Some describe a journey along a tunnel towards a light. Many say the light exudes warmth and forgiveness. Others report that gazing down on themselves in an operating theatre made them certain of life after death.
Throughout history, there have been accounts of people experiencing visions on the brink of death, what are now called near-death experiences. There are dozens of books and films on the subject, even a Journal of Near Death Studies in America, and a conference planned this October in Houston, Texas.
Today, new evidence is published that backs the idea that the near-death experience is a biological experience, rather than anything to do with a larger, spiritual dimension, a glimpse of heaven, or the existence of the soul.
People who have had near- death experiences are able to slip into dream sleep more easily than those who have not had one, according to a study published in Neurology, the journal of the American Academy of Neurology.
“I see it as an activation of certain brain regions that are also active during the dream state,” said Prof Kevin Nelson, a neurologist and lead study author, from the University of Kentucky, Lexington.
“However, I hesitate to call it dreaming or dreaming while awake. This is the first testable hypothesis of a biological basis for these experiences.”
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For his study, a near-death experience was defined as a time during a life-threatening episode when a person experienced a variety of feelings, including a sense of being outside of one’s body, unusual alertness, seeing an intense light, and a feeling of peace.
The study compared 55 people with near-death experiences with 55 people of the same age and gender who had not had them.
It found that people with near-death experiences were more likely to have a sleep-wake system in which the boundaries between sleep and wakefulness were not as clearly regulated, and the dream sleep state – when there is rapid eye movement – can intrude into normal wakeful consciousness.
Examples of “REM intrusion” include waking up and feeling that you cannot move – sleep paralysis – having sudden muscle weakness in your legs, and hearing sounds just before falling asleep or just after waking up that other people cannot hear.
Of the people with near- death experiences, 60 per cent reported REM intrusion, compared with 24 per cent of people who had not had near-death experiences.
“These findings suggest that REM-state intrusion contributes to near-death experiences,” said Prof Nelson.
Prof Nelson said other factors supported this. Several features of near-death experiences are also associated with the dream state, for example, the feeling of being outside of one’s body and being surrounded by light.
Because the brain turns off the body’s ability to move during dreaming, 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,” Prof Nelson said.
He added that a biological explanation was “spiritually neutral”. “We, as neurologists, address the how of these experiences coming about but not the why,” he said.