Gamma waves and 40 Hz

An EEG records voltage changes produced by the brain. Analysing that signal by frequency gives a spectrum, and its slices are named with Greek letters. Gamma is the fastest of the five usually described, above beta.

Mind Journeys uses 30 to 40 Hz for gamma, because 40 Hz is the fastest beat the app plays. EEG research draws the band differently: it conventionally starts around 30 Hz but extends well above 40, and studies divide it into lower and upper gamma in different places. As with every band, these are conventions for cutting a continuous spectrum, not natural boundaries.

In 1981, researchers recording from the scalp found that the brain's response to a sound, in the first tenth of a second after it, looks like three or four cycles of a 40 Hz wave. When sounds were repeated about 40 times a second, those responses combined into one stable, regular wave (Galambos et al., 1981). This is now called the 40 Hz auditory steady-state response. It appeared even with sounds close to the threshold of hearing, which is why the authors suggested it could be useful for testing hearing.

That is the solid part of the 40 Hz story: a sound pulsing at 40 Hz produces a measurable 40 Hz rhythm in the EEG. It is a description of how the auditory system responds to a stimulus. It says nothing about attention, mood or health.

A binaural beat is two steady tones, one in each ear, a little apart in pitch. The beat is the difference between them: 220 Hz in one ear and 260 Hz in the other gives a 40 Hz beat. It is produced by the auditory system from two separate signals, not present in the air (Oster, 1973), which is why it needs stereo headphones.

40 Hz sits at an awkward spot for a binaural beat. Binaural beats are perceived as beats for differences of about 1 to 30 Hz, so at 40 Hz most listeners hear a faint roughness in the tone rather than a pulse.

The brain does register it. A 2005 EEG study played a 40 Hz binaural beat and found a steady-state response at 40 Hz, but it was smaller than the response to an ordinary acoustic beat (the same two tones mixed in one ear), and it disappeared when the tones were above about 3 kHz. So a 40 Hz binaural beat is a real stimulus, but a weaker one than the pulsing sounds most 40 Hz research uses.

The most common use is as a background for focused work: studying, writing, coding, anything that benefits from staying with one task. People typically put a long 40 Hz session on under headphones at a low volume, often with brown noise or another steady sound underneath to mask the room.

Many 40 Hz tracks climb up from a slower beat rather than starting at 40, and come back down at the end. Some people treat the descent as a cue to take a break. These are descriptions of how people use the audio, not statements about what it does.

The MIT 40 Hz studies

In a 2016 study in a mouse model of Alzheimer's disease, driving particular brain cells at 40 Hz reduced levels of amyloid-beta, a protein that builds up in the disease, and a light flickering 40 times a second reduced it in the visual cortex (Iaccarino et al., 2016).

A 2019 follow-up in mice used tones repeated at gamma frequency. Seven days of the tones improved the mice's performance on spatial and recognition memory tasks and reduced amyloid in auditory cortex and hippocampus; combining sound with flickering light reached wider areas of the brain (Martorell et al., 2019).

In people, a 2022 paper reported a feasibility study (25 healthy volunteers and 16 patients with mild Alzheimer's dementia) and a randomised, placebo-controlled pilot in which 15 patients with mild probable Alzheimer's dementia used 40 Hz light and sound daily for three months. The authors reported that the stimulation was safe and produced 40 Hz activity in the brain, and found some differences favouring the active group on brain imaging, one memory test and daily activity rhythms. They called for a larger trial to test it properly.

Binaural beats and attention

On binaural beats generally, a 2019 meta-analysis of 22 studies reported that the direction and size of effects on memory, attention and anxiety depended on the frequency used. A 2023 meta-analysis of 15 studies concluded that binaural beats improved memory and attention, while reporting conflicting results for theta and beta beats; both analyses pool small studies with different protocols. Neither singles out 40 Hz gamma. And whether brain rhythms follow a binaural beat at all is contested: a 2023 systematic review found five of fourteen EEG studies consistent with entrainment and eight contradicting it (Ingendoh et al., 2023).

The headline 40 Hz findings are mostly in mice. A result in a mouse model of a disease does not necessarily carry over to people, and a reduction in amyloid in a mouse is not a change in anyone's memory.

The human evidence is small. The randomised pilot had 15 patients: enough to justify a larger trial, not enough to show a benefit, and the authors call for that larger trial rather than claiming one.

The studies did not use binaural beats. They used flickering light and tones repeated at gamma frequency. In a direct comparison of sounds, a 40 Hz binaural beat produced a smaller brain response than an ordinary acoustic beat (Schwarz & Taylor, 2005), so results from the pulsing stimuli cannot simply be carried over to binaural beats.

They are also about a disease, not about focus. Nothing in the 40 Hz dementia research tells you how well a healthy person concentrates with a 40 Hz track on, and the binaural-beat studies of attention are mixed and use different frequencies and protocols. Mind Journeys is not a treatment for Alzheimer's disease or any other condition, and nothing here suggests its audio affects one.

