The Promise of Sleep: Adequate shut-eye is good for your brain. Our experts explain why and how to get the amount you need.

Levine, Hallie

Neurology Now:
doi: 10.1097/01.NNN.0000513026.76891.7f
Departments: The Healthy Brain
In Brief

Adequate shut-eye is good for your brain. Find out why and how to get the amount you need.

Science has been telling us for years that sleep is important for both physical and emotional health, but for many it remains elusive: Only one out of three adults gets the recommended seven hours each night, according to a US Centers for Disease Control and Prevention (CDC) article published last February in Morbidity and Mortality Weekly Report. People who sleep fewer hours than that are at an increased risk of developing conditions such as obesity, diabetes, high blood pressure, and heart disease. Research also shows that sleep is vitally important for brain health as well.

“Increasingly, we're learning that sleep has definite effects not just on cognitive performance, but also on how well your brain functions day to day and possibly even your risk of developing neurologic conditions such as Alzheimer's disease,” says Adam Spira, PhD, associate professor in the department of mental health at the Johns Hopkins Bloomberg School of Public Health in Baltimore.

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MEMORY BOOST

While our bodies slumber, our brains are busy strengthening connections between brain cells, transferring information from the hippocampus (responsible for short-term memory) to the neocortex (responsible for long-term memory). “This process essentially shifts memories and skills to a more efficient brain region so they become more stable and you can easily recall them, a process called memory consolidation,” explains Beth Malow, MD, MS, FAAN, professor of neurology and pediatrics and director of the Vanderbilt Sleep Division at Vanderbilt University in Nashville.

Now, researchers are gaining insight into how that happens. At night while we're dozing, electrical brain waves circle around each side of our brains, creating a spiral-like pattern, according to a Salk Institute study published last November in the medical journal eLife. Up until now, experts had assumed these spindles popped up at the same time throughout the brain, but this study found that “they spread more like a wave that begins near your ear, spirals through your cortex toward the top of the back of your head, then moves onto the forehead area before circling back to the starting point,” says Dr. Malow. Each circuit takes about 70 milliseconds to complete and is repeated anywhere from 200 to 500 times during sleep. The researchers theorize that these circuits help strengthen connections between various parts of the brain that store different elements of the same memories—for example, sound, sight, and emotion. As a result, our memories are more vivid.

Sleep not only protects memories from fading, it also makes them easier to access, according to a 2015 University of Exeter study published in the journal Cortex. When participants were told an unfamiliar made-up word, then asked to remember it 12 hours later after either a period of sleep or wakefulness, those who had gotten rest were more likely to recall the word.

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TOXIN REMOVER

Perhaps the most important recent discovery about sleep and its effect on the brain is that it allows the brain a chance to do some much needed housekeeping. Specifically, when we're sleeping, our brain's glymphatic system—which clears waste from our brains—kicks into gear. This newly discovered system “acts like a janitorial system: it clears out all the waste products, such as beta-amyloid possibly, that clog up your brain,” says Jennifer Rose Molano, MD, FAAN, associate professor of neurology at the University of Cincinnati College of Medicine. It does this by releasing cerebrospinal fluid (CSF) that flushes toxins out.

When researchers looked at the flow of CSF through mice's brains when they were both awake and asleep, the greatest amounts occurred when the rodents were slumbering, according to a study published in a 2013 issue of the journal Science. Sleeping mice also got rid of twice as much beta-amyloid, the plaque linked to Alzheimer's disease, from their brains as conscious mice, according to the study. In another study, published in the journal Science Translational Medicine in 2012, researchers from Washington University in St. Louis found that amyloid and tau—two protein fragments linked to Alzheimer's disease—are at their peak during waking hours and lowest during deep sleep. “We can't prove that Alzheimer's disease is caused by sleep deprivation, but it appears to be a factor,” says Erik Musiek, MD, PhD, assistant professor of neurology at the Washington University School of Medicine.

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AGE AFFECTS SLEEP

More than half of elderly adults have insomnia, defined as difficulty falling asleep, staying asleep, or waking up too early, according to some studies. “As you get older, your sleep cycle changes, so you tend to have more frequent awakenings,” explains Dr. Molano. You also get less delta, or slow-wave sleep, a deeper stage of slumber that helps consolidate memory. Some sleep experts believe it's not the normal changes of aging that contribute to daytime sleepiness, but rather coexisting medical and psychiatric illnesses, she says.

Age also increases the likelihood of developing sleep apnea, a condition where you have one or more pauses in breathing or shallow breaths while you sleep. Left untreated, sleep apnea increases the risk of life-threatening conditions such as heart disease, stroke, diabetes, and depression. The effects may be almost immediate: Just six hours of fluctuating oxygen levels (similar to what you'd see in sleep apnea) can dramatically impact the body's ability to regulate its blood pressure, according to a Canadian study published last November in the American Journal of Physiology.

