40 Hz binaural beats: gamma waves for attention

What are 40 Hz gamma waves

The brain produces electrical rhythms of different speeds. Delta is the slowest and belongs to deep sleep; gamma is the fastest, 30 to 100 Hz, and appears when the brain binds information together: recognising a face, holding several things in mind, solving a problem.

Within the gamma band 40 Hz has a special place. It is the frequency at which the hearing system follows a rhythmic sound most readily, which is why audiologists and neuroscientists have used 40 Hz sounds for decades.

Gamma waves, attention and meditation

Gamma is usually linked to effort, and the most striking recording of it comes from stillness. In 2004 researchers at the University of Wisconsin recorded the brain activity of Buddhist monks with many years of practice. During meditation they produced sustained gamma oscillations of unusually high amplitude, synchronised across distant areas of the brain, and their gamma activity was higher than in beginners even at rest.

The finding changed how gamma is understood: not as a sign of strain, but as a sign of a brain that holds many things together at once. It also set expectations that sound cannot meet. The monks' gamma was the result of thousands of hours of training, not of listening.

Where gamma waves come from and why they are hard to measure

Gamma rhythms are made by a specific circuit. In 2009 two studies in Nature switched particular neurons on and off with light in mice. Driving fast-spiking parvalbumin interneurons created gamma rhythms; silencing them removed gamma. Gamma comes from a fast loop between excitatory neurons and these inhibitory cells, and what it is for is still debated.

Measuring it from the scalp is another matter. Tension in the muscles of the forehead, jaw and neck and tiny involuntary eye movements produce electrical signals in the same frequency range. In one study two people were recorded with and without complete drug-induced muscle paralysis, and power above 20 Hz differed 10 to 200 times between the two states. The authors concluded that most of the scalp recording above 20 Hz comes from muscles. Another team showed that a well-known burst of gamma just after a stimulus appears matched tiny eye movements, not a brain rhythm.

This matters for two reasons. The monk study above compared eight practitioners with ten much younger students and was recorded from the scalp, so its gamma comes with this caveat. And a home EEG headband that reports a gamma score mostly sees muscle activity. A 40 Hz steady-state response is easier to trust: it appears at the exact frequency of the sound and lasts as long as the sound does. More on how gamma is defined and measured is on the Gamma waves page, and all five bands side by side on the Brain waves page.

What do 40 Hz binaural beats do

First, the brain registers them. In a Canadian study each ear received a different tone, 40 Hz apart, and the recording of brain activity showed a steady response at exactly 40 Hz, although no 40 Hz sound was present in either ear. The response appeared with low tones around 400 Hz and became undetectable above 3000 Hz. It was smaller than the response to a beat that is physically present in the sound.

Second, they change how people perform. The results come from Leiden University, where three studies used the same setup: a 40 Hz beat against a constant 340 Hz tone.

These are effects on healthy adults during a task. They are real and modest: a 40 Hz beat is a nudge towards alertness, not a change of ability.

40 Hz binaural beats benefits: what is shown and what is not

Lists of benefits on the internet mix results from different methods. Here they are sorted by what was actually tested.

Which tones make the best 40 Hz binaural beat

Any two tones 40 Hz apart give a 40 Hz beat, but the brain does not respond to all pairs equally. In the recording study the response was clear with tones around 400 Hz and disappeared above 3000 Hz.

A difference of 40 Hz is large, so the two tones are heard as a slightly rough chord instead of one wavering tone. That roughness is normal.

40 Hz binaural beats for studying and focus

In the Leiden studies people listened for three minutes before the task and continued during it. That is the pattern to copy.

• Start the beat a few minutes before you begin and keep it on during the first block of work.
• Use it for tasks that need precision: proofreading, calculations, code review, learning formulas.
• Keep the volume low. A 40 Hz beat sounds like a rough buzz, and loudness makes it tiring, not stronger.
• For long reading or writing sessions a beta beat of 15 to 20 Hz is softer and has more evidence; see the page on binaural beats for focus.
• Stop in the evening. Gamma is an activating rhythm.

How long to listen to 40 Hz binaural beats

In the attention studies the sessions were short: three minutes before the task and the length of the task itself. In the brain recording study ten minutes were enough to measure the response.

For everyday use 10 to 20 minutes at the start of a working block is a sensible length. The MIT protocol of an hour a day belongs to a different method and a different purpose.

40 Hz, MIT and Alzheimer's disease

Much of the interest in 40 Hz comes from research at the Massachusetts Institute of Technology. In mice that model Alzheimer's disease, light flickering 40 times a second reduced amyloid in the brain, and later experiments added a sound pulsing at the same rate. The method is called GENUS, gamma entrainment using sensory stimulation.

In 2022 the first results in people were published. In a small pilot study 15 patients with mild Alzheimer's dementia used a device with 40 Hz light and sound every day for three months. It was safe and well tolerated, and the group with 40 Hz stimulation showed less shrinkage of the hippocampus and did better in a memory test than the control group. Larger trials followed; the next section describes them.

