Effects of environment on morphology of rat cerebral cortex and hippocampus.

Cortical depth differences were found between male rats exposed to enriched or impoverished environmental conditions for successively shorter times, i.e., for 15 days (from 25 to 40 days of age), for seven days (25 to 32 days of age), and for four days (26 to 30 or 60 to 64 days of age). If the experiments began at weaning (at 25 days of age), the cortical depth changes were caused primarily by impoverishment. If the animals were young adults (60 days of age), upon entering their respective conditions, the cortical changes were induced by enrichment. No cortical depth differences were found between enriched and impoverished rats after one day of differential experience, from 60 to 61 days of age. In every age group and for every duration, except for the one day group, the dorsal-medial segment of the occipital cortex responded to the environmental conditions. No significant hippocampal depth differences were noted between enriched and impoverished animals.