[Characteristics of the responses of cat visual cortex neurons to photic stimulation of different areas of their receptive fields].

The functions of intensity, thresholds of reactions, thresholds of inhibitory effects and differential sensitivity to intensity of local light stimulation of central and different peripheral regions of receptive fields of 96 units in the 17th field of visual cortex were investigated in immobilized and nonanesthetized cats in dark adaptation. Receptive fields of cells had wide threshold and superthreshold reliefs (3-30 degrees). Some of them had V-shape reliefs, while others--reliefs with alternating zones of high and low excitability. As a rule, sensitivity of excitatory and inhibitory inputs was maximal in the centre of the receptive field. In the investigated population of cells the inhibitory inputs were more standard in sensitivity and on the average of lower excitability. The threshold relief of the receptive fields was markedly narrowed under light adaptation mainly due to a decrease in the peripheral inputs sensitivity. The number of low-threshold units, the differential brightness sensitivity and sensitivity of the inhibitory system increased in the visual cortex as compared to the lateral geniculate and retinal units. The mechanisms of receptive field formation in the visual cortex and their plasticity depending on the adaptation level, the role of excitatory and inhibitory inputs in these effects and behavioral significance of the obtained data are discussed.