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NewsvineA missing fifth copy of an otherwise innocuous DNA sequence could be the cause of some traffic accidents that occur in the early morning hours, research by scientists at the University of Surrey suggests.
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The sequence is present in multiple copies — -sometimes four and sometimes five — in a region of the genome known as the PER3 gene. Professor Derk-Jan Dijk and his colleagues found that those who inherit two long versions of the gene are more likely be “early risers,” whereas those who inherit two short versions of the gene are more likely to go be “night owls.”
The early risers’ performance after 4 a.m. in the second day of a sleep-deprivation study showed a significant decline compared with that of the night owls.
Sleep-wake cycles are guided by two basic principles: They are linked to the light-dark cycle of the day, in what are known as circadian rhythms; and are aimed at making us sleep an average number of hours each night, called sleep homeostasis. If you don’t get enough sleep one night, you are likely to sleep longer and more deeply the next night to catch up; meanwhile, early and late risers have different patterns of brain wave activity and hormone production at different times of the day.
For the study, two dozen volunteers underwent a physiological monitoring in which the researchers observed aspects of their sleep under normal conditions, and then during two days of sleep deprivation.
During the two days of sleep deprivation, Dijk tested the participants’ working memory and attention. In the first day, the early-risers and the night owls performed equally well. But when the researchers ran the same tests between the hours of 4 and 8 a.m. on the second day, the early-risers performed much worse, while the night owls’ performance barely degraded at all. This could help explain why many sleepiness-related accidents occur — 4 a.m. is around when most such accidents occur outside of the laboratory.
Even after the end of sleep deprivation, the researches discovered significant new differences. After two full days of wakefulness, the participants were allowed to sleep — but while it took early-risers an average of eight minutes to fall asleep, night owls needed 18. Once asleep, early-risers spent 50 percent more of their time in slow wave sleep, or deep sleep, than night owls — something that didn’t happen normally. The researchers concluded that early-risers thus have a greater need for sleep, which explains their inferior cognitive performance when tired.
And in case young adults think that they can circumvent the conclusion of this research through willpower, Dijk found that indeed the opposite is true: the impact of your genetic endowment was most significant in their youngest studied age group: 18-29 years. Tough luck.
Contact Rachel Whelan at rpwhelan at stanford.edu.