Sleep apnea raises the risk for stroke, too, and impedes recovery from stroke, according to a study by German researchers published last August in Neurology. Because of this, the study authors recommend that anyone who experiences a stroke get tested for sleep apnea. You should also be tested if you snore, if your sleeping partner says you gasp or have pauses in breathing at night, if you feel sleepy during the day, or if you experience a headache as soon as you wake up that gradually fades as the morning goes on—whether you've had a stroke or not, says Dr. Molano.

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SLEEP-DISEASE LINK

As beneficial as sleep is, it can be particularly challenging if you have a neurologic condition such as Alzheimer's disease or Parkinson's disease, or if you've had a stroke. “It really becomes the chicken-or-the-egg phenomenon: Is lack of sleep worsening the condition, or are sleep disturbances a function of the actual disease?” says Todd Swick, MD, FAAN, assistant clinical professor of neurology at the University of Texas Health Sciences Center Houston School of Medicine.

Many people with Alzheimer's disease, for example, experience changes in their sleep patterns. “They wake more frequently during the night, and brain wave studies show decreases in all sleep stages,” says Dr. Swick. In the late stages of the disease, people spend about 40 percent of their time in bed at night wide awake, a phenomenon known as “sundowning.” Their day-night circadian rhythms get disrupted. They may get up and wander around at night and may even be agitated, and sleep for much of the day, Dr. Swick explains.

Specific sleep problems such as rapid eye movement (REM) sleep behavior disorder—acting out dreams in sleep, which can include yelling and thrashing around—can also be an early warning sign of Parkinson's disease, even before other motor symptoms, such as hand tremors, begin. “Up to 75 percent of patients with REM sleep disorder end up developing Parkinson's disease a decade or two later,” says Dr. Muziek. People with Parkinson's disease are also more likely to develop restless legs syndrome, an overwhelming urge to move your legs at night, and are more susceptible to sleep apnea. In fact, about 40 percent of patients have sleep apnea, according to the Parkinson's Disease Foundation. There also appears to be a link between Parkinson's disease and narcolepsy, a brain disorder that involves poor control of sleep-wake cycles, causing periods of extreme daytime sleepiness and sudden bouts of falling asleep. A study published in the Journal of Sleep Research in 2012 found that both patients with Parkinson's disease and those with narcolepsy display a loss of orexin/hypocretin (Hcrt) cells in the brain. “It's this loss of Hcrt cells in both conditions that most likely causes symptoms,” explains Dr. Muziek.

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LESS SLEEP, MORE PAIN

If pain is one of the symptoms of your condition, lack of sleep can make it worse, research shows. A 2015 study of more than 10,000 Norwegian adults published in the journal Pain found that those who reported insomnia more than once a week had a 52 percent higher sensitivity to pain than those who never had trouble sleeping.

“If you're up all night, your brain becomes irritable and has trouble functioning, which makes you much more susceptible to pain's effects,” explains Dr. Muziek. That's why it's crucial to treat sleep problems as soon as they arise. “We can't say with certainty that consistently getting a good night's sleep will reduce your risk of developing neurologic conditions, or even reverse them,” stresses Dr. Spira. “But we do know it can improve your daily functioning, your reaction time, and your cognitive abilities, which in turn improves your quality of life.”

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Smart Strategies for Better Sleep

You probably know the basics for getting a good night's rest—things like using your bedroom for sleep and sex only, going to bed and waking up at the same time every day even on weekends, and limiting napping. The National Sleep Foundation recommends 7 to 9 hours of sleep for adults 18 to 64 years old and 7 to 8 hours of sleep for those older than 65. We asked a few experts for some additional advice to help you get those recommended hours.

Make your bed. People who make their beds in the morning are 19 percent more likely to get a good night's sleep every night, according to a poll done by the National Sleep Foundation. One theory is that people who make their beds are more likely to feel good about their beds, which can lead to better sleep.

Work out in the morning. Women with insomnia who exercised in the morning averaged 70 percent better sleep than those who exercised at night, according to a 2012 study published in the journal Sleep. Researchers speculate that morning exercise sets your body clock for a day of activity and a night of sleep, says Beth Malow, MD, MS, FAAN, professor of neurology and pediatrics and director of the Vanderbilt Sleep Division at Vanderbilt University in Nashville.

Avoid afternoon caffeine. The effects of caffeine—whether from coffee, caffeinated teas, dark chocolate, or diet sodas—can last for hours in your system. “I recommend patients avoid caffeine after 3 PM, and even consider cutting it out by noon if they have insomnia or other sleep problems,” says Dr. Malow.

