Sleep is a universal phenomenon. Every living thing must rest, whether it’s the bear hibernating all winter, or the deer sleeping only two hours at a time. Even unborn babies sleep — about sixteen hours a day in the womb. Some scientists believe sleep is a time for the body to repair and balance itself — yet the body also does this while awake.
Sleep is in many ways a mystery. It’s like a balanced diet: it occurs in different stages and proportions. It is not just simple “rest.” During deep sleep, the body releases most of its growth hormone. Studies show that children with sleep apnea not only sleep poorly, they release less growth hormone and are shorter than their peers. And growth hormone doesn’t just make you taller; it’s a potent stimulator of the immune system.
A dry medical definition of sleep might be as follows: unconsciousness from which a person can be aroused, as contrasted to coma, from which a person cannot be awakened. But what happens when we lie in bed unconscious? Are we just passive, dead to the world, stretched out flat for eight hours?
Not at all. Sleep is actually a highly active state. Until the 1930s, most scientists believed sleep was passive, and that in sleep people simply shut down and stopped responding to their senses. Now it appears that sleep is a biochemical web of enormous complexity. The brain must send out chemicals to silence parts of itself and the body. It’s as if the brain is in a constant tug of war between a chemical web that keeps it awake and one that keeps it asleep. Cutting a specific part of the brain stem, in fact, leads to a brain that never goes to sleep. Centers deep within the brain stem actively inhibit other parts of the brain and allow sleep to occur.
Older people are told that they simply need less sleep. Unfortunately, the truth is that the quality of sleep tends to ebb with age. Sleep changes with age, and the fact that older people have trouble sleeping could actually be part of the degenerative process of aging. The systems that are actively responsible for arousal and inhibition lose a little of their juice. A thirty-year-old gets only about half as much deep sleep as a twenty-year-old. By age eighty-five, the average person spends about 20 percent of the night awake — though a contributing cause may be that the inactive elderly check in for more sleep than they actually need. And sleep may be more elusive for older people because of the “common” aches and pains associated with aging, as well as emphysema and other respiratory difficulties. Men, additionally, cope with benign prostate enlargement, which causes them to wake and urinate during the night. One study found that 50 percent of healthy people over age seventy have sleep irregularities.
We now know there are two types of sleep, and that during the night these two types alternate with each other. The first is called slow wave sleep — the deep, restful type of sleep that a person experiences during the first hour of sleep. Though we think of this sleep as the “deep, dreamless” kind, dreams and even nightmares can occur during this sleep. A second type of sleep, called REM (named after the rapid eye movements that occur during this process), happens every hour and a half, and lasts for five to thirty minutes. The dreams that we remember usually occur during REM sleep.
EEG studies of the brain during REM sleep are remarkably similar to waking patterns. That is why REM is sometimes called paradoxical sleep. It seems to be a paradox that a person can be asleep while the brain is highly active. Here are the important hallmarks of sleep:
Whether waking or sleeping, we tend to produce four types of brain waves — and at different times, different brain waves are dominant. They are as follows: