Cerebral changes in rats exposed individually to an enriched environment.

This study is part of a continuing attempt to define the environmental conditions necessary to bring about cerebral differences between rodents exposed to enriched and impoverished environments.Rats placed singly in large enriched-environment cages for 2 hr.per day over a 30-day period were found to develop differences from home.:'cage controllittermates in weights. of brain sections and in brain-enzyme activities.These differences are small, however, unless the rat's interaction with the stimulus objects is facilitated; such priming can be accomplished by putting the rat in the enriched environment in the dark under the influence of an excitant drug.Social stimulation, which heretofore has always been included in the enriched condition, is now found not to be necessary.