Maturation of Visual Cortex with and without Visual Experience
The evolution of the response properties of visual cortical cells was studied in two groups of kittens between 1 and 7 weeks of age—one group normally reared, the other reared in complete darkness. Four classes of striate neurones were defined: (a) non-activatable cells, (b) non-specific cells, (c) immature cells, (d) specific cells that are as selective for orientation as the simple or complex cells of the adult cat. The results confirm that as soon as neurones become visually activated, about 25% of the recorded visual units are definitely specific in terms of orientation selectivity. These neurones are present in earliest stages, even in the absence of any visual experience. However, active visual experience (visuomotor interaction) is necessary to maintain and develop these specific cells after the third week of postnatal life. Polar diagrams of the orientation encoded by specific cells show that for kittens under 3 weeks of age and whatever the rearing condition, there are more specific cells coding horizontal or vertical orientation than those coding oblique orientations. These horizontally and vertically oriented cells are preferentially driven by the contralateral eye. Thus, the ocular dominance distribution and the orientation selectivity appear as two linked parameters characterizing visual specificity in very young kittens independently of any visual experience. An hypothesis of “differential modifiability” is proposed: contralateral monocular “horizontal and vertical detectors” are supposed to be stable. They would remain so until they become binocular. Binocular cells, for which competition between two inputs occurs, are the labile units which can be despecified or be specified under the control of visual experience.
KeywordsReceptive Field Visual Experience Ocular Dominance Orientation Selectivity Oriented Cell
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