Early development of visual cortical cells in normal and dark‐reared kittens: relationship between orientation selectivity and ocular dominance.

Abstract

Units (535) were recorded in the primary visual cortex in 12 normally reared and 15 dark-reared kittens aged 8-50 days. These results were pooled with a previous study of 582 units recorded from 35 kittens reared in similar conditions. These 1117 cells were classified into 4 functional classes of neurons: visually unresponsive cells; non-specific cells which were sensitive to spots or slits of light moving in any direction; immature cells which were preferentially activated by a rectilinear stimulus but unselective regarding its precise orientation; and specific cells that appeared to be as selective for orientation as the simple or complex cells in the adult cat. Apparently cells having the same orientation-specific response properties as adult cortical visual neurons are present in the earliest stages of postnatal development, independent of visual experience. To maintain and develop these specific cells after the 3rd wk of post-natal life, visual experience is necessary. The ocular dominance of visual cells was not constant from the earliest stages of development. A significant increase in binocularly driven neurons occurred with age. Before 3 wk of age, whatever the rearing conditions, there were more specific cells coding horizontal and vertical orientations than those coding oblique orientations. These horizontal and vertical detectors are preferentially driven by the contralateral eye. After 4 wk of age, specific neurons were found at all orientations in normally reared kittens. At this stage of development the ocular dominance was independent of orientation preference, of the functional class of neurons considered and of the rearing conditions. The proportion of binocularly driven cells was slightly below adult standards. An hypothesis of differential plasticity was 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 2 inputs occurs, are the labile units which can be despecified or specified under the control of visual experience.