Dynamic tracking of social variables in simultaneous brain recordings of socially interacting monkeys

Primates are deeply social, but the underlying neural basis has been elusive because brain activity is often recorded in artificially constrained conditions. Here, we recorded wireless neural activity simultaneously from two macaque monkeys interacting socially in a natural setting. Neural activity in each monkey encoded key social variables such as allogrooming state, partner identity and joint movements. Surprisingly, neurons in the high-level visual cortex of each monkey continuously tracked a social favor signal, i.e. net duration of allogrooming given versus received, providing a neural basis for grooming reciprocity. In both monkeys, while grooming their partner, neural activity was predicted better by the partners joints and his brain activity. Thus, the receiver of grooming drove the social interaction, not the groomer. Taken together, our findings elucidate the rich and dynamic neural basis of primate social interactions in an ecologically valid setting.