BEIJING -- A team of Chinese scientists has demonstrated that simple, non-invasive sound therapy can produce significant and remarkably long-lasting biological changes in aged monkeys, offering new hope for a potential physical treatment for Alzheimer's disease.

The study, published in the latest issue of the Proceedings of the National Academy of Sciences (PNAS), was led by researchers from the Kunming Institute of Zoology (KIZ) of the Chinese Academy of Sciences.

This research effort centers on the use of a 40-hertz auditory tone, which is a low hum within the range of human hearing. While previous investigations in mice have suggested that 40-hertz stimulation may help clear Alzheimer's-related toxic proteins from the brain, this new work provides the first critical evidence emanating from non-human primates.

In Alzheimer's disease, a protein known as beta-amyloid tends to accumulate into plaques, damaging brain cells and impairing memory and cognition. The brain typically clears such waste through cerebrospinal fluid (CSF).

The research team worked with nine aged rhesus monkeys, whose brains naturally develop Alzheimer's-like plaques, making them a highly relevant model for investigating the human condition. The monkeys listened to a one-hour, 40-hertz tone daily for one week.

The results were striking, with key Alzheimer's-related protein levels in the monkeys' CSF more than doubling immediately after the treatment period -- meaning more waste was being cleared out.

"Most remarkably, the effect persisted. When we measured five weeks after the sound treatment ended, the beneficial change had not faded," said Hu Xintian, a researcher at the KIZ.

Current approved drug therapies for Alzheimer's, while effective for some, can carry risks like brain swelling and are also costly. In contrast, 40-hertz auditory stimulation represents a safe, low-cost physical intervention, Hu said.

"The long-lasting effect we see in primates supports developing this gentle approach as a future therapy for Alzheimer's," he added.