How 40Hz Light Affects the Brain: What the Research Actually Shows

If you've seen a BEACON40 or heard about "40Hz light therapy" and thought "okay, but does this actually do anything to my brain?" you're asking the right question. The honest answer: there's a real and growing body of research behind it, more than most people realize, and some of it comes from MIT. This post breaks down what the science actually says, what the open questions are, and why 40Hz specifically keeps showing up in cognitive research.

What is 40Hz light and why does the frequency matter?

40Hz light is visible light that flickers on and off at a rate of 40 times per second. What makes that specific frequency interesting isn't the light itself. It's what happens in the brain when it's exposed to it.

Your brain generates electrical rhythms at various frequencies all the time. The gamma frequency band, roughly 30-80Hz, sits at the high end of those rhythms and is associated with attention, memory consolidation, and the coordination of information across brain regions. 40Hz sits near the center of that range. Researchers noticed that people with Alzheimer's disease tend to show disrupted gamma activity, especially in the hippocampus, the region most involved in forming new memories. That observation is what prompted Li-Huei Tsai at MIT's Picower Institute to start testing whether externally stimulating the brain at 40Hz could have any measurable effect.

The 2016 paper that launched this line of research, published in Nature, found that 40Hz visual flicker reduced amyloid plaques in Alzheimer's model mice. That was the opening shot. What followed was a decade of research from labs around the world trying to understand what exactly 40Hz stimulation does, how it does it, and whether any of it applies to humans.

What happens in the brain when you're exposed to 40Hz light?

40Hz visual flicker activates multiple brain systems, not just the visual cortex. When the retina detects flickering light at that frequency, the signal travels through canonical visual pathways and appears to entrain neural activity well beyond the primary visual areas. A 2021 study using fMRI, published in Frontiers in Human Neuroscience, found that 40Hz blue light increased activation in the hippocampus during a recognition memory task and strengthened functional connectivity between the hippocampus and sensory-processing regions. That's meaningful because the hippocampus is the brain's primary memory-formation hub.

More recently, research published in Communications Biology in 2025 used intracranial EEG in epilepsy patients to map how 40Hz visual stimulation propagates through the brain. The study found that 40Hz flicker successfully entrained neural activity in the hippocampus, the temporal lobe, and the frontal cortex. It also increased synchronization between the hippocampus and other cortical areas. That synchrony is thought to be important for how memories get encoded and retrieved.

One of the more striking discoveries in this space involves the brain's glymphatic system, a plumbing-like network that clears metabolic waste from brain tissue, primarily during sleep. A 2024 study in Nature from Tsai's lab found that 40Hz audio and visual stimulation prompted interneurons to release a peptide (VIP) that drove increased glymphatic clearance of amyloid. This added a new piece to the puzzle: 40Hz stimulation may support brain health partly by helping the brain flush waste more efficiently.

Does 40Hz light affect sleep?

40Hz light flickering promotes sleep onset through a specific neurochemical pathway involving adenosine. A 2024 study published in Cell Research mapped this mechanism in detail. Exposure to 40Hz flickering light triggered neurons in the primary visual cortex to release adenosine, the same compound that builds up during wakefulness and signals to the brain that it's time to sleep. The effect was frequency-specific: 20Hz and 80Hz flickering produced less adenosine release than 40Hz.

The researchers also ran a clinical component of the study, exposing 49 children with insomnia symptoms to 30 minutes of 40Hz light before bed. The results showed decreased sleep onset latency, increased total sleep time, and less waking after sleep onset. This is a small study and shouldn't be read as a cure for insomnia, but the mechanism it identified adds to the broader picture of how 40Hz stimulation interacts with the brain's regulatory systems.

The sleep connection matters for cognitive performance beyond just feeling rested. During sleep, the brain consolidates memories, clears metabolic waste, and resets the systems involved in attention and mood. If 40Hz light can support sleep quality, those downstream benefits to cognition are worth taking seriously.

What does the research show for memory and focus in healthy people?

Most of the 40Hz research has focused on Alzheimer's disease populations, which is where the strongest effects have been documented. But some findings extend to healthy adults and non-disease cognitive function.

The fMRI study in Frontiers in Human Neuroscience mentioned above involved healthy participants, not people with Alzheimer's. It found that even in healthy brains, 40Hz light shifted hippocampal activity and functional connectivity in ways associated with better recognition memory performance. A 2022 study published in Frontiers in Aging Neuroscience found that cognitive tasks performed during 40Hz visual stimulation enhanced the neural entrainment response, suggesting the brain becomes more engaged when exposed to 40Hz light during active mental work.

Research from Scotland published in 2023, involving more than 100 participants, used combined audio and visual gamma stimulation at 37.5Hz (close to 40Hz) and found improvements in memory recall. The study is notable for its scale, as it's one of the larger human trials in this space.

A 2023 study in healthy adults found that 40Hz auditory stimulation was positively correlated with planning and problem-solving abilities. And a review article in eLife in 2024 synthesized the broader evidence and pointed out that 40Hz light stimulation has been shown to enhance short-term memory and social cognition in mice, alongside the well-documented effects in disease models.

The honest caveat is that this research is still developing, especially for healthy populations. Most of the largest and most rigorous human trials have been conducted in people with Alzheimer's disease or cognitive impairment. The evidence for healthy adults is promising but thinner.

Is there any contradicting research?

