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Abstract. Optical topography ͑OT͒ based on near-infrared spectroscopy is a noninvasive technique for mapping the relative concentration changes in oxygenated and deoxygenated hemoglobin ͑oxy-and deoxy-Hb, respectively͒ in the human cerebral cortex. In our previous study, we developed a small and light wearable optical topography ͑WOT͒ system that covers the entire forehead for monitoring prefrontal activation. In the present study, we examine whether the WOT system is applicable to OT measurement while walking, which has been difficult with conventional OT systems. We conduct OT measurements while subjects perform an attention-demanding ͑AD͒ task of balancing a ping-pong ball on a small card while walking. The measured time course and power spectra of the relative concentration changes in oxy-and deoxy-Hb show that the step-related changes in the oxy-and deoxy-Hb signals are negligible compared to the taskrelated changes. Statistical assessment of the task-related changes in the oxy-Hb signals show that the dorsolateral prefrontal cortex and rostral prefrontal area are significantly activated during the AD task. These results suggest that our functional imaging technique with the WOT system is applicable to OT measurement while walking, and will be a powerful tool for evaluating brain activation in a natural environment.

Neurocognitive research has the potential to identify the relevant effects of music therapy. In this study, we examined the effect of music mode (major vs. minor) on stress reduction using optical topography and an endocrinological stress marker. In salivary cortisol levels, we observed that stressful conditions such as mental fatigue (thinking and creating a response) was reduced more by major mode music than by minor mode music. We suggest that music specifically induces an emotional response similar to a pleasant experience or happiness. Moreover, we demonstrated the typical asymmetrical pattern of stress responses in upper temporal cortex areas, and suggested that happiness/sadness emotional processing might be related to stress reduction by music.

Near-infrared spectroscopy (NIRS) can measure the product of the optical path length and the concentration change in oxygenated hemoglobin (DeltaC'oxy), deoxygenated hemoglobin (DeltaC'deoxy), and their sum (DeltaC'total) in the human cerebral cortex, and it has been used for noninvasive investigation of human brain functions. We evaluate the within-subject reproducibility of the NIRS signals by repeated measurement of the sensorimotor cortex in healthy adults taken over a period of about 6 months using near-infrared (NIR) topography. The maximum signal amplitudes and the location of activation centers are compared between two sessions for each subject. The signal amplitudes vary between sessions and no consistent tendency in the changes is found among subjects. However, the distance between the activation centers identified in two sessions is relatively small, within 20 mm on average across subjects, which is comparable to the smallest distance between measurement positions in the NIR topography (21 mm). Moreover, within-subject comparisons of signal time courses show high correlation coefficients (>0.8) between the two sessions. This result, demonstrating a high within-subject reproducibility of the temporal information in NIRS signals, particularly contributes to the development of a new application of NIRS.