on the critical plastic shear strain is not monotonous. When the maximum critical plastic shear strain is reached, the least apparent shear localization occurs.

  3. Motor cortical plasticity in Parkinson’s disease

    Directory of Open Access Journals (Sweden)

    Kaviraja eUdupa

    2013-09-01

    Full Text Available In Parkinson’s disease (PD, there are alterations of the basal ganglia (BG thalamo-cortical networks, primarily due to degeneration of nigrostrial dopaminergic neurons. These changes in subcortical networks lead to plastic changes in primary motor cortex (M1, which mediates cortical motor output and is a potential target for treatment of PD. Studies investigating the motor cortical plasticity using non-invasive transcranial magnetic stimulation (TMS have found altered plasticity in PD, but there are inconsistencies among these studies. This is likely because plasticity depends on many factors such as the extent of dopaminergic loss and disease severity, response to dopaminergic replacement therapies, development of L-dopa-induced dyskinesias (LID, the plasticity protocol used, medication and stimulation status in patients treated with deep brain stimulation (DBS. The influences of LID and DBS on BG and M1 plasticity have been explored in animal models and in PD patients. In addition, many other factors such age, genetic factors (e.g. brain derived neurotropic factor and other neurotransmitters or receptors polymorphism, emotional state, time of the day, physical fitness have been documented to play role in the extent of plasticity induced by TMS in human studies. In this review, we summarize the studies that investigated M1 plasticity in PD and demonstrate how these afore-mentioned factors affect motor cortical plasticity in PD. We conclude that it is important to consider the clinical, demographic and technical factors that influence various plasticity protocols while developing these protocols as diagnostic or prognostic tools in PD. We also discuss how the modulation of cortical excitability and the plasticity with these non-invasive brain stimulation techniques facilitate the understanding of the pathophysiology of PD and help design potential therapeutic possibilities in this disorder.

  4. SLEEP AND OLFACTORY CORTICAL PLASTICITY

    Directory of Open Access Journals (Sweden)

    Dylan eBarnes

    2014-04-01

    Full Text Available In many systems, sleep plays a vital role in memory consolidation and synaptic homeostasis. These processes together help store information of biological significance and reset synaptic circuits to facilitate acquisition of information in the future. In this review, we describe recent evidence of sleep-dependent changes in olfactory system structure and function which contribute to odor memory and perception. During slow-wave sleep, the piriform cortex becomes hypo-responsive to odor stimulation and instead displays sharp-wave activity similar to that observed within the hippocampal formation. Furthermore, the functional connectivity between the piriform cortex and other cortical and limbic regions is enhanced during slow-wave sleep compared to waking. This combination of conditions may allow odor memory consolidation to occur during a state of reduced external interference and facilitate association of odor memories with stored hedonic and contextual cues. Evidence consistent with sleep-dependent odor replay within olfactory cortical circuits is presented. These data suggest that both the strength and precision of odor memories is sleep-dependent. The work further emphasizes the critical role of synaptic plasticity and memory in not only odor memory but also basic odor perception. The work also suggests a possible link between sleep disturbances that are frequently co-morbid with a wide range of pathologies including Alzheimer’s disease, schizophrenia and depression and the known olfactory impairments associated with those disorders.

  5. Plasticity modeling & computation

    CERN Document Server

    Borja, Ronaldo I

    2013-01-01

    There have been many excellent books written on the subject of plastic deformation in solids, but rarely can one find a textbook on this subject. “Plasticity Modeling & Computation” is a textbook written specifically for students who want to learn the theoretical, mathematical, and computational aspects of inelastic deformation in solids. It adopts a simple narrative style that is not mathematically overbearing, and has been written to emulate a professor giving a lecture on this subject inside a classroom. Each section is written to provide a balance between the relevant equations and the explanations behind them. Where relevant, sections end with one or more exercises designed to reinforce the understanding of the “lecture.” Color figures enhance the presentation and make the book very pleasant to read. For professors planning to use this textbook for their classes, the contents are sufficient for Parts A and B that can be taught in sequence over a period of two semesters or quarters.

  6. Modeling plasticity of materials with nanostructure

    Science.gov (United States)

    Kudinova, N. R.

    2017-02-01

    A new approach to modeling of the plasticity of materials with the particle size in the range from 3 to 20 nm (nanostructure) has been proposed. It is based on classical thermodynamic approach employing the surface tension of nanoparticles. Its main advantage is the minimum number of physical parameters in use. In the context of the proposed model, we calculated the dependence of the melting temperature on the nanoparticle size which is consistent with experimental data. The volume density of the surface energy of nanoparticles was also determined. This energy is assumed to be a significant part of the internal energy during deformation Yield point was interpreted as the result of changes of grains surface energy during the deformation. The obtained yield point dependence on the grain size was related to the Hall–Petch law, and this resulted in confirmation of the hypothesis on the crucial role of surface tension forces in the initial stage of plastic deformation of nanomaterials.

  7. Impact of the nature and concentration of plasticizers on the ability of PVC to sorb drug.

    Science.gov (United States)

    Al Salloum, H; Saunier, J; Aymes-Chodur, C; Barakat, H; Yagoubi, N

    2015-12-30

    The sorption of a drug by an infusion set may dramatically reduce the drug delivery efficiency. In this paper, we investigated how the drug sorption, in static conditions, is affected by the plasticizer's nature and ratio in the case of plasticized PVC, one of the most common material for infusion set tubing. Within the study, the drug concentration in diazepam solutions was studied after contact with PVC films containing different amounts of DEHP, DEHT, TOTM and DINCH® plasticizers. Moreover the partition coefficients between material and water were calculated. The drug sorption levels were equivalent for the different plasticizers and there was a plasticizer ratio for which the drug uptake was enhanced. As a consequence, the amount of sorbed drug might not be only linked to the amount of plasticizer in the film and to the solubility of the drug in the plasticizer alone: it must probably depend on specific interactions between plasticizer and PVC.

  8. Low temperature creep plasticity

    Directory of Open Access Journals (Sweden)

    Michael E. Kassner

    2014-07-01

    Full Text Available The creep behavior of crystalline materials at low temperatures (T < 0.3Tm is discussed. In particular, the phenomenological relationships that describe primary creep are reviewed and analyzed. A discussion of the activation energy for creep at T < 0.3Tm is discussed in terms of the context of higher temperature activation energy. The basic mechanism(s of low temperature creep plasticity are discussed, as well.

  9. New perspectives in plastic biodegradation.

    Science.gov (United States)

    Sivan, Alex

    2011-06-01

    During the past 50 years new plastic materials, in various applications, have gradually replaced the traditional metal, wood, leather materials. Ironically, the most preferred property of plastics--durability--exerts also the major environmental threat. Recycling has practically failed to provide a safe solution for disposal of plastic waste (only 5% out of 1 trillion plastic bags, annually produced in the US alone, are being recycled). Since the most utilized plastic is polyethylene (PE; ca. 140 million tons/year), any reduction in the accumulation of PE waste alone would have a major impact on the overall reduction of the plastic waste in the environment. Since PE is considered to be practically inert, efforts were made to isolate unique microorganisms capable of utilizing synthetic polymers. Recent data showed that biodegradation of plastic waste with selected microbial strains became a viable solution. Copyright © 2011 Elsevier Ltd. All rights reserved.

  10. Microelectronics plastic molded packaging

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, D.R. [Ktech Corp., Albuquerque, NM (United States); Palmer, D.W.; Peterson, D.W. [Sandia National Lab., Albuquerque, NM (United States)] [and others

    1997-02-01

    The use of commercial off-the-shelf (COTS) microelectronics for nuclear weapon applications will soon be reality rather than hearsay. The use of COTS for new technologies for uniquely military applications is being driven by the so-called Perry Initiative that requires the U.S. Department of Defense (DoD) to accept and utilize commercial standards for procurement of military systems. Based on this philosophy, coupled with several practical considerations, new weapons systems as well as future upgrades will contain plastic encapsulated microelectronics. However, a conservative Department of Energy (DOE) approach requires lifetime predictive models. Thus, the focus of the current project is on accelerated testing to advance current aging models as well as on the development of the methodology to be used during WR qualification of plastic encapsulated microelectronics. An additional focal point involves achieving awareness of commercial capabilities, materials, and processes. One of the major outcomes of the project has been the definition of proper techniques for handling and evaluation of modern surface mount parts which might be used in future systems. This program is also raising the familiarity level of plastic within the weapons complex, allowing subsystem design rules accommodating COTS to evolve. A two year program plan is presented along with test results and commercial interactions during this first year.

  11. Unusual predator-prey dynamics under reciprocal phenotypic plasticity.

    Science.gov (United States)

    Mougi, Akihiko

    2012-07-21

    Recent theories and experiments have shown that plasticity, such as an inducible defense or an inducible offense in predator-prey interactions, strongly influences the stability of the population dynamics. However, such plastic adaptation has not been expected to cause unusual dynamics such as antiphase cycles, which occur in experimental predator-prey systems with evolutionary adaptation in the defensive trait of prey. Here I show that antiphase cycles and cryptic cycles (a large population fluctuation in one species with almost no change in the population of the other species) can occur in a predator-prey system when both member species can change their phenotypes through adaptive plasticity (inducible defenses and offenses). I consider a familiar type of predator-prey system in which both species can change their morphology or behavior through phenotypic plasticity. The plasticity, that is, the ability to change between distinct phenotypes, is assumed to occur so as to maximize their fitness. I examined how the reciprocal adaptive plasticity influences the population dynamics. The results show that unusual dynamics such as antiphase population cycles and cryptic cycles can occur when both species show inducible plasticity. The unusual dynamics are particularly likely to occur when the carrying capacity of the prey is small (the density dependence of the prey's growth is strong). The unusual predator-prey dynamics may be induced by phenotypic plasticity as long as the phenotypic change occurs to maximize fitness.

  12. Viscosity and Plasticity of Latvian Illite Clays

    OpenAIRE

    2012-01-01

    Due to viscosity and plasticity, clays and clay minerals are used in civil engineering, pottery and also in cosmetics and medicine as thickening agents and emulsion and suspension stabilizers. The rheological properties of clay suspensions are complex. Mostly it is an interaction between mineral composition, clay particle size and pH value and also depends on clay minerals. Clay-water suspension is non-Newtonian fluid showing thixotropic and pseudoplastic properties. Results showed that plast...

  13. Recyclable plastics as substrata for settlement and growth of bryozoans Bugula neritina and barnacles Amphibalanus amphitrite.

    Science.gov (United States)

    Li, Heng-Xiang; Orihuela, Beatriz; Zhu, Mei; Rittschof, Daniel

    2016-11-01

    Plastics are common and pervasive anthropogenic debris in marine environments. Floating plastics provide opportunities to alter the abundance, distribution and invasion potential of sessile organisms that colonize them. We selected plastics from seven recycle categories and quantified settlement of (i) bryozoans Bugula neritina (Linnaeus, 1758) in the lab and in the field, and of (ii) barnacles Amphibalanus (= Balanus) amphitrite (Darwin, 1854) in the field. In the laboratory we cultured barnacles on the plastics for 8 weeks and quantified growth, mortality, and breaking strength of the side plates. In the field all recyclable plastics were settlement substrata for bryozoans and barnacles. Settlement depended on the type of plastic. Fewer barnacles settled on plastic surfaces compared to glass. In the lab and in the field, bryozoan settlement was higher on plastics than on glass. In static laboratory rearing, barnacles growing on plastics were initially significantly smaller than on glass. This suggested juvenile barnacles were adversely impacted by materials leaching from the plastics. Barnacle mortality was not significantly different between plastic and glass surfaces, but breaking strength of side plates of barnacles on polyvinyl chloride (PVC) and polycarbonate (PC) were significantly lower than breakage strength on glass. Plastics impact marine ecosystems directly by providing new surfaces for colonization with fouling organisms and by contaminants shown previously to leach out of plastics and impact biological processes.

