An “internal clock” is not a metaphor. Or rather, it is—you don’t have a tiny Timex in your cerebellum—but it’s also a real biological feature, a specialized bundle of cells that regulates our cyclical processes. These clocks are remarkably widespread. Single-cell creatures that lack even nuclei nonetheless have internal clocks; so do human beings with programmable cappuccino-makers. In plants, the clock can be located in leaves, stems, or roots. In slugs, it’s at the base of the eye. In many birds, it’s in the pineal gland, the structure near the center of the brain where Descartes thought future scientists would find the soul.
In mammals, the clock is located near the base of the brain, in a group of nerve cells known as the suprachiasmatic nucleus, or SCN. The SCN consists of only about 20,000 of the brain’s estimated 100 billion neurons; you could fit the entire thing on the tip of the second hand of an analog watch. Yet without it, you are profoundly screwed. If you replace the SCN of one hamster with that of another, the original hamster will begin sleeping, eating, and attending its manic hamster spin class on the schedule previously maintained by the other one. If you remove the SCN, the hamster’s behavior will lose all regularity. Similarly, people with brain lesions in the SCN region cannot maintain consistent sleep-wake patterns.
Assuming that you have a functioning SCN, you also have a chronotype—a genetically determined blueprint for sleepiness, hunger, hormone levels, body temperature, and so forth. Of these, Roenneberg focuses primarily on sleep, “the most conspicuous expression of the body clock in humans.”
That expression takes two forms: sleep timing (when you go to bed) and sleep duration (how much sleep you need). These variables are independent; you can be an early bird who needs ten hours of sleep, a night owl who needs six, or vice versa. You can also be neither. Sleep patterns form a bell curve, and the vast majority of people fall in the middle. What you cannot do—contrary to popular opinion—is change your clock through sheer force of will.
As a chronotypical outlier, I know this firsthand. Work-wise, I function best from around 10 p.m. to 4 a.m., a characteristic I share with roughly one percent of the population. That’s not an easy schedule to live with, so I once tried to train myself into a nine-to-five workday instead. Dismissing my conviction that I wrote better at night as so much Romantic preciousness, I diligently sat down to work each morning, spent eight hours watching the daylight fill and drain outside my window, then finally, well after dark, abruptly found myself able to write. After six months of this insanity—during which I more than doubled my workday without remotely upping my productivity—I gave up and went back to the other, better kind of craziness. The moral applies to every internal clock: Good luck trying to buck it.
Left to their own devices, internal clocks can get much stranger than mine. Roenneberg cites experiments in which subjects were confined to bunkers and deprived of all temporal cues. While most subjects maintained a day-night periodicity of roughly 24 hours (circa one day: hence, “circadian”), some people’s cycle doubled, to about 48 hours. Amazingly, they were oblivious to the change. They continued to eat three meals a “day,” and their sense of smaller time units doubled, too. Asked to estimate an hour, they estimated two instead.
by Kathryn Schulz, New York Magazine | Read more:
Photo: Christian Marclay. Courtesy of Paula Cooper Gallery, New York and White Cube, London
