The role of the amygdala in implicit evaluation of emotionally neutral faces

The amygdala is involved in the evaluation of novel stimuli, including faces. We examined whether the amygdala is engaged during the evaluation of emotionally neutral faces along trait-specific dimensions such as trustworthiness and attractiveness or along a general valence dimension. Using behavioral data from evaluation of faces on 14 trait dimensions and fMRI data from an implicit evaluation paradigm, we show that the extent to which the amygdala responds to variations of faces on specific dimensions is a function of the valence content of these dimensions. Variations on dimensions with clear valence connotations (e.g. trustworthiness) engaged the amygdala more strongly than variations on dimensions with less clear valence connotations (e.g. dominance). In addition to the amygdala, several other regions - right superior occipital gyrus, right middle temporal/occipital gyrus and bilateral fusiform gyri - were involved in valence evaluation of faces. However, the relation between these regions and face valence was accounted for by the amygdala's response to faces. The findings suggest that the amygdala (i) automatically evaluates novel faces along a general valence dimension; and (ii) modulates a face responsive network of regions in occipital and temporal cortices.