Neurobiology: Why We Need Sleep

You’ve probably all heard the motto “sleep is for the weak.” You’ve probably also seen energy drink commercials alleging that “no one ever regrets not having slept more in college,” or heard college students joke that “sleep is the new sex” (it’s harder to get).

This epidemic of sleep deprivation is not restricted to college students; as our global economy expects more production out of fewer workers, as electronic devices mean we’re expected to be in communication with our work at all house, as global competition mean that everyone is expected to work overtime, the expectation of getting a full eight hours of sleep per night has virtually vanished. This is deeply unfortunate. It’s also more than a little ironic; the banishing of the value of sleep in global culture has coincided with leaps forward in science’s understanding of why we need it.

Last year, I was treated to a wonderful lecture course on the neurobiology of sleep experts on different areas of sleep research around the United States. Even I, who am particularly prone to the effects of sleep deprivation, was surprised: sleep effects everything from immune function and heart disease to learning and depression. So, as I’ve increasingly heard more of this “sleep is for the weak” mantra, I thought I’d share a little bit about what that body does during sleep that it doesn’t do at any other time:

1. Learning and memory are reinforced. During REM sleep, a unique pattern of brain waves reinforces important synaptic connections while pruning back unimportant ones.

The magnitude of this effect is staggering: in lab mice, getting sufficient sleep increases performance on learning and memory tasks increase by 20-25%. The same effect has been shown in human studies, where an hours’ extra sleep has sometimes proven better for performance than an hours’ extra studying.

The link between REM sleep and cognitive performance is so strong that there’s a causal relation; after a day of being introduced to a lot of new information, your brain actually ups the amount of REM sleep it will ask you for the following night. Likewise, increases the duration of REM sleep has been found to predict improvements in waking performance. More REM = better performance.

2. Immune function happens. It turns out that the body makes antibodies especially well during sleep. No one’s sure why this is, but due to sleep’s relationship with stress hormones, it may also hold for other healing processes like tissue regeneration.

This probably explains why many people sleep a lot feel the need to sleep a lot when fighting illness; it may also explain why I rarely get sick when I answer my bodies’ demand for sleep. My class didn’t speak to this particular phenomena, but it makes sense.

Long-term sleep deprivation can lead to a suppressed immune system, and a higher rate of infection.

3. Blood sugar is controlled. You know those stress hormones I mentioned? They control a lot. In the wild, they’re our body’s way of telling us “you are being chased by a lion.” Unfortunately, in modern society, that sensation can follow us pretty much everywhere as work deadlines and bills loom overhead.

So perhaps it’s now especially important that sleep has a regulating effect on stress hormones. These hormones particularly effect blood sugar and blood pressure, two big contributors to America’s two biggest enemies, diabetes and cardiovascular disease.

The logic of this one is pretty simple, and also medically proven. Stressed people want fatty and sweet foods; that’s actually a survival reaction, as the brain figures that stress means some kind of survival challenge is imminent so we should stock up on all the energy-laden food we possibly can. Stress hormones also act to release more of the sugar our body already has into our bloodstream and raise our blood pressure, in anticipation of the lion-fleeing sprint it assumes we’ll have to perform at any moment.

Relaxed (and generally well-rested) people, with lower levels of stress hormones, are inclined toward far healthier foods, lower blood pressure, lower blood sugar, and overall healthier lifestyles. The body actually does know what’s good for it: it just gets confused when your stress hormones make it think you’re about to be chased by a lion all the time.

4. Athletic performance is enhanced. This, too, goes in the “no one is sure why” category. It may be that overall metabolic processes, including those of healing and muscle building, are enhanced during sleep. It could also be that the motor neurons responsible for motor skills like kicking a ball and keeping one’s balance, like neurons for learning and memory in the brain, also have their newly-acquired skills reinforced during sleep. Or it could simply be that stress-related fatigue is relieved during sleep.

But whatever the case, it’s been proven that college athletes, like college mathletes, do better on the track and field if they get enough sleep.

5. Depression is averted. It turns out that the neurotransmitter systems in the brain that are involved in REM sleep are also deeply involved in mood, anxiety, and depression. The relationship appears to work both ways: sleep disruption is a symptom of anxiety and depression disorders, and both of these disorders can also cause sleep disruption. This is because the same circuitry is involved in both; there are entire theories of depression built on its relationship with sleep.

The relationship between sleep, anxiety, and depression is complicated. A chronic lack of sleep leads to an increase in the body of stress hormones associated with these mood disorders. It also leads to a frenetic increase in brain activity specifically associated with anxiety. Perhaps the reason isn’t hard to figure out: if you’re not letting your brain sleep, it probably assumes there’s a reason. Probably that you’re being chased by a lion.

There is a silver lining to sleep deprivation: it turns out that acute sleep deprivation can temporarily alleviate depression. Again, no one is sure why; and it should be noted that “acute” means one night of 3-4 hours’ sleep. Doing that for several days running will make your situation worse.

So why do sleep scientists hate our modern culture? Because medical programs are still allowed to push young doctors to work for 36 hours straight, which, needless to say, leads to serious medical mistakes. Because although in some states driving while sleep deprived is a crime similar to driving while intoxicated, about 100,000 people still die in sleepiness-related accidents in the U.S. each year. Because although employers can sometimes be held liable for damages incurred due to work-related sleep deprivation, many continue to act as though the need for adequate sleep is not legitimate.

There is good news: it turns out that for healthy people, it is impossible to oversleep. This has been tested; volunteers were confined to bed in a dark room for 14 hours per day. They slept the full 14 hours at first, while up for sleep debt accrued from living normal lives in our culture (the average American gets about 1.2 fewer hours of sleep per night than a person should). But by the end of the study they were sleeping almost precisely 8.1 hours per night–no more, no less.

So next time somebody tells you “sleep is for the weak,” or “you can sleep when you’re dead,” you can use it as an opportunity to flaunt your superior academic and athletic achievements. Or just your superior knowledge of neuroscience.

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