For the study, a near death experience was defined as a time during a life-threatening episode of danger such as a car accident or heart attack when a person experienced a variety of feelings, including a sense of being outside of one's physical body, unusual alertness, seeing an intense light, and a feeling of peace.
The study, which is published in Neurology's "Views & Reviews" section, compared 55 people with near death experiences to 55 people of the same age and gender who had not had near death experiences.
The study found that people with near death experiences are more likely to have a sleep-wake system where the boundaries between sleep and wakefulness are not as clearly regulated, and the REM (rapid eye movement) state of sleep can intrude into normal wakeful consciousness. Examples of this REM intrusion include waking up and feeling that you cannot move, having sudden muscle weakness in your legs, and hearing sounds just before falling asleep or just after waking up that other people can't hear.
Of the people with near death experiences, 60 percent reported having times of this REM intrusion, compared to 24 percent of people who had not had near death experiences.
"These findings suggest that REM state intrusion contributes to near death experiences," said neurologist and study author Kevin R. Nelson, MD, FAAN, of the University of Kentucky in Lexington. "People who have near death experiences may have an arousal system that predisposes them to REM intrusion."
Nelson said several other factors support this hypothesis. Several features of near death experiences are also associated with the REM state. For example, the feeling of being outside of one's body has been associated with the REM state and the conditions of sleep paralysis, narcolepsy and seizures. The feeling of being surrounded by light could be based on the visual activity that occurs during the REM state, Nelson said. During the REM state, the muscles can lose their tone, or tension.
"During a crisis that occurs with REM state intrusion, this lack of muscle tone could reinforce a person's sense of being dead and convey the impression of death to other people," Nelson said.
REM state intrusion is also associated with other disorders, including narcolepsy and Parkinson disease.