Sleep remains one of the great mysteries of modern neuroscience. We spend nearly one-third of our lives asleep, but the function of sleep still is not known. Fortunately, over the last few years researchers have made great headway in understanding some of the brain circuitry that controls wake-sleep states. Scientists now recognize that sleep consists of several different stages; that the choreography of a night’s sleep involves the interplay of these stages, a process that depends upon a complex switching mechanism; and that the sleep stages are accompanied by daily rhythms in bodily hormones, body temperature and other functions.
Sleep disorders are among the nation’s most common health problems, affecting up to 70 million people, most of whom are undiagnosed and untreated. These disorders are one of the least recognized sources of disease, disability and even death, costing an estimated $100 billion annually in lost productivity, medical bills and industrial accidents. Research holds the promise for devising new treatments to allow millions of people to get a good night’s sleep.
Exercise 1. What do you know about sleep?
1. What is sleep? What processes take place in human organism during sleep?
2. What processes take place in the human brain during sleep?
3. How long does sleep last? What stages does it include?
4. What sleep disorders do you know?
5. Are you an early bird or a night owl? What other sleep habits do you have?
Exercise 2. Is sleep primarily to benefit the body or the mind? Read the following text to find the answer.
Why Do We Sleep?
By C. Claiborne Ray
“Sleep has many functions, and most of us think the main functions are not for the body but for the brain,” said Dr. Arthur Spielman, a sleep expert at City College of New York. “But,” he added, “you are talking to a brain scientist, and it depends on whom you ask.’’
The reason sleep occurs in the first place is tied to both mental and physiological cycles that evolved on a planet with a 24-hour cycle of light and dark, Dr. Spielman said. The internal biological clocks that developed in living things, from single cells to humans, allow them to anticipate the transitions from light to dark and from dark to light, so that they are ready for the functions appropriate to light, like metabolism and photosynthesis, and for those suited to darkness. “A physiologist might say sleep was to avoid wasting metabolic energy in the dark,’’ he said. “But a brain scientist would say that glycogen, the only fuel for the brain, is depleted during waking and restored during sleep.”
Sleep is useful for restoring particular parts of the brain that are quiet during sleep and return to functioning during waking, like the areas involved in attention, alertness and memory. Sleep is also important for regulating the timing of hormones under the control of the brain, Dr. Spielman said, like cortisol, the stress-response hormone, which is suppressed at the beginning of sleep and ramps up in anticipation of waking, and growth hormone, which is secreted at night during sleep characterized by slow brain waves. (August 15, 2006 NY Times)
Exercise 3. Read the chapter about sleep taken from the book Brain Facts: a Primer on the Brain and Nervous System, 2002 to check your answers in Exercise 1.
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