Processing of facial expressions and their significance for the observer in subregions of the human amygdala.

Amygdala responses to emotional faces can be influenced by concomitant gaze direction. As an explanation it has been suggested that the observer uses eye gaze as a cue to decipher the source of a potential threat in order to evaluate the significance of the situation. To test this assumption, we kept gaze direction ambiguous and replaced the information possibly provided by gaze direction with explicit, contextual information about intentions of angry and fearful faces. Using fMRI we show that this manipulation evokes a similar pattern of amygdala activation as prior gaze-related accounts: angry faces targeting at the observer elicited stronger amygdala responses than angry faces targeting at another person, whereas the opposite pattern was observed for fearful faces. We further combined our paradigm with high-resolution fMRI which enabled us to localize clusters of activation in amygdala subregions: purely facial-expression evoked signal changes were observed in the accessory basal nucleus, whereas our data suggest a critical role of the corticomedial amygdala in linking contextual information to emotional faces and in deciphering the significance of the faces for the observer.