Insular cortex to ventral striatum synapses encode valence of social interaction

Abstract The decision to approach or avoid a conspecific is fundamental for survival. Affiliative (prosocial) interactions favor approach behaviors, while antagonistic (aggressive) contacts trigger avoidance. Here we ask how the brain encodes the valence of social interaction. We focused on the nucleus accumbens (NAc), a brain region implicated in social reward processing. We observed that social interactions activate D1-expressing medium spiny neurons (D1-MSNs) regardless of their valence. However, afferent D1- expressing neurons of the anterior insular cortex (AIC) exhibited distinct activity patterns coding for prosocial and aggressive social interaction, respectively. As a result, distinct forms of synaptic plasticity were elicited at the AIC to NAc synapses. Thus, the valence of social interaction induces distinct neural activity in the AIC, which teaches the animal to approach and avoid conspecifics in the future.