Reassessment of near-infrared spectroscopy for measuring human cognitive function

The verbal fluency task (VFT) coupled with near infrared spectroscopy (NIRS) measurement is often used to test cognitive function in elders. However, it is reported that overlapping of oxygenated hemoglobin concentration in the scalp (∆[oxy-Hb]s) on that of the cortex (∆[oxy-Hb]c) is significant in NIRS measurement during performing VFT. In this investigation, we applied the hemodynamic separation method (HDSM) to divide ∆[oxy-Hb]s and ∆[oxy-Hb]c from NIRS signals obtained with commonly used the modified Beer-Lambert Law (∆[oxy-Hb]MBLL). The HDSM assumes differentiation in blood flow regulation between cerebral blood flow (CBF) and systemic blood flow, such as scalp blood flow (SBF), where the stimulus-induced changes in CBF shows antiparallel increase in ∆[oxy-Hb]c and deoxygenated Hb (∆[deoxy-Hb]c) while SBF shows parallel increase in them. In the present study, we evaluated the HDSM by comparing signals obtained by a laser Doppler tissue flowmeter (LDF) with those obtained by NIRS using the modified Beer-Lambert Law (MBLL) and HDSM. © 2021, Japan Soc. of Med. Electronics and Biol. Engineering. All rights reserved.