Repetition of verbal fluency task attenuates the hemodynamic activation in the left prefrontal cortex: Enhancing the clinical usefulness of near-infrared spectroscopy

In applications of near-infrared spectroscopy (NIRS) in clinical psychiatry settings in Japan, a phonemic verbal fluency test (VFT) that includes "switching" (the ability to shift efficiently to a new word subcategory) to assess phonemic fluency is employed to capture disease-specific hemodynamic changes in the prefrontal cortex (PFC). In this study, to extend the specific features of this test, the VFT was repeated to examine an activation change in NIRS measurements in 20 healthy males. Without task performance change, the hemodynamic activation induced by the VFT was significantly attenuated in the left PFC through repetition of the task. These findings suggest that the left PFC is involved in processing of the VFT. Further, it may be possible to extend the current VFT using this repetition to provide a more sensitive examination of the left PFC, whose dysfunction has been reported in several psychiatric diseases such as major depression, bipolar disorder, and schizophrenia.