Differences in Maze Performance of Group- vs Isolation-Reared Rats

A number of experimental investigations have verified that alterations in an animal's early experience may modify its normal pattern of behavior in adulthood (summarized by Denenberg, 1962 ) . Angermeier ( 1960), for example, found that animals reared together or in social isolation differ with respect to learning an instrumental response to obtain several kinds of social contacc. Recently, Woods (1959) confirmed the findings of Bingham and Griffiths (1952) and others (Forgays & Forgays, 1952) that rats reared in a restricted environment are inferior in later problem-solving ability to rhose reared in an enriched, free environment. In addition, however, Woods revealed that the restricted animals' inferiority in problem solving could be considerably reduced by adult exposure to free environmental experiences. Several years ago, it was observed in our laboratory that adult rats selected from large colony cages seemed to learn a maze in fewer trials chan rhose reared in individual cages after weaning. Additional evidence to this effect was summarized in an unpublisl~ed report by Myers and Jones.' Eight rats reared in a group for 120 days achieved criterion in a maze learning task more rapidly chan an equated group reared in isolation for the same period. The purpose of the present experiment was to replicate the latter srudy, and to determine the effects of much longer periods of isolation- and group-rearing on rats' maze performance. METHOD Szcbjects and appamtz!s.-Sixteen hooded rats of the Colgate strain were randomly selected from a large number of litters born at approximately similar times. Upon weaning at 21 days, eight rats were reared in isolation in individual cages, and the remaining eight were reared together in a single cage. The isolation cages were constructed so that Ss could not come into visual or physical contacc with each other at any time during the rearing period. Also, none of