  14. Interfacial interactions between plastic particles in plastics flotation.

    Science.gov (United States)

    Wang, Chong-qing; Wang, Hui; Gu, Guo-hua; Fu, Jian-gang; Lin, Qing-quan; Liu, You-nian

    2015-12-01

    Plastics flotation used for recycling of plastic wastes receives increasing attention for its industrial application. In order to study the mechanism of plastics flotation, the interfacial interactions between plastic particles in flotation system were investigated through calculation of Lifshitz-van der Waals (LW) function, Lewis acid-base (AB) Gibbs function, and the extended Derjaguin-Landau-Verwey-Overbeek potential energy profiles. The results showed that van der Waals force between plastic particles is attraction force in flotation system. The large hydrophobic attraction, caused by the AB Gibbs function, is the dominant interparticle force. Wetting agents present significant effects on the interfacial interactions between plastic particles. It is found that adsorption of wetting agents promotes dispersion of plastic particles and decreases the floatability. Pneumatic flotation may improve the recovery and purity of separated plastics through selective adsorption of wetting agents on plastic surface. The relationships between hydrophobic attraction and surface properties were also examined. It is revealed that there exists a three-order polynomial relationship between the AB Gibbs function and Lewis base component. Our finding provides some insights into mechanism of plastics flotation.

  15. Synaptic plasticity in inhibitory neurons of the auditory brainstem.

    Science.gov (United States)

    Bender, Kevin J; Trussell, Laurence O

    2011-04-01

    There is a growing appreciation of synaptic plasticity in the early levels of auditory processing, and particularly of its role in inhibitory circuits. Synaptic strength in auditory brainstem and midbrain is sensitive to standard protocols for induction of long-term depression, potentiation, and spike-timing-dependent plasticity. Differential forms of plasticity are operative at synapses onto inhibitory versus excitatory neurons within a circuit, and together these could serve to tune circuits involved in sound localization or multisensory integration. Such activity-dependent control of synaptic function in inhibitory neurons may also be expressed after hearing loss and could underlie persistent neuronal activity in patients with tinnitus. This article is part of a Special Issue entitled 'Synaptic Plasticity & Interneurons'.

  16. Use of recycled plastics in wood plastic composites - a review.

    Science.gov (United States)

    Kazemi Najafi, Saeed

    2013-09-01

    The use of recycled and waste thermoplastics has been recently considered for producing wood plastic composites (WPCs). They have great potential for WPCs manufacturing according to results of some limited researches. This paper presents a detailed review about some essential properties of waste and recycled plastics, important for WPCs production, and of research published on the effect of recycled plastics on the physical and mechanical properties of WPCs.

  17. Direct liquefaction of plastics and coprocessing of coal with plastics

    Energy Technology Data Exchange (ETDEWEB)

    Huffman, G.P.; Feng, Z.; Mahajan, V. [Univ. of Kentucky, Lexington, KY (United States)

    1995-12-31

    The objectives of this work were to optimize reaction conditions for the direct liquefaction of waste plastics and the coprocessing of coal with waste plastics. In previous work, the direct liquefaction of medium and high density polyethylene (PE), polypropylene (PPE), poly(ethylene terephthalate) (PET), and a mixed plastic waste, and the coliquefaction of these plastics with coals of three different ranks was studied. The results established that a solid acid catalyst (HZSM-5 zeolite) was highly active for the liquefaction of the plastics alone, typically giving oil yields of 80-95% and total conversions of 90-100% at temperatures of 430-450 {degrees}C. In the coliquefaction experiments, 50:50 mixtures of plastic and coal were used with a tetralin solvent (tetralin:solid = 3:2). Using approximately 1% of the HZSM-5 catalyst and a nanoscale iron catalyst, oil yields of 50-70% and total conversion of 80-90% were typical. In the current year, further investigations were conducted of the liquefaction of PE, PPE, and a commingled waste plastic obtained from the American Plastics Council (APC), and the coprocessing of PE, PPE and the APC plastic with Black Thunder subbituminous coal. Several different catalysts were used in these studies.

  18. Plastic Surgery and Suicide: A Clinical Guide for Plastic Surgeons.

    Science.gov (United States)

    Reddy, Vikram; Coffey, M Justin

    2016-08-01

    Several studies have identified an increased risk of suicide among patient populations which a plastic surgeon may have a high risk of encountering: women undergoing breast augmentation, cosmetic surgery patients, and breast cancer patients. No formal guidelines exist to assist a plastic surgeon when faced with such a patient, and not every plastic surgery team has mental health clinicians that are readily accessible for consultation or referral. The goal of this clinical guide is to offer plastic surgeons a set of practical approaches to manage potentially suicidal patients. In addition, the authors review a screening tool, which can assist surgeons when encountering high-risk patients.

  19. Motor cortical plasticity induced by motor learning through mental practice.

    Directory of Open Access Journals (Sweden)

    Laura eAvanzino

    2015-04-01

    Full Text Available Several investigations suggest that actual and mental actions trigger similar neural substrates. Motor learning via physical practice results in long-term potentiation (LTP-like plasticity processes, namely potentiation of M1 and a temporary occlusion of additional LTP-like plasticity. However, whether this neuroplasticity process contributes to improve motor performance through mental practice remains to be determined. Here, we tested skill learning-dependent changes in primary motor cortex (M1 excitability and plasticity by means of transcranial magnetic stimulation in subjects trained to physically execute or mentally perform a sequence of finger opposition movements. Before and after physical practice and motor-imagery practice, M1 excitability was evaluated by measuring the input-output (IO curve of motor evoked potentials. M1 long-term potentiation (LTP and long-term depression (LTD-like plasticity was assessed with paired-associative stimulation (PAS of the median nerve and motor cortex using an interstimulus interval of 25 ms (PAS25 or 10 ms (PAS10, respectively. We found that even if after both practice sessions subjects significantly improved their movement speed, M1 excitability and plasticity were differentially influenced by the two practice sessions. First, we observed an increase in the slope of IO curve after physical but not after motor-imagery practice. Second, there was a reversal of the PAS25 effect from LTP-like plasticity to LTD-like plasticity following physical and motor-imagery practice. Third, LTD-like plasticity (PAS10 protocol increased after physical practice, whilst it was occluded after motor-imagery practice. In conclusion, we demonstrated that motor-imagery practice lead to the development of neuroplasticity, as it affected the PAS25- and PAS10- induced plasticity in M1. These results, expanding the current knowledge on how motor-imagery training shapes M1 plasticity, might have a potential impact in

  20. Tree plastic bark

    OpenAIRE

    Casado Arroyo, Carlos

    2016-01-01

    “Tree plastic bark" consiste en la realización de una intervención artística en un entorno natural concreto, generando de esta manera un Site Specific(1). Como hace alusión Rosalind Krauss en sus reflexiones “La escultura en el campo expandido”(2), comenta que su origen esta claramente ligado con el concepto de monumentalidad. La escultura es un monumento, se crea para conmemorar algún hecho o personaje relevante y está realizada para una ubicación concreta. La investigación parte de la id...

  1. Fabrication of plastic biochips

    Energy Technology Data Exchange (ETDEWEB)

    Saaem, Ishtiaq; Ma, Kuo-Sheng; Alam, S. Munir; Tian Jingdong [Department of Biomedical Engineering and Institute for Genome Sciences and Policy, Duke University, Durham, North Carolina 27708 (United States); Department of Medicine and Human Vaccine Institute, Duke University, Durham, North Carolina 27708 (United States); Department of Biomedical Engineering and Institute for Genome Sciences and Policy, Duke University, Durham, North Carolina 27708 (United States)

    2010-07-15

    A versatile surface functionalization procedure based on rf magnetron sputtering of silica was performed on poly(methylmethacrylate), polycarbonate, polypropylene, and cyclic olefin copolymers (Topas 6015). The hybrid thermoplastic surfaces were characterized by x-ray photoelectron spectrometer analysis and contact angle measurements. The authors then used these hybrid materials to perform a sandwich assay targeting an HIV-1 antibody using fluorescent detection and biotinylated peptides immobilized using the bioaffinity of biotin-neutravidin. They found a limit of detection similar to arrays on glass surfaces and believed that this plastic biochip platform may be used for the development of disposable immunosensing and diagnostic applications.

  2. The commercialization of plastic surgery.

    Science.gov (United States)

    Swanson, Eric

    2013-09-01

    The last decade has brought a major challenge to the traditional practice of plastic surgery from corporations that treat plastic surgery as a commercial product and market directly to the public. This corporate medicine model may include promotion of a trademarked procedure or device, national advertising that promises stunning results, sales consultants, and claims of innovation, superiority, and improved safety. This article explores the ethics of this business practice and whether corporate medicine is a desirable model for patients and plastic surgeons.

  3. Recycling of plastic: accounting of greenhouse gases and global warming contributions.

    Science.gov (United States)

    Astrup, Thomas; Fruergaard, Thilde; Christensen, Thomas H

    2009-11-01

    Major greenhouse gas (GHG) emissions related to plastic waste recycling were evaluated with respect to three management alternatives: recycling of clean, single-type plastic, recycling of mixed/contaminated plastic, and use of plastic waste as fuel in industrial processes. Source-separated plastic waste was received at a material recovery facility (MRF) and processed for granulation and subsequent downstream use. In the three alternatives, plastic was assumed to be substituting virgin plastic in new products, wood in low-strength products (outdoor furniture, fences, etc.), and coal or fuel oil in the case of energy utilization. GHG accounting was organized in terms of indirect upstream emissions (e.g. provision of energy, fuels, and materials), direct emissions at the MRF (e.g. fuel combustion), and indirect downstream emissions (e.g. avoided emissions from production of virgin plastic, wood, or coal/oil). Combined, upstream and direct emissions were estimated to be roughly between 5 and 600 kg CO(2)-eq. tonne( -1) of plastic waste depending on treatment at the MRF and CO(2) emissions from electricity production. Potential downstream savings arising from substitution of virgin plastic, wood, and energy fuels were estimated to be around 60- 1600 kg CO(2)-eq. tonne( -1) of plastic waste depending on substitution ratios and CO(2) emissions from electricity production. Based on the reviewed data, it was concluded that substitution of virgin plastic should be preferred. If this is not viable due to a mixture of different plastic types and/or contamination, the plastic should be used for energy utilization. Recycling of plastic waste for substitution of other materials such as wood provided no savings with respect to global warming.

  4. Evolution of phenotypic plasticity and environmental tolerance of a labile quantitative character in a fluctuating environment.

    Science.gov (United States)

    Lande, R

    2014-05-01

    Quantitative genetic models of evolution of phenotypic plasticity are used to derive environmental tolerance curves for a population in a changing environment, providing a theoretical foundation for integrating physiological and community ecology with evolutionary genetics of plasticity and norms of reaction. Plasticity is modelled for a labile quantitative character undergoing continuous reversible development and selection in a fluctuating environment. If there is no cost of plasticity, a labile character evolves expected plasticity equalling the slope of the optimal phenotype as a function of the environment. This contrasts with previous theory for plasticity influenced by the environment at a critical stage of early development determining a constant adult phenotype on which selection acts, for which the expected plasticity is reduced by the environmental predictability over the discrete time lag between development and selection. With a cost of plasticity in a labile character, the expected plasticity depends on the cost and on the environmental variance and predictability averaged over the continuous developmental time lag. Environmental tolerance curves derived from this model confirm traditional assumptions in physiological ecology and provide new insights. Tolerance curve width increases with larger environmental variance, but can only evolve within a limited range. The strength of the trade-off between tolerance curve height and width depends on the cost of plasticity. Asymmetric tolerance curves caused by male sterility at high temperature are illustrated. A simple condition is given for a large transient increase in plasticity and tolerance curve width following a sudden change in average environment.

