| Abstract: | Dependence of response characteristics of 70 visual cortical neurons on intensity of photic stimuli (bars) of optimal shape, size, orientation, location, and duration, presented under conditions of photopic light adaptation, were studied in curarized cats. Intensity functions were used to estimate response thresholds of the neuron, its differential sensitivity, the optimal intensity and the band width of brightnesses which the neuron could effectively code. Most of the neurons tested (70%) had nonmonotonous intensity functions with marked inhibitory distortion of gradual dependence in the middle part of the brightness range studied. Threshold of neuronal responses to light differed by 5 or 6 orders of magnitude. The threshold of the response and its minimal latent period were directly connected: Neurons with the lowest response threshold mainly responded after the shortest latent period. The maximal discharge frequency and differential sensitivity of the cell also correlated directly. The range of intensities within which the neuron exhibited maximal differential sensitivity, i.e., was able to code the strength of the light most effectively, lay between 0 and –20 dB. A sharp increase in differential sensitivity of the cortical neurons was found under light adaptation conditions compared with dark adaptation. Differences in characteristics of cortical neurons with their receptive field in the central and peripheral parts of the visual field were found.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 15, No. 3, pp. 211–217, May–June, 1983. |
