What Science Tells Us About the Secrets Behind Sleep

Laura Lewis

You don’t have to be a scientist to know that sleep is essential to human health. But scientists will remind you that a good night’s sleep boosts everything from memory and energy to immune system function and even how successfully we age. And on the flip side, a growing body of evidence links poor sleep quality to a slew of health concerns—from cardiovascular disease to dementia.

Dr. Laura Lewis, a 2021 Pew biomedical scholar from the Massachusetts Institute of Technology, is engineering innovative methods to map the complex circuits in our brain that control states of sleep and wakefulness. She hopes her research can reveal what quality rest does for the brain—opening the door to new strategies for improving sleep quality or protecting the brain from disease when sleep is hindered. 

This interview with Lewis has been edited for length and clarity. 

Q: Why is sleep so key to wellness?

We know that sleep is really important for our health. You know it because if you miss a night of sleep, you immediately feel terrible. We need to understand why sleep affects our memory, mood, and attention—but also how it keeps us healthy. If we understand the circuits that control sleep, then even if someone's having problems falling asleep or they're having trouble with those circuits, then perhaps we can find other ways to try to recreate the benefits of sleep with new treatment methods.

Q: Do we know what controls sleep?

That’s one of the things we’re focusing on in my lab: What's the switch in the brain that makes you sleepy? To study that, we have to image a bunch of tiny structures that have traditionally been out of reach for us because they're so small and deep in the brain, which makes them very difficult to see with conventional imaging technology. We're trying to image across this whole network of little regions, looking at which ones play a role in sleep and wakefulness.

Q: What are your main challenges in studying sleep?

When you fall asleep, activity throughout your brain and body changes. That’s one of the big challenges: When everything is changing simultaneously, how do we figure out what’s causing what? You also can't control sleep. With most things neuroscientists study in the lab, we can set up very controlled experiments. But we conduct all of our studies with humans, and sleep just happens when it happens. We can't even ask someone if they're experiencing it. It’s hard to access something that happens so unpredictably and spontaneously.

Q: Tell us more about these studies.

Some of our studies recruit healthy volunteers for very basic science, but we also have studies in specific patient groups. For example, we have one study on people with major depressive disorder, to understand how sleep interacts with mood. We have another one on healthy aging, exploring how sleep contributes to successful cognitive outcomes. And we're just getting started now on hypersomnolence disorders, including narcolepsy, where people really struggle to stay awake during the day.

Q: You mentioned aging. Where does that come in?

We know that in the long term, people who don't sleep enough over their lives have a higher risk of disorders like Alzheimer’s disease. So, clearly, sleep is also doing something very protective for the brain. Another topic my lab is exploring is whether the flow of cerebrospinal fluid during sleep potentially plays a role in how healthfully we age.

Q: What’s that?

Cerebrospinal fluid, or CSF, is truly the bath of the brain. When your brain is active, it builds up waste products that then get flushed by CSF. One thing we discovered is that this liquid starts to pulse around the brain in large waves during sleep. So one big goal has been to understand what controls the flow of this fluid, why it happens when we’re asleep, and what happens if we don’t sleep.

Q: So poor sleep—or lack of sleep—negatively impacts this fluid flow?

If we don't sleep, this period of large fluid flow waves is being missed. We are now studying sleep deprivation in the lab to understand how that affects brain function. Intriguingly, our newest data suggests that the attentional dysfunction we experience after sleep deprivation is tightly linked to CSF flow, indicating an urgent need to switch into this high-flow state after a night of poor sleep.

Q: How could your research inform new treatments?

In the long term, this information could potentially help engineer a sleep medication that triggers restorative, refreshing sleep, instead of a sedative effect. Or, if we can understand what sleep is doing for the brain, then if someone isn’t sleeping well, maybe we can develop a different way to target that beneficial effect, regardless of whether they're sleeping enough. I also hope that our research will be useful for understanding sleep disorders, because they're incredibly common but vary widely across people. Our imaging technologies are noninvasive, so it's exciting that they can then be rapidly translated to study patients, to explore if these tools can help diagnose sleep problems and find their causes in individual people.