By monitoring mental activity of sleep-deprived volunteers as they struggled to perform simple mental tasks, scientists discovered that sleep deprivation dramatically affects how the brain functions.
"The sleepy brain is very different from the rested brain," said University of California-San Diego psychiatrist Christian Gillin at the San Diego Veterans Affairs Medical Center, who helped conduct the studies. "The way it is different will vary with the kind of mental task someone is doing."
They found that fatigued brains had a harder time with simple arithmetic problems than they did with verbal problems.
On average, the researchers found, people who have had a sleepless night do half as well on simple memory tests as well-rested people.
The scientists were especially surprised at the behavior of a brain region called the prefrontal cortex.
This part of the brain is involved in higher mental functions such as attention, working memory and the ability to handle multiple tasks. It is normally one of the most active areas of the brain. Researchers expected it to be among the most vulnerable to sleep deprivation -- but they were surprised. Instead, it became even more active than usual, in direct correlation with the subject's sense of sleepiness.
Another area of the brain, called the parietal lobe, normally quiescent during verbal tasks, also kicked into overdrive. Conversely, the temporal lobe, a brain region involved in language processing, stopped altogether in sleep-deprived subjects.
Just because these parts of the brain are showing more activity, however, doesn't mean they're working better. Instead, it's probable that they are having to work harder to compensate for the fatigue. One of the researchers said that the feeling you get of fighting through a fog when you're sleep-deprived may be a result of the brain working harder to do less.
Jim Horne, head of the Sleep Research Centre at Loughborough University in England, said it appears that the parts of the brain that work the hardest in wakefulness seem to show the greatest effects of sleep loss. They seem to try and compensate by pulling in other bits of spare brain capacity to help.
To read more about the scientific and medical side of sleep deprivation, see "Drowsy's as Deadly as Drunk" in the April 1999 issue of RoadStar.