Sleep: What's Going on Behind That Shut-Eye?

I love sleeping and always try to get enough so that I feel rested and refreshed when I awaken. So I'm always interested in reading about research that helps explain what exactly is going on in our brains and bodies when we sleep. In this article, a colleague of mine, Dr. Robert Shmerling, does just that:

Have you ever watched someone sleep and wondered what he or she was dreaming? The person's outward appearance would never give it away: slow breathing, eyes occasionally fluttering, but mostly the very picture of peace and stillness. But, appearances can be deceiving. When people sleep, there's a lot more going on than meets the eye. The notion of sleep as the body's ultimate "down time" has some truth to it, but sleep is also an active process, in which the brain can be remarkably active, even if the body remains (mostly) immobile.

There is much about sleep that remains mysterious, but experts divide it into two main categories, based on observations of sleeping persons and recordings of the brain's electrical activity during sleep:

·         Non-REM sleep– This is divided into four stages, with Stage 1 the lightest and Stage 4 the deepest.

·         Rapid-eye movement (REM) sleep - During REM sleep, dreaming is common, muscles (other than the eyes) are inactive, and electrical activity in the brain is similar to that of an awake person. The blood pressure and heart and breathing rates may suddenly increase for short periods of time, just as they do during wakefulness

During a typical eight-hour period of sleep, a person drifts from wakefulness to Stage 1 non-REM sleep, through Stages 2, 3 and 4 and finally REM sleep over the first several hours. During the last half of the night, REM sleep and Stage 2 sleep alternate for 90 to 120 minutes each. As we age, brief awakenings increase in frequency, while deeper stages of non-REM sleep decrease.

The function of sleep is not entirely clear, but researchers believe that REM sleep is important for solidifying memories, and perhaps for even more critical functions. Rodents completely deprived of REM sleep die after a few weeks. Non-REM sleep, meanwhile, seems to be important in providing a sense of restored energy and ability to concentrate during the day. A number of theories about sleep attempt to explain its role or roles: a restorative for the mind and body in preparation for the day ahead; or a way of reducing energy consumption, to save energy for activities occurring during the day. Some scientists believe that sleep is evolution's way of improving survival by preventing animals from preying on each other 24 hours a day.

It is hard to define just how much sleep is normal; different people seem to need different amounts. Sleep experts define "enough" sleep as how long a person would sleep if there were no alarm clocks; that is, left to decide entirely on your own, how long would you sleep? The other way to define it is how long one needs to sleep in order to feel alert and rested the next day. However, duration of sleep is not the only thing that matters –; the quality of sleep also matters.

Too little sleep or poor-quality sleep can cause a number of problems, including difficulty with short-term memory, concentration, depression, anxiety, irritability, poor energy and reduced libido. In short, quality of life at work and at home may suffer terribly due to insufficient or poor sleep. All of these problems may resolve when sleep duration increases or sleep quality improves.

One problem related to sleep deprivation deserves particular emphasis: Automobile and truck accidents attributed to sleepy drivers account for thousands of deaths each year.

Although the impact is uncertain in humans, sleep-deprived rodents have reduced immune function and higher susceptibility to infection.

The importance of sleep is self-evident, yet much remains unknown or uncertain about how we sleep, why we sleep and how to improve sleep. One thing is certain, however: Sleep is not a passive process or a complete "shut down" of the body – many stages of sleep are as active for the mind as being awake. So, the next time you see someone sleeping, keep in mind that though the body may look quiet and peaceful, there is much more to the story.

Would you like to know more about the sleep process? Post your questions.

Julie K. Silver, M.D., is an assistant professor in the Department of Physical Medicine and Rehabilitation at Harvard Medical School. She is also the Chief Editor of Books for Harvard Health Publications.

Sleep
Need better sleep? Learn how to get it with Improving Sleep: A guide to a good night's rest. This special report from Harvard Medical School describes the factors that can disturb sleep, the latest in sleep research, and, most importantly, what you can do to get a good night's sleep. It also includes in-depth information on sleep disorders, including restless legs syndrome, narcolepsy, and sleep apnea.

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