Photobiomodulation for Brain Fog, Memory and Cognitive Function

Brain fog is difficult to describe until you have experienced it.

You know the word you want, but cannot find it. You read the same paragraph twice. Multitasking becomes harder. Your memory is not quite as reliable as it used to be. Work that once felt easy takes more effort, and your brain seems to run out of energy earlier in the day.

Common symptoms include:

• poor concentration
• forgetfulness
• word-finding problems
• losing your train of thought
• slower thinking
• difficulty multitasking
• reduced mental stamina
• mental fatigue

The same symptoms can occur for very different reasons.  I see them during perimenopause and menopause, after chemotherapy, with Long COVID and other post-viral illnesses, following concussion, with chronic fatigue and poor sleep, and in people developing mild cognitive impairment.

Sometimes there is one obvious cause. More often, several things are contributing.

At Neff Functional Medicine, I am now using transcranial photobiomodulation (PBM) with the Vielight Neuro Duo 4 as an additional treatment for selected patients with cognitive symptoms.

The research is promising. We now have randomized trials in mild cognitive impairment, a sham-controlled pilot trial in Long-COVID brain fog, and a recent clinical study using the Neuro Duo 4 itself in women with persistent cognitive problems following chemotherapy.

PBM is not the answer to every case of brain fog. It is another tool we can use while we investigate and treat the reasons why your brain is not working as well as it should.

Photobiomodulation uses red or near-infrared light to influence cellular function.

For brain PBM, near-infrared wavelengths are of particular interest because some of the light applied to the head can penetrate the scalp and skull and reach superficial brain tissue.

The light does not travel through the head like a laser beam. It scatters and becomes progressively weaker as it passes through tissue.

Laboratory and human research suggests that PBM can influence:

• mitochondrial metabolism
• cellular energy production
• nitric oxide signalling
• cerebral blood flow
• inflammatory signalling
• oxidative stress
• neuroplasticity

These effects provide a plausible basis for studying PBM in cognitive and neurological conditions.

They do not mean that shining near-infrared light onto the head has been proven to treat every condition associated with brain fog.

I consider brain PBM most often in people experiencing persistent problems with:

• memory
• concentration
• word finding
• mental clarity
• processing speed
• mental stamina
• cognitive fatigue

This may include people with:

• mild cognitive impairment
• age-related cognitive change
• chemotherapy-related cognitive impairment or “chemo brain”
• Long COVID or post-viral brain fog
• persistent symptoms after concussion
• menopause-related cognitive symptoms
• chronic illness associated with cognitive fatigue

The strength of the evidence is different for each of these groups.  That distinction matters.

Brain fog is a symptom, not a diagnosis!  Before reaching for a PBM helmet, I want to understand what may be driving the problem.

Depending on the individual, this may include looking at:

• sleep quality and sleep apnoea
• menopause and hormonal changes
• thyroid function
• iron status
• vitamin B12 and folate
• vitamin D
• glucose regulation and insulin resistance
• cardiovascular and cerebrovascular risk
• medications
• alcohol
• nutrition
• physical activity and fitness
• stress, anxiety and depression
• previous concussion or brain injury
• cancer and cancer treatment
• Long COVID and other post-viral illness

New, progressive or unexplained cognitive impairment needs appropriate medical assessment.

PBM should not delay investigation of an underlying neurological or medical condition.

For home brain PBM I use the Vielight Neuro Duo 4.

The headset uses 810 nm near-infrared light delivered from several positions around the head together with an intranasal applicator.

It has two pulsing modes:

• Gamma – 40 Hz
• Alpha – 10 Hz

A treatment session lasts 20 minutes and the device switches itself off at the end.

For my initial cognitive programme, I generally use Gamma mode.

The device is portable and designed for home use. This is important because most of the cognitive PBM research has used repeated treatment over a period of weeks rather than occasional treatment in a clinic.

My usual starting protocol is:

• Vielight Neuro Duo 4
• 810 nm near-infrared light
• Gamma mode – 40 Hz
• 20 minutes
• six days per week
• eight weeks initially

I generally recommend using Gamma earlier in the day rather than close to bedtime.

Use the device as instructed and keep the treatment consistent.

Do not add extra sessions or increase the treatment time in the hope of getting a stronger effect.

With PBM, more is not necessarily better.

This eight-week protocol is my clinical starting protocol. It is not intended to suggest that every PBM study has used the same treatment schedule.

The Gamma setting pulses the 810 nm near-infrared light at 40 Hz.

Gamma-frequency brain activity is associated with attention, memory and information processing, and 40 Hz stimulation has become an active area of research in cognitive impairment and neurodegenerative disease.

Exactly how pulsed PBM affects the brain is not settled. Its effects may arise from cellular photobiomodulation, changes in neural activity, vascular effects and communication within brain networks rather than from a single mechanism.

I use Gamma as the initial setting for cognitive symptoms because it gives us a consistent protocol that can be assessed over time.

A 2025 systematic review and meta-analysis brought together 24 randomized trials involving 820 participants.

Across these studies, PBM was associated with improvement in overall cognitive function. The researchers also found benefits in working memory and some measures of attention and executive function.

The studies differed considerably in their populations, devices, wavelengths, treatment sites and doses.

There is a real clinical signal, but we do not yet know the optimal PBM protocol for every cognitive condition.

One of the more important recent studies was a 2026 randomized, double-blind, placebo-controlled trial involving 80 people with mild cognitive impairment due to Alzheimer’s disease.

