Modeling Visual Cortical Contrast Adaptation Effects

Abstract

We demonstrate model visual cortical circuits which exhibit robust contrast adaptation properties, consistent with physiological observations in V1. The adaptation mechanism we employ is activity-dependent synaptic depression at thalamocortical and local intra-cortical synapses. Model contrast response functions (CRF) shift so that cells remain maximally responsive to changes around the recent average stimulus contrast level. Hysteresis effects for both stimulus contrast and orientation are achieved; orientation hysteresis is weaker, and depends exclusively on intracortical adaptation. Following stimulation of the receptive field (RF) surround, RFs dynamically expand to ''fill in'' for the missing stimulation in the RF center; in our model this expansion results from adaptation of local inhibitory synapses, triggered by excitation from long range horizontal projections. All adaptation effects are achieved using the same synaptic depression mechanisms.