| Abstract: | On-responses of primary visual cortical neurons to local photic stimulation of the receptive field center by stimuli of scotopic and mesopic ranges of intensity were investigated in dark-adapted curarized cats. Only phasic excitation (type I) was observed in 16% of cells studied, phasic and prolonged excitation with phasic inhibition between them (type II) was observed in 68%, and prolonged inhibition (type III) alone in 16% of cells. The thresholds of phasic excitation in the neuronal responses lay between 0.7 and 2200 trolands (td) and coincided with thresholds of activation of the cone system, whereas thresholds of prolonged excitation lay within the range 0.02–9 td and coincided with thresholds of rod inputs. Inhibitory effects were manifested as phasic inhibition observed on peristimulus histograms, disturbances of the monotony of the responses versus stimulus intensity curve, and also as prolonged inhibition in on-responses. All inhibitory effects were observed in the mesopic range of intensities (0.7–2200 td) and were connected with functioning of the cones.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 359–366, July–August, 1982. |
