Reversal of the physiological effects of monocular deprivation in the kitten's visual cortex.

Abstract

Kittens (23) were monocularly deprived of vision until the age of 4, 5, 6 or 7 wk. Their deprived eyes were then opened, and their experienced eyes shut for another 3-63 days. After this time physiological recordings were made in the visual cortex, area 17. Three control kittens, monocularly deprived for various periods, showed that at the time of reverse-suturing, few neurons could be influenced at all from the deprived eye. Following reverse-suturing, the initially deprived eye regained control of cortical neurons. This switch of cortical ocular dominance was most rapid following reverse-suturing at the age of 4 wk. Delaying the age of reverse-suturing reduced the rate and then the extent of the cortical ocular dominance changes. The cortex of reverse-sutured kittens was divided into regions of cells dominated by 1 eye or the other. The relative sizes of these ocular dominance columns changed during reversed deprivation. The columns devoted to the initially deprived eye were very small in animals reverse-sutured for brief periods, but in animals that underwent longer periods of reversed deprivation, the columns driven by that eye were larger, while those devoted to the initially open eye were smaller. Clear progressions of orientation columns across the cortex were apparent in many of the kittens, but, in contrast to the situation in normal or strabismic kittens, these sequences were disrupted at the borders of eye dominance columns: the cortical representations of orientation and ocular dominance were not independent. Binocular units in these kittens were rather rare, but those that could be found often had dissimilar receptive field properties in the 2 eyes. Commonly, a cell had a normal orientation selective receptive field in 1 eye, and an immature, unselective receptive field in the other. Cells that had orientation selective receptive fields in both eyes often had greatly differing orientation preferences in the 2 eyes, occasionally by nearly 90.degree.. During the reversal of deprivation effects, the proportion of receptive fields exhibiting mature properties declined in the initially experienced eye, while the proportion increased in the initially deprived eye. Similarly, the average band width of orientation tuning of receptive fields in the initially deprived eye decreased, while that of receptive fields in the initially experienced eye increased. One kitten was reverse-sutured twice, to demonstrate that cortical ocular dominance may be reversed a 2nd time, even after 1 reversal of ocular dominance. The sensitive period for cortical binocular development probably consists of 2 phases. In the 1st phase, all cortical neurons may be modified by experience, but the rate at which they may be modified decreases with age. In the 2nd phase, an increasing number of cortical neurons becomes fixed in their properties, while those that remain modifiable are as modifiable as they were at the end of the 1st phase. While the innate endowment of cortical neurons is important for the normal course of development, it is overshadowed by environmental factors, since cortical neurons may develop normal mature receptive fields different from the ones that they were initially given, after the innate connections were abolished by deprivation.