The Experts below are selected from a list of 1152 Experts worldwide ranked by ideXlab platform
Yves Frégnac - One of the best experts on this subject based on the ideXlab platform.
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Shunting Inhibition, a silent step in visual cortical computation.
Journal of Physiology - Paris, 2003Co-Authors: Yves Frégnac, Cyril Monier, Frederic Chavane, Pierre Baudot, Lyle GrahamAbstract:Brain computation, in the early visual system, is often considered as a hierarchical process in which features extracted in a given sensory relay are not present in previous stages of integration. In particular, orientation preference and its fine tuning selectivity are functional properties shared by most cortical cells and they are not observed at the preceding geniculate stage. A classical problem is identifying the mechanisms and circuitry underlying these computations. Several organizational principles have been proposed, giving different weights to the feedforward thalamocortical drive or to intracortical recurrent architectures. Within this context, an important issue is whether intracortical Inhibition is fundamental for the genesis of stimulus selectivity, or rather normalizes spike response tuning with respect to other features such as stimulus strength or contrast, without influencing the selectivity bias and preference expressed in the excitatory input alone. We review here experimental observations concerning the presence or absence of inhibitory input evoked by non-preferred orientation/directions. Intracellular current clamp and voltage clamp recordings are analyzed in the light of new methods allowing us (1) to increase the visibility of inhibitory input, and (2) to continuously measure the visually evoked dynamics of input conductances. We conclude that there exists a diversity of synaptic input combinations generating the same profile of spike-based orientation selectivity, and that this diversity most likely reflects anatomical non-homogeneities in input sampling provided by the local context of the columnar and lateral intracortical network in which the considered cortical cell is embedded.
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visual input evokes transient and strong Shunting Inhibition in visual cortical neurons
Nature, 1998Co-Authors: Lyle J Borggraham, Cyril Monier, Yves FrégnacAbstract:. Here we present a new approach to studying Inhibition that is based on in vivo whole- cell voltage clamping. This technique allows the continuous measurement of conductance dynamics during visual activation. We show, in neurons of cat primary visual cortex, that the response to optimally orientated flashed bars can increase the somatic input conductance to more than three times that of the resting state. The short latency of the visually evoked peak of conductance, and its apparent reversal potential suggest a domi- nant contribution from g-aminobutyric acid ((GABA)A) receptor- mediated synapses. We propose that nonlinear Shunting inhibi- tion may act during the initial stage of visual cortical processing, setting the balance between opponent 'On' and 'Off ' responses in different locations of the visual receptive field.
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voltage clamp measurement of visually evoked conductances with whole cell patch recordings in primary visual cortex
Journal of Physiology-paris, 1996Co-Authors: Lyle J Borggraham, Cyril Monier, Yves FrégnacAbstract:Abstract Whole cell patch recordings have been realized in the primary visual cortex of the anesthetized and paralyzed cat, in order to better characterize input resistance and time constant of visual cortical cells in vivo. Measurements of conductance changes evoked by visual stimulation were derived from voltage clamp recordings achieved in continuous mode at two or more different subtreshold holding potentials. They show that the magnitude of the conductance increase can reach up to 300% of the mean conductance at rest. The observation of similar changes for the preferred and antagonist responses, when flashing ON and OFF, a test stimulus in pure ON and OFF subfields supports the hypothesis of a role for Shunting Inhibition in the spatial organization of simple receptive fields.
Alexey Semyanov - One of the best experts on this subject based on the ideXlab platform.
