Social reward: interactions with social status, social communication, aggression, and associated neural activation in the ventral tegmental area

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Nearly all species engage in a variety of intraspecific social interactions, and there is evidence that these interactions are rewarding. Less is known, however, about the factors that influence social reward. Using the conditioned place preference paradigm, we tested whether social interactions are rewarding for male Syrian hamsters. We also tested whether social stimuli increase neural activation in the ventral tegmental area (VTA), a component of the mesolimbic reward system, and how individual differences in social behavior and experience influence neural activation. In the present study, we found that hamsters developed a conditioned place preference for social interactions, but the effects were significantly stronger in dominant animals compared with subordinates. The number of Fos-immunoreactive cells in the VTA was significantly higher in hamsters that had engaged in a direct social encounter compared with hamsters exposed to a caged stimulus hamster or controls. Interestingly, socially experienced males had more Fos-immunoreactive cells in the VTA than socially naive males after exposure to a social stimulus. Surprisingly, the amount of Fos immunoreactivity in the VTA induced by a social stimulus was correlated with the amount of aggressive/dominance behaviors that had been observed during interactions that had occurred 2 months earlier. Our results indicate that social interactions between males are rewarding, and that social dominance increases the reward value. Social interactions stimulate the mesolimbic reward system, and social experience enhances its response to novel social stimuli and may produce long-term changes in the neural mechanisms that mediate the maintenance of dominance over long periods of time.