Forbes Magazine December 2016
For a long time, researchers weren’t quite sure why we sleep. There are a number of different theories. Some are evolutionary: For instance, sleep keeps us out of trouble at night and away from animals who wake up and hunt after the sun goes down. Some are physiological: Sleep lets us conserve precious energy. And some are anecdotal: Parents joke that they’d go nuts if sleep didn’t exist, since it affords them a much-needed break from their kids. But the reality is that the brain does a lot of work while we’re sleeping—even though we’re unconscious, this doesn’t at all mean the brain is “off.” In fact, in many ways, it’s incredibly “on.”
The RAND research group just came out with a 100-page analysis of how sleep affects us and what sleep deprivation can do to us—and to the economy. They estimate that between lost work and poor performance at work from lack of sleep, the U.S. alone loses $411 billion each year. Though businesses and policy makers may be interested in the financial repercussions of sleep deprivation, these repercussions stem from people being unwell because of it, which underlines the very real consequences of sleep deprivation.
Recent research has laid out some of the reasons why we need sleep, and all the functions the brain seems to perform while we’re sleeping. There’s more to figure out, but here are a few reasons why the brain needs sleep, and why things tend to go downhill without it.
Sleep helps solidify memory
One of the central functions of sleep is that it helps consolidate long-term memory—it seems to do this, not only through strengthening certain neural connections, but also through pruning back unwanted ones. The brain makes a lot of connections during the day, but not all of them are worth saving; so sleep is a time in which the brain streamlines the connections it “needs.”
Most people have probably observed the phenomenon whereby sleep helps us remember things we’ve learned during the day. And studies have borne this out. In one study, participants had to learn a motor routine (tapping buttons in a certain order). When learning the task and recalling the task were separated by a night of sleep, rather than the same amount of time during waking hours, the participants did much better. The theory is that the brain consolidates the memories it needs, but prunes back the ones it doesn’t. And research has shown that the brain tends to weaken the connections that form the memories that the brain deems unimportant.
One thing to be aware of is that sleep also seems to nail down negative memories, which probably plays a role in PTSD and depression. A very recent study showed that once negative emotional memories are consolidated during sleep, they’re less likely to be suppressed. And this means that bad memories in addition to the good ones more likely to stick around, and less likely to be forgotten.
Toxins, including those associated with Alzheimer’s disease, are cleared during sleep
One of the most illuminating discoveries in the last few years is that the brain clears out toxins much more rapidly while we’re asleep than when we’re awake.
“I think some of the most exciting work is on the glymphatic system,” says Michael Thorpy, director of the Sleep-Wake Disorders Center at Montefiore Health System and professor of clinical neurology at Albert Einstein College of Medicine. “There’s a lot of new research in this area in the last few years. The lymphatic system of the brain opens up at night, and removes toxins while we’re asleep.”
The space between brain cells expands significantly during sleep, which facilitates the clearing of the “gunk” through cerebrospinal fluid. And perhaps most astonishing is that much of this gunk is the β-amyloid protein, which is a precursor to the plaques in Alzheimer’s disease. These proteins and other toxins seem to accumulate during the day, and are cleared during sleep. Another incredibly strong reason to make sure we get enough.
Sleep is necessary for cognition
It doesn’t take a study to tell us that a lack of sleep affects our cognitive capacities, but luckily, there are a lot of them. Sleep deprivation can affect everything from cognition to attention to decision-making.
“We know that sleep is necessary for higher cortical function, the most important of which is multi-tasking” says Thorpy. “Sleep deprivation will definitely affect one’s ability to multitask. Driving is the most intensive multitasking activity we do—it uses hands, feet, vision, awareness of what’s going on. When you’re sleep-deprived, it strongly affects your ability to multitask. That’s why we have so many accidents with cars, and of course trains. Sleep deprivation drains your executive function.”
Sleep deprivation has also been shown to have a negative impact on cognitive functions like attention and working memory. One study found that just a little sleep deprivation—the loss of 2 hours of sleep per night for 14 nights—left participants with poorer performance on certain neurobehavioral tasks that involved attention and short-term memory.
