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Models of Neural Systems

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Modelling Contrast Adaptation and Contextual Effects in Primary Visual Cortex
Citation key Stetter1998f
Author Stetter, M. and Adorjan, P. and Bartsch, H. and Obermayer, K.
Title of Book Proceedings of the ICONIP 98 Conference, Kitakyushu
Pages 669 – 672
Year 1998
DOI 10.1.1.54.7043
Volume 2
Abstract Orientation selective cortical neurons show contrast-invariant orientation tuning curves, contrast saturation and contrast adaptation. Additionally, their responses are modulated by oriented stimuli outside the classical receptive field. We characterize the extent, to which these effects can be caused by a recurrent network of simple neurons, and which properties are probably due to plasticity of geniculocortical synapses. For this we compare the predictions of a mean-field-model based on cortical hypercolumns with those of a model that incorporates spiking neurons with detailed time-resolved synaptic dynamics. We find that in a mean-field model contrast-invariant orientation tuning and contextual effects can be generated by local and long-range intracortical circuitry respectively. However, they are incompatible with contrast-saturation and contrast-adaptation. Using a recurrent neural network of excitatory spiking neurons with adapting synapses, we then show that within that model framework (i) contrast saturation can be explained by fast adaptation of the lateral or the afferent synapses, (ii) phase advance with increasing contrast is due to fast adaptation of the afferent synapses, and (iii) adaptation of the synaptic transmitter release probability of the geniculocortical synapses is a necessary and sufficient mechanism for contrast adaptation. In summary, we suggest that recurrent lateral connections play a key role in orientation processing, while contrast processing is mainly a feed-forward phenomenon.
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