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What Happens During Sleep?
What will you, and everyone else on this planet, spend about one-third of your life doing? (If you live to be 70, that will add up to 204,400 hours that you will spend doing just this one activity!)
a. watching television
b. cleaning my house
c. sleeping at night
d. talking on the telephone
If you answered “sleeping at night,” you are correct. Even though we spend so much time asleep, scientists are just beginning to understand what happens during sleep.
Until about 60 years ago, everyone thought that when we sleep, very little happens in our brains. Scientists now know that sleep is much more than the opposite of being awake.
Every night while during healthy sleep, your brain goes through five different stages of sleep. You enter sleep through Stage 1. You then move through Stages 2, 3, and 4 sleep. After reaching Stage 4, the brain moves back into Stage 3, then Stage 2. Instead of going into Stage 1 again, you enter the fifth stage of sleep, called Rapid Eye Movement or Stage REM sleep.
The whole sleep cycle takes about 90 minutes. After the first cycle, you move back to Stage 2 sleep and go through the stages again. If you wake up at night, you will usually enter sleep again through Stage 1. Every night, you go through this cycle five or six times. Sleeping disorders may interfere with sleep, however, interfering with the stages of sleep and causing difficulties with daytime functioning.
Many people with neuromuscular disease have difficulties with sleep, and some research suggest that as many as 40 percent suffer from a sleeping disorder. Difficulties with sleep may include problems such as difficulty falling asleep, staying asleep, or breathing while asleep. If you have difficulty any of these difficulties, your physician may refer you to a sleeping disorders clinic to see a physician that specializes in sleep and for testing.
At a sleep laboratory, the electrical output from the brain can be measured during sleep by a special machine called a polysomnograph (PSG). The PSG also measures eye movements, muscle tension, breathing, and heart rate.
The PSG shows what happens in the brain and body while a person sleeps. Most sleep laboratories now use computers to record the results of the PSG. Let’s pretend you are hooked up to a PSG, and see what the PSG will show about what happens in your brain while you sleep.
When you are awake with your eyes open, the markings on the computer screen look fast, jagged and uneven. But, when you lie down and close your eyes, the marks change. They look more even and slower, but still sharp. Scientists call these brain waves alpha waves.
Scientists call the first stage of sleep Stage 1. During Stage 1, sleep is light and you are easy to awaken. If someone wakes you up, you might not even know that you have been asleep. You might say that you were thinking about something. The marks on the computer screen look a little bit slower, more even, and not so jagged.
During Stage 2, you go into a deeper sleep. If someone wakes you during Stage 2, you will probably know that you have been asleep. The polysomnograph shows special waves. K complexes look a bit like the letter K. Sleep spindles look like short bursts of very fast, sharp waves.
Scientists also call Stages 3 and 4 sleep slow wave sleep. Have people ever told you that they tried to wake you up, but you were so deep asleep that they could not wake you? You were probably in Stage 3 or 4 sleep. During these stages, the PSG shows slow, smooth brain waves. The amplitude, or height, of the brain waves appears to be much greater. Scientists believe that slow wave sleep is particularly important for body growth and repair.
If someone watches you in REM sleep (the fifth stage), he or she will see your eyes move back and forth quickly under your eyelids. REM stands for Rapid Eye Movement. If someone wakes you during Stage REM, you will probably remember a dream. During Stage REM, you have your most vivid, story-like dreams. In fact, your brain protects you from acting out your dreams by sending out a signal to most of your muscles to keep them from moving. Your brain waves will look much like when you are awake. In order to tell the difference between wakefulness and Stage REM, the person interpreting the PSG will look for rapid eye movement and for lack of muscle tension. REM sleep appears to be especially important for memory and learning.
So, as you can see, sleep is much more than the absence of being awake. Every night during healthy sleep, your brain goes through five stages of sleep. You cycle through these stages five or six times. You spend all of those hours asleep for good reasons. Without enough sleep, your body and brain cannot get the rest needed to maintain health and your quality of life. If you have difficulty sleeping or breathing during sleep, make sure to talk to your physician.
Kryger, M.H., Roth, T., Dement, W.C., (2005). Principles and Practices of Sleep Medicine (Fourth Edition). Elsevier: Philadelphia, PA.
Content copyright © 2013 by Jori Reijonen, Ph.D.. All rights reserved.
This content was written by Jori Reijonen, Ph.D.. If you wish to use this content in any manner, you need written permission. Contact Jori Reijonen, Ph.D. for details.
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