  5. Plastics recycling: challenges and opportunities

    National Research Council Canada - National Science Library

    Jefferson Hopewell; Robert Dvorak; Edward Kosior

    2009-01-01

    .... Advances in technologies and systems for the collection, sorting and reprocessing of recyclable plastics are creating new opportunities for recycling, and with the combined actions of the public...

  6. Americium behaviour in plastic vessels

    Energy Technology Data Exchange (ETDEWEB)

    Legarda, F.; Herranz, M. [Departamento de Ingenieria Nuclear y Mecanica de Fluidos, Escuela Tecnica Superior de Ingenieria de Bilbao, Universidad del Pais Vasco (UPV/EHU), Alameda de Urquijo s/n, 48013 Bilbao (Spain); Idoeta, R., E-mail: raquel.idoeta@ehu.e [Departamento de Ingenieria Nuclear y Mecanica de Fluidos, Escuela Tecnica Superior de Ingenieria de Bilbao, Universidad del Pais Vasco (UPV/EHU), Alameda de Urquijo s/n, 48013 Bilbao (Spain); Abelairas, A. [Departamento de Ingenieria Nuclear y Mecanica de Fluidos, Escuela Tecnica Superior de Ingenieria de Bilbao, Universidad del Pais Vasco (UPV/EHU), Alameda de Urquijo s/n, 48013 Bilbao (Spain)

    2010-07-15

    The adsorption of {sup 241}Am dissolved in water in different plastic storage vessels was determined. Three different plastics were investigated with natural and distilled waters and the retention of {sup 241}Am by these plastics was studied. The same was done by varying vessel agitation time, vessel agitation speed, surface/volume ratio of water in the vessels and water pH. Adsorptions were measured to be between 0% and 70%. The adsorption of {sup 241}Am is minimized with no water agitation, with PET or PVC plastics, and by water acidification.

  7. Thermoinduced plastic flow and shape memory effects

    Directory of Open Access Journals (Sweden)

    Xiao Heng

    2011-01-01

    Full Text Available We propose an enhanced form of thermocoupled J2-flow models of finite deformation elastoplasticity with temperature-dependent yielding and hardening behaviour. The thermomechanical constitutive structure of these models is rendered free and explicit in the rigorous sense of thermodynamic consistency. Namely, with a free energy function explicitly introduced in terms of almost any given form of the thermomechanical constitutive functions, the requirements from the second law are identically fulfilled with positive internal dissipation. We study the case when a dependence of yielding and hardening on temperature is given and demonstrate that thermosensitive yielding with anisotropic hardening may give rise to appreciable plastic flow either in a process of heating or in a cyclic process of heating/cooling, thus leading to the findings of one- and two-way thermoinduced plastic flow. We then show that such theoretical findings turn out to be the effects found in shape memory materials, such as one- and two-way memory effects. Thus, shape memory effects may be explained to be thermoinduced plastic flow resulting from thermosensitive yielding and hardening behaviour. These and other relevant facts may suggest that, from a phenomenological standpoint, thermocoupled elastoplastic J2-flow models with thermosensitive yielding and hardening may furnish natural, straightforward descriptions of thermomechanical behaviour of shape memory materials.

  8. [Erythropoietin in plastic surgery].

    Science.gov (United States)

    Günter, C I; Rezaeian, F; Harder, Y; Lohmeyer, J A; Egert, S; Bader, A; Schilling, A F; Machens, H-G

    2013-04-01

    EPO is an autologous hormone, which is known to regulate erythropoiesis. For 30 years it has been used for the therapy of diverse forms of anaemia, such as renal anaemia, tumour-related anaemias, etc. Meanwhile, a multitude of scientific publications were able to demonstrate its pro-regenerative effects after trauma. These include short-term effects such as the inhibition of the "primary injury response" or apoptosis, and mid- and long-term effects for example the stimulation of stem cell recruitment, growth factor production, angiogenesis and re-epithelialisation. Known adverse reactions are increases of thromboembolic events and blood pressure, as well as a higher mortality in patients with tumour anaemias treated with EPO. Scientific investigations of EPO in the field of plastic surgery included: free and local flaps, nerve regeneration, wound healing enhancement after dermal thermal injuries and in chronic wounds.Acute evidence for the clinical use of EPO in the field of plastic surgery is still not satisfactory, due to the insufficient number of Good Clinical Practice (GCP)-conform clinical trials. Thus, the initiation of more scientifically sound trials is indicated.

  9. Optogenetics and synaptic plasticity.

    Science.gov (United States)

    Xie, Yu-feng; Jackson, Michael F; Macdonald, John F

    2013-11-01

    The intricate and complex interaction between different populations of neurons in the brain has imposed limits on our ability to gain detailed understanding of synaptic transmission and its integration when employing classical electrophysiological approaches. Indeed, electrical field stimulation delivered via traditional microelectrodes does not permit the targeted, precise and selective control of neuronal activity amongst a varied population of neurons and their inputs (eg, cholinergic, dopaminergic or glutamatergic neurons). Recently established optogenetic techniques overcome these limitations allowing precise control of the target neuron populations, which is essential for the elucidation of the neural substrates underlying complex animal behaviors. Indeed, by introducing light-activated channels (ie, microbial opsin genes) into specific neuronal populations, optogenetics enables non-invasive optical control of specific neurons with milliseconds precision. These approaches can readily be applied to freely behaving live animals. Recently there is increased interests in utilizing optogenetics tools to understand synaptic plasticity and learning/memory. Here, we summarize recent progress in applying optogenetics in in the study of synaptic plasticity.

  10. Physics of Friction in Disposable Plastic Syringes

    Science.gov (United States)

    Liebmann-Vinson, A.; Vogler, E. A.; Martin, D. A.; Montgomery, D. B.; Sugg, H. W.; Monahan, L. A.

    1997-03-01

    Nosocomial applications of disposable plastic syringes demand excellent frictional behavior with no stick-slip over a broad velocity range and, simultaneously, a tight seal between stopper and barrel. However, when used in syringe pumps at slow injection speeds, stick-slip motion is frequently observed and high "break-out" forces are often necessary to initiate plunger movement after extended storage times. We have traced this frictional behavior to a velocity-dependent interaction between the elastomeric stopper and the plastic syringe barrel mediated by the syringe lubricant, almost universally a polydimethyl siloxane fluid. Lubricant properties were altered by crosslinking the surface of the silicone oil in an oxygen plasma. Changes in surface chemistry and morphology of the crosslinked oil were correlated with changes in frictional performance.

  11. Nonlinear plastic modes in disordered solids.

    Science.gov (United States)

    Gartner, Luka; Lerner, Edan

    2016-01-01

    We propose a theoretical framework within which a robust micromechanical definition of precursors to plastic instabilities, often termed soft spots, naturally emerges. They are shown to be collective displacements (modes) z[over ̂] that correspond to local minima of a barrier function b(z[over ̂]), which depends solely on inherent structure information. We demonstrate how some heuristic searches for local minima of b(z[over ̂]) can a priori detect the locus and geometry of imminent plastic instabilities with remarkable accuracy, at strains as large as γ_{c}-γ∼10^{-2} away from the instability strain γ_{c}. Our findings suggest that the a priori detection of the entire field of soft spots can be effectively carried out by a systematic investigation of the landscape of b(z[over ̂]).

  12. Plasticity and rectangularity in survival curves

    Science.gov (United States)

    Weon, Byung Mook; Je, Jung Ho

    2011-09-01

    Living systems inevitably undergo a progressive deterioration of physiological function with age and an increase of vulnerability to disease and death. To maintain health and survival, living systems should optimize survival strategies with adaptive interactions among molecules, cells, organs, individuals, and environments, which arises plasticity in survival curves of living systems. In general, survival dynamics in a population is mathematically depicted by a survival rate, which monotonically changes from 1 to 0 with age. It would be then useful to find an adequate function to describe complicated survival dynamics. Here we describe a flexible survival function, derived from the stretched exponential function by adopting an age-dependent shaping exponent. We note that the exponent is associated with the fractal-like scaling in cumulative mortality rate. The survival function well depicts general features in survival curves; healthy populations exhibit plasticity and evolve towards rectangular-like survival curves, as examples in humans or laboratory animals.

  13. Dynamics and plasticity of spinal locomotor circuits.

    Science.gov (United States)

    El Manira, Abdeljabbar

    2014-12-01

    Spinal circuits generate coordinated locomotor movements. These hardwired circuits are supplemented with neuromodulation that provide the necessary flexibility for animals to move smoothly through their environment. This review will highlight some recent insights gained in understanding the functional dynamics and plasticity of the locomotor circuits. First the mechanisms governing the modulation of the speed of locomotion will be discussed. Second, advantages of the modular organization of the locomotor networks with multiple circuits engaged in a task-dependent manner will be examined. Finally, the neuromodulation and the resulting plasticity of the locomotor circuits will be summarized with an emphasis on endocannabinoids and nitric oxide. The intention is to extract general principles of organization and discuss some onto-genetic and phylogenetic divergences.

  14. Stochastic synaptic plasticity with memristor crossbar arrays

    KAUST Repository

    Naous, Rawan

    2016-11-01

    Memristive devices have been shown to exhibit slow and stochastic resistive switching behavior under low-voltage, low-current operating conditions. Here we explore such mechanisms to emulate stochastic plasticity in memristor crossbar synapse arrays. Interfaced with integrate-and-fire spiking neurons, the memristive synapse arrays are capable of implementing stochastic forms of spike-timing dependent plasticity which parallel mean-rate models of stochastic learning with binary synapses. We present theory and experiments with spike-based stochastic learning in memristor crossbar arrays, including simplified modeling as well as detailed physical simulation of memristor stochastic resistive switching characteristics due to voltage and current induced filament formation and collapse. © 2016 IEEE.

  15. [Gingival recessions and periodontal plastic surgery].

    Science.gov (United States)

    de Quincey, G de; Padmos, J A D; Renkema, A M

    2015-11-01

    Periodontal plastic surgery is defined as the set of surgical procedures that are performed to prevent or correct developmental disorders and anatomical, traumatic and pathological abnormalities of the gingiva, alveolar mucosa, and alveolar bone. Root coverage procedures fall under this term and have been applied for more than fifty years with varying degrees of success. There are several indications for the treatment of gingival recessions. When the treatment of choice - a conservative approach - offers no solace (any more), gingival recessions can be treated by applying periodontal plastic surgery. The goal of this surgery is complete recovery of the anatomical structures in the area of the recession. To this end several surgical techniques have been developed during the last decades. The choice of a particular technique depends on various factors, such as the number of defects, their size and the amount of keratinized gingiva around the defect.

  16. Glutamatergic metabolites are associated with visual plasticity in humans.

    Science.gov (United States)

    Wijtenburg, S Andrea; West, Jeffrey; Korenic, Stephanie A; Kuhney, Franchesca; Gaston, Frank E; Chen, Hongji; Roberts, Meredith; Kochunov, Peter; Hong, L Elliot; Rowland, Laura M

    2017-02-10

    Long-term potentiation (LTP) is a basic cellular mechanism underlying learning and memory. LTP-like plasticity in the visual cortex can be induced by high frequency visual stimulation in rodents and humans. Since glutamate plays a fundamental role in LTP, this study investigated if visual cortical glutamate and glutamine levels, measured by proton magnetic resonance spectroscopy (MRS), relate to visual plasticity in humans. Since plasticity requires a delicate excitation and inhibition balance, GABA was also explored. Eighteen healthy participants completed MRS and a visual fMRI paradigm. Results revealed enhanced fMRI activations after high frequency visual stimulation, suggesting visual plasticity occurred. Higher activations were associated with higher resting glutamine levels after family wise error-correction. Exploratory analyses revealed that higher resting glutamate and GABA levels were associated with visual plasticity, suggesting there may be a critical excitation-inhibition balance necessary for experience dependent plasticity. This is the first empirical evidence that resting glutamine levels and potentially glutamate and GABA levels are associated with visual plasticity in humans.

