Corpus callosum: region-specific effects of sex, early experience and age.

In infancy, rats were provided handling stimulation and compared at 110 and 215 days of age with non-handled controls. Measurements were made of corpus callosum area, perimeter and length; and width measures were taken at 7 points along the longitudinal axis of the callosum. Callosal size was larger in males than in females, even when adjusted for the larger brain weight of the male. At 110 days handling stimulation increased callosal parameters and resulted in a more regular callosum in males, but this effect was no longer apparent by 215 days. Within the callosum, region-specific effects were found, suggesting that certain callosal fiber populations were involved. Handled males have previously been shown to be more lateralized than non-handled males; thus at least in this experimental system, increased callosal size and regularity is associated with greater hemispheric specialization.