Why Do We Sleep?

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Legend has it that when you can’t sleep at night, you’re awake in someone else’s dream.  

Scientists and sleepers alike have speculated about this for centuries, with legends that surround dreams and sleep being passed down through generations. Even the famous British television show, Doctor Who, has an episode titled Sleep No More (airdate: Nov. 14, 2015) chronicling what happens when humanity devises a method that renders sleep obsolete (spoiler: it ain’t pretty). Since we spend up to one third of our lives in this state, what’s really going on inside our brains while we’re zonked out?

Considering that most animals sleep in some form or another, science would hint that sleep poses an evolutionary advantage. One theory suggests that by using less energy, the demand for food is lowered, and this in turn prevents extinction, which could result from overhunting. If predators were able to hunt 24 hours a day (and night), they would quickly deplete their food supply, eventually driving themselves to extinction as well as their prey. Humans may have evolved to sleep at night as a method to conserve energy when it is hardest to find food.

On the other hand, lack of sufficient sleep can have drastic consequences. In humans, going without sleep for 20-25 hours impairs your performance as much as that of someone with a blood-alcohol level of 0.10 percent. In all U.S. states, that number will get you a DUI. According to Terry Cralle, a certified sleep educator in Virginia, going without sleep for 24 hours affects your judgment, impairs your memory, decreases your attention, and affects your hand-eye coordination. People have also been shown to be more emotional and there is a marked deterioration in decision making when denied adequate amounts of sleep.

So what actually takes place while you snooze? A nifty phenomenon called plasticity. This is not your brain turning to plastic; rather, it refers to the brain’s ability to manipulate its internal structure. Researchers at the University of Wisconsin Madison have found that during sleep, the brain produces cells that grow and repair myelin, a substance that acts as insulation around neurons. The production of these cells is doubled during sleep, especially during the REM phase (rapid eye movement), or when you dream.

There may also be some truth to the idea that after a good night’s sleep you wake up with a clearer mind. The hours spent asleep could give your brain a chance to cleanse itself. Researchers call this the “biological dishwasher,” where cerebral spinal fluid (CSF) is pumped around the brain and helps to flush out waste products. To date, this has only been observed in mice, but may have implications in humans as well. The mice’s brains were observed to shrink during sleep, allowing the CSF to flow ten times faster than when the animals were awake.

In short, sleep is vital. No organism can go for very long without it. And while scientists are still trying to figure out all the benefits it offers, we know that it’s evolved to help life on the planet continue smoothly. So go catch up on some z’s - now that you know how much good it does.