• near-infrared spectroscopy;
  • prefrontal cortex;
  • reproducibility;
  • test–retest reliability;
  • verbal fluency task

Aim:  To determine whether intrasubject reproducibility could be observed in the frontal cortex and to assess the mental-health status of subjects in each session.

Methods:  We measured changes in oxygenated hemoglobin concentration ([oxy-Hb]) during a letter version of the verbal fluency task using near-infrared spectroscopy imaging in twenty healthy adults over two sessions approximately two months apart. Additionally, the mental-health status of the subjects in each session was evaluated according to the State–Trait Anxiety Inventory, the Zung Self-rating Depression Scale, the Profile of Mood States, and the revised edition of the Neuroticism–Extroversion–Openness Personality Inventory. The association between those scores and [oxy-Hb] changes during the verbal fluency task in each session was investigated.

Results:  Performance on the verbal fluency task was about equal across the two sessions, and frontal activation during the task was observed globally in approximately the same region. In the test–retest reliability, acceptable values were shown in both the Intraclass Correlation Coefficients of the mean [oxy-Hb] changes and the correlation coefficients of the whole waveforms for each subject in the two sessions. Mental-health status as measured by several questionnaires was within the healthy range, and no correlation with the frontal activation was seen, except in several channels.

Conclusion:  The current results suggest that the measurement experience exerted very little influence, except for in a very small region. In addition, the intrasubject reproducibility of frontal activation measured by multi-channel near-infrared spectroscopy was well demonstrated in mentally healthy subjects at intervals of two months.