Early risers sleepier in evenings

William Atkins
Friday, 24 April 2009 18:48

Science - Biology

Specifically, ‘early birds’ are equally alert two hours after waking up as are those ‘night owls.” However, those people who are very early risers in the morning are less attentive about ten hours after waking up. And, they are much more tired and sleepy in the evenings than people who are very late risers in the morning.

The fMRI scans used by the researchers verified that the suprachiasmatic and the locus coeruleus, two areas of the brain, were more active in the late risers than in the early risers during the afternoon and the evening.

The suprachiasmatic part of the brain contains the circadian clock and the locus coeruleus is the part of the brain that controls sleepiness and wakefulness.

The researchers found that the circadian clock of early risers were more apt to cause early risers to be sleepy in the evenings than the later risers. In addition, the early risers fell into a “slow-wave sleep” quicker than the late risers when they did fall asleep in the evenings.

This type of sleep occurs when the sleep homeostat tells the body it is tired and it is time to sleep. In other words, early risers have less ability to resist the temptation to sleep when they begin to feel tired in the evenings.

They concluded that in extreme cases (very early risers and very late risers) “…  that maintaining attention in the evening was associated with higher activity in evening than morning chronotypes in a region of the locus coeruleus and in a suprachiasmatic area (SCA) including the circadian master clock. Activity in the SCA decreased with increasing homeostatic sleep pressure. This result shows the direct influence of the homeostatic and circadian interaction on the neural activity underpinning human behavior.” [Paper]

The researchers concluded that people are either early risers or late risers depending on whether the area of the brain the involves the circadian clock or the area of the brain that involves sleep homeostat is more active.

For people that are neither early risers nor late risers, what the researchers would call normal risers, these two areas are about equally active.

Dr. Peigneux stated, “Morning types may be at an advantage, because their schedule is fitting better with the usual work schedule of the society. It may represent a problem for evening types obliged to wake up early while having difficulties going to bed in the evening, eventually leading to a sleep debt." [National Geographic News: “Night Owls Stay Alert Longer Than Early Birds ”]

According to the Discover Magazine article Night Owls Have More Staying Power Than Early Birds, Brain Study Shows, “The study is the first to show that circadian rhythms and sleep pressure interact to govern behavior; researchers previously believed that the two systems operated independently.”

Although late risers appear to be more attentive during the day and less sleepy and tired in the evening, they do not alway have an easy time of fitting into society’s general routine of working from around 8 a.m. and 5 p.m. during the work week.

The researchers made the comment that late risers, who don’t get up until noon when on their own, are probably sleep deprived when they are forced to get up early to meet their career obligations.