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tonic gabaa conductance bidirectionally controls interneuron firing pattern and synchronization in the ca3 hippocampal network
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Ivan Pavlov, Leonid P Savtchenko, Inseon Song, Jaeyeon Koo, Alexey Pimashkin, Dmitri A Rusakov, Alexey SemyanovAbstract:The spiking output of interneurons is key for rhythm generation in the brain. However, what controls interneuronal firing remains incompletely understood. Here we combine dynamic clamp experiments with neural network simulations to understand how tonic GABAA conductance regulates the firing pattern of CA3 interneurons. In baseline conditions, tonic GABAA depolarizes these cells, thus exerting an excitatory action while also reducing the excitatory postsynaptic potential (EPSP) amplitude through Shunting. As a result, the emergence of weak tonic GABAA conductance transforms the interneuron firing pattern driven by individual EPSPs into a more regular spiking mode determined by the cell intrinsic properties. The increased regularity of spiking parallels stronger synchronization of the local network. With further increases in tonic GABAA conductance the Shunting Inhibition starts to dominate over excitatory actions and thus moderates interneuronal firing. The remaining spikes tend to follow the timing of suprathreshold EPSPs and thus become less regular again. The latter parallels a weakening in network synchronization. Thus, our observations suggest that tonic GABAA conductance can bidirectionally control brain rhythms through changes in the excitability of interneurons and in the temporal structure of their firing patterns.
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tonic gabaa conductance decreases membrane time constant and increases epsp spike precision in hippocampal pyramidal neurons
Frontiers in Neural Circuits, 2013Co-Authors: Agnieszka Wlodarczyk, Inseon Song, Maxim Doronin, Matthew C Walker, Alexey SemyanovAbstract:Because of a complex dendritic structure, pyramidal neurons have a large membrane surface relative to other cells and so a large electrical capacitance and a large membrane time constant (τm). This results in slow depolarizations in response to excitatory synaptic inputs, and consequently increased and variable action potential latencies, which may be computationally undesirable. Tonic activation of GABAA receptors increases membrane conductance and thus regulates neuronal excitability by Shunting Inhibition. In addition, tonic increases in membrane conductance decrease the membrane time constant (τm), and improve the temporal fidelity of neuronal firing. Here we performed whole-cell current clamp recordings from hippocampal CA1 pyramidal neurons and found that bath application of 10 µM GABA indeed decreases τm in these cells. GABA also decreased first spike latency and jitter (standard deviation of the latency) produced by current injection of 2 rheobases (500 ms). However, when larger current injections (3-6 rheobases) were used, GABA produced no significant effect on spike jitter, which was low. Using mathematical modelling we demonstrate that the tonic GABAA conductance decreases rise time, decay time and half-width of EPSPs in pyramidal neurons. A similar effect was observed on EPSP/IPSP pairs produced by stimulation of Schaffer collaterals: the EPSP part of the response became shorter after application of GABA. Consistent with the current injection data, a significant decrease in spike latency and jitter was obtained in cell attached recordings only at near-threshold stimulation (50% success rate, S50). When stimulation was increased to 2- or 3- times S50, GABA significantly affected neither spike latency nor spike jitter. Our results suggest that a decrease in τm associated with elevations in ambient GABA can improve EPSP-spike precision at near-threshold synaptic inputs.
Terrence J Sejnowski - One of the best experts on this subject based on the ideXlab platform.
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top down inputs enhance orientation selectivity in neurons of the primary visual cortex during perceptual learning
PLOS Computational Biology, 2014Co-Authors: Samat Moldakarimov, Maxim Bazhenov, Terrence J SejnowskiAbstract:Perceptual learning has been used to probe the mechanisms of cortical plasticity in the adult brain. Feedback projections are ubiquitous in the cortex, but little is known about their role in cortical plasticity. Here we explore the hypothesis that learning visual orientation discrimination involves learning-dependent plasticity of top-down feedback inputs from higher cortical areas, serving a different function from plasticity due to changes in recurrent connections within a cortical area. In a Hodgkin-Huxley-based spiking neural network model of visual cortex, we show that modulation of feedback inputs to V1 from higher cortical areas results in Shunting Inhibition in V1 neurons, which changes the response properties of V1 neurons. The orientation selectivity of V1 neurons is enhanced without changing orientation preference, preserving the topographic organizations in V1. These results provide new insights to the mechanisms of plasticity in the adult brain, reconciling apparently inconsistent experiments and providing a new hypothesis for a functional role of the feedback connections.