Yes, and it's worth knowing about. A 2023 study published in Nature Neuroscience by researchers at New York University found that 40Hz flickering light did NOT entrain gamma oscillations in the hippocampus or entorhinal cortex of Alzheimer's disease model mice. The mice in that study also appeared to avoid the 40Hz light, and the researchers did not find significant changes in amyloid plaques. This study was a direct challenge to some of the earlier MIT findings and generated significant debate in the field.

Tsai's lab and others have offered methodological responses to that study, including differences in the AD mouse models used and differences in how stimulation was delivered. But the disagreement is real, and it's not resolved. The scientific community is actively working through it.

The takeaway isn't that 40Hz research is junk science. The MIT findings have been replicated by multiple independent labs, and the mechanistic discoveries around glymphatic clearance and adenosine signaling are themselves significant contributions regardless of the Alzheimer's debate. But honest reporting means acknowledging that this field still has open questions, particularly around how well the animal data translates to humans and which specific populations benefit most.

Why 40Hz specifically? Why not 30Hz or 60Hz?

40Hz sits at a frequency that aligns with the brain's natural gamma rhythm, which is dominant during active cognitive engagement. The research from Tsai's lab has specifically tested other frequencies and consistently found stronger effects at 40Hz compared to neighboring frequencies. The adenosine sleep study found that 40Hz produced significantly more adenosine release than 20Hz or 80Hz. Other studies on amyloid clearance and neural synchrony have similarly found 40Hz to be the most effective frequency tested.

The proposed explanation is resonance: 40Hz flickering appears to entrain existing brain rhythms that are already operating near that frequency during memory and attention tasks. It's not creating a new signal so much as amplifying and synchronizing one that's already present, though weakened in aging and disease. That's why the effects are more pronounced in people whose gamma activity is already disrupted. And why, for healthy adults, the effects tend to be subtler.

The gamma rhythm is also the only brain oscillation known to coordinate activity across the hippocampus, prefrontal cortex, and sensory regions simultaneously, which is exactly the network involved in forming, storing, and retrieving memories. The specificity of 40Hz is one reason the research has focused there rather than at other frequencies.

How does BEACON40 fit into this research?

BEACON40 is a consumer device that delivers 40Hz flickering light, designed to be used passively during everyday activities. You place it within your peripheral field of view, 3-15 feet away, and use it for one hour daily while working, reading, or relaxing. The goal is to deliver the same frequency of stimulation being studied in the research without requiring you to sit and stare at anything.

It's worth being clear about what BEACON40 is and isn't. It's a wellness device, not a medical treatment. The clinical research cited in this post involves research-grade equipment under controlled conditions, and most of it is focused on disease populations. BEACON40 applies the same frequency principle to a consumer context, with the understanding that the mechanisms being studied, gamma entrainment, glymphatic support, adenosine release, may offer benefits for everyday cognitive performance even in healthy users.

Some BEACON40 users report improvements in focus, clearer thinking, and better sleep. These are consistent with what the research would predict, but anecdotal reports aren't the same as clinical trial results. The research is genuinely exciting. It's also still evolving. BEACON40 makes it accessible to people who want to incorporate this approach into a daily brain health routine without waiting for the science to be fully settled.

Frequently asked questions

What does 40Hz light do to the brain?
40Hz flickering light appears to entrain gamma-frequency neural oscillations in the brain, including in the hippocampus. Research suggests this may support memory-related brain activity, promote the clearance of metabolic waste via the glymphatic system, and trigger adenosine release that promotes sleep onset.

Is 40Hz light therapy scientifically proven?
Multiple peer-reviewed studies from MIT, Harvard, and independent labs support measurable neurological effects from 40Hz light stimulation. The strongest evidence is in Alzheimer's disease models. Evidence for healthy adults is smaller and still developing. Some conflicting findings exist in the literature and are an active area of debate.

Is 40Hz light safe?
Current evidence suggests 40Hz light at typical brightness levels is safe for daily use. It does not trigger photosensitive epilepsy at the brightness levels used in consumer devices, though people with photosensitivity should consult a doctor. Research studies and clinical trials have not identified adverse effects at standard exposure levels.

How long do you need to use 40Hz light to see effects?
Research studies have typically used daily sessions of 30 minutes to one hour, over periods of weeks to months. Most human trials showing cognitive or sleep effects used exposures in that range. BEACON40 recommends one hour daily as a consistent routine.

Does 40Hz light help with memory?
A 2021 fMRI study found that 40Hz blue light increased hippocampal activation and strengthened functional connectivity during a memory task in healthy adults. A 2023 study involving 100+ participants found improvements in memory recall with combined gamma stimulation at 37.5Hz. These findings are encouraging for memory support, though more large-scale human trials are needed.

Can you use 40Hz light while doing other things?
Yes. Research protocols and consumer device guidance both support using 40Hz light peripherally, meaning you don't need to stare at it directly. Placing it 3-15 feet away while reading, working, or relaxing allows passive exposure during normal activities. Some evidence suggests cognitive engagement during exposure may actually enhance the neural entrainment effect.

Does 40Hz light help with sleep?
A 2024 study in Cell Research identified a specific mechanism: 40Hz light triggers adenosine release in the visual cortex, and adenosine is the primary neurochemical signal for sleep pressure. A clinical component of the study found that 30 minutes of 40Hz light before bed improved sleep onset and quality in children with insomnia. More human research is needed to confirm effects in adults.

For more on how the gut microbiome influences cognitive function, see our post on how the gut impacts memory. And if you're curious about the supplement side of the BEACON40 brain health approach, Sharper Memory combines citicoline, lion's mane, bacopa, PQQ, resveratrol, and a probiotic blend to support the nutritional side of cognitive performance.