MIT 14 人小研究：掐准时机的粉红噪音短脉冲，增强了深睡慢波与脑脊液流动

• New research suggests pink noise may help flush waste out of the brain.
• The study used pink noise that was carefully-timed to try to enhance deep sleep and the flow of cerebrospinal fluid.
• Doctors say more work is needed to explore the practical benefits of this.

Your brain juggles a lot of tasks at once, from critical thinking and managing your body's movements to regularly cleaning itself. But new research suggests that you may be able to support your brain’s waste clean-up process by doing something super simple: listening to noise while you sleep.

There's a lot that happened in this study, including a very strategic use of pink noise to try to rid the brain of toxins and possibly even support deeper sleep. This is also one small study, making it a stretch to say flipping on an ambient noise machine at night will make you smarter or healthier.

But if you already enjoy listening to something like pink noise at night, it's helpful to know that there may be an added perk for your brain. Here's what the study found, plus why a sleep medicine specialist says more work is needed.

Meet the experts: Joshua Levitt, PhD, researcher and study co-author and Christopher Winter, MD, a sleep medicine specialist, neurologist, and author of The Sleep Solution: Why Your Sleep Is Broken and How to Fix It.

What did the study find?

For the study, which was published in the journal Science Translational Medicine, researchers from MIT recruited 14 healthy volunteers and monitored their brain activity while they napped in an MRI scanner.

The researchers used closed-loop auditory stimulation, which is a brain modulation technique that detects changes in brain activity and then delivers a low-volume acoustic cue (in this case, pink noise) to enhance or reset brain activity. For this study, participants were specifically subject to a 50-millisecond (or 0.05 second) burst of pink noise when their brains showed a peak in EEG slow waves. (EEG slow waves include delta waves, the slowest and highest-amplitude brain waves that are a defining characteristic of deep sleep.)

The researchers discovered that the short burst of pink noise was linked to an increase in the amplitude of delta waves, along with the flow of cerebrospinal fluid, or the protective clear fluid surrounding the brain and spinal cord that’s thought to help get rid of waste.

The findings can be "explored as a potential translational tool in clinical populations," the researchers wrote, which basically means there may be some health-boosting value to the general public, but exactly what isn’t clear yet.

Why might closed-loop auditory stimulation cause this?

The study didn’t look into that, but there are some theories. The EEG slow waves are probably the biggest factor, according to Joshua Levitt, PhD, researcher and study co-author.

"They represent moments of widespread, cyclical activation and deactivation of the neurons in our brain," he says. "When parts of the brain are less active, they consume less oxygen, and the body shunts oxygen-supplying blood flow away from them." When this is widespread, which is what happens when there are slow waves, it means there's a large flow of blood away from the brain, Levitt says.

"Because our skull is a fixed volume at constant pressure, if one liquid flows out, another must flow in to take its place," Levitt says. "So, when blood flows out following deactivation, cerebrospinal fluid flows in." There, it can help deliver nutrition to your brain and clean out waste.

Levitt says the findings are less about the pink noise itself and more about the technique of closed-loop auditory stimulation. "We chose pink noise to better match with some previous literature," he explains.

Closed-loop auditory stimulation is "basically playing sounds at night—it could be white noise or other frequency tones—that seem to affect the electrical signature of sleep, in this case, slow wave sleep," says Christopher Winter, MD, a sleep medicine specialist, neurologist, and author of The Sleep Solution: Why Your Sleep Is Broken and How to Fix It.

What's the takeaway here?

Closed-loop auditory stimulation is an area of neuroscience that's being heavily researched. But Dr. Winter points out that the practical real-world benefits of this—such as having enhanced memory or preventing disease—are still up for debate. "The theory is that playing the right tone/frequency at the right time in sleep will elevate the quality of sleep, [or] enhance deep sleep,” Dr. Winter says, noting skeptically that it’s often sold as biohacking or a way to extend longevity.

There doesn't seem to be harm in doing this, though. "If someone wants to try it, it's up to them," Dr. Winter says.

Levitt is continuing to research the technique in hopes of creating a product around it. "This [cerebrospinal fluid] flow is our brain's waste clearance mechanism, carrying off molecules like beta-amyloid and tau before they form plaques that can contribute to diseases like Alzheimer's," he says. "We are still a long way away from being able to say that our intervention had any beneficial effect on waste clearance or disease—we didn't even try to measure one—but I think this study opens up some interesting possibilities that we are currently investigating."

Carina Hsieh, MPH, is the deputy features editor of Women’s Health. She has more than a decade’s worth of experience working in media and has covered everything from beauty, fashion, travel, lifestyle, pets, to health.

She began her career as an intern in the fashion closet at Cosmopolitan where she worked her way up to Senior Sex & Relationships Editor. While covering women’s health there, she discovered her passion for health service journalism and took a break to get her Masters in Public Health. Post-grad school, she worked as a freelance writer and as The Daily Beast’s first Beauty, Health, and Wellness Reporter.

Carina is an alum of the Fashion Institute of Technology and the Yale School of Public Health. She and her French Bulldog, Bao Bao, split their time between Brooklyn and Connecticut. She enjoys reformer Pilates, (slow) running, and smelling the fancy toiletries in boutique fitness class locker rooms.