The early bird's brain v. the night owl's

	Daily variations in homeostatic sleep pressure and circadian alert signal. Click here for more information.

A new brain-imaging study may help explain why some people are most alert early in the day, while others hit their stride in the evening, researchers report in the April 24 issue of Science. Christina Schmidt and colleagues in Belgium and Switzerland now report that our alertness and ability to concentrate are affected by both how long we've been awake and the time of day, since our circadian rhythms operate according to a day-night cycle. The researchers used functional magnetic resonance imaging to monitor the brain activity of early birds and night owls who spent two consecutive nights in a sleep laboratory and periodically performed a task that required sustained attention. The results suggest that night owls generally outlast early birds in the length of time they can be awake before becoming mentally fatigued. After 10 hours of being awake, the early birds showed reduced activity in brain areas linked to attention, compared to the night owls. They also felt sleepier and tended to perform more slowly on the task. These brain areas include one that is home to the circadian master clock. Activity in this area decreased the longer the volunteers were awake (i.e. “sleep pressure” increased), suggesting that the behavioral difference between early birds and night owls are at least partly the result of interactions between the brain regions controlling sleep pressure and circadian rhythms.

Article #17: "Homeostatic Sleep Pressure and Responses to Sustained Attention in the Suprachiasmatic Area," by C. Schmidt; F. Collette; Y. Leclercq; V. Sterpenich; G. Vandewalle; C. Philipps; G. Tinguely; A. Darsaud; S. Gais; M. Schabus; M. Desseilles; T.T. Dang-Vu; E. Salmon; E. Balteau; C. Degueldre; A. Luxen; P. Maquet; P. Peigneux at University of Liege in Liege, Belgium; P. Berthomier; C. Berthomier at PHYSIP S.A. in Paris, France; C. Cajochen at Psychiatric University Clinics in Basel, Switzerland; P. Peigneux at Universite Libre de Bruxelles in Brussels, Belgium.