Motion sickness has long intrigued researchers. Scientists have believed for years that the symptoms arise when the brain receives conflicting signals about how the body is oriented -- as, for example, when a ship passenger's eyes see the indoor environment is stable but the nerves in the joints and the fluid in the inner ear say otherwise. But the only treatments available may also cause drowsiness or slowed reflexes -- a major drawback for many travelers and especially for pilots and astronauts.

Controversial new research suggests motion sickness may be triggered by the same phenomenon that causes certain types of seizures in epileptics. And preliminary studies indicate that a drug used to control epileptic seizures also can prevent motion sickness and do it without sedation. The drug is Dilantin, the brand name for the anti-convulsant drug, phenytoin, often given to epileptics.

The studies, conducted by William Chelen and five other researchers at the Air Force Institute of Technology, involved measuring subjects' brain waves while they became sick. The subjects sat on a rotating chair and wore a cigar box-sized electroencephalograph (EEG) machine on their heads that recorded the electrical activity from their brains.

"I wanted to look at everything from respiration to the mechanical motion of their intestines to eye motion to skin temperature to their EEG," Chelen said.

Chelen said he included the EEG because he considers it a basic measurement of the way the body works. When he analyzed the EEG waves, he found that many were the same type as some the brain produces in partial seizures, which occur in many epileptics. During these incomplete seizures, the person may shake one part of the body, such as a finger or leg, or may experience strange sensations, such as an unusual smell or a feeling that nearby objects are shrinking or growing.

Chelen reported his findings at the Aerospace Medical Association annual meeting last May.

Monitoring Brain Waves

Previous studies had looked at EEG recordings from volunteers before and after they got sick and had found no evidence of partial seizure changes. But the studies had not been able to monitor brain waves when the symptoms were actually arising because the conventional dishwasher-sized EEG machines are too big to fit on the special type of spinning chair experimenters use to make their subjects sick. To measure the waves, Chelen, an electrical engineer as well as a physician, had to design the cigar-type box.

The most widely accepted explanation of motion sickness is the sensory conflict theory. It says the brain uses three main sensory inputs to determine the body's orientation -- sensation coming from the vestibular apparatus, the tiny fluid-filled organs in the inner ears; proprioception, the input from nerve endings in the muscles and joints telling the brain how the body is positioned; and vision, which gives the brain a third clue as to which way is up.

It is believed that these inputs interconnect in a complex way in the brain stem, the more primitive part of the brain. When the signals disagree, the person gets sick.

Chelen says his findings help explain what happens when the signals conflict.

"This is consistent with the sensory conflict theory," he said. "The error signal {from the conflicting sensations} is the source of the stimulation that's leading to the presumed partial seizure."

The fact that people having partial seizures often feel nauseated, short of breath and sweaty -- much like a motion-sick person -- helps support his theory, Chelen said.

"Think about what happens when you begin retching and vomiting," he said. "You're not in control of it. In a sense that is a definition of a convulsion, an involuntary motor event."

The researchers also found Dilantin more than twice as effective in preventing motion sickness as any drug now available, such as scopolamine and dramamine. Chelen is now studying how well other anti-convulsants work.

If other studies confirm his findings and Dilantin is found to be effective, Chelen said, the drug could help everyone from plane and bus travelers to astronauts. According to the National Aeronautics and Space Administration, two-thirds of space shuttle astronauts develop motion sickness when not given any medication.

But Chelen's findings are controversial. So far, his group is the only one to find the EEG link between epilepsy and motion sickness. And only one of his studies, involving a small sample of seven people, has been accepted for publication. It is to appear in Aviation Space and Environmental Medicine, the journal of the Aerospace Medical Association.

Some also question how safe it is to give travelers Dilantin, a prescription drug whose side effects can include coordination changes, rashes and overgrowth of the gums.

"The medication he's using is pretty heavy-duty stuff," said David R. Jones, an aerospace medicine specialist who is editor of the journal. "It would take a whole lot of work to prove it was so safe that anybody could take it and fly an airplane."

Treating Space Sickness

Richard Jennings, a medical officer with NASA, said the space program is satisfied with promethazine to treat space motion sickness. Promethazine is a sedative, but Jennings said the astronauts are so stimulated by space flight that the drug usually does not make them sleepy.

Space sickness usually begins during the first day in space, but the agency does not schedule space walks during the first three days after liftoff. The worry is that vomiting inside a space suit might cause fatal suffocation. Before the program began using promethazine, space sickness is said to have incapacitated astronauts enough to result in a 10 percent reduction in efficiency.

"If you figure that one flight costs $100 million, you're wasting about $10 million," said Randall Lee Kohl, a NASA motion sickness researcher.

Jones said some may be skeptical about Chelen's work because it is unlike research anyone else is doing.

"It's very original thinking," he said. "It opens a whole new way of looking at motion sickness, it offers a new way of treatment, and also, if it works, it gives us a whole new way of thinking about motion sickness and nausea."