New fNIRS Method Measures Brain Activity Through Entire Head
Researchers have developed a new fNIRS method that detects brain activity across the entire head.
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Functional near-infrared spectroscopy (fNIRS), a noninvasive optical method for measuring brain activity, has long been valued for its portability and relatively low cost. It works by tracking how near-infrared light is absorbed by blood in the brain. However, a key limitation has persisted: light typically only penetrates around four centimeters into the tissue, restricting measurements to the surface of the brain.
Now, a team of researchers at the University of Glasgow has demonstrated a method that can detect light passing through the entire adult human head. Their findings, published in Neurophotonics, suggest the potential to extend the reach of fNIRS and related technologies.
Functional near-infrared spectroscopy (fNIRS)
A noninvasive optical imaging technique that measures changes in blood oxygenation in the brain by detecting how near-infrared light is absorbed by haemoglobin. It is commonly used to monitor brain activity.
How the team detected light across the head
In the study, the researchers used a pulsed laser source on one side of a participant’s head and a highly sensitive detector on the opposite side. The setup was carefully controlled to eliminate external light sources, allowing the team to capture the small number of photons that traversed the skull and brain tissue.
The experiment also incorporated computational modelling to simulate light transport through the complex layers of the head. The models accurately predicted the paths that photons would take, which were confirmed by the experimental results. According to the researchers, certain pathways within the brain, such as those involving cerebrospinal fluid, are less likely to scatter light, increasing the likelihood of transmission.
Cerebrospinal fluid
A clear, colourless body fluid that surrounds the brain and spinal cord. It cushions the brain, provides nutrients and removes waste. In optical imaging, its lower scattering properties can affect light propagation through the head.
A step forward, but not yet ready for clinical use
The current approach required a data collection period of 30 minutes and was demonstrated on a volunteer with fair skin and no hair, conditions chosen to maximise photon detection. At present, the technique is not suitable for routine brain imaging, but it highlights the possibility of future systems capable of probing deeper brain structures with portable equipment.
These findings may prompt further research into next-generation optical brain imaging tools. Deeper access to brain regions could improve the study of neural circuits involved in functions such as memory, emotion and movement. Additionally, it could support the development of affordable, accessible methods for investigating brain disorders in settings where advanced imaging technologies like MRI are not available.
Reference: Radford J, Gradauskas V, Mitchell KJ, Nerenberg S, Starshynov I, Faccio D. Photon transport through the entire adult human head. Neurophoton. 2025;12(02). doi: 10.1117/1.NPh.12.2.025014
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