Alzheimer's, Parkinson's, depression: what's the latest in neuro-photobiomodulation?

Could red or near-infrared light become a powerful ally for the brain in the fight against the most feared neurodegenerative diseases? Behind the term “neuro-photobiomodulation” lies a promising line of research being pursued by renowned scientific teams. Here is an honest overview—without making excessive promises—of current advances in the treatment of Alzheimer’s, Parkinson’s, and depression.

How light affects nerve cells

Photobiomodulation (PBM) is based on the absorption of light wavelengths in the red and near-infrared spectrum (between 630 and 1,100 nm) by the mitochondria of nerve cells. These small structures produce ATP, the energy molecule essential for the proper functioning of every neuron.

This absorption triggers several measurable biological responses: reduced oxidative stress, modulation of brain inflammation, and improved blood flow in targeted areas of the brain. Light-based brain stimulation also influences neurogenesis—that is, the brain’s ability to form new connections. Recent studies confirm its role in combating neuronal degeneration, a phenomenon underlying many diseases of the nervous system.

Transcranial or intranasal: how light reaches the brain

The light is delivered transcranially, using a helmet placed on the skull, or intranasally, through a channel that reaches the ventral regions of the brain just a few centimeters away. These non-invasive approaches have a very favorable side-effect profile, which is a major advantage for people whose health is already compromised by the disease.

The use of light for brain stimulation is not a new concept in the scientific literature. It is the growing number of studies and human trials in recent years that has lent it increasing legitimacy.

Alzheimer's Disease: Understanding the Symptoms and Diagnosis

Alzheimer's disease is the most common form of dementia worldwide. It is characterized by the progressive destruction of neurons, severe impairment of cognitive functions, and a decline in short-term and then long-term memory. Diagnosis often comes late: early symptoms, which are subtle, may appear several years before the first noticeable difficulties in daily activities.

Over time, the symptoms worsen. Those affected struggle to perform even the simplest tasks, lose their sense of time and place, and experience behavioral changes that can sometimes seem sudden to those around them. It is estimated that tens of millions of people worldwide are affected, a number that is steadily rising as the population ages.

The exact cause of Alzheimer’s disease remains poorly understood. Researchers agree that the accumulation of toxic proteins, including beta-amyloid and tau protein, plays a role in the progressive destruction of nerve cells in the brain. This mechanism is at the heart of current research efforts, including those exploring photobiomodulation.

How photobiomodulation helps people with Alzheimer's disease

Several recent clinical studies, conducted by French teams in collaboration with university hospitals, show positive trends in memory, executive function, and language. Treatment with PBM sessions is well tolerated, with no significant side effects reported.

Studies conducted in Canada and Japan are exploring devices that combine transcranial and intranasal application during home sessions, three to six times a week, for twenty minutes at a time. Trials published in The Journal of Prevention of Alzheimer’s Disease in 2025, co-authored by researchers from Paris-Saclay University and the Barrow Neurological Institute (United States), confirm that cerebral photobiomodulation reduces oxidative stress and promotes synaptogenesis.

The sample sizes of these studies remain small, and the findings need to be confirmed on a larger scale. However, the available evidence is sufficiently consistent to warrant further research.

The brain-gut axis: a novel approach to Alzheimer’s research

One aspect of current research deserves special attention: the role of the brain-gut axis in the progression of the disease. Researchers are using blood tests and studies of the gut microbiota to better understand how dementia progresses beyond the brain alone.

Biomarkers of inflammation, tau protein, and neuronal degeneration are monitored over time. This comprehensive approach, which goes beyond simple brain stimulation, opens up new possibilities for monitoring the progression of cognitive and behavioral disorders in the years following diagnosis.

Parkinson's Disease: Motor Symptoms, Dopamine, and Diagnosis

Parkinson's disease is associated with the progressive destruction of dopaminergic neurons in the substantia nigra, a deep region of the brain. The decline in dopamine levels in this region leads to the most characteristic motor symptoms: resting tremors, muscle rigidity, slowness of movement, and difficulty maintaining balance during locomotor activities.

The diagnosis of Parkinson's disease is based on the observation of these motor symptoms, combined with additional tests. It can sometimes take a long time to diagnose, as some early signs may go unnoticed for years, which delays treatment and increases the risk of complications.

However, the symptoms of Parkinson’s disease are not limited to motor symptoms. Chronic fatigue, severe sleep disturbances, difficulty concentrating, digestive problems, and mood disorders are frequently associated with the condition. For those affected, these non-motor symptoms often pose a daily burden that is just as heavy as difficulties with walking or movement.

