By Ruya Tazebay
Art by Lio Chan
Right now, I’m working on an article about sleep deprivation for the Grey Matters Journal at Columbia University. It’s so late at night—or is it already morning? The irony here isn’t lost on me. I still have more tasks to check off on my to-do list after this. I don’t know what time I’ll be done. Yet I can say, with the exhausted resignation that has become characteristic of college life, that I won’t be sleeping anytime soon. And although I’ll hopefully get to bed at some point or another, one thing that will always remain the same is my alarm clock blaring just in time for my morning class. Whether waking up for classes, work, or whatever other immovable commitments we have already penciled in, we can choose how we spend our time at night until the morning comes.
We have all heard throughout our lives that sleep deprivation is terrible for our health, yet 35 percent of American adults still do not get enough sleep . But what is “enough sleep”? While it varies from person to person, an uninterrupted period of seven hours is typically held as the benchmark . Indeed, the average adult needs at least seven hours of sleep each night for optimal health . When one consistently dips below that benchmark, they face perilous mental and physical consequences . People who sleep less than six hours a night are at higher risk for health complications including hypertension, diabetes, stroke, heart disease, obesity, and perhaps even death—the most perilous consequence of all .
If we do not sleep at all, we will die; this is probably not shocking news . Yet when I first asked myself why—why will we die if we don’t sleep, and why is sleep so critical for our very survival—I drew a blank. It turns out that scientists have also been drawing blanks. What vital processes are going on in our heads while we sleep?
So . . . why must we sleep?
Recent research indicates that sleep can clean our brains and bodies. As we go about our day, neurotoxic waste products build up in our central nervous system as a byproduct of metabolism, the ongoing chemical processes in our cells that sustain life [5,6]. The waste products collect in the interstitial fluid, which fills the space between our brain cells known as interstitial space [5,7]. These waste products are associated with neurodegenerative diseases . For example, the accumulated build-up of the tau protein (which normally stabilizes neural structures) and the amyloid β-protein (which normally helps with neural growth and repair) can clump together into plaques, collecting between neurons and disrupting cell function. This build-up contributes to the progression of Alzheimer’s disease, a neurological disorder in which the brain atrophies and connections between brain cells are severed . Therefore, waste products ideally should not remain in the interstitial fluid so close to our brain cells for too long. Yet interstitial fluid can’t leave the brain on its own, so how can we get rid of these waste products . The answer lies in cerebrospinal fluid (CSF), which, as the name implies, circulates in our brain and spinal cord. CSF interchanges with the interstitial fluid and, in doing so, provides nutrients to cells while removing waste from the interstitial fluid .
Sleep is critical for this cleaning process because of its role in the exchange of cerebrospinal and interstitial fluid . Groundbreaking research conducted by Lulu Xie and colleagues at the University of Rochester found that interstitial space increases by 60 percent when we sleep. This allows for much greater exchange between cerebrospinal and interstitial fluid, clearing out that metabolic waste . Let’s go back to the Alzheimer’s disease example for a moment: as you might have concluded, while chronic sleep deprivation increases buildup of tau and β-amyloid proteins, proper sleep can prevent their accumulation . So, when we sleep, our bodies can remove neurotoxic waste much more efficiently than when we are awake—sleep really is healing!
Sleep also plays a role in neuroplasticity . Neuroplasticity is the brain’s ability to reorganize itself, adapting to experiences and demands unique to each individual. It is how our brains learn and grow to best help us . For example, brains have cortical tissue in the motor cortex devoted to moving specific body parts . If a young mammal loses a certain body part, such as its right leg, its cortical tissue can reorganize to adjust for that loss. This might result in devoting more tissue to moving other body parts . A much less drastic example of neuroplasticity is how we consolidate memories and information we have learned . What does consolidating information even mean? Consolidation is the process by which the brain takes recent memories and moves them into long-term storage. Well, here is a simple way to think about it: cats spend around two-thirds of their lives asleep . Congratulations, you just learned something new! When we learn something new, our neurons “come together” to form neural connections that process and store this information, like information highways . As we recall that cats spend two-thirds of their lives asleep, we are “traveling” along that neural highway to access the information . If we do not access that memory enough, then our brains will weaken those particular connections between neurons. Conversely, connections between neurons grow stronger with repeated memory recall. In this way, our brains really are plastic: moldable and adaptive to our lives .
Sleep’s ability to regulate plasticity is related to the stages of sleep . So, let’s take a quick interlude to talk about sleep stages. There are four stages of sleep, each consisting of either non-rapid eye movement (non-REM) or rapid eye movement (REM) . When we first nod off, we enter three stages of non-REM sleep. The first stage is characterized by short, light sleep; it is the period between being fully awake and being fully asleep. If you’ve ever caught yourself falling asleep at your desk without realizing it, you know what I mean. One to five minutes later, we move on to the next stage of sleep, where our heart rate slows down and our body temperature drops. After another 25 minutes, we reach the third stage of non-REM sleep, known as deep sleep, where our body repairs and rebuilds our tissues, bones, muscles, and brain .
