What's a good night's sleep?

[jenk]

From the New York Times : Should humans really expect to sleep through the night?

It's a question that Dr. Thomas Wehr at the National Institute of Mental Health asked himself in the early 1990's. He conducted a landmark experiment in which he placed a group of normal volunteers in 14-hour dark periods each day for a month. He let the subjects sleep as much and as long as they wanted during the experiment.

The first night, the subjects slept an average of 11 hours a night, probably repaying a chronic sleep debt.

By the fourth week, the subjects slept an average of eight hours a night — but not consecutively. Instead, sleep seemed to be concentrated in two blocks. First, subjects tended to lie awake for one to two hours and then fall quickly asleep. Dr. Wehr found that the abrupt onset of sleep was linked to a spike in the hormone melatonin. Melatonin secretion by the brain's pineal gland is switched on by darkness.

After an average of three to five hours of solid sleep, the subjects would awaken and spend an hour or two of peaceful wakefulness before a second three- to five-hour sleep period. Such bimodal sleep has been observed in many other animals and also in humans who live in pre-industrial societies lacking artificial light.

Carol Worthman, an anthropologist at Emory University in Atlanta, has studied the sleep patterns of non-Western populations. From the !Kung hunter-gatherers in Africa to the Swat Pathan herders in Pakistan, Dr. Worthman documented a pattern of communal sleep in which individuals drifted in and out of sleep throughout the night.

She speculates that there may even be an evolutionary advantage to interrupted sleep. "When we lived in open exposed savanna, being solidly asleep leaves us vulnerable to predators."

With artificial light, modern humans have essentially managed to extend their daytime activities late into the night, when all other sensible creatures are busy sleeping.

As a result, we have compressed our natural sleep into artificially short nighttimes, but not all people are so easily tamed by artificial light. Some people, who may just have very strong circadian rhythms, still have this primitive bimodal sleep that they confuse with a sleep disorder.

This also ties in with the recommendation I read in Woman's Day: don't look at the clock once you're in bed. Set the alarm and turn the clock to the wall. Why? Watching the clock makes you aware that you're awake and how long you've been awake, which can make you anxious, which makes it harder to get to sleep. Personally I love drifting in and out of dreamy not-awake-not-asleep states...when I don't have to be anywhere soon.