Lewy bodies, alpha-synuclein, and related syndromes: understanding the mechanisms

At the molecular level, Parkinson’s disease is linked to the abnormal accumulation of a protein, alpha-synuclein, within neurons. These deposits, known as Lewy bodies, disrupt nerve cell function and accelerate their destruction. This mechanism is one of the primary targets for researchers working on approaches capable of slowing neuronal degeneration.

Lewy body disease is a neurocognitive syndrome distinct from Parkinson’s disease, yet it shares molecular characteristics with it. It combines cognitive impairments similar to those seen in Alzheimer’s-type dementia with motor symptoms similar to those of Parkinson’s disease. Its management is particularly complex: the use of certain antipsychotic medications is risky due to increased sensitivity in some individuals, which heightens interest in complementary non-pharmacological approaches.

How photobiomodulation helps people with Parkinson's disease

The preclinical data are robust: PBM protects dopaminergic neurons from toxic insults, reduces the accumulation of alpha-synuclein, and improves locomotor behavior in animal models of the disease. These findings justify moving forward to human trials.

In humans, a trial conducted in Grenoble using an intracranial device showed, after 24 months, an improvement in motor function and an increase in dopaminergic activity. Objective measurements taken before and after the sessions confirm a reduction in tremors and greater ease in performing daily movements.

The Clinatec fund, which supports the SomniBrain project among others, is studying the impact of near-infrared light on sleep quality in people with Parkinson’s disease. Since sleep disorders are one of the most common and debilitating symptoms of the disease, managing them is a major challenge for daily well-being.

Depression: When Conventional Treatments Aren't Enough

Depression is also a brain disorder. The cognitive impairments it causes—such as short-term memory loss, severe fatigue, and difficulty completing daily tasks—make it a heavy burden for those who suffer from it.

For a significant proportion of these patients, conventional treatments prove insufficient, and the risk of relapse remains high. Years of treatment without lasting improvement, side effects that are difficult to tolerate, and a quality of life that gradually deteriorates. It is precisely in cases of treatment-resistant depression that transcranial photobiomodulation is attracting the most attention from specialists.

What studies on PBM and depression show

When applied to the prefrontal cortex—a brain region involved in emotion regulation and decision-making—near-infrared light appears to modulate neural function and reduce neuroinflammation. A meta-analysis published in 2024 in Frontiers in Psychiatry, based on several randomized controlled trials, concluded that there was a significant improvement in depression scores following PBM sessions, with no serious side effects reported.

Research teams are exploring a novel combined approach: simultaneously co-stimulating the brain and the gut to influence the gut-brain axis, whose role in depressive disorders is becoming increasingly well documented. Early preclinical results indicate a reduction in depressive behaviors and a restoration of synaptic function in the hippocampus, a brain structure central to memory and mood regulation.

A large randomized controlled trial published in 2025 found no significant effect on depression with a self-administered wearable device, while confirming a real benefit in terms of sleep quality. Session parameters—wavelength, duration, and frequency of use—play a decisive role in the results obtained. This information will guide the design of future trials.

What science tells us today—and what it doesn't tell us yet

Neuro-photobiomodulation is not a one-size-fits-all solution, and the research itself candidly acknowledges this. Studies are still few and far between, and sample sizes are often small. However, what strikes researchers is the consistency of the results: across a wide range of contexts and for various conditions, the beneficial effects of light on nerve cells are confirmed study after study.

What is emerging, however, is a growing consensus on several points:

• The effects of red and near-infrared light on nerve cells are measurable and consistent across studies, whether they pertain to memory, motor function, or mood.
• Neuronal degeneration, brain inflammation, and cellular energy production respond favorably to light stimulation in preclinical models and, increasingly, in human trials.
• The brain-gut axis is emerging as an innovative approach that has the potential to enhance the benefits of therapy sessions on cognitive and behavioral functions, regardless of the specific condition.

Large-scale trials are currently underway in France, Japan, the United States, and Australia. The Clinatec fund, CEA-Leti, and several French universities are contributing to this effort with ambitious projects. The first solid findings are expected in the coming years.

A light that must not be extinguished

Neuro-photobiomodulation does not replace any existing treatments. It does not eliminate the tremors associated with Parkinson’s disease, cure Alzheimer’s dementia, or resolve severe depression. What it does offer is support for weakened nerve cells, a reduction in the inflammation that accelerates their decline, and, perhaps, a contribution to improving the long-term quality of life for those affected.

For those affected by these diseases and their loved ones, this is an avenue worth exploring—with an open mind and without unrealistic expectations. Science is making progress. And light continues to illuminate the path.

See also:

• Photobiomodulation: support for cognitive disorders
• What is photobiomodulation?