Brain habituation during repeated exposure to fearful and neutral faces: a functional MRI study.

Central nervous system habituation in humans was studied using functional magnetic resonance imaging and repeated presentations of single fearful and neutral faces. Habituation of blood-oxygenation-level-dependent (BOLD) signal during exposure to face stimuli, collapsed over fearful and neutral expressions, was evident in the right amygdala and hippocampus, as well as in the medial/inferior temporal cortex bilaterally. In the hippocampus, significantly greater habituation was evident on the right as compared to the left side, which could reflect the visual nature of the stimuli. There were no time by expression interaction effects in these regions, suggesting similar neural attenuation rates to fearful and neutral face stimuli. These results indicate that brain regions involved in novelty detection and memory processing habituate at similar rates regardless of whether the face in focus displays an aversive emotional expression or not.