The Enduring Mysteries of Sleep and Insomnia

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Kleitman later attributed his own "resistance to change" (note the hint of self-reproach) to his older age. But the resistance is older than Kleitman, in fact, far older than any of us. Our bodies are little changed from prehistoric times, scientists today believe: timed by the same deeply etched circadian rhythms. The impulse to awaken remains intrinsically linked to the rising of the sun, while dusk stimulates the brain's secretion of the hormone melatonin, inducing a natural drowsiness.

Our entire lives are shaped by such rhythms, gravitational forces, and seasonal cycles: day and night, ebb and flow, growth and decay. In my view, all these patterns may be echoed in grander cosmic schemes. None can truly be resisted, only tested and studied, in Kleitman's cave as in Plato's. Daylight to darkness, the body mimics the behavior of Earth itself. Perhaps this is why vexing sleep questions (Why do humans dream? Why do we wake up?) sound like metaphysical questions about the meaning of life, like excerpts from a timeless dialogue on truth and illusion, awareness and unconsciousness.

Clearly, Kleitman had the soul of an insomniac. In him, I see a mirror image of myself: a man obsessed with sleep, who thinks about it every waking moment, and views his own body as a laboratory for research. I could spend a month in a dark, quiet cave, too. It sounds like being in a perpetual state of bedtime: shut off from the rest of the world, occupied by only another man and a pile of books, and waiting for sleep to come.

These tendencies must begin in utero. Indeed, insomnia may be genetically imprinted at the very moment when sperm meets ovum. Yet sleeplessness cannot exist without sleep itself, embryonic forms of which are not evident until the last trimester of pregnancy. At seven months, scientists can detect brain waves in alternating bursts and hesitations—two to eight seconds each—that suggest the first signs of sleep as we know it. Finally, at eight months, periods of rest and activity—what would be called non-REM and REM sleep in adults—seem to be synchronous with the mother's own sleep cycle. (REM refers to rapid-eye movement, a telltale sign of sleep's active phase, which is associated with dreams.)

I'd like to know the exact moment when the switch is turned on and human sleep begins, or, looking at it the other way, when the switch is turned off. Just as sleep develops, along with organs and limbs, is there also a way in which wakefulness grows? Perhaps driven by this question, scientists at Oxford in the early 1970s performed a series of experiments on pregnant sheep. One of their discoveries was that the sheep fetus seemed to be breathing during periods of rapid electrical brain activity. Although air obviously could not fill the lungs, they speculated that this breathing motion could train the respiratory system for life outside the womb. Taking the first gasp of oxygen might not be possible without it. Previously unknown, the concept of "in-utero breathing" made them wonder if fetuses, animal and human, could be awake during some periods before birth.

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