This research does not use binaural beats. The sound in GENUS is physically pulsed, it is combined with light, and it is delivered daily for months. No study has shown that 40 Hz binaural beats affect Alzheimer's disease, and they should not be used in place of medical care.

40 Hz Alzheimer's trials: where things stand in 2026

The mouse results have grown, and they have been challenged. In 2019 the MIT group reported that seven days of 40 Hz tones improved memory and reduced amyloid in the auditory cortex and hippocampus of mice, and that sound combined with light, but neither alone, cleared plaques across a wider area of the cortex. In 2024 the same group reported that 40 Hz sound and light sped up the flow of fluid that washes waste out of the mouse brain, and that blocking this flow cancelled the amyloid reduction. In 2023 a team led by György Buzsáki at New York University repeated the light experiment in two mouse models, with electrodes placed deep in the brain. The 40 Hz flicker did not engage the brain's own gamma rhythm, hippocampal responses were weak, and there was no reliable change in plaques, microglia or amyloid levels. The mice also avoided the flickering light.

In people, the first larger test was the OVERTURE trial, published in 2024. 76 patients with mild to moderate Alzheimer's disease used a 40 Hz light and sound device or a sham device at home for one hour a day for six months; two in three received the real one. It was safe, no brain swelling was seen, and adherence was 85 to 90 percent. But on its primary outcome, and on two standard cognitive scales, the real device did no better than the sham. Some secondary measures, including everyday functioning, a short cognitive test and whole-brain volume on MRI, declined less, but the trial was not designed to prove a benefit.

The deciding study is HOPE, the pivotal trial of the same company's device: 670 participants at about 70 sites in the United States, randomised, double-blind, sham-controlled, with daily use at home for 12 months. Its main measure combines everyday functioning and a short cognitive test. Enrolment was complete by July 2025. As of 1 October 2026 no results had been published. Until they are, no 40 Hz device is approved for Alzheimer's disease, and figures from the secondary measures of the earlier trial that appear in advertising should not be read as proof.

This path is common in medicine: striking results in mice, safety in small human trials, and an open question that only a large trial can settle.

40 Hz binaural beat, isochronic tone or pure tone

The same number hides three different sounds.

If you search for a 40 Hz pure tone and hear nothing on your phone, the speaker is the reason. For a 40 Hz rhythm use the binaural or the isochronic mode, where the carrier tone is well within the range of any headphones.

40 Hz isochronic tones, binaural beats or flicker: which does the brain follow

The idea behind every 40 Hz method is the same: a rhythmic stimulus makes the brain answer at the same rate. That answer is called the steady-state response, and for sound it was first described in 1981. Robert Galambos and colleagues found that when sounds are repeated about 40 times a second, the brain's separate responses merge into one stable 40 Hz wave, which is present even when the sound is barely audible. A later review of the method confirmed that steady-state responses can be recorded to sounds repeated from 1 to 200 times a second, but in an awake person they are most prominent near 40 Hz. Audiologists use them to estimate hearing objectively.

The three methods differ in how directly they deliver the rhythm. An isochronic tone switches a sound on and off, so the pulse is in the sound itself and the hearing system follows it directly. A binaural beat exists only in the brain, and the response to it is smaller than to the same beat present in the sound. Flicker works through the eyes: in a study in which ten people watched light flickering from 1 to 100 Hz, the visual cortex followed every rate up to at least 90 Hz, with the strongest responses near 10, 20, 40 and 80 Hz.

Following a rhythm is not the same as changing anything else. A 2023 systematic review found 14 EEG studies of binaural beats: in five brain activity followed the beat, in eight it did not, and one was mixed. A 2019 meta-analysis of 22 studies found a medium-sized effect of binaural beats on memory, attention, anxiety and pain, and listening before a task worked better than listening only during it. That shows people respond to the beats, not that a brain wave changed. Studies of what isochronic tones do are almost absent: in a 2026 trial of 90 patients having a wisdom tooth removed, neither isochronic tones nor binaural beats reduced anxiety compared with no sound.

Flicker carries a risk that sound does not. Flashing light can trigger seizures in people with photosensitive epilepsy: rates of 15 to 25 Hz are the most dangerous, but anything from 1 to 65 Hz can do it, and about 1 in 4,000 young people aged 5 to 24 is at risk. Do not use flicker if you or a family member has epilepsy or has had a seizure.

This generator makes sound only. To play a single steady tone at any frequency, use the Tone generator page.

Can you use 40 Hz binaural beats for sleep

No. Gamma is the rhythm of an active brain, and the studies with 40 Hz beats measured attention. For sleep use a delta beat of 2 to 3 Hz, and for calming down an alpha beat of 10 Hz.

Is 40 Hz safe

In the studies with healthy adults no harm was reported. In the MIT pilot study daily 40 Hz stimulation for three months was well tolerated. In the 76-patient OVERTURE trial six months of daily use was safe and caused no brain swelling.

The usual cautions apply: keep the volume low, do not listen while driving, stop if you get a headache or feel uneasy. People with epilepsy should talk to their doctor before using any rhythmic sound or light.