Scientists have found that playing a specific low-frequency sound may trigger the brain to flush out toxic proteins linked to Alzheimer’s – raising the possibility of a simple, non-invasive treatment for the most common form of dementia.
The sound is pitched at exactly 40Hz – a steady, low hum, similar to the background noise of a fridge.
In a recent study, researchers at Kunming Institute of Zoology in China played the sound to elderly monkeys for one hour a day for one week, then measured levels of the protein beta-amyloid in cerebrospinal fluid (the liquid surrounding the brain and spinal cord) via a lumbar puncture – where a needle is used to syphon off tiny amounts of fluid for examination.
A build-up of beta-amyloid in brain deposits, called plaques, is linked to Alzheimer’s.In the monkeys, levels of beta-amyloid in the cerebrospinal fluid tripled after the sound stimulation, suggesting the protein was being cleared out of brain tissue and into the fluid.
The effect persisted for five weeks after the therapy ended, according to the study, published in the Proceedings Of The National Academy Of Sciences journal in January.
It builds on more than a decade of research, led by scientists at the Massachusetts Institute of Technology (MIT), suggesting stimulating the brain at 40Hz can reduce amyloid and slow cognitive decline. This particular low frequency was chosen because it synchronises the brain’s electrical activity.
The brain has its own waste disposal system, known as the glymphatic system.
‘Think of glymphatics as a car wash for your brain,’ professor Li-Huei Tsai, director of the Picower Institute for Learning and Memory at MIT, told Good Health. ‘When the system is activated, cerebrospinal fluid washes across the brain tissue, carrying away waste, including Alzheimer’s-associated proteins.’
A specific low-frequency sound may trigger the brain to flush out toxic proteins linked to Alzheimer’s
This process is driven by electrical activity known as gamma waves, which pulse at roughly 40 cycles per second – the same pulse rate as the sound waves at 40Hz.
In Alzheimer’s, the gamma rhythms weaken. As a result, the brain’s cleaning system slows down, allowing toxic proteins to accumulate and damage cells.
The low-frequency sound therapy is thought to act like a pacemaker for the brain, synchronising its electrical activity back to the 40Hz rhythm and reactivating this waste clearance process.
Professor Tsai first demonstrated, in research published in Nature in 2016, that 40Hz stimulation could reduce Alzheimer’s proteins in mice.
In a follow-up study in 2024, her team identified a possible mechanism – the sound activates specialised brain cells called interneurons, which release signals that increase blood flow and drive cerebrospinal fluid through brain tissue, helping to clear amyloid.
In mice, the treatment reduced both beta-amyloid and another harmful protein – called tau – and improved memory.
The new research is the first to show similar results in primates, whose brains are closer to our own.
Studies of this technology in humans are advanced, too. Cognito Therapeutics, founded by Professor Tsai, has developed a home-use headset that delivers 40Hz sound (and light, also thought to resynchronise the glymphatic system) to the brain.
Results from a trial, published in Frontiers In Neurology in 2024, found patients using the device for one hour a day over six months showed less brain shrinkage on MRI scans and slower decline in memory and daily functioning, compared with those given a dummy device.
A larger trial is now under way across 70 sites in the US, with more than 600 patients. Results are expected later this year.
Eve Bolland, a scientist specialising in auditory brain stimulation at King’s College London, said: ‘While the concept is intriguing and some studies do report improvements in cognitive scores, brain connectivity and sleep quality, the findings are not consistent across all studies.’
Meanwhile, the research also sheds light on why older adults can benefit from hearing aids. Hearing loss is recognised as a major modifiable risk factor for dementia.
Although hearing aids don’t deliver 40Hz stimulation, they amplify sounds across a range of frequencies. The theory is that ongoing sound input helps maintain the brain’s gamma rhythms.
Dr Alexander Khalil, a cognitive scientist at University College Cork, is part of a group investigating whether 40Hz frequencies can be built into earbuds or hearing aids, providing continuous, gentle exposure rather than requiring dedicated listening sessions.
‘People can only listen to these obtrusive sounds for so long every day,’ he says. ‘We are exploring a continuous type of stimulation throughout the day.’
So should you start listening to 40Hz tracks at home? Not yet.
‘Definitive results about the efficacy of 40Hz stimulation for human Alzheimer’s patients have not yet been reported,’ says Professor Tsai.
Furthermore, the frequencies in research studies are precisely calibrated and there’s no evidence DIY versions are effective.
