Visual cortical cells: their developmental properties in normal and dark reared kittens.

582 units were recorded in area 17 in twenty-one normally reared kittens, and fourteen dark reared ones, aged between 8 and 42 days. 2. Four classes of neurones were defined: (a) non-activable cells that cannot be excited by any peripheral stimulation; (b) non-specific cells that are sensitive to a visual stimulus moving in any direction; (c) immature cells that are preferentially excited by a rectilinear stimulus but are unselective for its precise orientation; (d) specific cells that appear to be as selective for orientation as the simple or complex cells of the adult cat. 3. 23% of the cells presenting adult characteristics of specificity in terms of directionality and orientation are present in both the normally reared and in the dark reared kittens as soon as the first visual response (12 days) appears. 4. In normally reared kittens the proportion of specific cells increases with age, while that of the non-specific cells decreases. 5. Up to 3 weeks of age there is no significant difference in the proportion of the different types of cells in the dark reared from the normal kittens. But thereafter in the dark reared kittens the specific cells tend to disappear while the non-specific cells increase in number. 6. This confirms the view that cells with some highly specific response properties of the adult visual cortical neurones, especially in relation to orientation specificity, are present in the earliest stages in the absence of all visual experience. However, visual experience is necessary to maintain and develop these specific cells after the third week of post-natal life.