The effects of early social isolation on the motivation for social play in juvenile rats.

Fifteen-day-old rats were subjected to one of three housing conditions: mother-and-peer (family), peer, and isolation conditions. At 24 days of age, all subjects were rehoused individually. In Experiment 1, play behaviors were monitored in like-raised pairs. Despite their gross lack of social experience, isolation-reared subjects did not exhibit a deficit in frequencies of rough-and-tumble play. It is concluded that the fundamental motivation for rough-and-tumble play is relatively independent of prior learning in rats. Indeed, their elevated dorsal contacts suggested that isolation-raised subjects may have higher appetitive motivation for play. In Experiment 2, the levels of social motivation were compared between family- and isolation-raised animals, using a T-maze. The isolation-raised animals made reliably more choices for social interaction reward over food reward than family-raised animals. Although inconclusive, the results from the two experiments suggest that prolonged social isolation increases the appetitive motivation for social play.