Environmentally induced changes in the dimensions of the rat cerebrum

Two groups of rats were reared under conditions of environmental complexity while their littermates were reared in isolation. Cerebral length and width were measured following 30 and 80 days of differential rearing. In the 30‐day group differences in neither cerebral length nor width reached significant levels but the product of the 2 parameters was 2.1 % (p < .02) greater in the stimulated animals. In the 80‐day group cerebral length was significantly greater (p < .001) in the stimulated animals than in their isolated littermates, but no significant differences in cerebral width were detected.