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Near-infrared spectroscopy (NIRS), which can be used to detect changes in the concentration of oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) in tissue by using illumination at two different wavelengths, is often applied to noninvasive measurements of human brain functions. It is common to use two wavelengths that are on opposite sides of the point where the optical absorptions of oxy- and deoxy-Hb are equal (about 800 nm) but an optimal wavelength pair has not yet been determined. In this study, we conducted simultaneous recordings at five wavelengths (678, 692, 750, 782, and 830 nm) to determine the best wavelength for pairing with 830 nm. A theory suggests that pairing a shorter wavelength with 830 nm can provide more sensitivity because of the larger difference in absorption coefficients of hemoglobin between two wavelengths. The changes measured in four cortical …