  17. Endocrine regulation of predator-induced phenotypic plasticity.

    Science.gov (United States)

    Dennis, Stuart R; LeBlanc, Gerald A; Beckerman, Andrew P

    2014-11-01

    Elucidating the developmental and genetic control of phenotypic plasticity remains a central agenda in evolutionary ecology. Here, we investigate the physiological regulation of phenotypic plasticity induced by another organism, specifically predator-induced phenotypic plasticity in the model ecological and evolutionary organism Daphnia pulex. Our research centres on using molecular tools to test among alternative mechanisms of developmental control tied to hormone titres, receptors and their timing in the life cycle. First, we synthesize detail about predator-induced defenses and the physiological regulation of arthropod somatic growth and morphology, leading to a clear prediction that morphological defences are regulated by juvenile hormone and life-history plasticity by ecdysone and juvenile hormone. We then show how a small network of genes can differentiate phenotype expression between the two primary developmental control pathways in arthropods: juvenoid and ecdysteroid hormone signalling. Then, by applying an experimental gradient of predation risk, we show dose-dependent gene expression linking predator-induced plasticity to the juvenoid hormone pathway. Our data support three conclusions: (1) the juvenoid signalling pathway regulates predator-induced phenotypic plasticity; (2) the hormone titre (ligand), rather than receptor, regulates predator-induced developmental plasticity; (3) evolution has favoured the harnessing of a major, highly conserved endocrine pathway in arthropod development to regulate the response to cues about changing environments (risk) from another organism (predator).

  18. Sustainable reverse logistics for household plastic waste

    NARCIS (Netherlands)

    Bing, X.

    2014-01-01

    Summary of the thesis titled “Sustainable Reverse Logistics for Household Plastic Waste” PhD Candidate: Xiaoyun Bing Recycled plastic can be used in the manufacturing of plastic products to reduce the use of virgin plastics material. The cost of recycled plastics is usually lower than th

  19. Sustainable reverse logistics for household plastic waste

    NARCIS (Netherlands)

    Bing, X.

    2014-01-01

    Summary of the thesis titled “Sustainable Reverse Logistics for Household Plastic Waste” PhD Candidate: Xiaoyun Bing Recycled plastic can be used in the manufacturing of plastic products to reduce the use of virgin plastics material. The cost of recycled plastics is usually lower than

  20. Sustainable reverse logistics for household plastic waste

    NARCIS (Netherlands)

    Bing, X.

    2014-01-01

    Summary of the thesis titled “Sustainable Reverse Logistics for Household Plastic Waste” PhD Candidate: Xiaoyun Bing Recycled plastic can be used in the manufacturing of plastic products to reduce the use of virgin plastics material. The cost of recycled plastics is usually lower than th

  1. Plastics recycling: challenges and opportunities.

    Science.gov (United States)

    Hopewell, Jefferson; Dvorak, Robert; Kosior, Edward

    2009-07-27

    Plastics are inexpensive, lightweight and durable materials, which can readily be moulded into a variety of products that find use in a wide range of applications. As a consequence, the production of plastics has increased markedly over the last 60 years. However, current levels of their usage and disposal generate several environmental problems. Around 4 per cent of world oil and gas production, a non-renewable resource, is used as feedstock for plastics and a further 3-4% is expended to provide energy for their manufacture. A major portion of plastic produced each year is used to make disposable items of packaging or other short-lived products that are discarded within a year of manufacture. These two observations alone indicate that our current use of plastics is not sustainable. In addition, because of the durability of the polymers involved, substantial quantities of discarded end-of-life plastics are accumulating as debris in landfills and in natural habitats worldwide. Recycling is one of the most important actions currently available to reduce these impacts and represents one of the most dynamic areas in the plastics industry today. Recycling provides opportunities to reduce oil usage, carbon dioxide emissions and the quantities of waste requiring disposal. Here, we briefly set recycling into context against other waste-reduction strategies, namely reduction in material use through downgauging or product reuse, the use of alternative biodegradable materials and energy recovery as fuel. While plastics have been recycled since the 1970s, the quantities that are recycled vary geographically, according to plastic type and application. Recycling of packaging materials has seen rapid expansion over the last decades in a number of countries. Advances in technologies and systems for the collection, sorting and reprocessing of recyclable plastics are creating new opportunities for recycling, and with the combined actions of the public, industry and governments it

  2. Plastics recycling: challenges and opportunities

    Science.gov (United States)

    Hopewell, Jefferson; Dvorak, Robert; Kosior, Edward

    2009-01-01

    Plastics are inexpensive, lightweight and durable materials, which can readily be moulded into a variety of products that find use in a wide range of applications. As a consequence, the production of plastics has increased markedly over the last 60 years. However, current levels of their usage and disposal generate several environmental problems. Around 4 per cent of world oil and gas production, a non-renewable resource, is used as feedstock for plastics and a further 3–4% is expended to provide energy for their manufacture. A major portion of plastic produced each year is used to make disposable items of packaging or other short-lived products that are discarded within a year of manufacture. These two observations alone indicate that our current use of plastics is not sustainable. In addition, because of the durability of the polymers involved, substantial quantities of discarded end-of-life plastics are accumulating as debris in landfills and in natural habitats worldwide. Recycling is one of the most important actions currently available to reduce these impacts and represents one of the most dynamic areas in the plastics industry today. Recycling provides opportunities to reduce oil usage, carbon dioxide emissions and the quantities of waste requiring disposal. Here, we briefly set recycling into context against other waste-reduction strategies, namely reduction in material use through downgauging or product reuse, the use of alternative biodegradable materials and energy recovery as fuel. While plastics have been recycled since the 1970s, the quantities that are recycled vary geographically, according to plastic type and application. Recycling of packaging materials has seen rapid expansion over the last decades in a number of countries. Advances in technologies and systems for the collection, sorting and reprocessing of recyclable plastics are creating new opportunities for recycling, and with the combined actions of the public, industry and governments it

  3. Learning through ferroelectric domain dynamics in solid-state synapses

    Science.gov (United States)

    Boyn, Sören; Grollier, Julie; Lecerf, Gwendal; Xu, Bin; Locatelli, Nicolas; Fusil, Stéphane; Girod, Stéphanie; Carrétéro, Cécile; Garcia, Karin; Xavier, Stéphane; Tomas, Jean; Bellaiche, Laurent; Bibes, Manuel; Barthélémy, Agnès; Saïghi, Sylvain; Garcia, Vincent

    2017-04-01

    In the brain, learning is achieved through the ability of synapses to reconfigure the strength by which they connect neurons (synaptic plasticity). In promising solid-state synapses called memristors, conductance can be finely tuned by voltage pulses and set to evolve according to a biological learning rule called spike-timing-dependent plasticity (STDP). Future neuromorphic architectures will comprise billions of such nanosynapses, which require a clear understanding of the physical mechanisms responsible for plasticity. Here we report on synapses based on ferroelectric tunnel junctions and show that STDP can be harnessed from inhomogeneous polarization switching. Through combined scanning probe imaging, electrical transport and atomic-scale molecular dynamics, we demonstrate that conductance variations can be modelled by the nucleation-dominated reversal of domains. Based on this physical model, our simulations show that arrays of ferroelectric nanosynapses can autonomously learn to recognize patterns in a predictable way, opening the path towards unsupervised learning in spiking neural networks.

  4. Neural field theory of plasticity in the cerebral cortex.

    Science.gov (United States)

    Fung, P K; Haber, A L; Robinson, P A

    2013-02-07

    A generalized timing-dependent plasticity rule is incorporated into a recent neural field theory to explore synaptic plasticity in the cerebral cortex, with both excitatory and inhibitory populations included. Analysis in the time and frequency domains reveals that cortical network behavior gives rise to a saddle-node bifurcation and resonant frequencies, including a gamma-band resonance. These system resonances constrain cortical synaptic dynamics and divide it into four classes, which depend on the type of synaptic plasticity window. Depending on the dynamical class, synaptic strengths can either have a stable fixed point, or can diverge in the absence of a separate saturation mechanism. Parameter exploration shows that time-asymmetric plasticity windows, which are signatures of spike-timing dependent plasticity, enable the richest variety of synaptic dynamics to occur. In particular, we predict a zone in parameter space which may allow brains to attain the marginal stability phenomena observed experimentally, although additional regulatory mechanisms may be required to maintain these parameters.

  5. Molecular bonding characteristics of Self-plasticized bamboo composites.

    Science.gov (United States)

    Xue, Qiu; Peng, Wanxi; Ohkoshi, Makoto

    2014-07-01

    Bamboo biomass fibers were gradually separated, prepared, and then self-plasticized for immune composites. The molecular bonding characteristics of the self-plasticized bamboo composites were investigated by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), and thermo gravimetric analysis (TG). The important results were as follows. (1) During self-plasticizing of bamboo biomass, the cross-linking between celluloses mainly depended on carboxylic acid anhydrides and carboxylic acid esters, that between cellulose and lignin depended on carboxylic acid esters and C=O groups of aliphatic hydrocarbons, and that of hemi cellulose had a ether bond and ester bond bridging effect between lignin and cellulose. The cross-linking effects of hemi cellulose, lignin, and cellulose could be stacked and coupled. (2) After self-plasticization, the crystallinity of the lingo cellulosic biomass, lignin cellulose, and cellulose were increased by 5.8%, 2.28%, and 11.67%, respectively. While the TG curves of all samples were basically similar in shape, the weight loss rate turning points of the self-plasticized samples were delayed compared with those of the bamboo biomass fibers. This result demonstrated that the molecular integration of the bamboo biomass was increased after self-plasticization, and confirmed that bond cross-linking between the hemi cellulose, lignin and cellulose of the bamboo biomass had occurred.

  6. Pannexin 1 regulates bidirectional hippocampal synaptic plasticity in adult mice

    Science.gov (United States)

    Ardiles, Alvaro O.; Flores-Muñoz, Carolina; Toro-Ayala, Gabriela; Cárdenas, Ana M.; Palacios, Adrian G.; Muñoz, Pablo; Fuenzalida, Marco; Sáez, Juan C.; Martínez, Agustín D.

    2014-01-01

    The threshold for bidirectional modification of synaptic plasticity is known to be controlled by several factors, including the balance between protein phosphorylation and dephosphorylation, postsynaptic free Ca2+ concentration and NMDA receptor (NMDAR) composition of GluN2 subunits. Pannexin 1 (Panx1), a member of the integral membrane protein family, has been shown to form non-selective channels and to regulate the induction of synaptic plasticity as well as hippocampal-dependent learning. Although Panx1 channels have been suggested to play a role in excitatory long-term potentiation (LTP), it remains unknown whether these channels also modulate long-term depression (LTD) or the balance between both types of synaptic plasticity. To study how Panx1 contributes to excitatory synaptic efficacy, we examined the age-dependent effects of eliminating or blocking Panx1 channels on excitatory synaptic plasticity within the CA1 region of the mouse hippocampus. By using different protocols to induce bidirectional synaptic plasticity, Panx1 channel blockade or lack of Panx1 were found to enhance LTP, whereas both conditions precluded the induction of LTD in adults, but not in young animals. These findings suggest that Panx1 channels restrain the sliding threshold for the induction of synaptic plasticity and underlying brain mechanisms of learning and memory. PMID:25360084

  7. Pannexin 1 Regulates Bidirectional Hippocampal Synaptic Plasticity in Adult Mice

    Directory of Open Access Journals (Sweden)

    Alvaro O. Ardiles

    2014-10-01

    Full Text Available The threshold for bidirectional modification of synaptic plasticity is known to be controlled by several factors, including the balance between protein phosphorylation and dephosphorylation, postsynaptic free Ca2+ concentration and NMDA receptor (NMDAR composition of GluN2 subunits. Pannexin 1 (Panx1, a member of the integral membrane protein family, has been shown to form non-selective channels and to regulate the induction of synaptic plasticity as well as hippocampal-dependent learning. Although Panx1 channels have been suggested to play a role in excitatory long-term potentiation (LTP, it remains unknown whether these channels also modulate long-term depression (LTD or the balance between both types of synaptic plasticity. To study how Panx1 contributes to excitatory synaptic efficacy, we examined the age-dependent effects of eliminating or blocking Panx1 channels on excitatory synaptic plasticity within the CA1 region of the mouse hippocampus. By using different protocols to induce bidirectional synaptic plasticity, Panx1 channel blockade or lack of Panx1 were found to enhance LTP, whereas both conditions precluded the induction of LTD in adults, but not in young animals. These findings suggest that Panx1 channels restrain the sliding threshold for the induction of synaptic plasticity and underlying brain mechanisms of learning and memory.

