A different approach to treating Alzheimer’s disease, involving flickering light and pulsing sound, has moved from revealing experiments in mice to a large human clinical trial.

For almost a decade, researchers at the Massachusetts Institute of Technology (MIT) have investigated whether stimulating the brain at 40 hertz — 40 times a second — could influence processes involved in Alzheimer’s disease.

The frequency corresponds to a type of brain activity known as gamma rhythms, which are associated with functions including attention, learning and memory.

Some of the most intriguing findings have come from laboratory studies.

In mouse models of Alzheimer’s, exposing animals to synchronised light and sound at 40Hz has reduced levels of amyloid and tau, proteins associated with the disease, while also protecting neurons and improving performance on memory tasks.

A 2024 study published in Nature provided a possible explanation. Researchers found the stimulation increased activity in the brain’s glymphatic system, which helps clear waste from brain tissue. Interfering with glymphatic clearance significantly reduced the amyloid-clearing effect of the stimulation.

Whether those effects translate meaningfully to people remains the crucial question.

An early MIT trial involving 15 people with mild Alzheimer’s found three months of daily 40Hz light and sound stimulation was well tolerated. Compared with controls, researchers reported less hippocampal atrophy, greater connectivity in some brain networks and better performance on one memory test. The study was small and was not designed to prove clinical effectiveness.

A subsequent long-term study followed just five participants who continued treatment for about two years. The three participants with late-onset Alzheimer’s declined more slowly on several cognitive and functional measures than matched patients from large research databases. Two also recorded reductions in a blood biomarker called pTau217.

The two participants with early-onset Alzheimer’s did not show similar cognitive benefits. Researchers stressed that the tiny, open-label study cannot establish that the treatment caused the differences.

The concept is now facing a much bigger test. MIT spinout Cognito Therapeutics has fully enrolled its pivotal HOPE study, a randomised, double-blind, sham-controlled trial involving about 670 people with mild-to-moderate Alzheimer’s. Participants use 40Hz sensory stimulation for an hour a day for approximately 12 months.

For now, 40Hz stimulation remains experimental. But an idea that began with flashing lights and sounds in laboratory mice has now progressed to a major human trial — one that could provide the clearest evidence yet of whether gamma stimulation can make a meaningful difference for people living with Alzheimer’s.