Near-infrared spectroscopy (NIRS) has been widely used to non-invasively assess brain function in various psychiatric disorders. Previous NIRS studies have extensively investigated prefrontal activation associated with cognitive tasks; in contrast, NIRS signals from prefrontal cortex in response to emotional stimuli have received little attention. We investigated spatiotemporal characteristics of hemodynamic response during an emotional activation task using fearful facial expression stimuli. We also evaluated gender difference and the relationship with anxiety-related personality traits. Subjects were 10 women and 10 men, all right-handed and matched for age, education and IQ estimated from the adult reading test. NIRS signals that are assumed to reflect regional cerebral blood volume were monitored over prefrontal regions by 52-channel NIRS. Women showed significantly increased [oxy-Hb] change relative to men in the right ventrolateral prefrontal cortex during the latter half of the task period. Frontopolar [deoxy-Hb] response correlated significantly with trait anxiety scores in the whole sample. These results suggest that gender and trait anxiety have an effect on individual variability of NIRS signals in response to emotional stimuli. This observation may help to establish NIRS as a clinical tool for monitoring prefrontal function on an individual basis.
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