  8. Green’s function molecular dynamics meets discrete dislocation plasticity

    Science.gov (United States)

    Venugopalan, Syam P.; Müser, Martin H.; Nicola, Lucia

    2017-09-01

    Metals deform plastically at the asperity level when brought in contact with a counter body even when the nominal contact pressure is small. Modeling the plasticity of solids with rough surfaces is challenging due to the multi-scale nature of surface roughness and the length-scale dependence of plasticity. While discrete-dislocation plasticity (DDP) simulations capture size-dependent plasticity by keeping track of the motion of individual dislocations, only simple two-dimensional surface geometries have so far been studied with DDP. The main computational bottleneck in contact problems modeled by DDP is the calculation of the dislocation image fields. We address this issue by combining two-dimensional DDP with Green’s function molecular dynamics. The resulting method allows for an efficient boundary-value-method based treatment of elasticity in the presence of dislocations. We demonstrate that our method captures plasticity quantitatively from single to many dislocations and that it scales more favorably with system size than conventional methods. We also derive the relevant Green’s functions for elastic slabs of finite width allowing arbitrary boundary conditions on top and bottom surface to be simulated.

  9. Spatiotemporal computations of an excitable and plastic brain: neuronal plasticity leads to noise-robust and noise-constructive computations.

    Science.gov (United States)

    Toutounji, Hazem; Pipa, Gordon

    2014-03-01

    It is a long-established fact that neuronal plasticity occupies the central role in generating neural function and computation. Nevertheless, no unifying account exists of how neurons in a recurrent cortical network learn to compute on temporally and spatially extended stimuli. However, these stimuli constitute the norm, rather than the exception, of the brain's input. Here, we introduce a geometric theory of learning spatiotemporal computations through neuronal plasticity. To that end, we rigorously formulate the problem of neural representations as a relation in space between stimulus-induced neural activity and the asymptotic dynamics of excitable cortical networks. Backed up by computer simulations and numerical analysis, we show that two canonical and widely spread forms of neuronal plasticity, that is, spike-timing-dependent synaptic plasticity and intrinsic plasticity, are both necessary for creating neural representations, such that these computations become realizable. Interestingly, the effects of these forms of plasticity on the emerging neural code relate to properties necessary for both combating and utilizing noise. The neural dynamics also exhibits features of the most likely stimulus in the network's spontaneous activity. These properties of the spatiotemporal neural code resulting from plasticity, having their grounding in nature, further consolidate the biological relevance of our findings.

  10. Genetic Analysis of Micro-environmental Plasticity in Drosophila melanogaster

    DEFF Research Database (Denmark)

    Morgante, Fabio; Sorensen, Daniel A; Sørensen, Peter

    Quantitative genetic models recognize the potential for genotype by environment interaction, whereby different genotypes have different plastic responses to changes in macro-environmental conditions. Recently, it has been recognized that micro-environmental plasticity (‘residual’ variance) may also...... be genetically variable. This study utilized the Drosophila Genetic Reference Panel (DGRP) to accurately estimate the genetic variance of micro-environmental plasticity for chill coma recovery time and startle response. Estimates of broad sense heritabilities for both traits are substantial (from 0.51 to 0.......77), of the same order as the heritability at the level of the trait mean for startle response and even larger for chill coma recovery. Genome wide association analyses identified molecular variants (from 15 to 31 depending on the sex and the trait) associated with micro-environmental plasticity. These findings...

  11. Becoming a mother-circuit plasticity underlying maternal behavior.

    Science.gov (United States)

    Elyada, Yishai M; Mizrahi, Adi

    2015-12-01

    The transition to motherhood is a dramatic event during the lifetime of many animals. In mammals, motherhood is accompanied by hormonal changes in the brain that start during pregnancy, followed by experience dependent plasticity after parturition. Together, these changes prime the nervous system of the mother for efficient nurturing of her offspring. Recent work has described how neural circuits are modified during the transition to motherhood. Here we discuss changes in the auditory cortex during motherhood as a model for maternal plasticity in sensory systems. We compare classical plasticity paradigms with changes that arise naturally in mothers, highlighting current efforts to establish a mechanistic understanding of plasticity and its different components in the context of maternal behavior.

  12. Influence of thickness on properties of plasticized oat starch films

    Directory of Open Access Journals (Sweden)

    Melicia Cintia Galdeano

    2013-08-01

    Full Text Available The aim of this study was to investigate the effect of thickness (between 80 and 120 µm on apparent opacity, water vapor permeability and mechanical properties (tensile and puncture of oat starch films plasticized with glycerol, sorbitol, glycerol:sorbitol mixture, urea and sucrose. Films were stored under 11, 57, 76 and 90% relative humidity (RH to study the mechanical properties. It was observed that the higher the thickness, the higher was the opacity values. Films without the plasticizer were more opaque in comparison with the plasticized ones. Glycerol:sorbitol films presented increased elongation with increasing thickness at all RH. Puncture force showed a strong dependence on the film thickness, except for the films plasticized with sucrose. In general, thickness did not affect the water permeability.

  13. Genetic Analysis of Micro-environmental Plasticity in Drosophila melanogaster

    DEFF Research Database (Denmark)

    Morgante, Fabio; Sorensen, Daniel A; Sørensen, Peter;

    Quantitative genetic models recognize the potential for genotype by environment interaction, whereby different genotypes have different plastic responses to changes in macro-environmental conditions. Recently, it has been recognized that micro-environmental plasticity (‘residual’ variance) may also...... be genetically variable. This study utilized the Drosophila Genetic Reference Panel (DGRP) to accurately estimate the genetic variance of micro-environmental plasticity for chill coma recovery time and startle response. Estimates of broad sense heritabilities for both traits are substantial (from 0.51 to 0.......77), of the same order as the heritability at the level of the trait mean for startle response and even larger for chill coma recovery. Genome wide association analyses identified molecular variants (from 15 to 31 depending on the sex and the trait) associated with micro-environmental plasticity. These findings...

  14. Strain gradient crystal plasticity effects on flow localization

    DEFF Research Database (Denmark)

    Borg, Ulrik

    2007-01-01

    In metal grains one of the most important failure mechanisms involves shear band localization. As the band width is small, the deformations are affected by material length scales. To study localization in single grains a rate-dependent crystal plasticity formulation for finite strains is presented...... in the absence of strain gradients. The model is used to study the effect of an internal material length scale on the localization of plastic flow in shear bands in a single crystal under plane strain tension. It is shown that the mesh sensitivity is removed when using the nonlocal material model considered...... for metals described by the reformulated Fleck-Hutchinson strain gradient plasticity theory. The theory is implemented numerically within a finite element framework using slip rate increments and displacement increments as state variables. The formulation reduces to the classical crystal plasticity theory...

  15. Regulation of Parvalbumin Basket cell plasticity in rule learning.

    Science.gov (United States)

    Caroni, Pico

    2015-04-24

    Local inhibitory Parvalbumin (PV)-expressing Basket cell networks shift to one of two possible opposite configurations depending on whether behavioral learning involves acquisition of new information or consolidation of validated rules. This reflects the existence of PV Basket cell subpopulations with distinct schedules of neurogenesis, output target neurons and roles in learning. Plasticity of hippocampal early-born PV neurons is recruited in rule consolidation, whereas plasticity of late-born PV neurons is recruited in new information acquisition. This involves regulation of early-born PV neuron plasticity specifically through excitation, and of late-born PV neuron plasticity specifically through inhibition. Therefore, opposite learning requirements are implemented by distinct local networks involving PV Basket cell subpopulations specifically regulated through inhibition or excitation.

  16. Plastic in North Sea Fish

    NARCIS (Netherlands)

    Foekema, E.M.; Gruijter, de C.; Mergia, M.T.; Franeker, van J.A.; Murk, A.J.; Koelmans, A.A.

    2013-01-01

    To quantify the occurrence of ingested plastic in fish species caught at different geographical positions in the North Sea, and to test whether the fish condition is affected by ingestion of plastics, 1203 individual fish of seven common North Sea species were investigated: herring, gray gurnard, wh

  17. The scope of plastic surgery

    African Journals Online (AJOL)

    2013-08-03

    Aug 3, 2013 ... areas of surgery (especially general surgery), plastic surgeons are arguably the .... Who do you feel are experts in laparoscopic surgery? e (general surgeons) a. Maxillofacial .... of pressure sore. ORIF = open reduction internal fixation. ... Plastic versus cosmetic surgery: What's the difference? Plast Reconstr.

  18. New Life for Old Plastics

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    Recycling joint venture utilizes innovative technology to reuse plastics Recycling,despite its green connotations,can be a messy business.In China,more than 400,000 companies are engaged in plastic recycling,but 70 percent of them are family enterprises,

  19. Computational strain gradient crystal plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2014-01-01

    of plane crystal plasticity are studied: pure shear of a single crystal between rigid platens as well as plastic deformation around cylindrical voids in hexagonal close packed and face centered cubic crystals. Effective in-plane constitutive slip parameters for plane strain deformation of specifically...

  20. Architecture of European Plastic Surgery

    NARCIS (Netherlands)

    Nicolai, J. -P. A.; Banic, A.; Molea, G.; Mazzola, R.; Poell, J. G.

    2006-01-01

    The architecture of European Plastic Surgery was published in 1996 [Nicolai JPA, Scuderi N. Plastic surgical Europe in an organogram. Eur J Plast Surg 1996; 19: 253-6.] It is the objective of this paper to update information of that article. Continuing medical education (CME), science, training,

  1. Plastics for corrosion inhibition

    CERN Document Server

    Goldade, Victor A; Makarevich, Anna V; Kestelman, Vladimir N

    2005-01-01

    The development of polymer composites containing inhibitors of metal corrosion is an important endeavour in modern materials science and technology. Corrosion inhibitors can be located in a polymer matrix in the solid, liquid or gaseous phase. This book details the thermodynamic principles for selecting these components, their compatibility and their effectiveness. The various mechanisms of metal protection – barrier, inhibiting and electromechanical – are considered, as are the conflicting requirements placed on the structure of the combined material. Two main classes of inhibited materials (structural and films/coatings) are described in detail. Examples are given of structural plastics used in friction units subjected to mechano-chemical wear and of polymer films/coatings for protecting metal objects against corrosion.

  2. Universal features of amorphous plasticity

    Science.gov (United States)

    Budrikis, Zoe; Castellanos, David Fernandez; Sandfeld, Stefan; Zaiser, Michael; Zapperi, Stefano

    2017-07-01

    Plastic yielding of amorphous solids occurs by power-law distributed deformation avalanches whose universality is still debated. Experiments and molecular dynamics simulations are hampered by limited statistical samples, and although existing stochastic models give precise exponents, they require strong assumptions about fixed deformation directions, at odds with the statistical isotropy of amorphous materials. Here, we introduce a fully tensorial, stochastic mesoscale model for amorphous plasticity that links the statistical physics of plastic yielding to engineering mechanics. It captures the complex shear patterning observed for a wide variety of deformation modes, as well as the avalanche dynamics of plastic flow. Avalanches are described by universal size exponents and scaling functions, avalanche shapes, and local stability distributions, independent of system dimensionality, boundary and loading conditions, and stress state. Our predictions consistently differ from those of mean-field depinning models, providing evidence that plastic yielding is a distinct type of critical phenomenon.

