A faint rush of sound, delivered at precisely the right moment, could improve brain health while people sleep, according to a new study.Researchers at MIT and Boston University found that carefully timed bursts of “pink noise” trigger stronger waves of cerebrospinal fluid, or CSF, that clear waste from the brain.Pink noise is a gentle, static-like sound. Like white noise, it contains a range of pitched frequencies, but its lower frequencies are louder, and its higher frequencies are softer. This creates a balanced sound similar to steady rain or a distant waterfall.The study, published Wednesday in Science Translational Medicine, involved 14 people who fell asleep during afternoon sessions inside an MRI scanner. It was designed as a proof of concept. The work grew out of research Laura Lewis, an MIT associate professor, conducted several years ago, when her team discovered large waves of cerebrospinal fluid moving through the brain during sleep. Those waves appeared to follow the slow electrical waves characteristic of non-REM sleep, the restorative portion of the sleep cycle when brain activity slows.“We were really fascinated by that because there’s lots of prior work from animal studies showing that sleep is a really important state for maintaining brain health,” Lewis said. “We thought, if we could make more of these electrical slow waves, would we actually be able to drive more of the CSF flow during sleep?”CSF is the clear liquid surrounding the brain and spinal cord. It cushions the brain and helps transport nutrients and waste as the brain burns energy. During non-REM sleep, waves of cerebrospinal fluid wash through the brain to help clear out metabolic waste. Lewis and her colleagues wondered if they could manipulate one to influence the other.“You can make more of these electrical slow waves through an auditory stimulus, if it comes at just the right time,” said Lewis. “Similar to a child on a swing, if you push them when they’re at the right moment in their movement, you can make that swing go farther. The challenge is: How do you find just the right time?”That requires more than a sound machine, she said.Participants wore special headgear and EEG equipment to measure their brain activity while they slept in an MRI scanner. An algorithm predicted the timing of their slow waves, allowing researchers to deliver 50-millisecond bursts of pink noise during wave peaks.The researchers found that the CSF response depended on where in the slow-wave cycle the sound arrived. Simply playing sounds during non-REM sleep did not produce the same effect, Lewis said. So, people shouldn’t expect to reproduce the experiment by pulling up a pink-noise track on their phone while scrolling in bed. “There’s no evidence” that simply playing continuous pink noise would have the same effect, Lewis said. “We had gone to a lot of trouble to play these at the specific correct times.”Lewis and the study’s lead author, Joshua Levitt, say they invented the “CSF-flow neurofeedback system” and are cofounders of Cerebloom Inc., with a patent pending, according to the paper’s disclosures.Levitt recently earned his PhD from Boston University and was a visiting graduate student in Lewis’ lab. Levitt started the company to develop a headband-like device that people could use at home to increase CSF flow by delivering an auditory stimulus at the right time.The findings are intriguing to them because disruptions in CSF circulation have been associated with aging and neurological disorders, including Alzheimer’s and Parkinson’s diseases. And it’s part of what Lewis wants to investigate next.“We did it all in healthy individuals,” she said. “It’s very important for us to test: Does this work in people who may be either much older or who may be showing signs of the beginnings of a neurological disorder?”Previous research has also suggested that manipulating slow waves could affect memory and other aspects of brain function. However, researchers didn’t test memory or cognitive outcomes. For people simply looking to sleep better tonight, Lewis said there is no reason to try to recreate the experiment at home.“I certainly hope that in future work we can start to develop things that will actually be transferable out of the lab environment, but we don’t have that now,” she said.She also cautioned against turning the pursuit of perfect sleep into another source of anxiety.“Worrying about it, I think, can even make it harder,” Lewis said. Some people prefer silence while others sleep better with continuous background noise, she said, and the new research doesn’t address whether one is better than the other.Rebecca Robbins, an assistant professor of sleep medicine at Harvard Medical School and an associate scientist at Brigham and Women’s Hospital said the new study doesn’t change the basic advice she gives people looking for a better night’s rest.“The best environment for sleep has three considerations: quiet, dark, and cool,” said Robbins.The bottom line for people who use sound to help them sleep, Robbins said, is to “find something consistent at home and while traveling to condition yourself that what comes next is sleep.”Sarah Rahal can be reached at sarah.rahal@globe.com. Follow her on X @SarahRahal_ or Instagram @sarah.rahal.
