Your Brain Emits a Faint Glow, Revealing How It Functions

A New Frontier in Brain Research: The Discovery of Brain Light

The human brain is often viewed through the lens of its electrical and chemical activity, but recent scientific discoveries have revealed a surprising new dimension — it also emits light. This faint, invisible glow has intrigued researchers for decades, but now, for the first time, scientists have directly measured ultraweak photon emissions (UPEs) from outside the skull. These minuscule bursts of light suggest that the brain doesn’t just think — it shines.

Nirosha Murugan, a biophysicist at Wilfrid Laurier University and senior author of the study, emphasizes that this discovery is significant. “The very first finding is that photons are coming out of the head — full stop,” she said. “It’s independent, it’s not spurious, it’s not random.”

While the exact meaning of these photons remains unclear, the study suggests a potential link between the brain’s metabolism and its optical signature. This endogenous glow could serve as a new kind of non-invasive signal, potentially revealing physiological or cognitive states through what researchers call “photoencephalography.” In other words, “brain light” may encode information in ways never previously considered.

A Different Kind of Brain Signal

The brain’s glow is not like bioluminescence — the firefly-like radiance created by special enzymes. Nor is it the infrared thermal radiation from body heat. Instead, it is thought to be the result of spontaneous photon release from biological metabolism. This light is unimaginably dim — millions of times weaker than what the human eye can see. Yet, it occurs constantly in all living tissues.

For nearly a century, scientists have speculated whether there’s more to these ultraweak emissions than meets the eye. They may represent a new mode of biological signaling. The idea dates back to the 1920s, when Russian scientist Alexander Gurwitsch proposed that dividing cells emit “mitogenetic rays,” which he believed could influence the behavior of nearby tissues. In the 1970s and 1980s, German physicist Fritz-Albert Popp coined the term “biophotons” and argued that these emissions might synchronize cellular processes across the body.

Despite such bold claims, most of the scientific community regarded biophotons as noise — a byproduct of molecular excitation, not a functional signal. But Murugan and her colleagues were interested in something new: Could these photons be used to monitor the brain, perhaps even track cognitive states, without sending any energy into it?

Capturing Light from the Thinking Brain

To find out, the researchers designed a sensitive experiment using photomultiplier tubes. These devices are capable of counting individual photons. They placed sensors just above two regions of the skull: the occipital lobes, which process visual information, and the temporal lobes, which handle sound. A third sensor captured background light.

Participants sat quietly in total darkness and completed a series of simple tasks: resting with eyes open or closed, or listening to rhythmic clicking sounds. Meanwhile, the scientists recorded photon counts from each detector, along with brainwave activity via EEG.

What they found surprised them. Not only did the photon detectors register a clear, consistent signal from the brain, but the signal changed with the tasks. The photons pulsed in slow rhythms, typically between once every 10 seconds and once per second, and the spectral characteristics and entropy of these pulses were distinct from background light. The researchers dubbed the method “photoencephalography.”

Light and Brainwaves: A Weak Link?

While the photon emissions were clearly real, their relationship to brain activity remained puzzling. The brain is a metabolically hungry organ, using about 20 percent of the body’s energy despite being just 2 percent of its mass. When neurons fire, they ramp up oxidative reactions that can release excited molecules — potential sources of UPEs.

This led researchers to suspect that photon counts might rise during more active mental states. And, in some ways, they did. For example, when participants closed their eyes (which typically boosts alpha brain waves), UPEs from the occipital lobe also changed. There was even a correlation between the variability of photon emissions and the spectral power of EEG signals during these periods.

But the patterns weren’t always clear or consistent. Some expected correlations between UPEs and brainwaves failed to appear. In other cases, light detected over one region of the brain correlated with activity in a different, distant region. Maybe some photons travel, scatter, or are absorbed in complex ways within the brain, but scientists just don’t know yet.

What Could These Photons Be Doing?

The study’s data leave room for multiple interpretations. One possibility is that these photons are just metabolic exhaust, the byproducts of oxidative stress and normal brain activity. Their frequency, variability, and spectral features may still provide useful biomarkers, even if the photons don’t carry information themselves.

Another possibility, more speculative, is that the photons do transmit information within the brain. Some researchers have suggested that certain neurons, especially myelinated axons, might act as optical waveguides, similarly to light-transmitting fibers like those in fiber optic cables. If that’s true, the brain might be using light to supplement or modulate its traditional electrochemical signals.

Still, even if the photons serve no purpose beyond indicating brain metabolism, the implications are significant. A future generation of photoencephalography devices might detect early signs of neurodegeneration, metabolic imbalance, or even trauma, based on patterns of faint light flickering from within the head.

The Road Ahead

For now, technical hurdles remain. The detectors used in the study could measure total photon counts but couldn’t distinguish between different wavelengths. This parameter is key if brain light is to be linked to aging, cognitive potential, and disease.

Future experiments will need denser sensor arrays, better spatial resolution, and selective filters that can identify specific spectral fingerprints. The goal is to turn faint glows into precise maps of brain function.

And then there’s the biggest unknown: What causes the photon emissions to change in the first place? In the end, it may turn out that we are not just electrical or chemical beings. We may also be faintly luminous ones.