After a long day, few things are as welcome as sinking into bed for a night of blissful sleep. It may feel as if you’re turning your brain “off,” but those hours of shut-eye are actually a time of immense activity important for overall functioning.
Just as quality sleep helps with everything from maintaining heart health to helping you heal from illness and injuries, it’s also critical for maintaining brain health, boosting memory, and more.
“Sleep is one of the pillars of brain health,” Dr. Rachel Salas, associate professor of neurology at Johns Hopkins School of Medicine, points out.
How sleep cleans your brain at night
Within your brain, there’s a crucial cleanup function that’s active primarily during those nighttime hours when you’re fast asleep: the glymphatic system, which flushes out the various waste products that accumulate.
The term “glymphatic” comes from combining the “g” from glial cells (a type of cell in the central nervous system) and “lymphatic” for the extensive lymph node system that runs throughout the body and performs numerous functions, including carrying waste products away from cells. The glymphatic system, discovered only a decade ago, performs a similar function within the brain.
“Glial cells can be really tightly packed,” explains Michael Scullin, Ph.D., an associate professor of psychology and neuroscience at Baylor University, who heads the university’s Sleep Neuroscience and Cognition Laboratory. “When they’re really tightly packed, there’s not a whole lot of flow of fluid throughout the brain space.”
While this is the case during our waking hours, the situation changes during sleep: The glial channels open up, and cerebrospinal fluid flows into these spaces to flush out waste products, which are then carried away. “There can be a fairly large increase in the velocity of the flow of fluid between the cells,” Scullin explains. He compares it to a blocked pipe: “The way a plumber would clear it out would be to blast it with a high-velocity fluid to clear out the waste products.”
The brain-cell waste carried away during this nightly cleanse includes various proteins that can otherwise cause damage if not regularly removed.
This includes the buildup of beta-amyloid, which is “one of the long-standing neuropathological hallmarks of Alzheimer’s disease,” Scullin explains.
The glymphatic system’s ability to clear away waste products naturally becomes less efficient as we age, but it’s also affected by lack of sleep, which cuts into its cleanup window. For this reason, improving sleep is a critical protective factor against Alzheimer’s and other forms of dementia.
Sleep's role in learning and memory
During your nightly sleep, your brain processes all of the new input you’ve gathered over the course of your day. This can’t take place when we’re awake and taking in new information, according to Robert Stickgold, professor of psychiatry at Harvard Medical School and co-author of “When Brains Dream.”
This nightly sorting includes assessing the new information and determining what’s most important to retain — the content of a conversation, for example, rather than the setting or what the other person was wearing — as well as integrating that new information with other knowledge and strengthening it so that it’s stored in long-term memory. In addition to helping you retain new information (known as declarative learning), sleep helps when acquiring new motor skills, whether it be riding a bike or perfecting a gymnastics tumbling pass.
“All of those sorts of processing go on outside of our conscious mind,” explains Stickgold.
But getting quality sleep isn’t just important after the fact; it’s essential beforehand as well. “If you’re cutting back on sleep,” Scullin says, “your brain is going to operate less efficiently because it will not have had sufficient time to consolidate the information from the prior day.”
In addition, being sleep-deprived may affect your motivation to learn, says Scullin. That can be a double whammy when it comes to learning: Not only do you process new information more slowly when you’re sleep-deprived, but it also feels more difficult to muster the motivation and energy to focus on the task at hand.
The consequences of sleep
As Scullin explains, one area of the brain affected by sleep loss is the frontoparietal network, which “helps us sustain attention over time.” This network includes portions of the prefrontal cortex, which is located at the front of the brain and plays a key role in executive functioning, and the posterior parietal cortex, located near the crown of the head, which works with the prefrontal cortex and other areas of the brain to help integrate various types of sensory inputs we encounter in the world.
When you’re sleep-deprived, the resulting decrease in what’s known as vigilant attention can have far-reaching consequences, making it harder to stay focused, whether you’re behind the wheel or just trying to hold a conversation.
You may feel like you’re still managing to function well when you’re sleep-deprived, but that’s not always the case. In fact, some studies have shown that when participants were sleep-deprived over a period of several days, their sense of sleepiness initially increased and then hit a plateau, but their focus continued to worsen.
There are also longer-term effects of poor sleep to consider. One study went back to participants who had experienced fragmented sleep in their mid-30s to late 40s and found that 11 years later, those same participants scored lower on cognitive tests.
How sleep can boost your mental health
Your mental outlook, which colors your days, also starts off with a good night’s sleep, explains Nancy Sin, Ph.D., associate professor of psychology at the University of British Columbia.
First, better sleep makes you more open to positive experiences. In a recent study, Sin found that people who slept more than usual also got more of an emotional lift from positive events the following day. They were also more likely to expect to have a good day overall.
After a good night’s sleep, “you’re feeling better, you’re feeling well-rested, and you might be in the mindset to allow you to notice positive experiences or brush away experiences that might be more negative,” Sin explains. “You also just have the energy and motivation to engage socially and to engage in activities that are important to you. I think of sleep as feeding all of those things.”
This includes your motivation to exercise (which in turn helps boost your mood), make healthier food choices, and engage in social interactions — all of which help boost and maintain a positive mood.
In addition to helping you maximize the positive, getting quality sleep helps you bounce back from negative experiences. Think of it as providing an emotional buffer: You’re better able to cope when dealing with stressful events after quality sleep.
This can include everything from coping with a major setback — for example, your car won’t start — to relatively minor ones (someone cuts in front of you in line). But it also includes encounters that may be innocuous or ambiguous: the tone of voice someone uses or whether you think they’re frowning at you. In fact, one study of sleep-deprived participants found that when they looked at photos of people whose expressions were neutral or friendly, they interpreted the expressions as threatening and had a corresponding physiological stress response.
“We end up seeing greater emotional reactivity after sleep loss than when individuals are well-rested, and this can manifest in so many different ways,” Scullin says. “It can manifest as greater fear in fearful situations, it can manifest as greater anger, it can manifest as changes in how we communicate with one another.”
4 tips on how to improve your sleep
Keeping your brain healthy and your emotions in check does indeed start with a good night’s sleep. Fortunately, “sleep is something that people have some control over,” says Salas.
To improve your sleep, she suggests focusing on your sleeping environment and behaviors but also seeking medical help if needed. Here are some ways to get started.
Make sleep-friendly choices: Your actions during the day can impact how well you sleep that night. Among the areas to consider: cutting back on caffeine or having it earlier in the day, ensuring you get enough light exposure to help keep your circadian rhythm on track, and being mindful that overly long daytime naps can make you less sleepy when it’s time to turn in for the night.
Create an environment conducive to sleep: Keeping your bedroom dark, cool, and quiet are all important for a good night’s sleep. If your sleep hygiene could use a tune-up, taking steps to eliminate these distractions can help you fall asleep faster and also help keep you from waking in the middle of the night.
Prioritize your sleep: Adults generally need seven to nine hours of nightly sleep. If you regularly fall short of this, focus on getting more sleep and being consistent.
Seek help for sleep issues: If you’re having trouble sleeping and have eliminated potential external causes such as caffeine use, it may be time to seek medical help. If you’re suffering from insomnia (which includes difficulty falling asleep and staying asleep), cognitive behavioral therapy for insomnia (CBT-I) is considered the gold standard for treatment. Or you may have another treatable issue, such as obstructive sleep apnea, or have treatable symptoms from other situations, such as menopause.
Regardless, by focusing on improving your sleep, you’re also helping keep your brain healthy. As Salas sums up, “The more we keep learning, the more we keep finding that sleep is more and more integral to brain health.”
