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Morning birds buckle under sleep pressure

Sleep-promoting system makes early risers inattentive by evening, study suggests

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3:39pm, April 23, 2009

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.

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