Spatially opponent excitation and inhibition in simple cells of the cat visual cortex

The receptive fields of simple cells in the cat visual cortex are, by definition, divided into ON and OFF subfields. There is little doubt that each subfield is generated by excitatory input from geniculate neurons of the appropriate center type: ON subfields by ON-center cells, and OFF subfields by OFF-center cells. In intracellular records, ON subfields can be detected as regions in which light elicits a barrage of EPSPs, while in OFF subfields, turning a light off does the same. In addition, visual stimuli can evoke strong IPSPs, but these IPSPs have a receptive field spatially opponent to that of the EPSPs: Inhibition is evoked by turning a light off in an ON region and turning a light on in an OFF region. This inhibition probably arises from other cortical simple cells, and may contribute to such receptive-field properties as antagonism between subfields, binocular disparity sensitivity, and orientation selectivity.