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 less reliable. 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 important point is that brain fog is a symptom, not a diagnosis.

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

Sometimes there is one obvious reason.

More often, several things are contributing.

At Neff Functional Medicine, I use transcranial and intranasal photobiomodulation (PBM) as an additional treatment for selected patients with persistent cognitive symptoms.

The research is promising, but PBM is not the answer to every case of brain fog.

Before reaching for a PBM headset, I want to understand what may be driving the symptoms.

Depending on the person, that may include looking at:

• sleep quality and sleep apnoea
• menopause and hormonal change
• 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 cardiovascular 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 requires appropriate medical assessment.

PBM should never delay investigation of an underlying neurological or medical problem.

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

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

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
• cognitive fatigue associated with chronic illness

The strength of the evidence is not the same for all of these conditions.

That distinction matters.

Brain PBM uses near-infrared light delivered through the scalp, and in some devices through the nasal cavity.

The light becomes progressively weaker as it passes through tissue, but enough can reach superficial cortical tissue to produce measurable biological effects.

Research suggests that transcranial PBM may influence:

• mitochondrial energy metabolism
• cerebral blood flow
• nitric oxide signalling
• oxidative stress
• inflammatory signalling
• neuronal activity
• neuroplasticity and brain-network function

These mechanisms provide a reasonable basis for studying PBM in cognitive and neurological conditions.

They do not mean that PBM has been proven to treat every cause of brain fog.

Overall cognitive function

A 2025 systematic review and meta-analysis brought together randomized trials of PBM and cognition across a range of populations.

Overall, PBM was associated with improvements in global cognitive function, with signals also seen in working memory, attention and executive function.

The studies were heterogeneous, however, using different devices, wavelengths, treatment locations and doses.

So the signal is encouraging, but there is not yet one universally established “best” brain PBM protocol.

Mild cognitive impairment

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 scores improved by 3.87 points in the active-treatment group, while the placebo group declined by 0.74 points.

This did not use the Vielight Neuro Duo, but it provides good evidence that repeated near-infrared transcranial PBM can influence cognitive performance in people with mild cognitive impairment. PubMed

It does not show that PBM prevents Alzheimer’s disease or reverses dementia.

Chemotherapy-related brain fog

A 2026 pilot study is particularly relevant because it used the Vielight Neuro Duo 4, the device I use clinically.

Thirty-one women with persistent cognitive problems following chemotherapy received 20-minute Gamma-mode treatments once weekly for at least ten weeks.

Average FACT-Cog scores increased substantially, from 63.3 before treatment to 101.2 after treatment, and 29 of the 31 participants improved.

This is encouraging, but it was a small uncontrolled pilot study rather than a sham-controlled trial.

It should therefore be seen as a promising clinical signal rather than proof of effectiveness. PubMed

For neuropathy caused by chemotherapy, I use a separate PBM protocol for the hands and feet.

Learn more about PBM for chemotherapy-induced peripheral neuropathy →

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

Long-COVID brain fog

A 2026 randomized, double-blind, sham-controlled pilot trial studied 43 adults with persistent cognitive symptoms following COVID.

Participants used home-based transcranial and intranasal PBM for 20 minutes, six days per week for eight weeks.

The overall cognitive outcome improved more in the active group than in the sham group, although the primary difference did not reach conventional statistical significance. Attention measures were more encouraging, and an exploratory analysis suggested a stronger response in younger participants.

No serious adverse events occurred.

The study was small and funded by Vielight, and the authors had financial relationships with the company, so larger independent trials are needed.

What about menopause-related brain fog?

Brain fog during perimenopause and menopause is common.

Women may notice changes in:

• word finding
• memory
• concentration
• multitasking
• mental stamina

Hormonal change may be part of the explanation, but sleep disruption, night sweats, mood, thyroid function, iron status, metabolic health, alcohol and physical fitness may 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 literature.

For selected women with persistent symptoms after the obvious contributors have been addressed, PBM may still be a reasonable additional option.

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.

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.

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 Neuro Duo is a significant investment.

I do not expect someone with brain fog or memory problems to purchase one without knowing whether PBM makes a meaningful difference.

For that reason, I offer a clinician-guided eight-week home PBM programme for existing Neff Functional Medicine patients.

Before starting, we establish where you are.

Depending on the problem, this may include:

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

Then you use the device at home for eight weeks.

At the end, we 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?
• Are you losing your train of thought less often?
• Are you forgetting fewer things?
• Can you get through the 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 improvement, 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?