Morning birds buckle under sleep pressure
Sleep-promoting system makes early risers inattentive by evening, study suggests
Early to bed, early to rise makes a man sleepy and inattentive at twilight.
A new brain imaging study suggests morning people’s circadian clocks can’t resist the biological pressure to sleep, while night owls don’t buckle as easily. The research, appearing in the April 24 Science, could change the way scientists view the relationship between sleep and the circadian clock.
Two systems control sleeping and waking — the circadian clock and the sleep homeostat. The circadian clock helps synch the body’s rhythms, such as the rise and fall of blood pressure and body temperature, with light and dark cycles. The homeostat is a biological accountant that keeps track of how long a person has been awake or asleep and how much sleep the person has had recently — inducing sleep when it’s been too long.
As the day goes on, the waking signal from the clock gets stronger, says Derk-Jan Dijk, a professor of sleep and physiology at the University of Surrey in Guildford, England. “It’s not just an alarm clock that gives one signal in the morning,” he says. “It’s really a process.” If the circadian clock operated alone, people would be most awake in the evening, but the homeostat counterbalances the clock’s wake signal.