The primate amygdala mediates acute fear but not the behavioral and physiological components of anxious temperament

Temperamentally anxious individuals can be identified in childhood and are at risk to develop anxiety and depressive disorders. In addition, these ind ividuals tend to have extreme asymmetric right prefrontal brain activity. A lthough common and clinically important, little is known about the pathophy siology of anxious temperament. Regardless, indirect evidence from rodent s tudies and difficult to interpret primate studies is used to support the hy pothesis that the amygdala plays a central role. In previous studies using rhesus monkeys, we characterized an anxious temperament endophenotype that is associated with excessive anxiety and fear-related responses and increas ed electrical activity in right frontal brain regions. To examine the role of the amygdala in mediating this endophenotype and other fearful responses , we prepared monkeys with selective fiber sparing ibotenic acid lesions of the amygdala. Unconditioned trait-like anxiety-fear responses remained int act in monkeys with>95% bilateral amygdala destruction. In addition, the le sions did not affect EEG frontal asymmetry. However, acute unconditioned fe ar responses, such as those elicited by exposure to a snake and to an unfam iliar threatening conspecific were blunted in monkeys with>70% lesions. The se findings demonstrate that the primate amygdala is involved in mediating some acute unconditioned fear responses but challenge the notion that the a mygdala is the key structure underlying the dispositional behavioral and ph ysiological characteristics of anxious temperament.