Heightened Play following Play Observation in the Absence of 22KHz Calls in Juvenile Rats

Emotional contagion, the process leading to emotional state matching between individuals is considered a cornerstone for the proper functioning of social groups, via its contribution to group coordination and cohesion, the ability to learn from others and engage in prosocial behaviors. However, to date, most studies of emotional contagion investigate the transfer of negative emotional states thereby bypassing the neurobiology of positive affect sharing. In this study, we aimed to leverage on the innately rewarding and salient nature of play behaviour, to investigate the potential contagiousness of positive affective states in juvenile rats. Observers that had been moderately socially deprived for varying durations first witnessed highly-playful (Play) or non-playful (Control) demonstrator rats prior to being reunited and given the opportunity to freely interact. Surprisingly, we observed the emission of negatively-valenced 22 kHz calls in a subset of sessions which was also associated with heightened play behavior of the demonstrators. We found that the reunited observers showed an increase in play behavior following observation in the Play condition compared to the Control condition, but only after short social isolation and in sessions without 22 kHz calls. In addition, an overall higher number of positively-valenced 50 kHz calls were emitted in the Play condition, again in sessions without 22 kHz emissions. Despite the limitations of the experimental procedure, our results highlight the complex nature of positive emotional sharing and provide encouraging first indications of using social play observation to study positive emotional contagion. Highlights- Social deprivation positively modulates play behavior and USV emission in reunited juvenile rats - Heightened play is associated with 22 kHz USVs following social deprivation - Heightened play was observed following play observation in the absence of 22 kHz USVs - Play observation was associated with an overall increased number of 50 kHz calls emissions - Play observation as an encouraging approach to study positive emotional contagion in rat