While there is currently no cure for Alzheimer’s disease, a new breakthrough involving a specific frequency of sound and a group of elderly monkeys has sparked hope among researchers.
The study, published in the Proceedings of the National Academy of Sciences, explored how exposure to a 40 Hz frequency could help clear β-amyloid from the brain into the cerebrospinal fluid (CSF), leading to a reversal of Alzheimer’s biomarkers and subsequent symptoms.
The team from the Kunming Institute of Zoology (KIZ) of the Chinese Academy of Sciences experimented on a group of aged rhesus monkeys and found that the specific auditory stimulation of 40 Hz can “significantly” elevate β-amyloid levels in the CSF, with the effect of this lasting for up to five weeks.
The promise of audio stimulation raises hopes for new and noninvasive physical therapies for treating Alzheimer’s disease.
Up to 139 million people across the world are expected to have dementia in 2050, with the condition and its many subvariants remaining a huge public health concern.
The research team, led by Hu Xintian from KIZ, used nine aged rhesus macaques (Macaca mulatta) that were between 26- and 31-years-old. These aged monkeys had developed widespread spontaneous amyloid plaques in their brains which mimic the Aβ pathological feature of Alzheimer’s disease in humans.
The monkeys were subjected to one hour of 40 Hz auditory stimulation, via a 1-kHz pure tone, for just one week.
After the week ended, the monkeys’ levels of key Aβ42 and Aβ40 proteins found in their CSF’s had increased by around 206 and 201 percent, respectively. Researchers also noted that these markers remained high for another five weeks after the simulation ended, instead of losing the potential treatment’s effectiveness instantly.
While the findings have unleashed new hope in researchers, they are not the first time that this specific sound has been proven to aid cognitive function.
40 Hz frequencies contain 40 vibrations per second and have long been positively linked to brain health and mood. These frequencies are designated as gamma waves, which are high-frequency brainwaves typically ranging from 30 to 100 Hz.
A 2016 study from Massachusetts Institute of Technology (MIT) showed that 40 Hz light stimulation induced gamma oscillations decreased amyloid levels and plaque loads in the primary visual cortex of transgenic mice with the Alzheimer’s biomarkers seen in humans.
The same group later extended the 40 Hz stimulation from visual to auditory, by adding 40 Hz auditory stimulations to stimulate the temporal cortex and hippocampus, two brain regions linked to learning and memory.
Results were positive, showing a loss of plaque loads and a boost in cognitive function.
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Reference
Iaccarino, H. F., Singer, A. C., Martorell, A. J., Rudenko, A., Gao, F., Gillingham, T. Z., Mathys, H., Seo, J., Kritskiy, O., Abdurrob, F., Adaikkan, C., Canter, R. G., Rueda, R., Brown, E. N., Boyden, E. S., & Tsai, L.-H. (2016). Gamma frequency entrainment attenuates amyloid load and modifies microglia. Nature, 540(7632), 230–235. https://doi.org/10.1038/nature20587
Wang, W., Huang, R., Lv, L., Ma, X., Li, Z., Zhang, Y., Wu, J., Wu, S., Xu, J., Hu, Y., Turck, C. W., Li, H., & Hu, X. (2026). Long-term effects of forty-hertz auditory stimulation as a treatment of Alzheimer’s disease: Insights from an aged monkey model study. Proceedings of the National Academy of Sciences, 123(2). https://doi.org/10.1073/pnas.2529565123