One of the Most Intriguing Brain Health Discoveries of the Last Decade

Most people think about brain health through the lens of chemistry — whether that’s nutrition, supplements, medications, hormones, neurotransmitters, inflammation, or sleep. Those things matter.

But there is another piece of the brain health conversation that most people have never been introduced to.

It starts with rhythm.

Your brain is electrical. It communicates through patterns of activity. Billions of neurons fire, pause, synchronize, and shift depending on what you are doing.

When you are in deep sleep, certain slower rhythms dominate.

When you are relaxed but awake, other rhythms become more prominent.

When you are paying attention, processing information, or using working memory, faster rhythms become important.

One of those faster rhythms is gamma.

Gamma rhythms are typically measured in the range of roughly 30 to 100 cycles per second. One particular gamma frequency, 40Hz, has become a focus of intense research because of its relationship to attention, memory, sensory processing, and communication between brain regions.

And in 2016, an MIT-led team published a finding that changed how many researchers think about the brain.1

They used light flickering at 40Hz — forty pulses per second — to influence gamma activity in Alzheimer’s-model mice.

What they observed helped open one of the most fascinating new directions in brain health research: the idea that the brain may respond not only to chemistry, but to timing.

Your brain runs on electrical rhythms, not just chemistry

When most people think about brain health, they think about what is happening inside the brain chemically.

All of that matters.

But the brain is also rhythmic.

Your brain cells do not communicate randomly. They organize into patterns. They synchronize. They coordinate. Those rhythms help different brain regions share information and work together.

This matters because attention requires coordination.

Memory requires coordination.

Sleep requires coordination.

Learning requires coordination.

Healthy aging requires coordination.

That is where 40Hz becomes interesting.

Researchers were not simply flashing a light and hoping something would happen. They were asking a much deeper question:

In 2016, MIT used 40Hz light to change brain activity in Alzheimer’s-model mice

The major turning point came in 2016, when a team including Dr. Li-Huei Tsai at MIT’s Picower Institute for Learning and Memory published a paper in Nature titled “Gamma frequency entrainment attenuates amyloid load and modifies microglia.”1

The study used Alzheimer’s-model mice. That context matters: these were preclinical animal findings, not human results.

But what the researchers observed was remarkable.

In these mice, gamma activity was disrupted before plaque formation or measurable cognitive decline. That suggested that changes in brain rhythm might appear early in the disease process, not only as a late-stage consequence.

Then the researchers tested whether they could drive gamma activity at 40Hz.

Using 40Hz visual stimulation — light flickering at forty times per second — they observed reductions in amyloid-beta levels in the visual cortex. In older mice with existing pathology, they also observed reduced plaque load in that region.

They also observed changes in microglia, the brain’s immune cells. Microglia help monitor the brain’s environment, respond to injury, and clear waste. In this study, 40Hz stimulation appeared to shift microglial activity in ways connected to amyloid clearance.

That is why the study captured so much attention.

The rhythm of your brain may matter as much as its chemistry

The 2016 finding opened a larger question.

Most brain health research focuses on what is present in the brain: amyloid, tau, inflammation, oxidative stress, neurotransmitters, and hormones.

The 40Hz research pointed toward something different:

Gamma rhythms are one part of that coordination. When gamma activity is well-organized, brain regions can communicate more effectively. When rhythms are disrupted, that communication may become less efficient.

That framing — brain health as coordination, not just chemistry — is what makes 40Hz one of the most interesting frequencies being studied today.

By 2019, 40Hz had reached memory-related brain regions

After the 2016 MIT study, one of the biggest questions was whether the effect was limited to the visual cortex.

If 40Hz light only influenced the part of the brain that processes vision, the discovery would still be interesting, but limited.

In 2019, research published in Neuron helped expand the story.2

The study explored whether 40Hz visual stimulation could influence broader brain networks in mouse models of neurodegeneration. Researchers reported that gamma entrainment reached not only the visual cortex, but also regions including the hippocampus and prefrontal cortex.

Those regions matter.

The hippocampus is central to learning and memory.

The prefrontal cortex is involved in attention, decision-making, and higher-level cognition.

The study also reported preservation of neuronal and synaptic density across multiple brain regions and changes in cognitive performance measures.

This shifted the story.

40Hz was no longer only about amyloid.

It was no longer only about the visual cortex.

It was becoming a story about brain networks — how regions communicate, synchronize, and stay connected.

The first human studies showed 40Hz was safe, usable, and produced real signals

Animal research can be exciting, but the real question is always the same:

In 2021, researchers published a clinical study in Frontiers in Systems Neuroscience testing daily 40Hz stimulation in people with mild to moderate Alzheimer’s disease.3

Participants used the stimulation at home. The study examined safety, adherence, sleep, and daily function.

The findings were encouraging. Researchers reported a positive safety profile, high adherence, and signals related to improved sleep quality and maintenance of functional abilities.

This was important for a practical reason.

A brain health intervention cannot only work in a laboratory. It has to be tolerable. It has to be usable. It has to fit into daily life.