Eat a light dinner. Folks who ate an evening meal high in fiber and low in saturated fat fell asleep faster and reported better quality sleep than when they ate a larger, higher fat one, according to a study published in the Journal of Clinical Sleep Medicine last January

Impose an electronic curfew. No TV, computer, backlit e-book, or phone for 90 minutes before lights out. If you start your night with blue light from a screen, your sleep may be less restful—even if you're sleeping as much as usual. People who read from a screen before bed found it harder to wake up in the morning and feel alert, even though they slept the same amount, according to a Harvard study published in the Proceedings of the National Academy of Sciences in 2014. The reason? The blue light emitted from the e-book suppresses melatonin, a sleep-promoting hormone.

Cool the bedroom. Your body temperature reaches its lowest level around 5 AM. If the room's too hot, it may interfere with your body's natural dip and make you more restless throughout the night. Most folks sleep best when the room temperature is around 68 degrees, says Dr. Malow.

Flick on a fan or white noise machine. These will mask background sounds like a car driving by, a dog barking, or a door closing. These sounds may not wake you up fully, but they rouse you out of the deep restorative sleep your body needs to stay energized, according to the World Health Organization's Night Noise Guidelines.

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5 Ways to Treat Insomnia

Almost 10 percent of Americans experience chronic insomnia, according to the US Centers for Disease Control and Prevention, which means they have trouble sleeping at least three nights per week. It's also more likely to happen as you get older. The sleep cycle changes with age, making it harder to fall asleep and causing more frequent awakenings, says Beth Malow, MD, MS, FAAN, professor of neurology and pediatrics and director of the Vanderbilt Sleep Division at Vanderbilt University in Nashville.

Consider these 5 therapies to help overcome insomnia.

1 COGNITIVE BEHAVIOR THERAPY (CBT): Considered the gold standard when it comes to treating insomnia. It's so effective, the American College of Physicians recommended it last May as the first therapy to try. A 2015 study published in the Annals of Internal Medicine found that CBT improved all aspects of sleep, including how fast people fell asleep, how long they slept, and how well rested they felt.

How it works: You learn how to control negative thoughts and worries that keep you awake at night and how to develop good sleep habits. Most people require about eight sessions over a period of several weeks.

2 RELAXATION TRAINING: A 2010 study published in the Journal of Clinical Nursing found that relaxation training improved sleep and reduced fatigue in women undergoing chemotherapy for breast cancer.

How it works: One technique focuses on tensing and relaxing muscles in different areas of your body one after the other to calm yourself and induce sleep. The other technique aims to prompt a relaxation response by having you lie comfortably, eyes closed, and focus on one peaceful word or image.

3 MINDFULNESS MEDITATION: Adults who had trouble sleeping and completed a mindfulness awareness program where they met once a week for six weeks for two hours reported less insomnia and fatigue at the end than a control group who took a sleep education class, according to a 2015 study in the Journal of the American Medical Association.

How it works: You sit comfortably and focus on your breath, bringing yourself completely into the present and letting thoughts come in and out of your consciousness without engaging with any of them.

4 STIMULUS CONTROL: This type of therapy focuses on strengthening the association between your bedroom and sleep and weakening associations that don't promote sleep. Stimulus control was pioneered in the early 1970s to treat insomnia by Richard Bootzin, PhD, professor of psychology at the University of Arizona in Tucson. Since then, studies demonstrate that it can improve total sleep time, sleep efficiency, sleep quality, and decrease daytime sleepiness.

How it works: You learn to limit bedroom activities to sleeping and sex, explains Dr. Malow. That means no reading, watching TV, eating, staying awake worrying, or clock-watching. If you've been in bed awake for more than what feels like 20 minutes, you need to leave your bedroom and do another relaxing activity in other room (like reading or listening to soothing music) until you feel sleepy again.

5 MEDICATIONS: Prescription sleeping pills can help you get to sleep and stay that way, but doctors don't recommend using them for more than six weeks at a time. “They can get you to sleep, but they can't get to the root of the problem or behaviors that keep you awake,” says Todd Swick, MD, FAAN, assistant clinical professor of neurology at the University of Texas Health Sciences Center Houston School of Medicine. They can also be addictive and come with side effects such as daytime sleepiness, nausea, and dizziness, he notes. They can also interfere with other medications and may worsen insomnia over time.

For trouble falling asleep, doctors may recommend a short-acting drug such as zaleplon (Sonata), zolpidem (Ambien), or ramelteon (Rozerem). If you have trouble staying asleep, a longer-acting medication such as zolpidem extended release or eszopiclone (Lunesta) are options. If you wake up in the middle of the night, both zaleplon and an under-the-tongue tablet form of zolpidem have been developed for this problem, with the caveat that you need to stay in bed for at least four hours after taking them.

It's recommended that you avoid over-the-counter sleep aids that contain diphenhydramine and doxylamine. Older adults who take these drugs regularly show more memory problems and appear to have a higher risk of dementia, according to an Indiana University study published in JAMA Neurology last April.

The dietary supplement melatonin, which increases levels of the sleep-promoting hormone your body naturally makes, may help, but first talk to your doctor about the appropriate dosage.

© 2017 American Academy of Neurology