Amygdala response to happy faces as a function of extraversion.

Cognitive neuroscience aims to delineate principles of brain-behavior relations by characterizing both common mechanisms across, and individual differences among, individuals. Both approaches are relevant for the study of the amygdala, a critical structure for the processing of emotional signals (1). Consistent activation to fearful facial expressions (2– 4 ) may reflect a shared neural mechanism, whereas inconsistent activation to happy facial expressions (2– 4 ) may reflect individual differences in the personality trait of extraversion (5), given that amygdala activation to positive emotional scenes varies as a function of this trait (6 ). We used functional magnetic resonance imaging (fMRI) to examine whether amygdala activation to fearful expressions is independent of extraversion and whether amygdala activation to happy expressions varies with extraversion (7 ). Significant amygdala activation across participants was found only for fearful expressions (Fig. 1, left). Amygdala activation for happy expressions correlated positively and significantly with the degree of extraversion (Fig. 1, middle and right). The center of the correlation cluster was located in the amygdala but extended into regions of the uncus and hippocampus. The specificity of the relation between extraversion and amygdala activation to happy expressions was supported in three ways: (i) Extraversion did not correlate significantly with activation to other emotional (angry, fearful, and sad) expressions; (ii) neuroticism did not correlate significantly with activation to any expression; and (iii) this correlation was the largest of all possible correlations among the “big 5” major personality traits factors (extraversion, neuroticism, openness, agreeableness, and conscien-