The 2021 study helped show that 40Hz stimulation could make that transition from the lab into the home.

MIT then measured 40Hz effects in the human brain

In 2022, MIT researchers published additional human research in PLOS ONE on an approach called GENUS, which stands for Gamma ENtrainment Using Sensory stimulation.4

The research included a Phase 1 feasibility study and a small Phase 2A pilot study in people with mild probable Alzheimer’s disease.

The Phase 1 study looked at whether 40Hz stimulation could be delivered safely and whether it could induce measurable brain entrainment.

The Phase 2A study looked at daily 40Hz stimulation over three months.

The findings included signals worth noting: less ventricular dilation and hippocampal atrophy in the active group, differences in functional connectivity, improved performance on a face-name association memory task, and improvements in daily activity rhythmicity compared with the control group.

This was small, early research.

But it helped answer an important question:

The early evidence suggested yes.

In 2024, researchers connected 40Hz light to sleep and brain clearance

In 2024, the research took another fascinating turn.

A paper published in Cell Research studied 40Hz light flickering and sleep. Researchers found that 40Hz light flicker triggered a rapid and sustained increase in extracellular adenosine levels in the visual cortex and other brain regions.5

Adenosine is one of the body’s natural sleep-pressure signals. It builds during wakefulness and helps create the feeling that your brain is ready for rest.

The researchers reported that 40Hz light flickering promoted sleep onset and sleep maintenance in mice and in children with insomnia.

Another 2024 paper, published in Cell Discovery, looked at 40Hz light flickering and the glymphatic system.6

The glymphatic system is often described as the brain’s waste-clearance pathway. It helps move cerebrospinal fluid through the brain and supports the removal of metabolic waste.

In mice, researchers found that 40Hz light flickering increased glymphatic flow, including improved cerebrospinal fluid movement in multiple brain regions. The study also connected this effect to adenosine signaling, aquaporin-4 polarization, arterial vasomotion, and cerebral blood flow.

That sounds technical, but the bigger idea is simple:

The 40Hz story was no longer about one protein, one region, or one mechanism.

It was becoming a story about rhythm, networks, immune activity, sleep, and clearance.

Six-month clinical trials showed strong safety and early promising results

Also in 2024, results from the OVERTURE study were published in Frontiers in Neurology.7

This was a randomized, double-blind, sham-controlled, six-month trial in people with mild to moderate Alzheimer’s disease.

Participants used the intervention at home for one hour daily. The study reported that the intervention was safe and well tolerated, with high adherence. Researchers also reported promising signals in clinical and imaging outcomes.

An ongoing clinical trial called the HOPE Study is now testing daily 40Hz stimulation in people with mild to moderate Alzheimer’s disease in a randomized, double-blind, sham-controlled design.8

The larger question is still being studied.

What is clear is that 40Hz has moved from an unusual mouse study to an active area of translational brain research.

In 2025, 40Hz visual stimulation was detected deep inside the human memory system

One of the most persistent questions about 40Hz light has been depth.

Can a flickering light actually influence brain regions beyond the visual cortex?

In 2025, a study published in Communications Biology gave one of the clearest answers yet.9

Researchers used intracranial EEG recordings from people with epilepsy who already had electrodes placed inside the brain for clinical monitoring. This allowed scientists to measure brain activity more directly than standard scalp EEG.

The study found that 40Hz visual stimulation successfully entrained neural activity beyond early visual areas, including the hippocampus and regions of the temporal and frontal lobes.

It also found increased synchronization between the hippocampus and other cortical areas.

This matters because the hippocampus is one of the brain’s most important memory-related regions.

The finding helped show that 40Hz visual stimulation was not producing only a surface-level visual response. It was reaching deeper networks involved in memory and communication.

This research has been published for a decade. Most people have never seen it.

Despite the research, 40Hz is still not widely understood outside neuroscience and biohacking circles.

Part of the reason is that it does not fit neatly into how people usually think about brain health.

That makes it easy to overlook.

But the brain itself runs on rhythms. And when you understand that, 40Hz starts to make sense.

A metronome can help musicians stay in time.

A sunrise can help reset the body’s circadian rhythm.

A lullaby can help settle the nervous system.

A flashing emergency light can instantly sharpen attention.

The nervous system is constantly responding to timing.

40Hz research takes that idea into the brain’s gamma range. It asks whether a precise sensory rhythm can help influence the brain’s own rhythmic activity.

That is the fascinating part.

What the science actually says right now

While the findings are promising, much of the research remains early, and larger long-term human studies are still underway.

The 40Hz story began with a surprising MIT discovery.

But it did not end there.

Over the last decade, researchers have continued testing, expanding, and refining the idea that stimulation at 40Hz can influence brain activity.

The science has moved from animal models to human studies.

From the visual cortex to the hippocampus.

From one mechanism to a network of connected effects.

From short lab studies to longer clinical trials.

From brain rhythm to broader questions about memory, sleep, clearance, and neural coordination.

There is still more to learn.

But one thing is already clear: