• Your reaction time slows and you have trouble paying sustained attention. Driving is "the worst kind of thing," especially in bumper-to-bumper situations or lonely roads, said Edward Stepanski of the Rush University Medical Center in Chicago. "You’re forced to sit still, so you can’t move around and do things people ordinarily do to keep awake, and you’re staring at the road."
• You have trouble keeping tabs on multiple sources of information. So you ignore some of them to focus on a few, and "you fail to notice that you’re running out of gas," said David Dinges at the University of Pennsylvania School of Medicine.
• Creativity suffers. You get stuck on bad solutions and can’t think of better ones.
• You can’t remember as much, and "a sleepy brain is just not very good at learning new information," Stepanski said.
• Your brain just can’t do some critical things in a hurry.
If given the luxury of time, it actually does pretty well with tasks like making decisions and solving complicated problems, says Hans Van Dongen at the University of Pennsylvania. That’s because the brain has "an almost stunning ability to find tricks" to get around some hurdles imposed by sleep loss, he said.
So if you work late in your office answering e-mails without any reason to hurry, you’ll probably do all right, though you might have to read some sentences a couple times, he said. But then, as you drive home, you have to react and make decisions – right away.
"And you find that, oops, you’re still impaired, after all, even though you didn’t notice it," Van Dongen said. "And now you’ve got a problem."
Microsleeps reflect "a kind of struggle inside the brain at the most fundamental biological level" between sleep and wakefulness, producing a sort of in-between state of reverie or inattentiveness, Dinges said. A person might look awake to a casual observer during microsleeps of a couple seconds, or the episodes can be more obvious.
Think of trying to stay awake at a meeting after partying all night. As Dinges observes in lab experiments, the eyeballs try to roll, the eyelids move unusually slowly and neck muscles start to go limp, which suggests that even muscle-control parts of the brain participate in sleepiness.
Work in Dinges’ lab has shown that after a few nights of too little sleep, people stop realizing their daytime performance is suffering. So researchers are studying whether machines can do a better job of spotting sleep-deprived people.
Dinges said federal investigators are now seeing whether specialized monitors can track slowly closing eyelids in truckers. Studies suggest that’s a reliable sign of impairment, he said.
Along with researchers from the National Aeronautics and Space Administration, Dinges has studied how much benefit a sleepy person gets from taking a break and moving around. The results suggest it might buy 10 to 20 minutes of wakefulness. Napping can be more effective as long as you doze at least 10 minutes, he said.
How about coffee? "Caffeine is not buying you a lot when you’ve taken it first thing in the morning after you’ve first awakened," said James Wyatt of the Rush University Medical Center in Chicago. At that point, coffee is probably just treating symptoms of caffeine withdrawal, which include sleepiness, confusion and irritability, he said.
For fighting effects of sleep deprivation, caffeine helps a lot more when it’s taken after at least eight hours of wakefulness, he said.
To come up with better drugs to help people sleep or stay awake, scientists are studying just what happens in the sleep-deprived brain itself.
The brain has at least two major systems that govern sleep. One is the well-known pacemaker that keeps our bodies on a 24-hour rhythm. It’s found in the hypothalamus, and it drives the sleep-wake cycle. Scientists aren’t sure yet just how it sends its timing signals to the body.
But people can obviously override the pacemaker, staying up through most of the night. That’s when a second, "homeostatic" system kicks in. It basically keeps track of how short you are on sleep, either from one bad night or a buildup of sleep deprivation over time. And it does its best to make sure you pay this "sleep debt" off.
Much less is known about this system. Where is it? How does it keep track of your sleep debt, especially if the debt builds night after night? And how does sleep debt impair the brain?
The theory goes like this: as brain cells function during wakefulness, they give off adenosine, which mounts up outside the cells in the basal forebrain. There, the adenosine acts to inhibit brain cells that normally promote wakefulness and play key roles in brain function. So you feel sleepy and your mental functioning declines. When you finally fall asleep, your brain cells work less hard and adenosine is taken back into cells, relieving its pressure on the wakefulness circuitry of the brain.
Caffeine blocks drowsiness by interfering with adenosine’s ability to affect brain cells, says Robert McCarley, a researcher at the VA Medical Center in Brockton, Massachusetts, and Harvard Medical School. Further studies of how the brain responds to adenosine might lead to more effective wake-up agents and better sleeping pills, McCarley said.
To really understand how lack of sleep alters the brain, Dinges said, scientists will need to develop a few more tools. They’ll need to find a way to mimic those mental and behavioral changes in animals, for example. And they’ll need more detailed brain scans that can capture the very tiny brain structures that play a role in the process.
But such advances are nearly at hand, Dinges said.
"Over the next five years," he said, "there will be an exciting amount of work."
Information on sleep:
www.nhlbi.nih.gov/health/public/sleep/index.htm
www.sleepfoundation.org/publications.cfm