Robust learning of affective trait associations with faces when the hippocampus is damaged, but not when the amygdala and temporal pole are damaged.

People can form evaluative associations with faces after obtaining a small amount of behavioral information. We studied whether patients with medial temporal lobe amnesia can form such associations. Participants were presented with trustworthy- and untrustworthy-looking faces paired with positive or negative descriptions of behaviors. After the learning task, they were asked to rate the same faces on trait dimensions--trustworthiness, likeability and competence--and to make forced-choice judgments between faces. Normal young and older adults judged faces that had been associated with positive behaviors more positively than faces that had been associated with negative behaviors. A patient with hippocampal lesions showed similar learning effects. In contrast, two patients with hippocampal lesions that extended into the left amygdala and temporal pole showed little evidence of learning. All patients judged trustworthy-looking faces more positively than untrustworthy-looking faces. The findings suggest that the hippocampus is not critical for learning affective associations between traits and faces.