Your brain has a built-in cleansing cycle. While you sleep, the glymphatic system bathes your brain in a liquid called cerebrospinal fluid (CSF) to flush out the waste particles that accumulate throughout the day. But disordered sleep and the natural effects of aging can disrupt this nightly routine, potentially leading to the accumulation of harmful particles that increase your risk for neurodegenerative disease. Now, research published in Science Translational Medicine shows that listening to short bursts of fuzzy-sounding “pink noise” timed with brain waves during sleep can encourage CSF flow.
There have been few promising treatments to improve the glymphatic system’s functioning without major tradeoffs, says University of Rochester glymphatic biologist Lauren Hablitz, who was not involved in the study. “The biggest challenge to the CSF and glymphatic brain-clearance field right now … is really therapies,” she adds. Compared with drugs and surgeries to increase flow, which are still experimental, using pink noise “could be really powerful in a much less invasive way.”
Researchers knew that certain waves of brain activity during sleep, called slow waves, precede CSF flow. They also knew that people can enhance their slow waves by listening to bursts of staticky pink noise—a fuzz of sound defined by louder low pitches and quieter high ones—at the same time as the waves’ peaks. The study authors placed electrode caps on participants’ heads while they slept in a magnetic resonance imaging machine, and they used an algorithm to time the pink noise with slow-wave peaks. Brain scans showed that CSF flow was higher when the pink noise played during slow waves than it was during control periods with no noise alongside the waves.
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The team doesn’t fully know why the timed noises increased CSF flow but suspects the sound may activate a special type of slow wave that helps the brain avoid responding to noises during sleep, such as cars passing by. The brain is less active and draws in less blood during part of the slow wave, so CSF flows in to help maintain pressure in your head.
Lead author Joshua Levitt, a biomedical engineer who recently completed his Ph.D. at Boston University, says the effect is less about the pink noise itself and more about its timing with brain waves. “You can’t just play pink noise all night and get the same effect,” he says. Sounds with different frequency balances, such as white noise, might also be effective.
If validated by future work, selective noise-playing could potentially unlock more restorative sleep in a home environment, the researchers say. They’re particularly interested in testing the method in older individuals and in people with sleep disorders. Study co-author Laura Lewis, a neuroscientist at the Massachusetts Institute of Technology, says an important next step is testing whether the increased CSF flow actually helped to clear waste particles from the brain. Confirming that “is very tough to do in a human,” she says, so follow-ups in animals will be key.
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