By CZERNE M. REID

The Lowell W. and Josephine Q. Berry Professor of Psychiatry and Behavioral Sciences presented new research last week at an emergency medicine grand rounds talk on the effects of paying off "sleep debt" — the difference between the amount of sleep required and the amount taken.

Preliminary analysis shows that when individuals eliminate their sleep debt their behavioral and cognitive performance, as measured using alertness and problem solving tests, improves beyond what is usually considered normal. And they stop feeling tired.

Sleep debt can be repaid in a lump sum by, for example, getting 10 hours of sleep a night on vacation. "It’s like managing a credit card," Dement said, "if the debt gets huge all you’re doing is paying interest."

People should "manage their sleep debt for optimal existence" instead of operating on "zombie equilibrium" said Dement in his talk titled "Optimal alertness and performance: new insights." Although most people have a large sleep debt, they may be kept awake by sensory stimuli such as noise and light or emotional stimuli such as anger and excitement.

People with large sleep debts have reduced alertness and impaired function that may lead to injury or fatal accidents. Sleep deprivation and disorders such as sleep apnea are often mistaken for chronic fatigue syndrome, Dement said, adding that many people who thought they had the syndrome were cured simply by getting enough sleep.

Rebecca Smith-Coggins, MD, associate professor of surgery who introduced Dement at the lecture, met him as a Cornell University undergraduate while doing research for a film on narcolepsy. "Nobody in emergency medicine knows about this," she said of sleep research.

Smith-Coggins currently is devising measures to counteract sleepiness among night-shift workers including emergency medicine residents. "We are trying to get people to sleep better during the day," she said, adding that the work at Stanford is on the leading edge of a national movement.

Dement said each person has to figure out his or her own sleep requirement. He defines individual sleep need as the average daily amount of sleep someone must get to avoid building up a sleep debt. That, he said, is about eight hours a night, on average.

Mimi Schultz, a third-year medical student and one of approximately 50 attending physicians, residents and students at the lecture, said she did not get enough sleep during her first year of medical school but she has gotten the message. "You have to learn what your body needs," she said. "I learned to go to sleep a little earlier."

To illustrate the relatively low premium that people place on sleep, Dement recalled giving a talk titled "Know how to sleep and live longer" to a gathering of high-level executives in 1982. Only about 10 people attended while the room down the hall was packed. Curious, Dement went to see what that other talk was: "How to hang on to your personal wealth." But according to Dement, getting enough sleep is key to hanging on to personal health.

Dement considers among his most important contributions to medicine to be the methods he developed to deal with daytime sleepiness in a quantitative scientific manner.

The multiple sleep latency test he created in 1978 is now used worldwide in sleep research. Performed several times a day on each subject, the test measures the time people take to fall asleep when on a comfortable bed in a quiet, dark room. In one study, Dement found that on average subjects started feeling sleepy within five minutes of the start of the test. In a large international study, only 0.1 percent of subjects did not fall asleep within 20 minutes. When subjects were restricted to five hours of sleep a night, they started falling asleep earlier and earlier on consecutive days.

Sleep tendency increases if you are losing sleep but decreases if you get extra sleep, Dement said. "The awake brain is always trying to go to sleep but the strength of the urge varies depending on the level of sleep debt." Dement said research shows that a person with zero sleep debt cannot sleep at all or get extra sleep.

"How do you know when your sleep debt is paid up?" a resident at the lecture asked. "You feel great!" answered Dement.

Sleep legend Dement keeps last class wide awake (3/19/03)

Center begins first long-term study of sleep apnea (10/23/02)

Researchers ID best hours to sleep when time is limited (5/28/03)