Orientation column

About: Orientation column is a research topic. Over the lifetime, 1142 publications have been published within this topic receiving 130169 citations.

Orientation-selective neurons in the squirrel visual cortex

Abstract: The organization of receptive fields of neurons sensitive to orientation of visual stimuli was investigated in the squirrel visual cortex. Neurons with mutually inhibitory on- and off-areas of the receptive field, with partially and completely overlapping excitatory and inhibitory mechanisms, were distinguished. Neurons of the second group are most typical. They exhibit orientation selectivity within the excitatory area of the receptive field because, if the stimulus widens in the zero direction, perpendicular to the preferred direction, lateral inhibition is much stronger than if it widens in the preferred direction. Additional inhibitory areas (outside the excitatory area) potentiate this inhibition and increase selectivity. It is suggested that there is no strict separation of simple (with separate excitatory and inhibitory mechanisms in the receptive field) and complex (with overlapping of these mechanisms) neurons in the squirrel visual cortex.

Study of the functional characteristics of visual cortex neurons in the cat upon local photic stimulation of their receptive fields

Abstract: Functional characteristics of 103 neurons in field 17 of the visual cortex were studied in immobilized and unanesthetized cats. Unit responses to modification of local light stimuli wer recorded under conditions of light adaptation. Mean photic threshold of investigated neurons was -32 dB, mean critical temporal summation 57 ms, duration of reactivity recovery 190 ms and sharpness of orientation tuning 37 degrees. As compared to dark adaptation, under light adaptation reduction of light sensitivity, sharpening of orientation tuning as well as a lengthening of temporal summation and a shortening in time of reactivity recovery were observed. A number of neuronal characteristics depended on excentricity of their receptive fields: cells with centrally localized receptive fields had a lower threshold, a short summation and rapid recovery of reactivity; their activity was of higher frequency, and they generated brief transient responses more often than cells with receptive fields in the periphery of a visual field. Mechanisms responsible for change of neuronal properties in the central and peripheral visual channels under light and dark adaptation are discussed. Several inhibitory subsystems are suggested by means of which neuronal activity of the visual cortex is regulated.