Spontaneously emerging direction selectivity maps in visual cortex through STDP |
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Authors: | Oliver G Wenisch Joachim Noll J Leo van Hemmen |
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Institution: | (1) Leibniz-Rechenzentrum, Barer Strasse 21, 80333 München, Germany;(2) Physik Department, TU München, 85747 Garching bei München, Germany |
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Abstract: | It is still an open question as to whether, and how, direction-selective neuronal responses in primary visual cortex are generated
by feedforward thalamocortical or recurrent intracortical connections, or a combination of both. Here we present an investigation
that concentrates on and, only for the sake of simplicity, restricts itself to intracortical circuits, in particular, with
respect to the developmental aspects of direction selectivity through spike-timing-dependent synaptic plasticity. We show
that directional responses can emerge in a recurrent network model of visual cortex with spiking neurons that integrate inputs
mainly from a particular direction, thus giving rise to an asymmetrically shaped receptive field. A moving stimulus that enters
the receptive field from this (preferred) direction will activate a neuron most strongly because of the increased number and/or
strength of inputs from this direction and since delayed isotropic inhibition will neither overlap with, nor cancel excitation,
as would be the case for other stimulus directions. It is demonstrated how direction-selective responses result from spatial
asymmetries in the distribution of synaptic contacts or weights of inputs delivered to a neuron by slowly conducting intracortical
axonal delay lines. By means of spike-timing-dependent synaptic plasticity with an asymmetric learning window this kind of
coupling asymmetry develops naturally in a recurrent network of stochastically spiking neurons in a scenario where the neurons
are activated by unidirectionally moving bar stimuli and even when only intrinsic spontaneous activity drives the learning
process. We also present simulation results to show the ability of this model to produce direction preference maps similar
to experimental findings |
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