The human amygdala is necessary for developing and expressing normal interpersonal trust

► Unilateral damage to the human amygdala resulted in increases in trust following defections from others. ► Normal healthy adults repay trust or defections from others in Tit-for-Tat manner. ► The human amygdala is necessary for developing and expressing interpersonal trust and may relate to the abnormal social behavior often following amygdala damage.