Operant social reward in animal models: behavior, brain mechanisms, and implications to neurodevelopment and psychiatric disorders, stress, and pain

Social connection is a fundamental animal need, and its maintenance primarily depends on the rewarding nature of positive social interactions. A central feature of several medical conditions, including neuropsychiatric disorders, is decreased interest in positive social interactions and a tendency toward social isolation, which can in turn worsen these conditions. Numerous studies using animal models have identified brain mechanisms underlying both unconditioned and conditioned (using conditioned place preference) social interactions, where the interaction is imposed by the experimenter. In contrast, much less is known about the brain mechanisms involved in volitional, rewarding social interactions that are initiated by the animals themselves. This is critical as social interactions between humans are often voluntary. Early studies showed that rats will perform a volitional operant response to gain access to social interaction with a peer. More recently, the operant social self-administration procedure has been used to investigate the brain mechanisms of rewarding social interaction in mice, rats, prairie voles, and hamsters.In this review, we summarize behavioral and neurobiological studies that have used the operant social self-administration procedure. We then discuss how this model has been used to study the effect of volitional social interaction across neurodevelopmental disorders, addiction, stress, pain, and inflammation, including its role in drug self-administration and relapse in rats, the identification of heroin-addiction–vulnerable individuals, and to study how pain and social stress disrupt volitional social interaction. We conclude by briefly discussing future research directions and potential clinical applications.