Cross-Modal Representation of Identity in Primate Hippocampus

Faces and voices are the dominant social signals used to recognize individuals amongst human and nonhuman primates ( 1 – 4 ). Yet it is not known how these critical signals are integrated into a cross-modal representation of individual identity in the primate brain. Here we show that while, like humans ( 5 – 7 ), single neurons in the marmoset hippocampus exhibit selective responses when presented with the face or voice of a specific individual conspecific, a parallel mechanism for representing the cross-modal identities for multiple individuals is evident within single neurons and at a population level. Manifold projections likewise showed separability of individuals, as well as clustering for others’ families, suggesting that multiple learned social categories are encoded as related dimensions of identity in hippocampus. These findings demonstrate that neural representations of identity in hippocampus are both modality-independent and reflect the hierarchical structure of the primate social network. One-Sentence Summary We show that cross-modal representations of identity in primate hippocampus can be achieved by at least two distinct neural mechanisms and comprise multiple social categories that reflect different relationships.