Gamma Waves: What They Do and What 40 Hz Studies Found

Gamma waves are the brain's fastest rhythm, about 30 to 100 Hz. What they do, why 40 Hz became famous, and what the studies in people found.

Gamma waves are the fastest rhythm your brain makes, somewhere between 30 and 100 cycles a second. They rise when you concentrate hard or hold something in mind.

The number you'll see everywhere is 40 Hz. It got famous in 2016, when an MIT lab flickered a light 40 times a second at mice and watched a protein tied to Alzheimer's go down. Ten years on, labs are still testing what 40 Hz can do, and the results in people are mixed.

What frequency are gamma waves?

Your brain's electrical activity is sorted into bands by speed, measured in hertz, or cycles per second:

Delta, below 4 Hz, mostly in deep sleep.
Theta, about 4 to 8 Hz, drowsy and dreamy.
Alpha, about 8 to 12 Hz, awake and relaxed, often with your eyes closed.
Beta, about 13 to 30 Hz, the busy thinking of an ordinary day.
Gamma, roughly 30 to 100 Hz, the fastest.

40 Hz sits in the lower part of the gamma band, and it's the frequency most research uses.

If you ever see gamma on a home EEG headband, read it with care. Your scalp muscles fire at the same speeds.

When researchers recorded two volunteers under full muscle paralysis, most of what looked like brain activity above 20 Hz disappeared. It had been coming from muscle all along.

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What do gamma waves do in the brain?

Gamma is linked with attention, memory and perception.

The rhythm has a pacemaker. A small class of fast-firing cells sets its tempo, and in a 2009 experiment researchers used light to switch those cells on directly in mice.

Driving them at 40 Hz made a gamma rhythm appear. Driving other cells at the same rate didn't.

That paper opens with the reason the field cares: gamma oscillations "predict increases in focused attention."

You can also raise your own gamma. In a well-known 2004 study, long-term Buddhist meditators produced large, unusually synchronized gamma while they meditated. Their gamma was higher than a control group's even at rest.

Why 40 Hz?

In Alzheimer's disease, gamma rhythms weaken early. So the MIT lab asked whether you could put the rhythm back from the outside.

In the 2016 study, mice sat in a dark chamber for an hour while an ordinary LED bulb flickered 40 times a second. Afterwards, the amyloid in their visual cortex had dropped. Flicker at 20 or 80 Hz didn't do it, and neither did steady light.

The effect of one hour wore off within a day.

Three years later the same group added sound, a click 40 times a second played from speakers above the cage. Light and sound together cleared amyloid across more of the brain than either one alone, and the mice did better on memory tasks.

By 2024 the lab had a possible mechanism: the rhythm seemed to help the brain flush waste out through its own drainage system.

Your hearing favors the same rate. When researchers played binaural beats sweeping from 3 to 60 Hz, people's brains responded most strongly at 40 Hz.

What does 40 Hz do in people?

The big trial

A company spun out of MIT gave 74 people with mild to moderate Alzheimer's an hour of 40 Hz light and sound a day for six months. The trial missed its main goal.

On other measures, though, the treated group's brains shrank more slowly on MRI, and they declined less on some scores of everyday function and thinking.

A much bigger trial, with 670 people, has finished enrolling and hasn't reported yet. That result is the one the field is waiting for.

The memory study

In Glasgow in 2023, people learned new material while light and sound pulsed together at 37.5 Hz. Shifting the timing between the light and the sound by a few thousandths of a second changed how much they recalled later.

The attention study

Researchers gave 80 students binaural beats in 16 different combinations. A 40 Hz beat on a low tone, with white noise behind it, improved their attention the most.

The ones that went the other way

Not every lab has found the same thing. One group ran the flicker on mice and found a 40 Hz response in the visual cortex that didn't spread deeper, and no drop in plaque. The MIT lab disputes their methods.

In nine aged monkeys, a week of 40 Hz sound raised amyloid instead of lowering it.

And when 20 healthy adults had a single 40 Hz session, their brainwaves locked on to it, but their attention and memory stayed the same.

So your brain reliably follows 40 Hz. In people, the best results so far are slower brain shrinkage in one small trial and better attention with one specific beat. It isn't medicine, but it's easy to try as a sound for focused work.

How to listen to 40 Hz

You'll find three kinds of 40 Hz sound.

A binaural beat plays one tone in your left ear and a slightly different one in your right, 40 Hz apart. Your brain makes the beat itself, so it only works in headphones.

An isochronic beat is a tone switched on and off 40 times a second. It works on speakers, and it's the closest thing to the click trains the trials used.

A monaural beat mixes the two tones before they reach you, so it works on speakers too.

Beacon is Lissa's 40 Hz isochronic beat, so it plays on speakers or headphones. In the app, your screen's light and your phone's haptics pulse on the same beat, the way the MIT studies paired light with sound.

If you'd rather work with a binaural beat, set up your headphones first:

Turn off spatial audio. With your AirPods in, open Control Center, touch and hold the volume slider, then turn Spatial Audio off.
Turn off Mono Audio, in Settings > Accessibility > Audio & Visual.
Set the volume low and comfortable.

Then give it a fair test. Play it through the long, steady parts of your day, like reading, writing or answering a pile of email. Compare a week of days with it against days without, by what you got done.

For more ways to set up a work block, see Focus.

Is listening to gamma waves safe?

The sound is as safe as any sound. Keep the volume moderate, especially over hours in headphones.

Flicker is different. 40 Hz light falls inside the range that can trigger seizures in people with photosensitive epilepsy, although it's above the riskiest rates of 15 to 25 Hz. If you have epilepsy, or a history of seizures, talk to a doctor before you use anything that flickers.

And if you or someone you love is living with Alzheimer's, 40 Hz isn't a treatment yet. Ask a clinician about trials you could join.

Questions people ask

What do gamma waves do?

They're linked with attention, working memory and perception, and they rise when you concentrate. Many researchers think they help the brain combine what you see and hear into one picture.

How do you increase gamma waves?

Meditation has the best evidence: long-term meditators produce more gamma than other people, during practice and at rest. Listening to a 40 Hz sound or watching a 40 Hz light also makes your brain follow that rate while it plays.

How long should you listen to 40 Hz?

The animal and Alzheimer's studies used an hour a day. For focus, nobody has found a best length, so try it for one work block of 25 to 60 minutes.

Does 40 Hz actually work?

Your brain reliably follows a 40 Hz sound or light. Whether that changes how you think is less clear: one study found better attention with a 40 Hz binaural beat, and a single session in healthy adults changed nothing.

Can 40 Hz help with Alzheimer's?

In mice it lowered the proteins linked to the disease. In people, a small trial missed its main goal but showed slower brain shrinkage, and a large trial is still to report. It isn't an approved treatment.

Is gamma higher than beta?

Yes. Beta runs from about 13 to 30 Hz, and gamma starts where beta ends.

For the full research, read Forty Times a Second, a decade of 40 Hz studies, and Binaural Beats: What They Do and How to Use Them.