Faces, trust and the amygdala

Abstract

Extensive animal studies have demonstrated that the amygdala is involved in emotional and social functions with emphasis on fear and aggression in particular[ 1 Kling, A.S. and Brothers, L.A. (1992) in The Amygdala: Neurobiological Aspects of Emotion, Memory and Mental Dysfunction (Aggleton, J.P., ed.), pp. 353–378, John Wiley and Sons Google Scholar ]. In humans the neuropsychological and functional neuroimaging evidence indicates that this structure plays a role in the recognition of emotional facial expressions[ 2 Adolphs R. Tranel D. Damasio H. Damasio A. Impaired recognition of emotion in facial expressions following bilateral damage to the human amygdala. Nature. 1994; 372: 669-672 Crossref PubMed Scopus (1685) Google Scholar ]. Adolphs, Tranel and Damasio now provide evidence that the human amygdala is involved in human social judgments that are based upon facial appearance[ 3 Adolphs R. Tranel D. Damasio A.R. The human amygdala in social judgment. Nature. 1998; 393: 470-474 Crossref PubMed Scopus (964) Google Scholar ]. Three subjects with complete bilateral damage to the amygdala were asked to look at a series of 100 pictures of unfamiliar faces. The task was to judge from the appearance of the pictures whether the individuals depicted were approachable and trustworthy. The results demonstrated that the patients with bilateral damage to the amygdala judged unfamiliar faces to be more approachable and trustworthy than did brain-damaged control subjects. (Subjects with unilateral damage to the amygdala did not differ from controls.) Moreover, this impairment in social judgment was most obvious for those faces that the control group rated the most unapproachable and untrustworthy individuals. Indeed, the subjects with bilateral amygdala damage were not impaired when rating the 50 most positively rated faces. Interestingly, this impairment in social judgment did not extend to judgments based on written or verbal descriptions of individuals. The authors contend that these data suggest that the amygdala appears to be necessary for the retrieval of information, particularly in response to visual stimuli, on the basis of prior social experience or an innate bias with respect to certain classes of face. Future research will be required to elaborate upon these findings to determine whether the role of the amygdala in social judgment of faces is based upon innate or acquired information.