Amygdala and insular responses to emotionally valenced human faces in small animal specific phobia

Background Contemporary neurobiological models suggest that the amygdala plays an important role in the pathophysiology of anxiety disorders. However, it is not clear to what extent this concept applies across anxiety disorders. Several studies have examined brain function in specific phobias but did not demonstrate amygdala responses or use specific probes of the amygdala. Methods Ten subjects with specific small animal phobia and 10 matched control subjects were studied with functional magnetic resonance imaging. Subjects viewed emotionally expressive and neutral faces, and amygdala blood oxygenation level dependent responses from each group were compared. Results There was a significant response to the fearful versus neutral faces in the amygdala across both groups but no diagnosis × condition interaction. Post hoc analysis of the whole brain revealed a significantly greater response to the fearful versus neutral faces in the right insular cortex of the specific phobia group than in the control group. Conclusions Amygdala hyperresponsivity to emotional faces was not observed in subjects with small animal specific phobia, in contrast to findings in other anxiety disorders (e.g., posttraumatic stress disorder). This suggests a restricted role for the amygdala in specific phobia. The insular hyperresponsivity to fearful versus neutral faces in the subjects with specific phobias warrants further study.