How Does Light Change the Brain? The Scientific Principles of Near-Infrared Brain Light Regulation.

Near-infrared light (especially the 810 nm wavelength) acts like a special light that “recharges and repairs” the brain. By activating the mitochondria—the cell’s “energy factories”, it triggers a cascade of reactions from molecules to neural networks. Ultimately, it protects neurons, enhances memory, and improves brain function, all in a non-invasive and safe way.

The key to this process is photobiomodulation (PBM). Simply put, it is the interaction between light energy and brain tissue, converting photons into biochemical signals that the brain can use. Through mitochondrial activity, this process ultimately leads to healthier neurons and improved brain function.

🧠Physical foundation: How does light “penetrate” into the brain?🧠

The best “penetrating light”:
810 nm near-infrared light is most suitable for penetrating the brain—it can pass through 15–20% of the skull. Although the energy decreases by 40% for every additional centimeter of brain tissue it travels through (with gray matter blocking more light than white matter), deep brain nuclei can still receive 5–8% of effective light.

Key parameters:
The irradiance should be controlled at 20–50 mW/cm², with a total energy of 1–60 J/cm². If the intensity is too high, it may damage tissue; if it is too low, it will not produce an effect.

The “penetration path” of light:
After 810 nm light shines on the head, 30% is scattered by the skull, 15% is reflected by the pia mater on the brain surface, and 40% is absorbed by the superficial cortex. Ultimately, 5–8% reaches deep brain regions (such as the hippocampus and striatum).

🧠Molecular-level response: first “fuel” the mitochondria, then trigger a chain reaction of signals.🧠

This is the most critical step. It is similar to light first activating the “energy factory,” and then the factory sending out “repair signals.”

Activating mitochondria (the brain’s “photo-battery”)
Light receptor: The cytochrome c oxidase (CCO) on mitochondria, which specifically absorbs the energy of 810 nm light.

Photochemical reaction: The photon energy causes nitric oxide (NO) bound to CCO to detach. This is equivalent to “unlocking” the energy factory, making the electron transport chain more active. As a result, the energy molecule ATP increases by 35–60% (this effect can appear after 4–10 minutes of illumination). At the same time, harmful reactive oxygen species (ROS) can decrease by 40%, helping the brain maintain redox balance (less oxidative damage and less cellular stress).

Triggering signaling pathways (sending “repair instructions”)

Anti-inflammatory pathway (NF-κB):
Inhibits the release of inflammatory factors (such as TNF-α and IL-6), reducing the “inflammatory storm” in the brain and protecting neurons from inflammation-related damage.

Neurotrophic factor pathway (CREB phosphorylation):
Promotes the expression of BDNF and NGF, which act as “neural nutrients,” supporting neuron growth and survival.

Angiogenesis pathway (HIF-1α stabilization):
Increases vascular endothelial growth factor (VEGF), helping the brain form more capillaries, thereby improving blood and oxygen supply.

🧠Cells and neural circuits: strengthening neural connections and making brain networks function more smoothly.🧠

At the neuronal level: After light activation, neurons become more active (with increased energy) and are less likely to undergo cell death. It also promotes the formation of new synapses (connections between neurons), allowing information to be transmitted more smoothly.

Brain network remodeling (focusing on two key pathways):

Default Mode Network (DMN, the brain’s “resting network”):
After irradiating the posterior cingulate cortex with 810 nm light at 40 mW/cm², fMRI shows stronger connectivity within this network (β-band coherence increases by 15%). This can slow the “disintegration” of brain networks in patients with Alzheimer’s disease, helping prevent rapid decline in memory and cognition.

Cortico-striatal pathway (a key pathway controlling movement):
In mouse experiments, irradiating the prefrontal cortex increased the expression of dopamine D1 receptors, improved motor coordination, and reduced tremor symptoms in Parkinson’s disease models by 40% (equivalent to improving motor dysfunction).

 🧠Technical challenges and solutions.🧠

Problem 1: Light does not penetrate deeply enough (deep brain regions cannot be reached).
Solution:
① Intranasal irradiation (light enters through the nose and reaches the limbic system—such as the hippocampus—via the cribriform plate).
② Multi-point array light sources (multiple light sources illuminate simultaneously, using phase interference to focus light in deeper regions).

Problem 2: Different effects for different individuals (large individual variation).
Cause: Each person has a different skull thickness (1.5–7 mm), which leads to up to a 300% difference in the actual light dose reaching brain tissue (sufficient for some people, insufficient for others).

Solution: Use fNIRS (functional near-infrared spectroscopy) and EEG (electroencephalography) for synchronized monitoring, providing real-time feedback on the effects of light, and then adjust the irradiation parameters to achieve personalized treatment.

 🧠Scientific essence and core process 🧠

Scientific essence:
Near-infrared light regulating the brain is essentially a three-stage transformation: “light energy → biological energy → neural function.” Photons act as the “fuel,” mitochondria function as the “photo-battery,” converting this fuel into ATP (biological energy) and various biochemical signals. These signals ultimately regulate brain plasticity (growth, repair, and connectivity), enabling non-invasive neuromodulation.

Core process (in one sentence):
Photons → mitochondrial CCO (energy reception) → increased ATP / reduced ROS (more energy, less damage) → activation of signaling pathways → promotion of gene expression and protein synthesis → synaptic remodeling (stronger neural connections) → improved brain function (enhanced memory, movement, and cognition).