Critical periods for effects of monocular deprivation: differences between striate and extrastriate cortex.

The critical period of susceptibility to effects of monocular deprivation was compared in striate cortex and the lateral suprasylvian (LS) visual area of cortex. Twenty-three cats received monocular lid suture for a period of 4 weeks beginning at 4, 12, 18, 26, or 35 weeks of age or as adults. Immediately following the deprivation, single cell recordings were carried out in both cortical areas of each cat. Recordings also were made from five normally reared control cats. For both striate and LS cortex, early monocular deprivation had marked effects on neuronal ocular dominance, including an increased percentage of cells dominated by the nondeprived eye, a decreased percentage of cells dominated by the deprived eye, and a decreased percentage of binocularly driven cells. In both cortical areas, these effects were maximal in animals deprived at 4 weeks of age. Both areas then showed similar monotonic declines in effects of the deprivation following onsets from 4 to 18 weeks of age. However, in older animals there were clear differences in the effects of monocular deprivation on LS and striate cortex. In LS cortex, the monotonic decline in effects continued until 26 weeks of age, and no significant abnormalities were present in animals deprived at 26 weeks of age or older. In striate cortex, however, the effects of monocular deprivation remained relatively constant following onsets from 18 to 35 weeks of age, and significant abnormalities in all measures of ocular dominance were present when deprivation was begun as late as 35 weeks of age. Within-animal comparisons indicated that the greater effects of monocular deprivation on striate cortex than on LS cortex were present in every cat deprived at 26 or 35 weeks of age. Neither cortical area showed significant abnormalities following monocular deprivation in adult cats. These results indicate that the critical period for effects of the same regime of monocular deprivation is over sooner in LS cortex (between 18 and 26 weeks of age) than in striate cortex (after 35 weeks of age). This observation has important implications for an understanding of the sites and mechanisms of effects of visual deprivation and the mechanisms that control critical periods of development.