Individual differences in social play behaviour in rats: behavioural microstructure and communication.

Social play behaviour is rewarding and important for the development of brain and behaviour. Disruptions of social play behaviour in rats have been associated with social and cognitive deficits. How natural variation in social play contributes to development of brain and behaviour remains unclear. It is common knowledge that there are differences in the amount of play behaviour between strain and sexes. Furthermore, even within a strain and within a sex, individuals differ in how much they play. Findings that show that individual differences in play lead to a different response to neural manipulations suggests that individual differences in playfulness may also be a valuable avenue for studying the neuro-behavioural mechanisms that regulate play.
To this end, male Lister hooded rats were characterized as high, medium and low players (HP, MP and LP) based on the sum rank score of the amount of play they initiated and received across three days with an unfamiliar partner. Once animals were categorized in player-types, microstructural analyses of play were conducted to assess differences in the way animals play. To investigate differences in communication during play, ultrasonic vocalizations (USVs) were recorded.
Our data shows that the player-types differ significantly in the amount of play they initiate but less in the amount they receive. Furthermore, the microstructure of play differs between HP and LP as well as the communication during play. These results give insight into how individual animals behave and communicate during social play. Future research may indicate whether individual differences in play also lead to differences in the brain.