  3. Phenotypic Plasticity and Species Coexistence.

    Science.gov (United States)

    Turcotte, Martin M; Levine, Jonathan M

    2016-10-01

    Ecologists are increasingly interested in predicting how intraspecific variation and changing trait values impact species interactions and community composition. For many traits, much of this variation is caused by phenotypic plasticity, and thus the impact of plasticity on species coexistence deserves robust quantification. Partly due to a lack of sound theoretical expectations, empirical studies make contradictory claims regarding plasticity effects on coexistence. Our critical review of this literature, framed in modern coexistence theory, reveals that plasticity affects species interactions in ways that could impact stabilizing niche differences and competitive asymmetries. However, almost no study integrates these measures to quantify the net effect of plasticity on species coexistence. To address this challenge, we outline novel empirical approaches grounded in modern theory.

  4. Imaging brain plasticity after trauma

    Institute of Scientific and Technical Information of China (English)

    Zhifeng Kou; Armin Iraji

    2014-01-01

    The brain is highly plastic after stroke or epilepsy;however, there is a paucity of brain plasticity investigation after traumatic brain injury (TBI). This mini review summarizes the most recent evidence of brain plasticity in human TBI patients from the perspective of advanced magnetic resonance imaging. Similar to other forms of acquired brain injury, TBI patients also demonstrat-ed both structural reorganization as well as functional compensation by the recruitment of other brain regions. However, the large scale brain network alterations after TBI are still unknown, and the ifeld is still short of proper means on how to guide the choice of TBI rehabilitation or treat-ment plan to promote brain plasticity. The authors also point out the new direction of brain plas-ticity investigation.

  5. Size effects in crystal plasticity

    DEFF Research Database (Denmark)

    Borg, Ulrik

    2007-01-01

    Numerical analyses of plasticity size effects have been carried out for different problems using a developed strain gradient crystal plasticiy theory. The theory employs higher order stresses as work conjugates to slip gradients and uses higher order boundary conditions. Problems on localization...... of plastic flow in a single crystal, grain boundary effects in a bicrystal, and grain size effects in a polycrystal are studied. Single crystals containing micro-scale voids have also been analyzed at different loading conditions with focus on the stress and deformation fields around the voids, on void...... growth and interaction between neighboring voids, and on a comparison between the developed strain gradient crystal plasticity theory and a discrete dislocation plasticity theory. Furthermore, voids and rigid inclusions in isotropic materials have been studied using a strain gradient plasticity theory...

  6. On innovations in plastic surgery.

    Science.gov (United States)

    Mehta, Hemant

    2009-04-01

    The progress of surgery has been utterly dependent on continuing innovations by surgeon innovators, largely because surgeons work in an environment that is very conducive to innovating. Of all clinicians surgeons excel at improvisations and innovations. The aim of this review is to outline some of my innovations, the circumstances leading to their origin, and to explain some of the fundamental concepts behind those innovations, with a view to inviting and encouraging younger surgeons to consider breaking away - sensibly - from convention at times, and embark on a journey towards innovation. The context and the qualities required of a would-be innovator are explained and the process of innovation itself is analysed. Rigid adherence to prevailing assumptions and practices stifles originality, while adopting a questioning attitude with a smidgen of irreverence facilitates innovation. That an innovation has resulted purely by a chance observation or occurrence - serendipity - may render it less glamorous but never less useful. Innovations in surgical techniques necessitate adoption of a novel pragmatic surgical philosophy. Confined as they are to Oculoplasty, the concepts of innovations cited and illustrated in this review, are equally valid for Plastic surgery and indeed for Surgery in general. Working in a small hospital or an isolated Institution need not be a hindrance to a would-be innovator.

  7. Nano-Ceramic Coated Plastics

    Science.gov (United States)

    Cho, Junghyun

    2013-01-01

    Plastic products, due to their durability, safety, and low manufacturing cost, are now rapidly replacing cookware items traditionally made of glass and ceramics. Despite this trend, some still prefer relatively expensive and more fragile ceramic/glassware because plastics can deteriorate over time after exposure to foods, which can generate odors, bad appearance, and/or color change. Nano-ceramic coatings can eliminate these drawbacks while still retaining the advantages of the plastic, since the coating only alters the surface of the plastic. The surface coating adds functionality to the plastics such as self-cleaning and disinfectant capabilities that result from a photocatalytic effect of certain ceramic systems. These ceramic coatings can also provide non-stick surfaces and higher temperature capabilities for the base plastics without resorting to ceramic or glass materials. Titanium dioxide (TiO2) and zinc oxide (ZnO) are the candidates for a nano-ceramic coating to deposit on the plastics or plastic films used in cookware and kitchenware. Both are wide-bandgap semiconductors (3.0 to 3.2 eV for TiO2 and 3.2 to 3.3 eV for ZnO), so they exhibit a photocatalytic property under ultraviolet (UV) light. This will lead to decomposition of organic compounds. Decomposed products can be easily washed off by water, so the use of detergents will be minimal. High-crystalline film with large surface area for the reaction is essential to guarantee good photocatalytic performance of these oxides. Low-temperature processing (nano-ceramic coatings (TiO2, ZnO) on plastic materials (silicone, Teflon, PET, etc.) that can possess both photocatalytic oxide properties and flexible plastic properties. Processing cost is low and it does not require any expensive equipment investment. Processing can be scalable to current manufacturing infrastructure.

  8. Biodegradability of degradable plastic waste.

    Science.gov (United States)

    Agamuthu, P; Faizura, Putri Nadzrul

    2005-04-01

    Plastic waste constitutes the third largest waste volume in Malaysian municipal solid waste (MSW), next to putrescible waste and paper. The plastic component in MSW from Kuala Lumpur averages 24% (by weight), whereas the national mean is about 15%. The 144 waste dumps in the country receive about 95% of the MSW, including plastic waste. The useful life of the landfills is fast diminishing as the plastic waste stays un-degraded for more than 50 years. In this study the compostability of polyethylene and pro-oxidant additive-based environmentally degradable plastics (EDP) was investigated. Linear low-density polyethylene (LLDPE) samples exposed hydrolytically or oxidatively at 60 degrees C showed that the abiotic degradation path was oxidative rather than hydrolytic. There was a weight loss of 8% and the plastic has been oxidized as shown by the additional carbonyl group exhibited in the Fourier transform infra red (FTIR) Spectrum. Oxidation rate seemed to be influenced by the amount of pro-oxidant additive, the chemical structure and morphology of the plastic samples, and the surface area. Composting studies during a 45-day experiment showed that the percentage elongation (reduction) was 20% for McD samples [high-density polyethylene, (HDPE) with 3% additive] and LL samples (LLDPE with 7% additive) and 18% reduction for totally degradable plastic (TDP) samples (HDPE with 3% additive). Lastly, microbial experiments using Pseudomonas aeroginosa on carbon-free media with degradable plastic samples as the sole carbon source, showed confirmatory results. A positive bacterial growth and a weight loss of 2.2% for degraded polyethylene samples were evident to show that the degradable plastic is biodegradable.

  9. Plasticity and beyond microstructures, crystal-plasticity and phase transitions

    CERN Document Server

    Hackl, Klaus

    2014-01-01

    The book presents the latest findings in experimental plasticity, crystal plasticity, phase transitions, advanced mathematical modeling of finite plasticity and multi-scale modeling. The associated algorithmic treatment is mainly based on finite element formulations for standard (local approach) as well as for non-standard (non-local approach) continua and for pure macroscopic as well as for directly coupled two-scale boundary value problems. Applications in the area of material design/processing are covered, ranging from grain boundary effects in polycrystals and phase transitions to deep-drawing of multiphase steels by directly taking into account random microstructures.

  10. Epigenetic Control of Phenotypic Plasticity in the Filamentous Fungus Neurospora crassa.

    Science.gov (United States)

    Kronholm, Ilkka; Johannesson, Hanna; Ketola, Tarmo

    2016-12-07

    Phenotypic plasticity is the ability of a genotype to produce different phenotypes under different environmental or developmental conditions. Phenotypic plasticity is a ubiquitous feature of living organisms, and is typically based on variable patterns of gene expression. However, the mechanisms by which gene expression is influenced and regulated during plastic responses are poorly understood in most organisms. While modifications to DNA and histone proteins have been implicated as likely candidates for generating and regulating phenotypic plasticity, specific details of each modification and its mode of operation have remained largely unknown. In this study, we investigated how epigenetic mechanisms affect phenotypic plasticity in the filamentous fungus Neurospora crassa By measuring reaction norms of strains that are deficient in one of several key physiological processes, we show that epigenetic mechanisms play a role in homeostasis and phenotypic plasticity of the fungus across a range of controlled environments. In general, effects on plasticity are specific to an environment and mechanism, indicating that epigenetic regulation is context dependent and is not governed by general plasticity genes. Specifically, we found that, in Neurospora, histone methylation at H3K36 affected plastic response to high temperatures, H3K4 methylation affected plastic response to pH, but H3K27 methylation had no effect. Similarly, DNA methylation had only a small effect in response to sucrose. Histone deacetylation mainly decreased reaction norm elevation, as did genes involved in histone demethylation and acetylation. In contrast, the RNA interference pathway was involved in plastic responses to multiple environments.

  11. International policies to reduce plastic marine pollution from single-use plastics (plastic bags and microbeads): A review.

    Science.gov (United States)

    Xanthos, Dirk; Walker, Tony R

    2017-02-18

    Marine plastic pollution has been a growing concern for decades. Single-use plastics (plastic bags and microbeads) are a significant source of this pollution. Although research outlining environmental, social, and economic impacts of marine plastic pollution is growing, few studies have examined policy and legislative tools to reduce plastic pollution, particularly single-use plastics (plastic bags and microbeads). This paper reviews current international market-based strategies and policies to reduce plastic bags and microbeads. While policies to reduce microbeads began in 2014, interventions for plastic bags began much earlier in 1991. However, few studies have documented or measured the effectiveness of these reduction strategies. Recommendations to further reduce single-use plastic marine pollution include: (i) research to evaluate effectiveness of bans and levies to ensure policies are having positive impacts on marine environments; and (ii) education and outreach to reduce consumption of plastic bags and microbeads at source.

  12. Pyrolysis of plastics and tyres wastes

    Energy Technology Data Exchange (ETDEWEB)

    Miranda, Miguel; Costa, Paula; Pinto, Filomena; Gulyurtlu, Ibrahim; Cabrita, Isabel [INETI/DEECA, Lisboa (Portugal)

    2002-07-01

    The main aim of the work is to characterize the nature of liquids produced by pyrolysing various blends of wastes were several mixtures of tyres and plastics wastes were pyrolysed. The plastics wastes used were polyethylene (PE), polypropylene (PP) and polystyrene (PS). The tyre waste also included natural rubber (NR), styrene butadiene rubber (SBR) and butadiene rubber (BR).The influence of the following operating conditions as well as different mixture of wastes on nature of the products was investigated; run temperature: 380-450 deg C, run pressure: 0.2-8.0 MPa, reaction time: 10 to 60 minutes, waste composition: several mixtures of plastics and tyres in different quantities. The final objective was to optimize operating condition to maximize the production of liquids and to achieve selectivity in the nature of the liquids obtained. The results obtained showed that the composition of the end products was highly dependent of the components of the blend of wastes used. Several solvents with different H-donor capacity were also added to the reaction mixture to investigate the nature of liquids formed to verify if a higher degree of selectivity could be achieved with regard to the nature of liquid products. Solvents used included 1,2,3,4 - Tetrahydronaphthalene and 1,2,3,4 - tetrahydroquinoline. Liquids yields obtained so far were found to be very promising, reaching values around 70% (v/v), while gas and residual solid amounts were around 10% (v/v) and 20% (v/v).

