Fig. 1.

Assessing brain hemodynamic responses using functional near-infrared spectroscopy (fNIRS). Near-infrared (NIR) light (e.g., at 760 nm and 850 nm) is emitted through the subject’s skull (left panel). Changes in intensity of light absorption and scattering in response to a stimulus are continuously recorded by a NIR light detector. Based on the modified Beer-Lambert Law (mBLL), the measured light intensity can be converted into estimations of cerebral total hemoglobin (HbT) and differentiated into oxygenated and deoxygenated hemoglobin (HbO/HbR) (right panel, t = time, s = seconds, c = concentration).