Artigo referido pela AMICOR Maria Inês Reinert Azambuja
Chronobiology: Stepping out of time
- Nature
- 497,
- S10–S12
- doi:10.1038/497S10a
- Published online
How can people better adapt to an 'unnatural' world of artificial lighting and alarm clocks?
Subject terms:
By the time Elizabeth Klerman boards the train to go to her office at Brigham & Women's Hospital in Boston, Massachusetts, the conductor has been awake for hours, rising in the dead of night for his first train at four o'clock. This schedule is not merely demanding, but contrary to most people's circadian rhythms, the pattern of physiological and metabolic activity that is roughly in synchrony with the rising and setting of the Sun.
NASA EARTH OBSERVATORY/NOAA NGDC
Exposure to light after sunset tricks the body into thinking it's still daytime, delaying the onset of 'biological' night.
“Some people are trying to live and work with an abnormal relationship between their circadian rhythm and the clock,” says Klerman, who studies human sleep patterns. Most of us have experienced this mismatch in the form of jetlag. For shift-workers and others with 'unnatural' routines, however, this desynchronization occurs every day and can result in chronic sleep deficits. Researchers are now trying to understand the prevalence and severity of the problem, and to devise strategies that can help reset these clocks.
The time machine
Many body tissues have their own timetables, organized by cyclic oscillations in the expression of a network of numerous 'clock genes'. “The entire body is a clock,” says Derk-Jan Dijk, director of the Surrey Sleep Research Centre in Guildford, UK. “It's a house with clocks in every room and every corner, yet in one way or another they work in an organized way.” The timing of all these various 'peripheral oscillators' can profoundly affect metabolic activity, immune cell proliferation, and numerous other critical functions. But there is a central pacemaker that gives the body a sense of the time of day: the suprachiasmatic nucleus (SCN), a group of neurons in the hypothalamus (see 'The anatomy of sleep', page S2).
When melanopsin photoreceptors in the eye detect light, the SCN is activated and responds by initiating a host of rhythm-establishing physiological responses, including suppressing production of the hormone melatonin by the pineal gland (see 'The light switch'). The peripheral oscillators can be shifted by physical activity or by altering meal times, but most research suggests that light exposure is by far the most important determinant of rhythms driven by the SCN. “If you look at the data for humans, every time they suggested that exercise or food may shift the clock, they also suggest that light may have been involved,” says Debra Skene, who studies chronobiology at the University of Surrey, UK./.../
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