News/Blog series · Part 1
What is fNIRS?
How near-infrared light lets us watch the brain at work, explained in four steps.
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.
Sources and detectors
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.
Why near-infrared light?
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.
Try it: the optical window
760 nm: inside the window
Tissue is relatively transparent here, so light reaches the cortex and can make it back to a detector.
Follow the light
Click a layer, or switch between a brain at rest and an active brain, to see what the detector picks up.
Brain at rest
Light from the source (S) travels through the scalp and skull to the surface of the cortex, scatters, and part of it reaches the detector (D).
From light to brain activity
A source optode on the scalp emits near-infrared light, typically between 650 and 900 nm.
The light penetrates the scalp and skull and reaches the surface of the cerebral cortex, where it scatters and is partially absorbed.
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.
References
See fNIRS in action
HiveOne brings wearable fNIRS to your research, with setup in minutes.