Ji Young Hwang¹ (), Allen Chen¹, Jerry Jin¹, Heejae Kim¹, Lydia M. Hopper¹, Charles E. Connor¹; ¹Johns Hopkins University

Face information in ventral visual cortex is primarily structural and encodes face identities by their locations in a structural “face space”. Face responsive regions in medial temporal lobe memory structures, including amygdala, associate specific identities with personal characteristics, such as aggressiveness (expression) and social rank. Here, we found that face responsive regions of amygdala and entorhinal cortex also encoded interpersonal relationships between individuals in stable social groups of 5–10 macaque monkeys. This naturally required that individual neurons encode information about multiple individuals, which depended on a radial coding format, centered on individual monkeys and rate encoding the relationship levels of other monkeys to that central individual. Thus, a given neuron might represent how submissive every other monkey was to monkey X. To characterize interpersonal relationships within four macaque social groups, we collected multi-camera surveillance videos in both indoor and outdoor runs across a three-month time frame. We analyzed these videos to measure frequencies of affiliative, aggressive, and submissive behaviors between all pairs of monkeys within each group. Two subject monkeys from the same group were studied with linear array probe recording in amygdala and adjacent entorhinal cortex while viewing photographs of monkeys from the home, neighboring, and unfamiliar groups. We analyzed neural coding of personal social knowledge about home and neighboring groups, using unfamiliar monkeys as a control. We found that many neurons in amygdala and entorhinal cortex encode social knowledge about interpersonal relationships involving either the subject monkey relating to other monkeys (self to other) or relationships not involving the self (other to other). In both cases, information about interpersonal relationships was represented in a radial coding format, in which the self or another monkey was the central node and the responses to other monkeys’ faces correlated with a behavioral frequency relative to the central monkey.