Resting Amygdala and Medial Prefrontal Metabolism Predicts Functional Activation of the Fear Extinction Circuit

Objective: Individual differences in a person's ability to control fear have been linked to activation in the dorsal anterior cingulate cortex, the ventromedial prefrontal cortex, and the amygdala. This study investigated whether functional variance in this network can be predicted by resting metabolism in these same regions. Method: The authors measured resting brain metabolism in healthy volunteers with positron emission tomography using [F-18]fluorodeoxyglucose. This was followed by a 2-day fear conditioning and extinction training paradigm using functional MRI to measure brain activation during fear extinction and recall. The authors used skin conductance response to index conditioned responding, and they used resting metabolism in the amygdala, the dorsal anterior cingulate cortex, and the ventromedial prefrontal cortex to predict responses during fear extinction and extinction recall. Results: During extinction training, resting amygdala metabolism positively predicted activation in the ventromeclial prefrontal cortex and negatively predicted activation in the dorsal anterior cingulate cortex. In contrast, during extinction recall, resting amygdala metabolism negatively predicted activation in the ventromedial prefrontal cortex and positively predicted activation in the dorsal anterior cingulate cortex. In addition, resting metabolism in the dorsal anterior cingulate cortex predicted fear expression (as measured by skin conductance response) during extinction recall. Conclusions: Resting brain metabolism predicted neuronal reactivity and skin conductance changes associated with the recall of the fear extinction memory.