Dinges, who directs sleep research at the Institute of Pennsylvania Hospital, scoffs at those who argue that they have methods of coping effectively with less than their biological sleep quotient.
"When you are chronically sleep-deprived, you lose your ability to judge your alertness," he says.
The longest sleep-deprivation study on humans lasted 12 days, says Dinges. At the end, the subjects suffered misperceptions, loss of fine motor skills, memory problems and cognitive slowing, and they were unable to pick up on key perceptual signals.
"Your ability (to concentrate) is completely gone," says Dinges. "You get very stubborn, insisting on a method that hasn't worked, and you can't shift."
Brown's Carskadon has found that creativity suffers in people operating with a sleep deficit.
"One of the things that goes is the capacity for divergent thinking--loss of the ability to free-associate," she says. "It might be harder to do a crossword puzzle or develop a successful ad campaign after several days of inadequate sleep."
In industry, the concern is over the quality of work performed on odd shifts. Sleep deprivation may be harder to detect in a basketball player whose work involves constant motion and physical exertion, with the added stimulation of competition. But in a desk-bound worker, whose job demands finely focused attention to detail, inadequate sleep can dramatically affect performance.
Monjan cites the catastrophic nuclear accidents at Chernobyl and Three Mile Island and the fatal chemical leak at the Union Carbide plant in Bhopal, India, as incidents at least partly attributed to human error on the night shift.
Says Dinges: "We now have a lot more automation in the workplace. In our cars we have power steering, multi-speaker sound and cruise control. So that leaves people with the one task they don't do well when they are sleepy: Monitor the machines."
It is not simply inadequate sleep that plagues night-shift workers who may put off sleep in order to spend time with family or others on a conventional schedule. It is the quality of sleep during daylight. The biological clock, which took millions of years to evolve as a regulator of physiological function, appears strongly linked to the daily cycle of sunlight and darkness.
That was demonstrated in a study by Charles Czeisler of Harvard University's Center for Circadian and Sleep Disorders Medicine at Brigham and Women's Hospital in Boston. Czeisler found that night-shift workers' alertness, physiological systems, job performance and quality of daytime sleep matched that of daytime workers only if they were exposed to very bright light during their work hours and returned home to sleep in a completely darkened room.
Subjects who were exposed at work to bright light approximating the intensity of sunlight changed their sleep/wake rhythms by the fourth day, Czeisler reported in the New England Journal of Medicine in May, 1990. Normal indoor lighting was not sufficient to flip-flop the circadian clock. A control group of subjects, men aged 22 to 29, working in normal office light, did not adapt by the sixth night.
Other researchers are looking into theories that inadequate sleep lowers the body's resistance to illness.
Dr. James M. Krueger, professor of physiology at the University of Tennessee, has approached the question by studying the impact of illness on the body's need for sleep.
"Everyone seems to know that when you are sick, you sleep more," Krueger says. "Physicians always tell patients to go home and get rest, but until now there has been no scientific evidence to support that it does any good."
What Krueger and his colleagues found was that rats and rabbits produced more cytokines--proteins that boost the immune system--when they were fighting a bacterial or viral infection. Some of these cytokines were found to have the additional effect of inducing sleepiness in the animal, biochemically linking the animals' disease-fighting efforts to an increased need for sleep. Krueger cautions that animal sleep patterns differ greatly from human, and that human studies confirming the link between immune response and sleep needs remain to be done. But the animal experiments lend the first scientific support to what has long been popular wisdom: When you are sick, go to bed early and sleep late.
Joyce Terhaar and Geoff Long managed to stay healthy during those first bleary-eyed weeks of parenthood, but sleepiness became a constant, day and night. Gradually, though, Connor settled down, letting his parents indulge their sleep cravings for as long as four hours at a stretch. One day, Geoff actually got away from the Capitol early and spelled Joyce so that she was able to get an unbroken night's sleep. The next day she discovered what so many do on Saturday and Sunday after burning the candle ends all week: A sleep deficit built over several days can be erased by one extended night of sleep.
Things were going so well, in fact, that the couple decided they were ready for a night out with friends.
"We went to their house and we brought Connor," Terhaar recalls. "He was really good between 6 and 10--usually his fussy period--so we had a nice time and were in a really good mood coming home. But then, as soon as we got home, he started fussing, and it lasted until nearly midnight. It was as if he put it off just to keep us up again.
"We just sat there completely unable to deal with it. When you're tired you just can't deal with the frustration, I guess."