![]() ![]() The average American today sleeps less than seven hours a night, about two hours less than a century ago. “It seems as if we are now living in a worldwide test of the negative consequences of sleep deprivation,” says Robert Stickgold, director of the Center for Sleep and Cognition at Harvard Medical School. Yet an imbalance between lifestyle and sun cycle has become epidemic. Redder light is best at night because it has less power to alert the brain or reset the biological clock. Light rich in blue wavelengths promotes alertness and is good in daytime, Lockley says. When this circadian rhythm breaks down, recent research has shown, we are at increased risk for illnesses such as diabetes, heart disease, and dementia. The 2017 Nobel Prize in medicine was awarded to three scientists who, in the 1980s and 1990s, identified the molecular clock inside our cells that aims to keep us in sync with the sun. Our sleep-wake pattern is a central feature of human biology-an adaptation to life on a spinning planet, with its endless wheel of day and night. It’s only in the past few decades, though, as imaging machines have allowed ever deeper glimpses of the brain’s inner workings, that we’ve approached a convincing answer to Aristotle.Įverything we’ve learned about sleep has emphasized its importance to our mental and physical health. In 1924 German psychiatrist Hans Berger invented the electroencephalograph, which records electrical activity in the brain, and the study of sleep shifted from philosophy to science. For the next 2,300 years no one had a good answer. We sleep.Īround 350 B.C., Aristotle wrote an essay, “On Sleep and Sleeplessness,” wondering just what we were doing and why. We are sexually stimulated, men and women both, repeatedly. Our eyes, however, periodically dart about behind closed lids as if seeing, and the tiny muscles in our middle ear, even in silence, move as though hearing. For a while, we become almost entirely paralyzed. Our brain profoundly alters its behavior and purpose, dimming our consciousness. Nearly every night of our lives, we undergo a startling metamorphosis. This story appears in the August 2018 issue of National Geographic magazine.
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