Hippocampal-cortical interactions in the consolidation of social memory

Episodic memories are initially encoded in the hippocampus and subsequently undergo systems consolidation into the neocortex. The nature of memory stored in the hippocampus and neocortex also differs, with the cortex shown to encode memories in more generalized forms. Although several brain regions are known to encode social information, the specific cortical regions and circuits involved in the consolidation of social memory and the nature of the information encoded in the cortex remain unclear. Using in vivo Ca ²⁺ imaging and optogenetic manipulations, we found that infralimbic (IL) neurons projecting to the nucleus accumbens shell (IL ^→NAcSh ) neurons store consolidated social memory. Inactivating IL ^→NAcSh neurons that responded to a familiar conspecific impaired the recognition of other familiar mice including littermates, demonstrating that these neuronal activities support social familiarity. Furthermore, inactivating hippocampal ventral CA1 neurons projecting to the IL disrupted the consolidation of memory for newly familiarized mice while sparing the recognition of littermates. These findings demonstrate the critical role of hippocampal-cortical interactions in the consolidation of social memory.