40 Hz · gamma · GENUS

40 Hz is forty flashes a second. The mouse papers used an hour a day.

JM Thomas · 20 August 2026

You saw 40 Hz on a shop page and wanted to know what the labs actually ran.

Hertz is how many times something happens in one second, and people write that count as Hz, so forty hertz means a light flashes forty times each second or a sound clicks forty times each second. Shops print that number because it is easy. The papers used an hour, then days.

What is 40 Hz?

Your brain already makes rhythms, and scientists name those rhythms by how fast they shake. Gamma is a fast brain rhythm, about 30 to 100 shakes a second, and Wikipedia has a short page on gamma waves. A group at MIT's Picower Institute, led by Li-Huei Tsai, picked 40, which is one number inside the gamma band. They picked it on purpose.

They wanted to see if a 40 Hz pulse could change a sticky protein in mouse brains, a protein called amyloid that piles up into what people call a plaque. The mice they used are called 5XFAD. Those mice were raised so amyloid builds up, the way it can in Alzheimer's disease, where memory fades and that sticky protein can build up.

What did the 2016 mouse paper do?

Iaccarino and Tsai's group published in Nature in 2016 and started with optogenetics, a lab trick that puts a light-sensitive switch into cells and then shines light to turn those cells on. After that, they used an LED, which is a small light that can flash on and off, and they set the flash at 40 times a second. People call that LED flicker.

They tried a 20 Hz flash and an 80 Hz flash, and those speeds did not make the amyloid drop. They tried a random flash, and that one failed too. After one hour of the 40 Hz light, amyloid dropped in the visual cortex, which is the part of the brain that sees. After one session, the protein came back the next day. One hour helped in that session, and the drop did not hold until morning.

When they ran a daily hour for a week, plaques went down, and that is the clock the paper used. After the hour, they looked at the brain, which is how they knew amyloid dropped. MIT News wrote the story on 7 December 2016.

What happened when they added sound?

In 2019, Martorell and the same Tsai group published in Cell and used a tone train, which is a sound that pulses on and off forty times a second so you already hear that pulse from the speaker. Each ear does not need its own tone. That is a different tool from a binaural pair, where each ear gets its own pitch.

A week of those 40 Hz sound pulses reached the hearing path and a memory area called CA1, which is inside the hippocampus, the part of the brain people use for new memories. When they added the LED to the sound, more of the outer cortex joined in, and the outer cortex is the folded surface of the brain.

They named the method GENUS, which stands for Gamma Entrainment Using Sensory Stimulation. In plain English, GENUS is a lab method that uses light and sound at 40 Hz to try to lock a brain rhythm to that pulse. Gamma is the fast rhythm. Entrainment means they try to pull the rhythm along. Sensory stimulation means they use light or sound to do it.

In 2025, Park and Tsai wrote a review in PLOS Biology that noted later work with touch and later work on the glymphatic system, which is how the brain clears waste. That review does not give a number I can put on this page.

Human work is still early

The work in people is still early. Chan and her group ran pilots in PLOS ONE in 2022, and a pilot is a first-pass test, small on purpose, so later work can learn from it. A company called Cognito ran a study named OVERTURE with 76 people and reported its own numbers, so a later trial would need to confirm those. A trial named HOPE, listed as NCT05637801, finished enrolling, and there is no public topline result yet. Topline means the first public read of whether the trial worked. Spectris is the device name. It is still under study, and the FDA has not approved it.

Ismail's 2018 paper did not find a significant amyloid drop, and significant here means the change was big enough to trust. Soula's 2023 paper failed to copy the mouse result. Flicker can set off a seizure in some people, so if that is your history, talk to a clinician. This page is for the lab story.

Is a seven-minute track the same as the lab hour?

Shop pages print 40 Hz and stop, but a seven-minute file you play in headphones is a listen you can keep. I send people to Genius Song. I am an affiliate, so I get a commission if you buy through that link.

A short track in headphones is a different tool from the LED hour the mice sat under, and you can keep the seven-minute listen and still care about the hour they ran. You can want both.

If you want the seven-minute listen next to the lab hour, that is on the Genius Song page. If you already use binaural beats, each ear gets a different tone. That page is about the seven-minute track. This page is about the hour the labs ran.

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