From the Journal of Duh — pardon, Current Directions in Psychological Science — new evidence that Your Mom Was Wrong: Horseplay Is An Important Part Of Development:
For example, adult rats deprived of peer interaction, (and thus rough and tumble play), reveal an inability to comprehend the hierarchy of social structures. In the rat kingdom, when a young male attempts to establish residency in a colony, he is promptly targeted for attack by the dominant male rat. Rats that have been reared with peers quickly learn to remain crouched and motionless in such an instance in order to avoid the dominant male’s attention. Play deprived rats, on the other hand, continue to scurry about which ultimately invites further serious attacks.Coordinated movements appear to suffer in the absence of rough and tumble play as well. Rats, as most other mammals, rely heavily on coordinated movement for both cooperative (e.g. sex) and competitive (e.g. defending a piece of food) situations. Rats that are reared in isolation have impaired ability to coordinate their movements appropriately with opponents. This coordination, say the authors, can be learned through the constantly shifting body motions that take place during playfighting.
Deprivation from peer interaction appears to have neurological consequences as well. Juvenile play fighting has been found to stimulate the release of certain chemical growth factors in the cerebral cortex, an area the authors describe as the “social brain.” Among the structures in the social brain is the orbitofrontal cortex, an area known to be involved in social discrimination and decision. As logic would tell us, the less growth is promoted in this area, the greater the likelihood of impaired movement coordination, perception of social cues, and the like.