Differential prefrontal cortex and amygdala habituation to repeatedly presented emotional stimuli

Repeated presentations of emotional facial expressions were used to assess habituation in the human brain using fMRI. Significant fMRI signal decremen t was present in the left dorsolateral prefrontal and premotor cortex, and right amygdala. Within the left prefrontal cortex greater habituation to ha ppy vs fearful stimuli was evident, suggesting devotion of sustained neural resources for processing of threat vs safety signals. In the amygdala, sig nificantly greater habituation was observed on the right compared to the le ft. In contrast, the left amygdala was significantly more activated than th e right to the contrast of fear vs happy. We Speculate that the right amygd ala is part of a dynamic emotional stimulus detection system, while the lef t is specialized for sustained stimulus evaluations. NeuroReport 12:379-383 (C) 2001 Lippincott Williams & Wilkins.