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Losing Sleep Over Fatigue

Everyone knows that ordinary tasks can seem daunting when the mind is fogged by exhaustion. Now researchers have technology to track which parts of the brain are involved and how their activity is affected.


Everyone knows firsthand the struggles of sleeplessness--that drowsy daytime feeling of leaden thoughts mired in deep mental mud, when the mind seems to work so much harder to accomplish so much less.

Indeed, researchers believe that America is a society of the sleepless, with often catastrophic consequences.

Almost half of all heavy truck accidents can be traced to driver fatigue, while the Challenger disaster, the Chernobyl nuclear reactor meltdown and the Exxon Valdez oil spill can all be partly linked to people severely deprived of sleep by round-the-clock work schedules. In all, the frayed temper, short attention span and fuzzy thinking caused by sleep deprivation cost $150 billion a year in reduced workplace productivity, the National Commission on Sleep Disorders has estimated.

For the first time, researchers have been able to take a direct accounting of the mental toll exacted by a sleepless night by measuring the brain activity of sleep-deprived volunteers struggling to perform simple mental tasks.

By monitoring mental activity with a high-speed medical imaging device, the scientists discovered that sleep deprivation dramatically affects how the brain functions.

Vast Differences Depending on Task

"There are a lot of sleepyheads in this world but we don't know much about the sleepy brain," said UC San Diego psychiatrist Christian Gillin at the San Diego Veterans Affairs Medical Center, who helped conduct the studies. "The sleepy brain is very different from the rested brain. The way it is different will vary with the kind of mental task someone is doing."

Some key portions of the sleepy brain work harder than normal to solve simple verbal problems but the brain appears to stall completely when attempting to perform simple arithmetic problems, they determined.

On average, 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, which is involved in higher mental functions such as attention, working memory and the ability to handle multiple tasks. During normal waking hours, the prefrontal cortex is one of the most active areas of the brain, so researchers naturally expected it to be among the most vulnerable to sleep deprivation.

Instead, it became even more active than usual, in direct correlation with the subject's sense of sleepiness; the sleepier the subject felt, the greater the activity in that region of the brain.

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.

"After sleep deprivation, the brain was performing in a fundamentally different way than it was after a normal night of rest," said clinical psychologist Sean Drummond at the Tucson Veteran Affairs Medical Center, who conducted the experiment with Gillin as his dissertation project.

"There were a few new areas that came online as a compensation for being sleepy," Drummond said. "Often, when I don't sleep, I have the experience of feeling that I am in a fog I have to fight through. That may be the subjective experience of the brain working harder to do less."

Their experiments were published recently in Nature and NeuroReport.

Jim Horne, head of the Sleep Research Centre at Loughborough University in England, said the research offered "an unexpected twist" in the understanding of what happens in the brain when people lose sleep.

"What's going on is a bit more complicated than we realized," Horne said. "Those bits 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 out."

To see just what happens inside a brain running on too little sleep, the researchers used a new noninvasive technique called functional magnetic resonance imaging (fMRI), which can track high-speed variations in the neural blood flow that accompany shifts in mental activity.

Effects on Memory

When an area of the brain is activated, the pattern of blood flow can change within as little as 200 milliseconds. For those analyzing the images, that is the speed of thought.

For this study, 13 normal, healthy volunteers were kept awake and carefully monitored in a hospital sleep laboratory for about 35 hours.

As the volunteers struggled to stay awake, they tried to memorize a short list of words and subtract a series of numbers while undergoing fMRI scans.

The scanner produced images of their brain activity that revealed increased and decreased activation of specific regions of the brain. The volunteers also were imaged as they performed the same tasks after a good night's sleep.

Under the stress of sleeplessness, the brain behaved differently doing arithmetic than when memorizing words.

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