Creativity needs sleep
Sleep seems to beget creativity—and sleep deprivation strips it away. We know this from anecdotes and from evidence. When people are sleep-deprived, certain types of thought seem to be affected more than others: For instance, divergent thinking—thinking outside the box, in new and imaginative ways—seems to be the first thing that goes when one is sleep-deprived, whereas convergent thinking—being able to figure out the correct answer, as on standardized tests—stays intact. One study deprived participants of sleep for 32 hours and tested them on various aspects of thinking. People who were sleep-deprived for the 32 hours performed significantly worse on most types of divergent thinking, including fluency, flexibility and originality. And they had the tendency to perseverate on verbal memory tests: In this case, to come up with the same answer again and again, cross it out, and try again, which is a sign that the creative mind isn’t doing so well.
On the flipside, sleep seems to promote creativity: One study had participants learning a task involving numbers, in which they had to detect a pattern hidden in the questions. People who got a night of sleep were much more successful at figuring it out than people who were sleep-deprived.
And aside from the studies, experiencing creative insights during sleep, or just as one is waking up from it, has been documented for many hundreds of years.
Sleep loss and depression are intertwined
Depression and sleep problems are intimately connected. People with depression often have a hard time sleeping, or, on the flipside, they may sleep a lot. It also seems to be true that sleep deprivation can, if not cause depression, certainly worsen it. So it’s a bit of a chicken-or-egg relationship. Studies have found that people who sleep less than six hours per night or more than eight hours per night are more likely to be depressed than people in the middle. And people with insomnia are many more times likely to have depression and anxiety. Part of the explanation for these connections may come from the fact that the part of the brain that governs circadian rhythm (daily sleep-wake cycle, and all the body functions that depend on it) is disrupted in depressed people. Which may partly explain why depression and sleep problems go hand-in-hand.
Physical health and longevity
Although the body doesn’t technically need sleep in the same way the brain does, there are a number of physical diseases and disorders it seems to affect. A new study presented at the Radiological Society of North America’s annual conference found that when health professionals (radiologists) got an average of three hours of sleep during a 24-hours shift, their hearts suffered for it. The participants had increases in contractility of their hearts, blood pressure, heart rate and levels of thyroid hormone and the stress hormone cortisol.
Other studies have linked lack of sleep to overweight and obesity, and poorer glucose control. Lots have studies have linked poor sleep to mortality—but there seems to be a sweet spot, where people getting under six hours are at greater risk, and those getting nine or more hours per night are at risk. The effects of sleep deprivation likely have to do with its effects on hormones, mentioned above, which can increase heart and diabetes risk, as well as inflammation, which itself may increase one’s risk of cancer.
“The sleep-wake cycle has an important impact on all organ systems,” says Thorpy. “We can’t minimize the fact that the sleep-wake pattern has effects on the whole body, not just the brain. The most direct function of sleep does seem to be its effects on the central nervous system. But I wouldn’t ignore the fact that body organs are affected as well.”
Kids need their sleep
If you have kids, you know that without sleep, they can be a tad difficult. Sleep deprivation in children has lots of short-term ramifications, and over the long term, it may even affect brain development. Sleep is especially important for the growing brain, which is why babies, kids and teens sleep so much.
Some studies have reported that kids who are sleep-deprived because of nighttime breathing problems are significantly more likely to have ADHD symptoms than kids who sleep well. Others have found that a little extra sleep can make a significant difference in school performance: Just 18 more minutes per night was linked to better grades in math and English in elementary school kids.
And sleep deprivation seems to have slightly different effects in kids vs. adults. One recent study found that the brain changes that a half-night of sleep deprivation affects the back regions of the brain instead of the front regions, as it does in adults. It’s not clear exactly what this means for brain development, it just points to a fundamental difference that needs more exploration.
Some schools, having kept an eye on the research, have begun shifting their school day so that it starts later, to accommodate the need for sleep for the developing brain. Hopefully more will follow suit as more research helps us understand what the brain is doing while you’re asleep.
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Sleep can feel like an indulgence, especially when we’re busy or stressed; and it’s often the first thing to go at these times. But as the research shows, sleep isn’t a luxury—it’s a necessity, and brain will probably rebel if it doesn’t have enough. So it may be time to change our attitudes about sleep and give it a little more attention than it usually gets.