New Study Finds Deep Sleep Washes Your Brain & May Prevent Alzheimer's

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At mbg, we know how important sleep is for our well-being. Our modern lifestyles might keep us from getting in the recommended eight hours every night, but time and time again, research shows us how important our circadian rhythms are for our health—from our gut microbiome to weight loss to overall brain health. In terms of the latter, it can be difficult to understand what parts of our brain are benefiting from sleep—and how these processes work.

A new study published in the journal Science, however, is now able to explain how our brains wash away toxins as we sleep. Experts have already discussed how our brains go through a "self-cleaning" process as we get some much-needed shut-eye, which is why a good night's sleep is most likely to give you way better results than that grueling "all-nighter." 

This study, however, is the first one to show how cerebrospinal fluid (CSF) washes through the brain during sleep, removing waste and making space for this cleanup process.

Researchers also found that CSF is closely related to slowing brain-wave activity and blood flow. As we age, our brains generate fewer slow waves, which also reduces this rush of CSF. If this fluid doesn't wash away toxins while we sleep, waste can build up in our brains and ultimately cause cognitive decline

How did they make this connection?

During the study, researchers analyzed the brain waves of 13 people between the ages of 23 and 33 who were tasked with falling asleep while inside an MRI machine (if you've ever had an MRI before, you can imagine how difficult this probably was). The researchers realized this limitation, and so they already have proposed a new study with older individuals that would include a better sleeping environment.

"We have so many people who are really excited to participate because they want to get paid to sleep," co-author of the study Laura Lewis, Ph.D., jokes. "But it turns out that their job is actually—secretly—almost the hardest part of our study. We have all this fancy equipment and complicated technologies, and often a big problem is that people can't fall asleep because they're in a really loud metal tube, and it's just a weird environment."

Despite the noisy MRI, participants were able to (finally) catch some zzz's, and the researchers could measure their CSF waves. As soon as they reached deep sleep, Lewis noticed how the CSF came rushing in ready to wash out any toxic, memory-impairing proteins. The effect was like clockwork: Once the participants were asleep, the CSF was awake and ready to do its job.

"It's such a dramatic effect," Lewis notes. "[CSF pulsing during sleep] was something we didn't know happened at all, and now we can just glance at one brain region and immediately have a readout of the brain state someone's in."

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What does this mean for our sleep habits?

Because measuring CSF is such an important marker for deep sleep, this research has the potential to diagnose cognitive disorders such as autism and Alzheimer's that are associated with disrupted sleep patterns. If CSF can help wash away specific toxins that play a role in Alzheimer's, this level of deep sleep could even potentially prevent the disease itself.

The study could shed light on normal, age-related cognitive decline as well. As people age and their brains generate fewer waves (and reduce CSF as a result), their memory function could decline even if they don't suffer from a specific disorder like Alzheimer's.

So what's the next move for sleep studies?

Now that they've realized the rush of CSF occurs in tandem with brain waves and blood flow, the next step for Lewis and her team is to study why these brain processes occur in a specific order as we sleep.

"What are the causal links? Is one of these processes causing the others? Or is there some hidden force that is driving all of them?" Lewis asks.

It seems that with this study, there might be more questions than answers. It makes sense—we're talking about the brain here, after all. But one finding remains paramount from this experiment: Reaching a point of deep sleep is essential for flushing out toxins and preventing cognitive decline. 

No matter your age, this study is not something to sleep on.

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