Scientists have long used near-infrared light to study the brain without surgery. This method, called functional near-infrared spectroscopy (fNIRS), shines light into the head to measure how blood absorbs it. Blood absorption shows brain activity because active brain areas use more oxygen. Near-infrared light is light just beyond what the human eye can see. fNIRS is popular because it is portable and cheap compared to machines like MRI, which uses magnets to create detailed brain images. However, fNIRS has a big limit: it can only see about 4 centimeters into the brain, enough to study the brain’s surface but not deeper areas that control things like memory or movement.
A New Discovery
Researchers at the University of Glasgow have found that light can be detected after passing all the way through an adult human head. This was thought impossible because the skull and brain scatter light too much. This research is published in Neurophotonics.
The researchers used a strong laser and a sensitive detector to catch the tiny amount of light that made it through. They aimed the laser at one side of a volunteer’s head and placed the detector on the other side.
The setup blocked out extra light to focus on the photons that traveled the whole way. Computer simulations helped predict how light moves through the head’s layers, like skin, bone, and brain. The simulations matched the experiment, proving the light went through the entire head. The light followed paths with less scattering, like areas with cerebrospinal fluid, a clear liquid around the brain.
This discovery could lead to new fNIRS devices that see deeper brain areas. The method is not ready for everyday use yet - it took 30 minutes to collect data and worked best on someone with fair skin and no hair. Still, it shows what might be possible. With more work, this could create affordable, portable tools for doctors to check brain conditions like strokes or injuries, especially where big machines are not available.