Sensory modulation of juvenile play in rats.

A series of experiments was conducted to determine the extent to which somatosensory stimulation is necessary for the elaboration of juvenile play in rats. Anesthetization of the dorsal body surface of juvenile rats with xylocaine reduced the frequency of pinning, an indicator variable for play, by 35% to 70%, while motivation to play, as measured by dorsal contacts, an index of play solicitation, remained largely intact. These data suggest that dorsal body surface anesthetization impairs the ability of juvenile rats to perceive and/or respond to playful gestures. When untreated animals were paired with xylocaine-treated animals, the xylocaine-treated animals consistently pinned the untreated pups more than vice versa, further suggesting that somatosensation may be involved in the establishment and/or maintenance of play dominance relations. A preliminary examination assessing potential involvement of other modalities in the play of rats was also conducted, with the data suggesting a possible role for audition in the play of this species.