With each subsequent stage of non-REM sleep, we enter deeper and deeper sleep. These three stages take about 60 to 90 minutes in total . Once we move past the third stage, we enter the fourth stage of sleep known as REM. This is the part of sleep where we have our most complex dreams. Our skeletal muscles do not move, but our eyes do. Our first REM cycle is about ten minutes long, but subsequent cycles lengthen throughout the night. After that, we move back through the second and third stages of non-REM sleep, then back to REM sleep, then back to non-REM, then back to . . . you get the picture . Up until our alarm inevitably goes off in the morning.
Back to plasticity! Both non-REM sleep and REM sleep are crucial for neuroplasticity. Interrupted or withheld deep sleep has been associated with decreased performance,
learning, and memory consolidation, which is the conversion of recent experiences into long-term memories [16,17]. However, the causal connection that disrupted sleep interferes with neuroplasticity had not been established until recently. New research has shown that extended wakefulness and interrupted deep sleep impair our brain’s ability to undergo neuroplastic changes and learn efficiently, while uninterrupted deep sleep enhances neuroplasticity and learning . An additional study has discovered that deep sleep serves to increase plasticity and performance . But REM sleep, which actually decreases plasticity, stabilizes the learning gained in the previous states of non-REM sleep. Ultimately, non-REM and REM sleep work together as we rest to promote brain learning and growth .
And what happens when we skimp on sleep?
We’ve talked quite a bit about what happens as we sleep, how our brains remove potentially dangerous waste products and promote neuroplasticity [5-18]. It is also useful to think about what happens when we don’t sleep. I don’t just mean that lengthy list of health conditions I mentioned in the beginning, but the more immediate, yet still detrimental, ways that a lack of sufficient sleep affects our brains.
A famous comparison has been drawn between sleep deprivation and intoxication. Moderate drowsiness, defined as 17 hours of sustained wakefulness, lowers performance, measured in tasks of hand-eye coordination, even more than moderate intoxication does . You won’t get a DUI for driving after an all-nighter—but please do refrain from driving while drowsy!
Along with performance, our memory and attention are negatively affected by a lack of sleep . Sleep deprivation can even contribute to the formation of false memories as people who are sleep-deprived are more likely to remember inaccurate information during memory retrieval tasks . This finding ties back into what we’ve discussed regarding brain plasticity. If we do not give the brain the time to consolidate memories and reorganize itself while we are unconscious, then we will suffer the repercussions when we are awake . Short-term sleep deprivation also puts us at higher risk for mood disorders, increases our stress levels and pain perception, and reduces our subjective quality of life [20,22].
The detrimental effects on brain performance accumulate every day with continual sleep deprivation . I had thought—or hoped—that brain performance could return to normal after we get some catch-up sleep after a prolonged period of sleep deprivation. Unfortunately, that’s not the case. Even if someone has three days of “recovery sleep” (that is, eight hours of sleep) after a period of moderate sleep deprivation, brain performance does not recover fully. Performance improves and is obviously better than it would be with continued sleep deprivation, but it does not reach the same levels it had prior to the period of sleep deprivation. This suggests that our brains adapt to sleep deprivation, which is both good news and bad news. The good news is that even when sleep deprived, our brains do their best to stabilize our performance, albeit at a much-reduced level in comparison to normal sleep. The bad news is that we are stuck at this reduced capacity for several days even after we start getting sufficient sleep again . In other words, it is not as simple as “catching up on sleep” during the weekend to make up for lost time during the week. Every night counts.
So when we as college students skip out on sleep, sometimes for the sake of studying more, we wake up (assuming we slept at all!) far from ready to learn. Sleep deprivation impairs the same brain functions that we typically utilize during class and while studying, such as attention, working memory, processing speed, and long-term memory [24-26]. As we have discussed, the brain’s ability to undergo neuroplastic changes is weakened with reduced sleep; so it is no wonder that all of these cognitive functions revolving around learning are similarly affected [20-26]. Even partial sleep deprivation, generally defined as four to six hours of sleep per night over an extended period, lowers our attention [24,27]. It is not surprising, then, that chronic sleep deprivation is associated with lower grade point averages (GPA) and decreased chances of college graduation [28-32]. Oftentimes, staying up late and sacrificing sleep feels like our only choice to succeed academically. Yet this sets us up for failure in both the short-term (an exam the next day) and the long-term (our GPA). It’s a dilemma; we either sacrifice study time by getting sleep or suffer the neurological consequences of slacking on sleep.