Expectation is hard to separate from the sound. A focus track is chosen by people who want to focus and expect it to help, and most outcomes in this research are self-reports or task scores that expectation can move.

Two hours on a 240 Hz carrier: a 10-minute climb from 10 Hz to 40 Hz, a 100-minute hold at 40 Hz, then a cool-down to 14 Hz, with brown noise and a light wind underneath. Use stereo headphones; on speakers you hear the tones but not the beat.

More full-length journeys are on the Mind Journeys videos page.

One built-in journey reaches gamma, and it is free to play with stereo headphones.

18 → 40 Hz Deep Work · 50 minutes · 14 → 40 Hz

On a 240 Hz carrier with soft brown noise, the beat lifts from 14 Hz to 18 Hz in beta over five minutes, climbs to 40 Hz over the next ten, holds at 40 Hz for a 30-minute block, then eases back to 18 Hz over the last five. The hold is meant for one piece of work; the ease-down at the end is a natural place to stop.

What are gamma waves?

Gamma is the name EEG research gives to the fastest band of brain activity it routinely describes, conventionally starting around 30 Hz. Where it ends varies between sources, and many studies look well above 40 Hz. Gamma activity is studied mainly in perception and attention. Like every band, it is a slice of a frequency analysis, not a state the brain switches into.

Why does 40 Hz get so much attention?

Two reasons. Since 1981 it has been known that sounds repeated about 40 times a second produce a stable, regular 40 Hz response in the EEG. And from 2016, MIT studies in mice, followed by a small pilot in people, tested 40 Hz light and sound stimulation in Alzheimer's disease research. Those studies used flickering light and repeated tones, not binaural beats.

Do 40 Hz binaural beats do the same thing as the MIT studies?

No study has shown that. The MIT work used light flickering 40 times a second and tones repeated at gamma frequency. A 40 Hz binaural beat is a different stimulus: the 40 Hz exists only as the difference between two tones. A 2005 EEG study found the brain's response to a 40 Hz binaural beat was smaller than its response to an ordinary 40 Hz beat.

Can you hear a 40 Hz binaural beat?

Not as a slow pulse. Binaural beats are perceived as beats for differences up to about 30 Hz, according to a 2023 review, so at 40 Hz most listeners hear a faint roughness or flutter in the tone rather than a distinct beat. That is expected and does not mean anything is wrong with your headphones.

Is gamma or beta better for focus?

There is no good evidence either way. Beta, at 13 to 30 Hz, is the band associated with alert, active thinking; gamma is studied in attention and perception. Meta-analyses of binaural beats report that effects depend on the frequency used, with conflicting results for different bands, and none ranks gamma against beta. People choose one or the other as a background for focused work, not because research has ranked them.

• what beta waves areThe band of alert, active thinking, and the range most focus journeys climb into.
• how theta waves are definedThe drowsy edge between waking and sleep, and the band most meditation journeys sit in.
• what a binaural beat is and how one is madeThe pillar explainer: the two tones, the perceived beat, and where the evidence currently stands.
• why binaural beats need stereo headphonesWhy speakers cancel the effect, what to listen on, and how loud is too loud.
• what delta waves are and how they are scoredThe slowest rhythm, dominant in dreamless deep sleep and the floor a night-time journey settles onto.

Browse all guides — the binaural beat and brainwave explainers, grouped by topic.

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2. Schwarz, D. W. F., & Taylor, P. (2005). Human auditory steady state responses to binaural and monaural beats. Clinical Neurophysiology, 116(3), 658–668. https://doi.org/10.1016/j.clinph.2004.09.014
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4. Ingendoh, R. M., Posny, E. S., & Heine, A. (2023). Binaural beats to entrain the brain? A systematic review of the effects of binaural beat stimulation on brain oscillatory activity, and the implications for psychological research and intervention. PLOS ONE, 18(5), e0286023. https://doi.org/10.1371/journal.pone.0286023
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7. Iaccarino, H. F., Singer, A. C., Martorell, A. J., et al. (2016). Gamma frequency entrainment attenuates amyloid load and modifies microglia. Nature, 540(7632), 230–235. https://doi.org/10.1038/nature20587
8. Martorell, A. J., Paulson, A. L., Suk, H.-J., et al. (2019). Multi-sensory gamma stimulation ameliorates Alzheimer's-associated pathology and improves cognition. Cell, 177(2), 256–271. https://doi.org/10.1016/j.cell.2019.02.014
9. Chan, D., Suk, H.-J., Jackson, B. L., et al. (2022). Gamma frequency sensory stimulation in mild probable Alzheimer's dementia patients: Results of feasibility and pilot studies. PLOS ONE, 17(12), e0278412. https://doi.org/10.1371/journal.pone.0278412