The Mysteries of Sleep
You spend one-third of your life sleeping. Sleeping! Believe it or not, if you live to be 75, the hours you sleep each night will add up to about 25 years of slumber.
It might seem like all that sleep is a giant waste of time. But scientists now know that while you’re snoozing quietly in your bed, there’s lots going on inside your brain and body.
Cycling through Sleep
For one thing, you sleep a cycle of five different types of sleep, over and over each night. When you first lie down and begin to fall asleep, your body enters what sleep experts call Stage 1 sleep. You’re still very close to being awake, but your brain begins to work more slowly. Your body relaxes, and your closed eyes start to roll around. If someone woke you from this stage, you’d probably say that you weren’t even asleep yet. After several minutes, you sink a little deeper, into Stage 2 sleep. You’d still be easy to wake up, but you’d probably know you’d been snoozing.
Then you really relax and fall deeply asleep, into Stage 3 sleep. Your heart slows down, and you breathe more slowly, too. Noises nearby would probably not wake you. Finally, you sink into the deepest sleep of all, called Stage 4. Once you’re in Stage 4 sleep, you’re very hard to wake up. And if someone does manage to wake you, you’ll be very confused about where you are and what’s happening.
The first time you reach Stage 4 sleep after going to bed, you stay there for almost 20 minutes. That’s the longest chunk of deep sleep you’ll have all night. After that, you slowly move back up through Stages 3 and 2.
And then your sleep gets really interesting.
Sweet Dreams
As you come back up through a period of Stage 2 sleep, you shift into Rapid Eye Movement, or REM, sleep. It’s called REM sleep because when you’re in it, your eyes-behind your closed eyelids-slide quickly back and forth, and back and forth, as though you were watching the ball in a tennis game. Your brain becomes much more active during this sleep stage, almost as active as when you’re awake. Instead of resting, a brain in REM sleep is racing! And while your eyes are darting from side to side, a very detailed story is running through your head: you’re dreaming.
It’s during REM sleep that you dream your strangest dreams, the ones that sound so very mixed-up when you describe them the next morning. As you drift into a REM-sleep dream of singing toothbrushes or a dog that says he’s your uncle, your body changes, too. Your breathing and heart rate sometimes speed up. Scientists say that your brain waves-measurements of the electrical activity in your brain-look almost the same during REM sleep as they do when you’re awake. When you enter REM sleep, you go from being completely relaxed to being ready for action. And yet, you never move. That’s because you can’t. You’re paralyzed!
When you’re in REM sleep, your brain cuts off all the messages that might tell your body to move. You never pull up the covers or even roll over. Except for your shifting eyes, your breathing, and a twitch every now and then, you lie perfectly still as you dream. Scientists guess that may be to prevent you from acting out any wild scenes in your dream and hurting yourself.
Does Dreaming Make You Smarter?
You’ll spend more than two hours each night in REM sleep, dreaming. Why do you dream? Scientists are still trying to figure that out.
One idea is that dreaming helps you organize your memories. It gives your brain a chance to sort through everything that happened during the day, storing what you need to remember and tossing out details that don’t matter.
Experiments show that REM sleep definitely can help you learn better. In one test, volunteers were taught a new skill. That night, some of them were awakened whenever they entered REM sleep. The others were awakened the same number of times but only during non-REM sleep. The next day, the people who got their REM sleep tested better than the others at performing the new skill.
Researchers now think dreams may be like exercise for your brain, and dreaming may actually help your brain develop. Newborn babies spend almost half of their sleep time in REM sleep! But adults, whose brains aren’t developing so much anymore, spend only about one-fifth of their sleep time dreaming.
Going without Sleep
During the day your muscles are busy stretching and pulling as you run, jump, or even just sit. Lying down asleep and fairly still gives those muscles a chance to repair and grow stronger. Scientists carried out an experiment on weight-lifters. For one night, they allowed the athletes to sleep only three hours. The next day, none of the athletes could lift as much weight as they had before. If you didn’t sleep, you wouldn’t be as strong either.
As you lie snoozing, you’re busy healing and growing. Your body is releasing more of the chemicals that help it create new bits of skin, muscle, and other parts of you. Sleep is so important for healing that when you’re injured or sick, your body releases chemicals to make you feel sleepier. Just recovering from a sunburn can make you sleep longer.
