Brain Mechanisms in Japanese Verbal Fluency Test: Evidence from Examination by NIRS (Near-Infrared Spectroscopy)

The aim of this study was to examine the sensibility of NIRS in observation of brain activation during a verbal fluency test. Twenty-three participants were given letter fluency and semantic fluency tests and the hemodynamism was measured by NIRS. Thirty-three pairs of optodes were attached, so they can measure signals from 52 channels consisting of adjacent pairs of emitters and detectors. Results were investigated in terms of the change of blood flow volume value of OxyHb for word generation. The results showed a significant interaction between task (letter fluency and semantic fluency) and cortical area (prefrontal and temporal) in the analysis of variance. Here, the prefrontal area showed marked activation in the left hemisphere during letter fluency task, whereas the temporal area showed activation in the semantic fluency task performance. These findings by NIRS confirmed different cerebral functions between semantic and letter fluency tasks, which were coincident with the findings by previous fMRI studies. Based on these findings, it is clear that NIRS is useful and provides sensitive new brain imaging techniques, which may provide a new horizon in the examination of human language perception and generation processes.