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Top-Down Inputs Enhance Orientation Selectivity in Neurons of the Primary Visual Cortex during Perceptual Learning
2014Co-Authors: Samat Moldakarimov, Maxim Bazhenov, Terrence J SejnowskiAbstract:Perceptual learning has been used to probe the mechanisms of cortical plasticity in the adult brain. Feedback projections are ubiquitous in the cortex, but little is known about their role in cortical plasticity. Here we explore the hypothesis that learning visual orientation discrimination involves learning-dependent plasticity of top-down feedback inputs from higher cortical areas, serving a different function from plasticity due to changes in recurrent connections within a cortical area. In a Hodgkin-Huxley-based spiking neural network model of visual cortex, we show that modulation of feedback inputs to V1 from higher cortical areas results in Shunting Inhibition in V1 neurons, which changes the response properties of V1 neurons. The orientation selectivity of V1 neurons is enhanced without changing orientation preference, preserving the topographic organizations in V1. These results provide new insights to the mechanisms of plasticity in the adult brain, reconciling apparently inconsistent experiments and providing a new hypothesis for a functional role of the feedbac
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Shunting Inhibition Controls the Gain Modulation Mediated by Asynchronous Neurotransmitter Release in Early Development
2010Co-Authors: Vladislav Volman, Herbert Levine, Terrence J SejnowskiAbstract:The sensitivity of a neuron to its input can be modulated in several ways. Changes in the slope of the neuronal input-output curve depend on factors such as Shunting Inhibition, background noise, frequency-dependent synaptic excitation, and balanced excitation and Inhibition. However, in early development GABAergic interneurons are excitatory and other mechanisms such as asynchronous transmitter release might contribute to regulating neuronal sensitivity. We modeled both phasic and asynchronous synaptic transmission in early development to study the impact of activity-dependent noise and short-term plasticity on the synaptic gain. Asynchronous release decreased or increased the gain depending on the membrane conductance. In the high shunt regime, excitatory input due to asynchronous release was divisive, whereas in the low shunt regime it had a nearly multiplicative effect on the firing rate. In addition, sensitivity to correlated inputs was influenced by Shunting and asynchronous release in opposite ways. Thus, asynchronous release can regulate th
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Shunting Inhibition controls the gain modulation mediated by asynchronous neurotransmitter release in early development.
Public Library of Science (PLoS), 2010Co-Authors: Vladislav Volman, Herbert Levine, Terrence J SejnowskiAbstract:The sensitivity of a neuron to its input can be modulated in several ways. Changes in the slope of the neuronal input-output curve depend on factors such as Shunting Inhibition, background noise, frequency-dependent synaptic excitation, and balanced excitation and Inhibition. However, in early development GABAergic interneurons are excitatory and other mechanisms such as asynchronous transmitter release might contribute to regulating neuronal sensitivity. We modeled both phasic and asynchronous synaptic transmission in early development to study the impact of activity-dependent noise and short-term plasticity on the synaptic gain. Asynchronous release decreased or increased the gain depending on the membrane conductance. In the high shunt regime, excitatory input due to asynchronous release was divisive, whereas in the low shunt regime it had a nearly multiplicative effect on the firing rate. In addition, sensitivity to correlated inputs was influenced by Shunting and asynchronous release in opposite ways. Thus, asynchronous release can regulate the information flow at synapses and its impact can be flexibly modulated by the membrane conductance
Lyle J Borggraham - One of the best experts on this subject based on the ideXlab platform.
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the computation of directional selectivity in the retina occurs presynaptic to the ganglion cell
Nature Neuroscience, 2001Co-Authors: Lyle J BorggrahamAbstract:Directional selectivity is a response that is greater for a visual stimulus moving in one (PREF) direction than for the opposite (NULL) direction, and its computation in the vertebrate retina is a classical issue in functional neurophysiology. To date, most quantitative experimental studies have relied on extracellular responses for identifying properties of the directionally selective circuit. Here I describe an intracellular analysis using whole-cell patch recordings of the synaptic events underlying the spike response in directionally selective ganglion cells of the turtle retina. These quantitative measurements allowed me to distinguish among various explicit classes of circuit models that can, in principle, account for ganglion cell directional selectivity. I found that ganglion cell directional selectivity is due to an excitatory input that itself is directionally selective, and that the crucial Shunting Inhibition implicated in this computation must act on cells presynaptic to the ganglion cell.