  13. Ice sheets on plastically-yielding beds

    Science.gov (United States)

    Hewitt, Ian

    2016-11-01

    Many fast flowing regions of ice sheets are underlain by a layer of water-saturated sediments, or till. The rheology of the till has been the subject of some controversy, with laboratory tests suggesting almost perfectly plastic behaviour (stress independent of strain rate), but many models adopting a pseudo-viscous description. In this work, we consider the behaviour of glaciers underlain by a plastic bed. The ice is treated as a viscous gravity current, on a bed that allows unconstrained slip above a critical yield stress. This simplified description allows rapid sliding, and aims to investigate 'worst-case' scenarios of possible ice-sheet disintegration. The plastic bed results in an approximate ice-sheet geometry that is primarily controlled by force balance, whilst ice velocity is determined from mass conservation (rather than the other way around, as standard models would hold). The stability of various states is considered, and particular attention is given to the pace at which transitions between unstable states can occur. Finally, we observe that the strength of basal tills depends strongly on pore pressure, and combine the model with a description of subglacial hydrology. Implications for the present-day ice sheets in Greenland and Antarctica will be discussed. Funding: ERC Marie Curie FP7 Career Integration Grant.

  14. Reversible phenotypic plasticity with continuous adaptation.

    Science.gov (United States)

    Pfab, Ferdinand; Gabriel, Wilfried; Utz, Margarete

    2016-01-01

    We introduce a novel model for continuous reversible phenotypic plasticity. The model includes a one-dimensional environmental gradient, and we describe performance of an organism as a function of the environmental state by a Gaussian tolerance curve. Organisms are assumed to adapt their tolerance curve after a change of the environmental state. We present a general framework for calculating the genotype fitness if such adaptations happen in a continuous manner and apply the model to a periodically changing environment. Significant differences of our model with previous models for plasticity are the continuity of adaptation, the presence of intermediate phenotypes, that the duration of transformations depends on their extent, fewer restrictions on the distribution of the environment, and a higher robustness with respect to assumptions about environmental fluctuations. Further, we show that continuous reversible plasticity is beneficial mainly when environmental changes occur slow enough so that fully developed phenotypes can be exhibited. Finally we discuss how the model framework can be generalized to a wide variety of biological scenarios from areas that include population dynamics, evolution of environmental tolerance and physiology.

  15. Phenotypic plasticity, costs of phenotypes, and costs of plasticity

    DEFF Research Database (Denmark)

    Callahan, Hilary S; Maughan, Heather; Steiner, Uli

    2008-01-01

    Why are some traits constitutive and others inducible? The term costs often appears in work addressing this issue but may be ambiguously defined. This review distinguishes two conceptually distinct types of costs: phenotypic costs and plasticity costs. Phenotypic costs are assessed from patterns...... of covariation, typically between a focal trait and a separate trait relevant to fitness. Plasticity costs, separable from phenotypic costs, are gauged by comparing the fitness of genotypes with equivalent phenotypes within two environments but differing in plasticity and fitness. Subtleties associated with both...... types of costs are illustrated by a body of work addressing predator-induced plasticity. Such subtleties, and potential interplay between the two types of costs, have also been addressed, often in studies involving genetic model organisms. In some instances, investigators have pinpointed the mechanistic...

  16. Biodegradable plastics from renewable sources.

    Science.gov (United States)

    Flieger, M; Kantorová, M; Prell, A; Rezanka, T; Votruba, J

    2003-01-01

    Plastic waste disposal is a huge ecotechnological problem and one of the approaches to solving this problem is the development of biodegradable plastics. This review summarizes data on their use, biodegradability, commercial reliability and production from renewable resources. Some commercially successful biodegradable plastics are based on chemical synthesis (i.e. polyglycolic acid, polylactic acid, polycaprolactone, and polyvinyl alcohol). Others are products of microbial fermentations (i.e. polyesters and neutral polysaccharides) or are prepared from chemically modified natural products (e.g., starch, cellulose, chitin or soy protein).

  17. Plastics recycling: challenges and opportunities

    OpenAIRE

    Hopewell, Jefferson; Dvorak, Robert; Kosior, Edward

    2009-01-01

    Plastics are inexpensive, lightweight and durable materials, which can readily be moulded into a variety of products that find use in a wide range of applications. As a consequence, the production of plastics has increased markedly over the last 60 years. However, current levels of their usage and disposal generate several environmental problems. Around 4 per cent of world oil and gas production, a non-renewable resource, is used as feedstock for plastics and a further 3–4% is expended to pro...

  18. Circadian Regulation of Synaptic Plasticity

    Directory of Open Access Journals (Sweden)

    Marcos G. Frank

    2016-07-01

    Full Text Available Circadian rhythms refer to oscillations in biological processes with a period of approximately 24 h. In addition to the sleep/wake cycle, there are circadian rhythms in metabolism, body temperature, hormone output, organ function and gene expression. There is also evidence of circadian rhythms in synaptic plasticity, in some cases driven by a master central clock and in other cases by peripheral clocks. In this article, I review the evidence for circadian influences on synaptic plasticity. I also discuss ways to disentangle the effects of brain state and rhythms on synaptic plasticity.

  19. PLASMA GASIFICATION OF WASTE PLASTICS

    Directory of Open Access Journals (Sweden)

    Tadeusz Mączka

    2013-01-01

    Full Text Available The article presents the process of obtaining liquid fuels and fuel gas in the process of plasma processing of organic materials, including waste plastics. The concept of plasma pyrolysis of plastics was presented and on its basis a prototype installation was developed. The article describes a general rule of operating the installation and its elements in the process and basic operation parameters determined during its start-up. Initial results of processing plastics and the directions further investigations are also discussed. The effect of the research is to be the design of effective technology of obtaining fuels from gasification/pyrolysis of organic waste and biomass.

  20. Human mirror neuron system and its plasticity

    Institute of Scientific and Technical Information of China (English)

    Wei Chen; Tifei Yuan; Yin Wang; Jun Ding

    2008-01-01

    The mirror neuron system (MNS) was first discovered in non-human primates; these neurons fire when a monkey performs an action or observes another monkey (or even some people) performing that same action. Recent findings have suggested that neural rehabilitation might be achieved through the activation of the MNS in patients after stroke. We propose two major mechanisms (one involving adult neurogenesis and another involving brain-derived neurotrophic factor) that may underlie the activation, modulation and expe-rience-dependent plasticity in the MNS, for further study on promoting central nerve functional reconstruc-tion and rehabilitation of patients with central nervous system injury.

  1. Improved Barrier Properties in Flexible Plastic Substrates

    Science.gov (United States)

    2009-01-01

    high surface roughness of commercially available plastic substrates such as polyethylene terephthalate ( PET ), polycarbonate (PC) and cyclic olefin...PolyTetraFlouro Ethylene (PTFE), PolyEthylene Terephthalate ( PET ) and PolyEthylene Naphthalate(PEN), the permeation rates are typically >1x103g/m2day for...oxygen and >1g/m2day for water depending on the thickness of the polymer.10 WVTR for a 25nm thick PEN and PET is 6.7 g/m2day11 and 21.3 g/m2day11 and

  2. Recycling of Reinforced Plastics

    Science.gov (United States)

    Adams, R. D.; Collins, Andrew; Cooper, Duncan; Wingfield-Digby, Mark; Watts-Farmer, Archibald; Laurence, Anna; Patel, Kayur; Stevens, Mark; Watkins, Rhodri

    2014-02-01

    This work has shown is that it is possible to recycle continuous and short fibre reinforced thermosetting resins while keeping almost the whole of the original material, both fibres and matrix, within the recyclate. By splitting, crushing hot or cold, and hot forming, it is possible to create a recyclable material, which we designate a Remat, which can then be used to remanufacture other shapes, examples of plates and tubes being demonstrated. Not only can remanufacturing be done, but it has been shown that over 50 % of the original mechanical properties, such as the E modulus, tensile strength, and interlaminar shear strength, can be retained. Four different forms of composite were investigated, a random mat Glass Fibre Reinforced Plastic (GFRP) bathroom component and boat hull, woven glass and carbon fibre cloth impregnated with an epoxy resin, and unidirectional carbon fibre pre-preg. One of the main factors found to affect composite recyclability was the type of resin matrix used in the composite. Thermoset resins tested were shown to have a temperature range around the Glass Transition Temperature (Tg) where they exhibit ductile behaviour, hence aiding reforming of the material. The high-grade carbon fibre prepreg was found to be less easy to recycle than the woven of random fibre laminates. One method of remanufacturing was by heating the Remat to above its glass transition temperature, bending it to shape, and then cooling it. However, unless precautions are taken, the geometric form may revert. This does not happen with the crushed material.

  3. Newton method for the optimization of a new constitutive equation for the plastic flow dependent on the strain. Application to magnesium alloys AZ80 and AZ61; El metodo de Newton para la optimizacion de una nueva ecuacion constitutiva para la fluencia plastica dependiente de la deformacion. Aplicacin a las aleaciones de magnesio AZ80 y AZ61

    Energy Technology Data Exchange (ETDEWEB)

    Gutierrez, V.; Roeorp, R.; Carsi, M.; Ruano, O. A.

    2013-07-01

    A new numerical algorithm has been developed, based on Newton's method, for optimizing the parameters of a new strain dependent constitutive equation, based on the Garofalo equation. The adjustment is direct, with second order algorithms, for an equation derived from that of Garofalo with a nonlinear objective function. This new optimization algorithm has been applied to creep data of two magnesium alloys AZ80 and AZ61, having an unusual plastic behavior. A certain pseudo-stationary exists in the curves studied, in the sense that the usual deformation states are not manifested in an obvious way. The parameters of the new constitutive equation, dependent on strain, have been determined for these alloys. For analyzing the precision of the parameters and the accuracy of modeling of the stress-strain curves, a statistical treatment has been applied which allows assessing the quality of the constitutive equation proposed and the consistency of these parameters. Stress-strain curves have been compared with the modeling results, reaching a good agreement between the experimental data and the resulting modeling. (Author)

  4. Electromigration-induced plasticity and texture in Cu interconnects

    Energy Technology Data Exchange (ETDEWEB)

    Advanced Light Source; Tamura, Nobumichi; Budiman, A. S.; Hau-Riege, C.S.; Besser, P. R.; Marathe, A.; Joo, Y.-C.; Tamura, N.; Patel, J. R.; Nix, W. D.

    2007-10-31

    Plastic deformation has been observed in damascene Cu interconnect test structures during an in-situ electromigration experiment and before the onset of visible microstructural damage (ie. voiding) using a synchrotron technique of white beam X-ray microdiffraction. We show here that the extent of this electromigration-induced plasticity is dependent on the texture of the Cu grains in the line. In lines with strong <111> textures, the extent of plastic deformation is found to be relatively large compared to our plasticity results in the previous study [1] using another set of Cu lines with weaker textures. This is consistent with our earlier observation that the occurrence of plastic deformation in a given grain can be strongly correlated with the availability of a <112> direction of the crystal in the proximity of the direction of the electron flow in the line (within an angle of 10{sup o}). In <111> out-of-plane oriented grains in a damascene interconnect scheme, the crystal plane facing the sidewall tends to be a {l_brace}110{r_brace} plane,[2-4] so as to minimize interfacial energy. Therefore, it is deterministic rather than probabilistic that the <111> grains will have a <112> direction nearly parallel to the direction of electron flow. Thus, strong <111> textures lead to more plasticity, as we observe.

