Two years of daily 40 Hz light and sound in five people with mild Alzheimer’s

The 40 Hz story began in mice, where flickering light and clicking sound at gamma frequency appeared to reduce Alzheimer’s pathology. Chan and colleagues report what happened when five people with mild Alzheimer’s disease used a combined light-and-sound device for an hour a day for two years, continuing after an earlier trial ended.

Nothing bad happened, which matters for a therapy people might use at home for years. Three of the five, all women with late-onset disease, kept showing strong 40 Hz entrainment on EEG and declined less on standard cognitive and function scales than matched patients drawn from large Alzheimer’s registries. Blood was available for two of them, and both showed a drop in pTau217, a marker tied to Alzheimer’s pathology.

The authors describe this as the first link between long-term 40 Hz stimulation and a biomarker change in people, and as grounds for larger trials.

Limitations. Five people, no randomized or concurrent control group, no blinding, and a biomarker result in two of them. Comparisons against registry patients cannot rule out that the people who stuck with two years of daily sessions were different to begin with. This is a safety-and-feasibility report from the originating lab. It is worth knowing about; it does not show that 40 Hz stimulation treats Alzheimer’s.