As a night owl myself, I look at those who are bright and chipper early in the morning and think "why?" To me, being awake and functioning before 10am is fairly difficult to comprehend. Even looking back on my life, I have no idea how I managed to wake up, clean up, and drive the 30 minutes into the city each day for four years in high school. Yet others will look at me with puzzlement when I state my usual bedtime—many of my Nobel Intent contributions have come from after midnight.

A new study, carried out by a team of Belgian and Swiss researchers and published in last week's issue of Science, looked at the underlying cause of what makes one an early bird or a night owl, and what effects this has on day-to-day life. The study consisted of 31 participants, 16 morning people, and 15 night owls—the night owls' days were shifted an average of four hours later than those of the early birds. Each participant was instructed to go about their lives, sticking to their bedtime/wake routines for a week before they spent two days in a sleep lab. Once under the more controlled conditions of the lab, researchers examined the participants' brains using functional magnetic resonance imaging (fMRI) while the subjects attempted a psychomotor vigilance task—a simple reaction time test.

Each person was given two rounds of fMRIs and cognitive tests, one day in the morning (1.5 hours after they woke up) and the other day in the evening (10.5 hours after they woke up). The evening test showed statistically different measures for the two groups: night owls maintained their response times better than the early birds. The morning test found the two results to be statistically identical. Using the data from fMRI imaging, the cognitive testing, and a measure of the individual's circadian phase, the researchers found that behavioral differences manifested themselves only in the evening.

Using the results from the fMRI, which allowed them to see the active areas of the subject's brain, the authors saw differences in the locus coerulues and in a suprachiasmatic area, the regions of the brain that are known to house the circadian master clock. They conclude that there are behavioral differences between extreme chronotypes (morning and evening people). The optimal alertness of morning people is diminished in the evening hours because there is a more pronounced negative influence due to sleep homeostasis on the areas of the brain known to control our circadian rhythms.

With a known physiological basis for this phenomena, I need to send a copy to my bosses for the next time they give me a hard time for not showing up at the office at the crack of dawn.

Science,

2009. DOI: 10.1126/science.1167337