What is fNIRS?
Functional near-infrared spectroscopy (fNIRS) is a non-invasive brain imaging technology that uses near-infrared light, typically in the 650–900 nm range, to monitor neural activity. An fNIRS system consists of two key components: a source optode that emits near-infrared light, and a detector optode that measures it; both are placed on the scalp’s surface. Because biological tissue is relatively transparent to near-infrared light, the emitted light penetrates the scalp and skull, reaching the surface of the cerebral cortex, where it scatters and is partially absorbed before being detected by the adjacent detector. By measuring changes in light intensity across multiple wavelengths, fNIRS estimates the concentrations of oxyhemoglobin (HbO) and deoxyhemoglobin (HbR) in the underlying tissue. Since neural activity increases local metabolic demand, triggering a rise in blood flow and oxygenation, these hemodynamic changes serve as an indirect, yet reliable, indicator of brain activity.
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