DIFFERENTIAL REARING AFFECTS CORPUS-CALLOSUM SIZE AND COGNITIVE FUNCTION OF RHESUS-MONKEYS

This study investigated the effects of different rearing conditions on neural and cognitive development of male rhesus monkeys (Macaca mulat ta). Infants raised individually in a nursery from 2 to 12 months of a ge (NURSERY, n = 9) were compared to age-matched infants raised in a s emi-naturalistic, social environment (CONTROL, n = 11). Various brain regions were measured by MRI. Although overall brain volumes did not d iffer between NURSERY and CONTROL animals, corpus callosum (CC) size, measured in mid-sagittal sections, was significantly decreased in the NURSERY group. Group differences were most evident in the posterior as pects of the corpus callosum and appeared to result from changes in th e number of cross-hemispheric projections rather than from a decrease in cortical gray matter volume. The decrease in corpus callosum size i n the NURSERY animals persisted after 6 months of social housing in a peer-group. Rearing group differences were not found in other structur es analyzed, including the hippocampus, cerebellum and anterior commis sure. In cognitive testing, NURSERY animals had more difficulty acquir ing the delayed non-matching to sample (DNMS) task, but showed no defi cits in subsequent memory performance when a 2 or 10 min delay was imp osed. The NURSERY infant monkeys were also impaired in object, but not in spatial, reversal learning, although there were no differences in a simple object discrimination task. The cognitive deficits exhibited by the NURSERY animals were significantly correlated with the alterati ons found in the CC. In summary, rearing environment was associated wi th sustained differences in cross-hemispheric projections, white matte r volume and cognitive performance. (C) 1998 Elsevier Science B.V. All rights reserved.