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17 April 2014 12:48 pm ,
Vol. 344 ,
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Steady Body Clocks Don't Run Down
25 June 1999 12:00 pm
Computers, rats, and gila monsters all require precise internal clocks to function properly. Now, it appears, so do people. Researchers report in today's Science that our internal clock, or circadian rhythm, ticks on a precise 24 hour, 11 minute schedule. Contrary to conventional wisdom, the clock runs at exactly the same rate in older people as in younger people. By understanding how the internal clock normally works, doctors may be able to detect abnormal circadian rhythms responsible for sleeping disorders.
The brain's internal timekeeper, called the superchiasmatic nucleus (SCN), serves as a kind of master control for body temperature, hormone blood levels, and--most noticeably--desire to sleep. When deprived of sunlight and other cues, people's internal clocks seemed to vary from 13 to 65 hours, with an average of 25. But in 1996, Charles Czeisler, a neuroscientist at Harvard University, discovered that lightbulbs are bright enough to reset our internal clocks--and probably skewed the previous studies.
In a new study, Czeisler's team isolated 24 volunteers, some in their 20s and some in their 60s, for a month in a room with no external time cues that might reset their internal clocks. They lit the rooms with 10-watt lightbulbs that were turned on and off on a regular 20-hour or 28-hour cycle. (This was far enough off the natural rhythm to keep the internal clock from resetting itself.) After measuring hormone levels, body temperature, and recording sleep habits, the scientists found that circadian rhythms were much more consistent than in earlier studies: Only two volunteers had rhythms that deviated from the 24-hour, 11-minute mean by more than 10 minutes.
The finding reinforces the importance of a dependable internal clock, according to Robert Moore of the University of Pittsburgh, who discovered the SCN. "Clearly, nature would not go to the trouble of constructing such an elegant, functional, and durable timepiece if it was not critical to us throughout our lives," Moore says. He adds that Czeisler's methods might lead to better detection and treatment for people with "phase delay sleep disorder," a form of insomnia that typically begins in the teenage years.