Thinking and Sleep

There is an important article in a recent issue of the Journal of the American Medical Association (Effects of Sleep Inertia on Cognition Adam T. Wertz; Kenneth P. Wright Jr; Joseph M. Ronda; Charles A. Czeisler JAMA. 2006;295:163-164.)

The study by a team at the Brigham and Women’s Hospital in Boston and the University of Colorado examined the phenomenon of sleep inertia: how long it takes for someone to wake up and think effectively, and to compare that with thinking after a person has been awake for 24 hours. For most of the first three years after I graduated from medical school, I worked on what was then known as a “one in two” on-call roster: every other night and every other weekend. Fortunately that inhumane system was abandoned some years ago, but it was not uncommon to be up and working for three straight days at the weekends, and we all became absolute experts on sleep and how to handle sleep deprivation. The problem was that if we did manage to get a few minutes sleep, there was always the chance of being awoken and being asked immediately to perform important tasks that would require very high levels of thinking and analysis. The results of this new study will not be a surprise to anyone who has done night work, or anyone who has been out all night burning the candle at both ends.

The study participants had had six nights of monitored sleep lasting eight hours per night, they were given a performance test that involved adding randomly generated, two-digit numbers. Based on the results of this test, the researchers concluded the subjects exhibited the most severe impairments to their short-term memory, counting skills and cognitive abilities from sleep inertia within the first three minutes after awakening. The most severe effects of sleep inertia generally dissipated within the first 10 minutes, although its effects were often detectable for up to two hours.

The study follows other research that has looked at the effects of going without sleep for over 24 hours, and found that the cognitive impairments were roughly the same as being drunk. Yet in the Colorado experiments, the cognitive skills of test subjects were worse upon awakening than after extended sleep deprivation: In a nutshell, the effects of sleep inertia may be as bad as or worse than being legally drunk. The most likely explanation is that certain areas of the brain take longer to "wake up".

Previous research has shown that the prefrontal cortex, which is responsible for executive functions: planning, problem solving, complex thought and emotional control, is one of the brain regions that takes longer to come "on-line" following sleep.

What should be the conclusions from these studies?

1. Ideally, nobody should be doing anything really important for 15 to 30 minutes after they wake up.

2. If you are asleep, it’s a much bigger transition to go from that to being awake, rather than staying awake, even for a long time, because then you will be aware that you are drowsy.

3. The study did not examine emotion and motivation, and that may come in to play. If you are asleep in a hotel and the fire alarms go off, you may well be able to wake up and think very well and very quickly for a few minutes, but then you brain plays “catch-up,” and you will once again we groggy and cognitively impaired.

As a young doctor, there was no option: I had to wake up fast and be able to think straight. So I just did it, and fortunately the quality of my decisions seemed to be fine when older and wiser physicians checked them the next morning. Though I am VERY pleased not to have to work like that any more!

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