The clock within us all
Much of our knowledge about the body’s circadian clock comes from people who volunteer to live for a while in “time-isolation.” In Europe, such studies first took place in bunkers and caves in the 1960s. In the U.S., the first time-isolated lab was built on the fifth floor of an old hospital wing in the Bronx in the 1970s.
In the 18th century, famed English surgeon John Hunter documented that body temperature drops each night during sleep. In the 20th century, scientists confirmed that temperature rises and falls throughout the day and night -- as do alertness and levels of growth hormone, cortisol and potassium.
That led some scientists, including New York neurologist Elliott Weitzman, to wonder: What would happen to the body’s clock if external clues on when to sleep (such as the rising and setting of the sun) were taken away? He founded the first time-free lab in the U.S. at New York’s Montefiore Medical Center to find out.
The lab’s “control station” monitored a pair of windowless, soundproofed, climate-controlled apartments devoid of all time cues (known as zeitgebers); no clocks, radios, televisions or telephones.
Shedding their wristwatches, the lab’s human volunteer subjects checked in for a few months at a time. They were promised a “normal” living environment, as long as they didn’t mind not knowing the day or time or sporting a uniform of rectal probes, catheters and electrodes. The wires and gadgets took subjects’ temperatures every minute, blood every 20 minutes, and monitored brainwaves as they slept.
The lab’s staff was computer-assigned to a randomized work schedule so the subjects couldn’t guess the time by who was working when. The staff came and went through a double door that blocked any trace of daylight. They gave up their watches and traded in “good mornings” and “good nights” for simple “hellos.” The men among them shaved just before entering, to erase any five o’clock shadow.
After about a week of lights-out at midnight and lights back on at 8 a.m., the subjects were free to sleep, wake and eat at will.
An artist living in Weitzman’s lab completed a dozen paintings, a retiree wrote a book on economic theory, and an undergraduate used his unstructured time to catch up on overdue coursework. A reporter for the New York Times stayed in the lab for 25 days and wrote on her experience for the paper. And all subjects, unprompted, shifted their schedules to what scientists now know is the human body’s natural biological day: roughly 25 hours.
Free of all time constraints and cues, the study subjects generally went to sleep an hour later night after night and woke an hour later each morning, slowly shifting their schedules forward.
They experienced other changes too: Temperature fell just before sleep, not during; dreaming took place earlier during the night; and hormone patterns shifted slightly compared with those in people sleeping and rising on a 24-hour schedule.
Weitzman (who died in 1983) and his colleagues concluded that humans are constantly “entraining” themselves -- using alarm clocks for example -- to stick to a 24-hour day, instead of their biologically natural 25-hour one. This circadian clock, it seems, can only be reset within reason: to day lengths between 23 to 28 hours.
