Shared neural codes for eye-gaze and valence

Abstract

The eye-gaze of others is a prominent social cue in primates and crucial for communication1-7, and atypical processing occurs in several conditions as autism-spectrum-disorder (ASD)1,9-14. The neural mechanisms that underlie eye-gaze remain vague, and it is still debated if these computations developed in dedicated neural circuits or shared with non-social elements. In many species, eye-gaze signals a threat and elicits anxiety, yet can also serve as a predictor for the outcome of the encounter: negative or positive2,4,8. Here, we hypothesized and find that neural codes overlap between eye-gaze and valence. Monkeys participated in a modified version of the human-intruder-test8,15 that includes direct and averted eye-gaze and interleaved with blocks of aversive and appetitive conditioning16,17. We find that single-neurons in the amygdala encode gaze18, whereas neurons in the anterior-cingulate-cortex encode the social context19,20 but not gaze. We identify a shared amygdala circuitry where neural responses to averted and direct gaze parallel the responses to appetitive and aversive value, correspondingly. Importantly, we distinguish two shared coding mechanisms: a shared-intensity scheme that is used for gaze and the unconditioned-stimulus, and a shared-activity scheme that is used for gaze and the conditioned-stimulus. The shared-intensity points to overlap in circuitry, whereas the shared-activity requires also correlated activity. Our results demonstrate that eye-gaze is coded as a signal of valence, yet also as the expected value of the interaction. The findings may suggest new insights into the mechanisms that underlie the malfunction of eye-gaze in ASD and the comorbidity with impaired social skills and anxiety.