Friend or foe? Brain systems involved in the perception of dynamic signals of menacing and friendly social approaches.

During every social approach, humans must assess each other's intentions. Facial expressions provide cues to assist in these assessments via associations with emotion, the likelihood of affiliation, and personality. In this functional magnetic resonance imaging (fMRI) study, participants viewed animated male characters approaching them in a hallway and making either a happy or an angry facial expression. An expected increase in amygdala and superior temporal sulcus activation to the expression of anger was found. Notably, two other social brain regions also had an increased hemodynamic response to anger relative to happiness, including the lateral fusiform gyrus and a region centered in the middle temporal gyrus. Other brain regions showed little differentiation or an increased level of activity to the happy stimuli. These findings provide insight into the brain mechanisms involved in reading the intentions of other human beings in an overtly social context. In particular, they demonstrate brain regions sensitive to social signals of dominance and affiliation.