A quick "dose" of light rather than an array of pills may soon prove to be the answer for people suffering from sleeping problems after a long jet flight or working the swing shift.

Dr. Howard Roffwarg, president-elect of the American Sleep Disorders Association, predicts the most effective ways of resetting sleep cycles will likely be based on understanding how changes in body temperature and light levels affect the brain's wake-sleep pacemaker."The 24-hour temperature cycle is an important sign of what the sleep-wake cycle is doing," said Roffwarg, who is a psychiatrist at University of Texas Southwestern Medical Center.

The body's temperature drops gradually during sleep and rises before waking. "We know that as we change sleep stages, the body changes temperature," Roffwarg said. "If you try to sleep when your body temperature is on the rise, you don't sleep long."

Scientists are working to understand how temperature changes affect disruptions in the body's circadian, or 24-hour, rhythms. It may explain why people do not do well when they move between different time zones or change work shifts frequently.

"If you keeping changing time zones or sleep cycle, you never catch up with yourself," Roffwarg said.

Changes in body temperature also appear to affect bodily functions such as the production of certain key hormones. What researchers do not know is why the body produces the bulk of its supply of adrenal cortisol, the stress hormone, during sleep, he said.

Since exposure to light can affect body temperature, researchers are studying how environmental light levels affect the brain's pacemaker and various biological cycles.

In the past, sleep researchers have been able to reset an individual's sleep-wake cycle naturally over a period of about two weeks. Roffwarg said it now appears that brief exposure to high light levels can reset sleep-wake cycles within 48 hours.

"It may be that we can help people going on trips or facing abrupt shift changes in industry with strategic short exposure to light," Roffwarg said.

Psychologist John Herman, an associate of Roffwarg's at the Dallas medical center, said he envisions booths in airports where foreign travelers can drop in for a "dose" of light to reset their biological clocks.

Understanding how the sleep-wake cycle works means doctors now can use behavioral means of treating sleep problems rather than relying on drugs that may have adverse side effects.

Researchers now know that insomnia, the inability to sleep, is a symptom, like pain.

"We used to think insomnia was all psychological. Now we know only about 50 to 60 percent of it is psychological," Roffwarg said during a recent interview.

About 10 percent of people who complain of insomnia actually do sleep, but are unable to differentiate between being asleep and awake, Roffwarg said.

The rest is linked to breathing difficulties and body movements.