Engagement of amygdala in third-person view of face-to-face interaction

Humans often watch interactions between other people without taking part in the interaction themselves. Strikingly little is, however, known about how gestures and expressions of two interacting humans are processed in the observer's brain, since the study of social cues has mostly focused on the perception of solitary humans. To investigate the neural underpinnings of the third-person view of social interaction, we studied brain activations of subjects who observed two humans either facing toward or away from each other. Activations within the amygdala, posterior superior temporal sulcus (pSTS), and dorsomedial prefrontal cortex (dmPFC) were sensitive to the interactional position of the observed people and distinguished humans facing toward from humans facing away. The amygdala was most sensitive to face-to-face interaction and did not differentiate the humans facing away from the pixelated control figures, whereas the pSTS dissociated both human stimuli from the pixel figures. The results of the amygdala reactivity suggest that, in addition to regulating interpersonal distance towards oneself, the amygdala is involved in the assessment of the proximity between two other persons.