How can we sleep more and sleep better?
Not sleeping enough is bad for us, but you probably already knew that. The importance of sleep is emphasized in schools and workplaces, repeated by friends and family, and becomes all too apparent when we’re facing a miserable morning after pulling an all-nighter. However, I hope that since we have delved into the effects of sufficient sleep (good!) and insufficient sleep (not good . . . ), we can further prioritize proper sleep in our own lives.
The negative effects of sleep deprivation—the build-up of dangerous waste products, reduced neuroplasticity, increased stress and pain, lowered memory and attention—are not just happening to the participants of the studies discussed earlier [5-32]. They are happening to us! If we do not sleep enough, we will be at a greater risk for serious illnesses and death . If we do not sleep enough, we’ll suffer reduced levels of memory, attention, and mood. Ultimately, if we don’t choose to prioritize sleep, we’ll be forced to; we can’t overcome this biological requirement . So, if we know that there is no option other than to sleep, how can we sleep more and sleep healthier?
There is no one-size-fits-all answer . Everybody has different factors that shape their activities and health, and sometimes our responsibilities do in fact control our sleep schedules and sleep activity . To tell people that “you should just sleep more” is naive and, frankly, offensive. Instead, I’ll turn the question around: what other ways do you have in your life to sleep more and sleep better?
I’ll be honest, when considering ways to achieve better sleep, I first thought about naps. They are very convenient for when we need an “extra boost” of rest to get through our day. And naps can be useful . . . in moderation. Naps on their own are not a suitable remedy for a bad night’s sleep, but they can serve as a useful supplement when needed . The magic number here is 30; naps shorter than 30 minutes are associated with increased wakefulness, performance, and memory formation . Researchers found similar results in short scheduled napping for essential workers and medicine residents during a night shift [36,37]. When we nap for an hour or two (or three), we wake up (usually) groggy and (always) with a much more reduced homeostatic sleep drive, which is a fancy term for the body’s need to sleep . This reduced need for sleep will make it harder to go to sleep at our regular times at night, which will then affect our nighttime sleep quality and duration .
On the topic of sleep quality: understanding our own sleep time preferences can help too! While we might already have an idea of whether we’re an early bird or a night owl (or somewhere in between, like me), assessments like the morningness-eveningness questionnaire give us a way to learn about our biological clock and perhaps make adjustments to our lifestyle based on that knowledge . If you’d like to learn more about your own biological clock, scan the QR code
for an online version of the questionnaire by the Center of Environmental Therapeutics! Sticking to a consistent sleep-wake schedule—ideally, one that aligns with our sleep time preference—can greatly improve the quality of our sleep [40,41].
Exercise is also often recommended for better sleep quality. In fact, consistent daily exercise improves self-reported sleep quality for adults . After exercising, we take less time to fall asleep and feel less sleepy waking up the next day . As a kid, I always slept well at night after playing sports during the day; I thought that tiring out the body would tire out the mind, leading to a better night’s sleep. While that is a catchy sentiment, there is a bit more to the science behind exercise and sleep quality.
With regards to sleep, exercise does two things. It causes the release of endorphins in the body and raises the core body temperature [44,45]. Endorphins are neurotransmitters that inhibit stress hormones in our body, such as cortisol [45,46]. Linked to pain perception and mood, they contribute to that wonderful post-workout feeling [45,46].
While endorphins provide a great rush, it can be pretty hard to sleep while their levels are elevated in our brain, making us feel more energized and alert . For that reason, it is best to wait a few hours between exercising and sleeping to give our endorphin levels a chance to wind down.
As for core body temperature, our body temperature varies throughout the day, and it typically starts to drop before bedtime . Since we raise our body temperature while we exercise, it will naturally fall back to normal levels after our workout . A decrease in body temperature is associated with sleepiness, regardless of whether it is brought about by our natural fluctuations or a workout . In this way, exercise initially works as a deterrent against sleep because elevated endorphins and an increased body temperature keep us energized . But after a few hours, with a drop in endorphins and body temperature, we’re in good shape for good sleep. So, if you want to be asleep by midnight, try working out in the afternoon or early evening!
Again, a lot of this advice—taking short naps when you can, sleeping and waking at consistent times, and exercising—is easier said than done. Hopefully, though, these sleep strategies will help you improve your sleep or even inspire other ideas for better sleep. As this article emphasized, no sleep, or not enough sleep, is very bad for us . The upside is that the reverse is true as well: a good sleep helps lead to a good day, which in turn leads to a better you [5,10,11]. Remember: cats spend two-thirds of their lives asleep (whether you remembered that might depend on how much you’ve been sleeping) . If you get the optimal seven hours of sleep per night, you’ll spend one-third of your life asleep, so there is plenty of time to experiment and see what might work for you!
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