Brief daily binocular vision prevents monocular deprivation effects in visual cortex.

Even short periods of early monocular deprivation result in reduced cortical representation and visual acuity of the deprived eye. However, we have shown recently that the dramatic deprivation effects on vision can be prevented entirely if the animal receives a brief period of concordant binocular vision each day. We examine here the extent to which the cortical deprivation effects can be counteracted by daily periods of normal experience. Cats received variable daily regimens of monocular deprivation (by wearing a mask) and binocular vision. We subsequently assessed visual cortex function with optical imaging of intrinsic signals and visually evoked potential recordings. Regardless of the overall length of visual experience, daily binocular vision for as little as 30 min, but no less, allowed normal ocular dominance and visual responses to be maintained despite several times longer periods of deprivation. Thus, the absolute amount of daily binocular vision rather than its relative share of the daily exposure determined the outcome. When 30 min of binocular exposure was broken up into two 15-min blocks flanking the deprivation period, ocular dominance resembled that of animals with only 15 min of binocular vision, suggesting that binocular experience must be continuous to be most effective. Our results demonstrate that normal experience is clearly more efficacious in maintaining normal functional architecture of the visual cortex than abnormal experience is in altering it. The beneficial effects of very short periods of binocular vision may prevent any long-term effects (amblyopia) from brief periods of compromised vision through injury or infection during development.