[Characteristics of inhibition in the receptive fields of the cat visual cortex]

The responses of visual cells in the 17th cortical area to stimulation with bright strips of various width were studied in immobilized cats. The impulse activity was counted in successive time intervals from the beginning of the stimulation and plotted as a function of the stimulus area. Significant differences in time course of the inhibitory process were found between the cortical and geniculate levels. The lag of inhibition behind excitation was much smaller in the cortex than in the geniculate body. Similar data were obtained from cortical response elicited by simultaneous or successive application of two bright strips, one in the excitatory centre and the second in the inhibitory zone of the receptive field. If both strips were placed in the excitatory zone of the field, inhibition depended on the order of illumination of the strips. When this order coincided with the direction in which a moving stimulus had a maximal effect, a large facilitation of the response to the second stimulus was obtained. When the order of presentation was reversed, a strong inhibition appeared. This selectivity of the inhibitory mechanism was attenuated at the periphery of the field where any succession of the stimuli elicited an inhibitory effect.