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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.