Collins, R. 1970. Experimental modification of brain weight and behavior in mice: An enrichment study. Psychobiology 3, 145-155.

The effects of environmental enrichment and isolation on cortical weight and learning ability were measured in mice from lines selectively bred for high and low brain weight and from an unselected control line from the same foundation population. Animals from these selected lines differed not only on brain weight, but on discrimination task performance as well. Isolated and enriched animals did not differ in cortical weight, nor was there any significant interaction of rearing conditions with lines. Those animals reared in enrichment were superior to those reared in isolation, both for initial acquisition and for number of reversal tasks performed on a water maze discrimination task. High brain weight animals did not differ from low brain weight animals on initial acquisition across treatment conditions. However, high brain weight animals made significantly more reversals within the testing period. The high, control, and low brain weight animals did not order themselves linearly on the behavioral measures: control line animals performed poorest for both initial acquisition and number of reversals.