  5. Hormone signaling and phenotypic plasticity in nematode development and evolution.

    Science.gov (United States)

    Sommer, Ralf J; Ogawa, Akira

    2011-09-27

    Phenotypic plasticity refers to the ability of an organism to adopt different phenotypes depending on environmental conditions. In animals and plants, the progression of juvenile development and the formation of dormant stages are often associated with phenotypic plasticity, indicating the importance of phenotypic plasticity for life-history theory. Phenotypic plasticity has long been emphasized as a crucial principle in ecology and as facilitator of phenotypic evolution. In nematodes, several examples of phenotypic plasticity have been studied at the genetic and developmental level. In addition, the influence of different environmental factors has been investigated under laboratory conditions. These studies have provided detailed insight into the molecular basis of phenotypic plasticity and its ecological and evolutionary implications. Here, we review recent studies on the formation of dauer larvae in Caenorhabditis elegans, the evolution of nematode parasitism and the generation of a novel feeding trait in Pristionchus pacificus. These examples reveal a conserved and co-opted role of an endocrine signaling module involving the steroid hormone dafachronic acid. We will discuss how hormone signaling might facilitate life-history and morphological evolution.

  6. Non-adaptive plasticity potentiates rapid adaptive evolution of gene expression in nature.

    Science.gov (United States)

    Ghalambor, Cameron K; Hoke, Kim L; Ruell, Emily W; Fischer, Eva K; Reznick, David N; Hughes, Kimberly A

    2015-09-17

    Phenotypic plasticity is the capacity for an individual genotype to produce different phenotypes in response to environmental variation. Most traits are plastic, but the degree to which plasticity is adaptive or non-adaptive depends on whether environmentally induced phenotypes are closer or further away from the local optimum. Existing theories make conflicting predictions about whether plasticity constrains or facilitates adaptive evolution. Debate persists because few empirical studies have tested the relationship between initial plasticity and subsequent adaptive evolution in natural populations. Here we show that the direction of plasticity in gene expression is generally opposite to the direction of adaptive evolution. We experimentally transplanted Trinidadian guppies (Poecilia reticulata) adapted to living with cichlid predators to cichlid-free streams, and tested for evolutionary divergence in brain gene expression patterns after three to four generations. We find 135 transcripts that evolved parallel changes in expression within the replicated introduction populations. These changes are in the same direction exhibited in a native cichlid-free population, suggesting rapid adaptive evolution. We find 89% of these transcripts exhibited non-adaptive plastic changes in expression when the source population was reared in the absence of predators, as they are in the opposite direction to the evolved changes. By contrast, the remaining transcripts exhibiting adaptive plasticity show reduced population divergence. Furthermore, the most plastic transcripts in the source population evolved reduced plasticity in the introduction populations, suggesting strong selection against non-adaptive plasticity. These results support models predicting that adaptive plasticity constrains evolution, whereas non-adaptive plasticity potentiates evolution by increasing the strength of directional selection. The role of non-adaptive plasticity in evolution has received relatively

  7. Plasticity and creep of metals

    CERN Document Server

    Rusinko, Andrew

    2011-01-01

    Here is a systematic presentation of the postulates, theorems and principles of mathematical theories of plasticity and creep in metals, and their applications. Special attention is paid to analysis of the advantages and shortcomings of the classical theories.

  8. American Society of Plastic Surgeons

    Science.gov (United States)

    ... PRS PRS GO PSN PSEN GRAFT Contact Us Cosmetic Surgery New procedures and advanced technologies offer plastic surgery ... David Berman MD 14 Pidgeon Hill Drive Berman Cosmetic Surgery & S... Sterling, VA 20165 Website Franklin Richards MD Suite ...

  9. Plastic deformation of nanocrystalline nickel

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    A high-resolution electron microscopy study has uncovered the plastic behavior of accommodating large strains in nanocrystalline (NC) Ni subject to cold rolling at liquid nitrogen temperature. The activation of grain-boundary-mediated-plasticity is evidenced in NC-Ni, including twinning and formation of stacking fault via partial dislocation slips from the grain boundary. The formation and storage of 60? full dislocations are observed inside NC-grains. The grain/twin boundaries act as the barriers of dislocation slips, leading to dislocation pile-up, severe lattice distortion, and formation of sub-grain boundary. The vicinity of grain/twin boundary is where defects preferentially accumulate and likely the favorable place for onset of plastic deformation. The present results indicate the heterogeneous and multiple natures of accommodating plastic strains in NC-grains.

  10. Plastic deformation of nanocrystalline nickel

    Institute of Scientific and Technical Information of China (English)

    WU XiaoLei

    2009-01-01

    A high-resolution electron microscopy study has uncovered the plastic behavior of accommodating large strains in nanocrystalline(NC)Ni subject to cold rolling at liquid nitrogen temperature.The acti vation of grain-boundary-mediated-plasticity is evidenced in NC-Ni,including twinning and formation of stacking fault via partial dislocation slips from the grain boundary.The formation and storage of 60° full dislocations are observed inside NC-grains.The grain/twin boundaries act as the barriers of dislocation slips,leading to dislocation pile-up,severe lattice distortion,and formation of sub-grain boundary.The vicinity of grain/twin boundary is where defects preferentially accumulate and likely the favorable place for onset of plastic deformation.The present results indicate the heterogeneous and multiple natures of accommodating plastic strains in NC-grains.

  11. Exceptional plasticity of silicon nanobridges

    Energy Technology Data Exchange (ETDEWEB)

    Ishida, Tadashi; Sato, Takaaki; Toshiyoshi, Hiroshi; Collard, Dominique; Fujita, Hiroyuki [University of Tokyo, Institute of Industrial Science, 4-6-1 Komaba Meguro, Tokyo 153-8505 (Japan); Cleri, Fabrizio [Institut d' Electronique Microelectronique et Nanotechnologie (CNRS UMR 8520), Universite de Lille I, Avenue Poincare BP60069 59652 Villeneuve d' Ascq (France); Kakushima, Kuniyuki [Tokyo Institute of Technology, 4259, Nagatsuda, Midori, Yokohama, Kanagawa 226-8502 (Japan); Mita, Makoto [Department of Spacecraft Engineering, Japan Aerospace Exploration Agency, 3-1-1, Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan); Miyata, Masaki; Itamura, Noriaki; Sasaki, Naruo [Department of Materials and Life Sciences, Seikei University, 3-3-1, Kitamachi, Kichijoji, Musashino, Tokyo 180-8633 (Japan); Endo, Junji, E-mail: tadashii@iis.u-tokyo.ac.jp [FK Optical laboratory, 1-13-4 Nakano Niiza Saitama, 352-0005 (Japan)

    2011-09-02

    The plasticity of covalently bonded materials is a subject at the forefront of materials science, bearing on a wide range of technological and fundamental aspects. However, covalent materials fracture in a brittle manner when the deformation exceeds just a few per cent. It is predicted that a macroscopically brittle material like silicon can show nanoscale plasticity. Here we report the exceptional plasticity observed in silicon nanocontacts ('nanobridges') at room temperature using a special experimental setup combining a transmission electron microscope and a microelectromechanical system. When accounting for surface diffusion, we succeeded in elongating the nanocontact into a wire-like structure, with a fivefold increase in volume, up to more than twenty times the original length. Such a large plasticity was caused by the stress-assisted diffusion and the sliding of the intergranular, amorphous-like material among the nanocrystals.

  12. Globally Oriented Chinese Plastics Industry

    Institute of Scientific and Technical Information of China (English)

    Liao Zhengpin

    2004-01-01

    @@ Through continued endeavor and persistent opening to the whole world the Chinese plastics industry has been developed into a comprehensive industrial system that forms the basic material industries side by side with the steel, cement and the timber industry.

  13. Reelin Supplementation Enhances Cognitive Ability, Synaptic Plasticity, and Dendritic Spine Density

    Science.gov (United States)

    Rogers, Justin T.; Rusiana, Ian; Trotter, Justin; Zhao, Lisa; Donaldson, Erika; Pak, Daniel T.S.; Babus, Lenard W.; Peters, Melinda; Banko, Jessica L.; Chavis, Pascale; Rebeck, G. William; Hoe, Hyang-Sook; Weeber, Edwin J.

    2011-01-01

    Apolipoprotein receptors belong to an evolutionarily conserved surface receptor family that has intimate roles in the modulation of synaptic plasticity and is necessary for proper hippocampal-dependent memory formation. The known lipoprotein receptor ligand Reelin is important for normal synaptic plasticity, dendritic morphology, and cognitive…

  14. Computational materials science: Nanoscale plasticity

    DEFF Research Database (Denmark)

    Jacobsen, Karsten Wedel; Schiøtz, Jakob

    2002-01-01

    How does plastic deformation of polycrystalline materials with grain sizes less than 100 nm look at the atomic scale? A large-scale molecular dynamics simulation of nanocrystalline alluminium reveals some surprising behaviour.......How does plastic deformation of polycrystalline materials with grain sizes less than 100 nm look at the atomic scale? A large-scale molecular dynamics simulation of nanocrystalline alluminium reveals some surprising behaviour....

  15. Sorting Techniques for Plastics Recycling

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    This paper presents the basic principles of three different types of separating methods and a general guideline for choosing the most effective method for sorting plastic mixtures. It also presents the results of the tests carried out for separation of PVC, ABS and PET from different kinds of plastic mixtures in order to improve the grade of the raw input used in mechanical or feedstock recycling.

  16. [Modern neuroimaging of brain plasticity].

    Science.gov (United States)

    Kasprian, G; Seidel, S

    2010-02-01

    Modern neuroimaging methods offer new insights into the plasticity of the human brain. As the techniques of functional MRI and diffusion tensor imaging are increasingly being applied in a clinical setting, the examiner is now frequently confronted with the interpretation of imaging findings related to regenerative processes in response to lesions of the central and also of the peripheral nervous system. In this article individual results of modern neuroimaging studies are discussed in the context of structural and functional plasticity of the CNS.

  17. Plastic bronchitis: a management challenge.

    Science.gov (United States)

    Eberlein, Michael H; Drummond, Michael B; Haponik, Edward F

    2008-02-01

    Plastic bronchitis is an uncommon and underdiagnosed entity, characterized by recurrent expectoration of large, branching bronchial casts. We describe a 39-year-woman with no prior lung disease who had episodic wheezing, severe dyspnea with expectoration of large and thick secretions, branching in appearance, which she described as resembling squid. A comprehensive evaluation revealed no specific cause and a diagnosis of idiopathic plastic bronchitis was made. In plastic bronchitis the bronchial casts may vary in size from small segmental casts of a bronchus to casts filling the airways of an entire lung. Plastic bronchitis can therefore present as an acute life-threatening emergency if mechanical obstruction of major airways occurs. The casts are differentiated into type I, inflammatory casts, or type II, acellular casts. The type I inflammatory casts are often associated with bronchial disease and often have an acute presentation. The acellular type of cast production is often chronic or recurrent. Numerous systemic illnesses are associated with plastic bronchitis, but often, as in our patient, no underlying cause can be identified. The treatment of plastic bronchitis includes acute therapy to aid the removal and expectoration of casts, and specific short- or long-term treatments attempting to address the underlying hypersecretory process. The therapeutic options are supported only by anecdotal evidence based on case reports as the rarity and heterogeneity of plastic bronchitis confounds systematic investigations of its treatment. Improved understanding of the regulation of mucus production may allow for new treatment options in plastic bronchitis and other chronic lung diseases characterized by hypersecretion of mucus.

  18. Microstructural Characterization Of Quenched And Plastically Deformed Two-Phase α+β Titanium Alloys

    Directory of Open Access Journals (Sweden)

    Motyka M.

    2015-09-01

    Full Text Available Development of microstructure in two-phase α+β titanium alloys is realized by thermomechanical processing – sequence of heat treatment and plastic working operations. Analysis of achieved results indicates that hot plastic deformation – depending on deformation degree – causes significant elongation of α phase grains. Following heat treatment and plastic deformation processes lead to their fragmentation and spheroidization. Characterization of microstructure morphology changes during thermomechanical processing of quenched Ti-6Al-4V and Ti-6Al-2Mo-2Cr alloys is presented in the paper. The effect of martensitic phase α’(α” on microstructure development in plastic deformation process was confirmed.

  19. <