40 Hz sound exposure may raise Alzheimer's-related proteins in aged monkeys

A PNAS study reported that one week of 40 Hz auditory stimulation in nine aged rhesus macaques increased cerebrospinal fluid levels of Aβ42 and Aβ40 by about 206% and 201%, and those elevated levels persisted for up to five weeks.

Researchers reported that brief exposure to a 40 Hz auditory stimulus changed markers linked to Alzheimer's disease in an aged monkey model. The study was published in the Proceedings of the National Academy of Sciences and led by a team at the Kunming Institute of Zoology. Nine rhesus macaques aged 26 to 31, which had spontaneous amyloid plaques, received one hour per day of 40 Hz auditory stimulation via a 1‑kHz pure tone for one week. The work follows earlier laboratory studies that applied 40 Hz visual and auditory stimulation in rodent models. Key findings: - The study used nine aged rhesus macaques (26–31 years) exposed to one hour per day of 40 Hz auditory stimulation for one week. - After the stimulation week, cerebrospinal fluid (CSF) levels of Aβ42 and Aβ40 rose by about 206% and 201%, respectively. - The elevated CSF Aβ levels were reported to persist for up to five weeks after the stimulation ended. - The authors describe these changes as associated with movement of β‑amyloid from brain tissue into CSF. - The research builds on a 2016 study that reported 40 Hz light and later auditory stimulation reduced amyloid in transgenic mice and affected cognitive measures in those models. Summary: The study reports that short-term 40 Hz auditory stimulation produced sustained increases in CSF amyloid‑beta markers in an aged monkey model and connects to prior animal research using 40 Hz stimulation. Whether similar effects occur in humans or lead to clinical benefit is undetermined at this time.