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After you close your eyes ...

October 09, 2006|Susan Brink | Times Staff Writer

Many people insist they do just fine with far less than seven or eight hours of sleep a night. Almost all of them are kidding themselves.

By watching the brain-wave activity of sleepers, researchers have charted, with the squiggly lines of electroencephalograph, or EEG, readings, what a typical good night's sleep looks like. The long day's wind down starts in the evening when the brain's pineal gland releases melatonin, signaling bedtime.

The architecture of a perfect night's sleep begins with 15 to 20 minutes in the quiet dark, before the night's descent into oblivion begins. In a nonsleep-deprived state, the head hits the pillow and the body, calm but still aware, gradually relaxes -- slower heart rate and breathing, limp muscles, a slight drop in temperature.

Nudge these nearly asleep people, and they'll claim to be awake, but an EEG would show a shift from the day's rapid beta waves to slower alpha waves. The brain is already slowing down.

When alpha waves are next replaced by theta waves, the sleeper has entered the sensory void of stage 1 sleep, unaware of sounds, smells or the snuggly feel of flannel pajamas. From there, it's an elevator ride down and up and down again, all night long, through stages 2, 3, 4, deeper and deeper into unconsciousness and toward the dream stage of REM, or rapid eye movement.

Growth hormone is released in the early night's phases of stage 3 and 4 sleep. After 90 minutes, the brain has traveled down to REM sleep with its startling visions of nonsensical chaos and colors that make up dreams. The brain travels up and down these stages all night, each time experiencing a slightly longer, more intense REM phase. The hormone cortisol, which stimulates alertness, builds through the night and peaks in the morning, allowing the well slept to awaken refreshed and alert.

While everyone's sleep needs may vary, most sleep experts agree that most people need between seven and eight hours of sleep each night. One National Institute of Mental Health study found that when volunteers spent 14 hours in bed in the dark for four weeks, a natural sleep pattern of about eight hours a night emerged. But within that eight hours, free to sleep and wake at will, volunteers slept in two distinct chunks, with a period of wakefulness in between.

The study fits what may be an ancient human pattern, according to findings of historian A. Roger Ekirch of Virginia Tech, author of "At Day's Close: Night in Times Past." "The dominant pattern in the Western world until the Industrial Revolution was not seamless sleep, but segmented sleep," he says. Diaries and literary references going back to Homer referred to "first sleep" and "second sleep," each about four hours. In between, in the dark of night, people would talk, use the chamber pot, slap at fleas and lice, be on the alert for predators and have sex, he says.

Most people's real lives no longer allow for that human pattern of natural sleep.

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