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There was no real difference between the early birds and the night owls in their performance on the morning test. But the evening test was a different story: night owls were less sleepy and had faster reaction times than early birds.
So even though both groups were sleeping and waking according to their preferred schedule, night owls generally outlasted early birds in how long they could stay awake and mentally alert before becoming mentally fatigued. The fMRI supported the behavioral results: 10.5 hours after waking up, the early birds had lower activity in brain regions linked to attention and the circadian master clock, compared to night owls.
teromakotero on 2009-06-21A new study, in the journal Science, reports some intriguing differences between the brain-activity patterns of the two types that underlie the behavioral differences.