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visual input evokes transient and strong Shunting Inhibition in visual cortical neurons
Nature, 1998Co-Authors: Lyle J Borggraham, Cyril Monier, Yves FrégnacAbstract:. Here we present a new approach to studying Inhibition that is based on in vivo whole- cell voltage clamping. This technique allows the continuous measurement of conductance dynamics during visual activation. We show, in neurons of cat primary visual cortex, that the response to optimally orientated flashed bars can increase the somatic input conductance to more than three times that of the resting state. The short latency of the visually evoked peak of conductance, and its apparent reversal potential suggest a domi- nant contribution from g-aminobutyric acid ((GABA)A) receptor- mediated synapses. We propose that nonlinear Shunting inhibi- tion may act during the initial stage of visual cortical processing, setting the balance between opponent 'On' and 'Off ' responses in different locations of the visual receptive field.
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voltage clamp measurement of visually evoked conductances with whole cell patch recordings in primary visual cortex
Journal of Physiology-paris, 1996Co-Authors: Lyle J Borggraham, Cyril Monier, Yves FrégnacAbstract:Abstract Whole cell patch recordings have been realized in the primary visual cortex of the anesthetized and paralyzed cat, in order to better characterize input resistance and time constant of visual cortical cells in vivo. Measurements of conductance changes evoked by visual stimulation were derived from voltage clamp recordings achieved in continuous mode at two or more different subtreshold holding potentials. They show that the magnitude of the conductance increase can reach up to 300% of the mean conductance at rest. The observation of similar changes for the preferred and antagonist responses, when flashing ON and OFF, a test stimulus in pure ON and OFF subfields supports the hypothesis of a role for Shunting Inhibition in the spatial organization of simple receptive fields.
Jeffrey C Magee - One of the best experts on this subject based on the ideXlab platform.
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network mechanisms of theta related neuronal activity in hippocampal ca1 pyramidal neurons
Nature Neuroscience, 2010Co-Authors: Attila Losonczy, Boris V Zemelman, Alipasha Vaziri, Jeffrey C MageeAbstract:Although hippocampal theta oscillations represent a prime example of temporal coding in the mammalian brain, little is known about the specific biophysical mechanisms. Intracellular recordings implicate a particular abstract oscillatory interference model of hippocampal theta activity; the soma-dendrite interference model. To gain insight into the cellular and circuit level mechanisms of theta activity we implemented a similar form of interference using the actual hippocampal network in mice in vitro. We found that pairing increasing levels of phasic dendritic excitation with phasic stimulation of perisomatic projecting inhibitory interneurons induced a somatic polarization and action potential timing profile that reproduced most common features. Alterations in the temporal profile of Inhibition were required to fully capture all features. These data suggest that theta-related place cell activity is generated through an interaction between a phasic dendritic excitation and a phasic perisomatic Shunting Inhibition delivered by interneurons; a subset of which undergo activity-dependent presynaptic modulation.
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network mechanisms of theta related neuronal activity in hippocampal ca1 pyramidal neurons
Nature Neuroscience, 2010Co-Authors: Attila Losonczy, Boris V Zemelman, Alipasha Vaziri, Jeffrey C MageeAbstract:Although hippocampal theta oscillations represent a prime example of temporal coding in the mammalian brain, little is known about the specific biophysical mechanisms. Intracellular recordings support a particular abstract oscillatory interference model of hippocampal theta activity, the soma-dendrite interference model. To gain insight into the cellular and circuit level mechanisms of theta activity, we implemented a similar form of interference using the actual hippocampal network in mice in vitro. We found that pairing increasing levels of phasic dendritic excitation with phasic stimulation of perisomatic projecting inhibitory interneurons induced a somatic polarization and action potential timing profile that reproduced most common features. Alterations in the temporal profile of Inhibition were required to fully capture all features. These data suggest that theta-related place cell activity is generated through an interaction between a phasic dendritic excitation and a phasic perisomatic Shunting Inhibition delivered by interneurons, a subset of which undergo activity-dependent presynaptic modulation.