Environmental influences on brain and behavior of year-old rats

The brains of rats, almost a year old, were found to be similarly susceptible to the influences of differential housing as had been those of weanling rats. In 3 experiments, male S1 rats, about 285 days of age, remained for 30, 60, or 90 days in enriched (EC), impoverished (IC), or standard colony (SC) conditions before sacrifice for measures of weights and enzymatic activities of standardized brain sections. Occipital and total cortical brain weights increased significantly after EC, whereas subcortical regions seemed to be resistant to environmental influences. Year‐old rats responded with greater cortical weight increases and enhanced occipital cholinesterase activities from a period of enrichment extended beyond 60 days than SC agemates. The cortices of IC rats, in contrast, showed a decline in weights with longer duration in isolation. Environmental enrichment, furthermore, disposed year‐old rats to faster learning in the Lashley III maze.