Analytical approach to the temporal changes in NIRS signals to separate hemodynamic change from brain activity.

In brain function measurements by near-infrared spectroscopy (NIRS), we focus on the temporal changes in the oxygenated and deoxygenated hemoglobin concentrations and propose an analytical approach to the temporal changes of the hemoglobin concentrations' cross-correlation coefficient in the brain functional signals. The cross-correlation coefficient between the oxygenated and deoxygenated hemoglobin concentrations shows negative values for brain activity and positive values for hemodynamic changes. Experiments with a 16-channel functional NIRS system show that our proposed approach clarifies the interpretation of the measured NIRS signals and it can be used to estimate the influence of hemodynamic change on brain activity.