| Abstract: | The characteristics of neurons in Area 17 of the visual cortex in cats were investigated by extracellular recording of their activity. Unit responses to flashes modulated by intensity and duration (100 µsec-1 sec) were recorded. Of 80 neurons tested, 67.6% were spontaneously active and 32.4% were silent. The threshold responses of the neurons to flashes varied by 7 logarithmic units. The distribution curve of the cells by response thresholds had one maximum corresponding to an energy of the order of 1–10 lm·sec. The time during which the cells could summate excitation did not exceed a mean value of 34 msec. Depending on the latent periods of the visual cortical neurons they can be divided into three groups. The first group includes neurons responding 20–40 msec after stimulation, the second and third neurons responding after 100–120 and 160–180 msec, respectively. Photic stimulation considerably altered the ratio between the numbers of cells generating spikes with high and low frequency. No correlation was found between the sensitivity of the visual cortical cells to light, the latent period of their response, and the critical time of summation. This shows that the cortex contains many duplicate units which are grouped together on the basis of only one of the functional characteristics of their spike response.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 2, pp. 173–179, March–April, 1970. |
