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Anton Krukowski, Ken Miller; Orientation response properties of inhibitory cells in a model of cat primary visual cortex. Journal of Vision 2001;1(3):434. doi: https://doi.org/10.1167/1.3.434.
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While much is known about the response properties of excitatory cells in cat primary visual cortex (V1), precious little is known about the response properties of inhibitory cells. We have previously demonstrated that a simple, experimentally-motivated model of the thalamocortical and corticocortical circuit of the thalamic input-recipient layer of V1, layer IV, can account for many aspects of excitatory cell orientation tuning, including its invariance to changes in stimulus contrast (Troyer et al. J. Neurosci 18:5908, 1998). A major prediction of this study was that a population of layer IV inhibitory cells, although tuned for orientation, should respond in a contrast-dependent manner to gratings at all orientations, including the null orientation (perpendicular to the preferred). This property was required by the model in order to counteract the excess mean thalamocortical excitatory input onto cortical excitatory cells at the null orientation. We now report that consideration of additional mechanisms renders this prediction more subtle. Short term synaptic depression in thalamocortical synapses can filter out much of the excess mean thalamic input at the null orientation, and, as a result, significantly lower inhibitory cell response to the null orientation, particularly at lower temporal frequencies. Thus the key test of the model is to study orientation tuning at higher temporal frequencies, e.g. 8 Hz. Furthermore, the mean spike rate of inhibitory cells is not well tuned to orientation without the intracortical excitatory-to-inhibitory connections, which do not otherwise significantly affect the behavior of the model, making the orientation tuning of the model inhibitory cells similar to the “complex” layer IV inhibitory cells that have recently been characterized in vivo. (Hirsch et al., Soc for Neuroscience Abstracts 408.7, 2000).
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