MONOCULAR DEPRIVATION AND RECOVERY DURING SENSITIVE PERIOD IN KITTENS

Sixteen kittens received 10 days of monocular visual deprivation. In seven animals, this period was followed immediately by single-unit recording in primary visual cortex. The remainder were studied after a delay of at least 10 days, during which both eyes were open, both were closed, or the initially deprived eye was open and the other eye was closed. Four normally reared kittens provided control data. After 10 days of monocular deprivation beginning at the age of 28 days, only 3% of recorded units responded to visual stimulation through the deprived eye, as opposed to 87% in normal controls. A strong effect was also seen following monocular deprivation of the same duration beginning on days 18, 28, 38, 48, or 58. When a 10-day period of monocular deprivation beginning on day 28 was followed by approximately 30 days of binocular vision, extensive recovery occurred. Many recorded units (61%) gave responses to stimulation through the deprived eye. Cells recorded at this time appeared normal in most regards. They were well tuned for stimulus orientation, preferred the same orientation when stimulated through either eye (in the case of binocular cells), and were arranged in ocular-dominance columns. However, abnormally few units (34%) were binocular, indicating that many neurons had acquired functional connections from the other eye. This failure of binocular connectivity may have been caused by interocular misalignment. In kittens subjected to bilateral eye closure for approximately 30 days following monocular deprivation, many units became visually unresponsive. Among those that did give visual responses, only 20% could be driven through the initially deprived eye. Reversal of eye closure caused a rapidly developing and virtually complete reversal of the initial monocular-deprivation effect. After 10-17 days of reverse suture, 96% of recorded units displayed excitatory input from the initially deprived eye and most of these cells were monocular. We conclude that neurons in striate cortex may regain their responsiveness to an eye that has been unilaterally closed early in the critical period. Recovery is largely dependent on visual stimulation of the initially deprived eye and is enhanced considerably by closing the other eye. Evidence is discussed suggesting that neurons which become responsive to the monocularly deprived eye during a subsequent period of binocular vision may be the same ones that it dominated prior to deprivation.