The early bird may get the worm, but the night owl has more stamina, a new study suggests.
The differences come from the interactions between two regions of the brain, including one that is home to the master circadian clock.
It has long been known that some people have a predilection for the "early to bed, early to rise" sleep schedule, while others prefer to sleep in and stay up until the wee hours.
Researchers at the Université de Liège in Belgium used functional magnetic resonance imaging (fMRI) to monitor the brains of individuals from both groups to look for changes in how their attention was focused throughout the day.
The participants went to a sleep clinic, where they followed their normal sleep schedule. At 1.5 hours after waking up and again at 10.5 hours, they had to perform a task that required sustained attention.
The researchers found no difference in the attention levels of the two groups at 1.5 hours after waking, but the night owls were more focused than the early birds after 10.5 hours spent awake.
The difference was a result of the shift in the balance between the two mechanisms that control alertness: the light-triggered circadian signal and the buildup of the pressure to sleep through the day (called the homeostatic process), the researchers said. As the day wears on and the time since sleep becomes greater, the pressure to sleep mounts; at the same time, the continued daylight triggers the circadian signal that promotes wakefulness.
While researchers had thought that the two systems operated independently, the study found that "the two are always interacting together," said study co-author Phillipe Peigneux.
In the night owls, increased activity was seen in two parts of the brain at 10.5 hours — the suprachiasmatic nucleus area and the locus coeruleus — that are involved in regulating the circadian signal. Essentially, the circadian signal was winning out over the pressure to sleep.
In the early birds, on the other hand, "the sleep pressure prevents the expression of the circadian signal," so those individuals were less able to keep their attention focused, Peigneux told LiveScience.
Peigneux said this information could be useful in job decisions: "If you have a night job, it's better to be an evening person," he said.
However, other research has shown that night shift work could cause symptoms that, if left untreated, could lead to diabetes, obesity and cardiovascular disease.
Peigneux and his colleagues, including Christina Schmidt, who led the new study, hope to see how these differences affect other cognitive tasks, such as learning and memory.
The study, detailed in the April 24 issue of the journal Science, was supported by the Belgian Fond National de la Recherche Scientifique, the Fondation Médicale Reine Elisabeth, and the University of Liège.
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