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

Abstract

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.

Fig. 1

The relation between the amygdala's response to emotionally neutral faces and variations of these faces on trait dimensions. A coronal brain slice showing face responsive voxels in bilateral amygdala (A). An intensity color plot showing correlations between the response in left and right amygdalae to faces and trait judgments of these faces (B). The first two columns show zero-order correlations and the fourth and fifth columns show partial correlations controlling for the valence content of the judgments. The third column shows the correlations between trait judgments and a valence component derived from a principal components analysis of the judgments. The traits are ordered according to their correlations with the valence component (Table 1). Scatter plots of the amygdala's response to faces (C for right and D for left) and their values on the valence component. Each point represents a face.

Fig. 2

Scatter plots of the variance accounted for by the valence component in each of 14 trait judgments and the variance accounted for by these judgments in the amygdala's response to emotionally neutral faces (A for right and B for left amygdala).

Fig. 3

The relation between the response in regions in temporal and occipital cortices to emotionally neutral faces and variations of these faces on trait dimensions. Coronal brain slices showing face-responsive voxels in right superior occipital gyrus (A), bilateral fusiform gyri (B) and right middle temporal/occipital gyrus (C). An intensity color plot showing correlations between the response in these regions to emotionally neutral faces and trait judgments of these faces (D). The first four columns show zero-order correlations and the second four columns show partial correlations controlling for the valence content of the judgments. The traits are ordered according to their correlations with the valence component (Table 1).