The effect of visual deprivation on the number of callosal cells in the cat is less pronounced in extrastriate cortex than in the 17/18 border region.

It has been shown that neonatal bilateral enucleation and dark rearing in cats markedly reduce the number of callosal cells in the 17/18 border region, but whether these deprivation paradigms have the same effect in extrastriate cortex is unknown. By comparing numbers of callosal cells retrogradely labeled with horseradish peroxidase in both cortical regions, we found that enucleation and dark rearing had significantly less effect in extrastriate cortex. While less than 20% of the complement of callosal cells normally found at the 17/18 border region was present in this region in deprived cats, at least 60% of the normal complement of callosally-projecting cells was present in extrastriate cortex of deprived cats. These results suggest that visual experience plays a less prominent role in the stabilization of callosal connections in extrastriate visual cortex than in the 17/18 border region.