Participants used 808 nm transcranial PBM over the prefrontal cortex six times per week for 12 weeks.

Average MoCA cognitive scores improved by 3.87 points in the active treatment group, compared with a decline of 0.74 points in the placebo group.

This study did not use the Vielight Neuro Duo 4.  It does, however, provide good evidence that repeated near-infrared transcranial PBM can affect cognitive performance in people with mild cognitive impairment.  It does not establish that PBM prevents Alzheimer’s disease or reverses dementia.

A recent study is particularly relevant to the device I use because the researchers used the Vielight Neuro Duo 4.

The study included 31 women with persistent cognitive problems following chemotherapy. 
They received a 20-minute Gamma-mode treatment once weekly for at least ten weeks.
Average FACT-Cog scores increased from 63.3 before treatment to 101.2 afterwards, with 29 of the 31 women showing improvement.

The results are encouraging, but this was a small study without a sham-treatment group. Some participants also received whole-body PBM, making it impossible to attribute all of the improvement to the helmet.

It is therefore a promising clinical result rather than proof of effectiveness.

For patients experiencing chemotherapy-induced peripheral neuropathy, I use a different PBM approach. Read about photobiomodulation for chemotherapy neuropathy.

Long COVID can cause a striking combination of poor concentration, slower processing, memory problems and mental exhaustion.

PBM has now been tested directly in this setting. A 2026 randomized, double-blind, sham-controlled pilot trial included 43 adults with persistent cognitive symptoms following COVID.
Participants used transcranial and intranasal PBM at home for 20 minutes, six days per week for eight weeks.
The primary overall cognitive outcome improved more in the active group, but the difference did not reach conventional statistical significance. Attention measures were more encouraging, and an exploratory analysis suggested a stronger response in participants under 45.
No serious adverse events occurred.

The study was small and funded by Vielight, with the authors receiving compensation from the company. Larger independent trials are needed.

Of particular interest for our programme is the treatment schedule: 20 minutes, six days per week for eight weeks. This is very similar to the initial protocol I use.

Brain fog during perimenopause and menopause is common.

Women may notice problems with word finding, memory, concentration, multitasking and mental stamina.

Hormonal change may be part of the explanation, but it is rarely the only thing worth looking at. Sleep disturbance, hot flushes and night sweats, stress, mood, alcohol, thyroid function, iron status, metabolic health and physical fitness can all contribute.

There are not yet good clinical trials showing that PBM specifically treats menopausal brain fog.

Using PBM in this setting is therefore an extrapolation from the wider cognitive PBM research.

If cognitive symptoms persist after looking properly at the other contributors, PBM becomes a reasonable additional option to consider.

The Neuro Duo costs several thousand dollars.

I do not expect somebody with brain fog or memory problems to buy one before knowing whether it makes any difference to them.

For that reason, I have introduced a clinician-guided eight-week home PBM programme.  We establish where you are before starting treatment and then lend you a Neuro Duo 4 to use at home.

Depending on the problem, baseline assessment may include:

• memory
• concentration and attention
• word finding
• mental clarity
• mental stamina
• fatigue
• sleep
• mood
• ability to work and manage normal daily activities
• formal cognitive testing such as the MoCA where appropriate

We then reassess.  The numbers are useful, but I am equally interested in what has changed in normal life.

• Are you finding words more easily?
• Can you read or work for longer without losing concentration?
• Are you following conversations better?
• Are you forgetting fewer things?
• Can you get through an afternoon without your brain running out of steam?
• Does your head simply feel clearer?

If there is a worthwhile improvement, we can decide whether continuing PBM makes sense.  If there is no meaningful change, there is little reason to continue simply because the technology is interesting.

I do not treat brain fog with a helmet alone.

Improving cognitive function may also mean working on:

• sleep
• nutrition
• exercise and resistance training
• cardiovascular fitness
• metabolic health and insulin resistance
• menopause and hormones where appropriate
• nutritional deficiencies
• alcohol
• stress and mental health
• medications
• vascular risk
• other underlying medical or neurological problems

Selected nutraceuticals may also have a place depending on the individual.

Someone struggling with concentration during menopause needs a different assessment from a person recovering from chemotherapy, someone with Long COVID, or an older person developing progressive memory problems.

The symptoms may look similar.

The reasons behind them may be very different.

The aim is not simply to stimulate the brain. It is to create the conditions in which the brain can work as well as possible.

Transcranial PBM has generally been well tolerated in clinical studies.

Reported effects can include:

• headache
• dizziness
• temporary fatigue
• restlessness
• changes in sleep

I screen patients before starting treatment.  Extra caution is appropriate with a history of seizures, bipolar disorder or mania, recent neurosurgery, intracranial tumours, significant photosensitivity, or new and unexplained neurological symptoms.

New or worsening neurological symptoms need medical assessment rather than simply continuing PBM.
The device should be used according to the manufacturer’s instructions, including avoiding prolonged direct viewing of the illuminated LEDs.

You do not need to assume that photobiomodulation will work for you.

We establish where you are now, use the Neuro Duo 4 at home for eight weeks, and then look at what has changed.

Memory. Concentration. Word finding. Brain fog. Mental stamina. Daily function.

At the end of the trial, there is one question that matters:

Is your brain working better?

Written by Dr Stephan Neff, MD, FANZCA, DipDHM — Functional & Integrative Medicine Doctor