Control of their environment reduces emotionality in rats.

Rats reared from birth in a "contingent environment" in which they controlled lighting conditions and the delivery of food and water were compared as adults to rats reared in an environment in which they received the same food, water, and lighting conditions, but without control over their occurrence. Rats reared in the contingent environment were less emotional, as judged by activity and defecation scores in open-field testing.