For hundreds of years, people of all ages from all over the world have been telling similar stories about moments when their lives were in danger: an intense white light, a sense of calm, and the feeling that they somehow hover over their bodies.
For neurologists, these so-called near-death experiences have a neuronal basis that, according to new findings, may be similar to that in the brain that occurs in certain sleep disorders.
"One theory suggests that near-death experiences can occur when the brain is still functionally and structurally intact," Dr. Daniel Kondziella, neurologist at the University of Copenhagen.
Kondziella is the lead author of new research on near-death experiences presented on Saturday at a congress of the European Academy of Neurology. His findings, which have not yet been published in a journal, suggest that the typical features of such episodes as bright white light and a sense of calm are most likely due to neuronal activity in the brain, similar to "I think these experiences can be triggered in situations of imminent death, "Kondziella told NBC News. "But as we perceive these experiences, brain networks are working to save, revive, recapture and share these experiences."
"I think before we faint, they have the near-death experience, so when they are revived, the last thing they remember is that experience," he said.
Near-Death Disorder and Sleep Paralysis
Kondziella's study was based on questionnaires that were sent anonymously to 1,034 people online. The questionnaires started with a single question: Have you ever had a near-death experience?
The definition of such an experience was broad: "Any conscious perceptual experience, including emotional, self-centered, spiritual and / or mystical, occurring in a person near death or in situations of intense physical or emotional danger." And there the answers came from anonymous persons, it was impossible for the researchers to confirm any of the answers.
Apart from these reservations, the researchers found that 106 people or about 10 percent of respondents stated what they considered a "true" near-death experience.
In addition, participants reporting near-episode episodes were more likely to have a history of extreme and vivid sleep disturbances known as REM sleep intrusion (REM is rapid eye movement).
This finding confirmed, according to the researchers, the theory that these experiences have a neurological basis.
"REM sleep is the kind of sleep in which we perform most of our vivid dreaming," Dr. Kevin Nelson, a neuromuscular neurologist at the University of Kentucky. He was not involved in the study, but published similar research more than a decade ago.
Nelson explained that there are only three states of consciousness in which the brain can exist: wakefulness, non-REM sleep, and REM sleep.
] Sometimes I wake up at night and can not move.
During REM sleep, when a person dreams, most muscles in the body are paralyzed, so dreams are not physically performed.
A switch in the brain allows people to seamlessly switch from one state of consciousness to another. But sometimes this switch does not work properly, so the REM sleep and waking up mix together.
"So you have elements of the REM system that occur while a person is essentially awake," Nelson said. "People can wake up and be paralyzed and unable to move, they may have visual or auditory hallucinations, they are usually scared."
This phenomenon is referred to as sleep paralysis and has been described by some respondents in the study. "Sometimes I wake up at night and can not move," wrote one participant. "I see strange things like ghosts or demons at my door, and after a while I see them coming in. I can not move or talk, and they sit on my chest, it scares the hell out of me!" 19659002] A 2011 review found that nearly 8 percent of the world's population experienced at least one episode of sleep paralysis in their lifetime and not all experiences are so alive or scary.
Both Kondziella and Nelson propose the brain mechanisms responsible for this. Sleep disturbances also allow people to visualize experiences when their lives are really in danger. This hypothesis is supported by the finding of the study that there is overlap between those reporting both phenomena.
"People whose brains are more likely to mix REM and wakefulness – in the right circumstances – are more likely to have a near-death experience," Nelson said.
Nelson also said the part of the brain that allows people to know where they are physically located. Getting up, lying down, sitting in a chair – is switched off during REM sleep. This may partly explain why some people have out-of-body experiences.
Are near-death experiences real?
Some external experts were skeptical of the study, notably finding that one in ten people had such experiences had a near-death experience.
"If anything, I think it's more likely that people will mistakenly report sleep events as near-death experiences based on this study," Dr. Donn Dexter, a member of the American Academy of Neurology and a neurologist in the health care system of the Mayo Clinic.
Kondziella quickly defended what people experience as near-death episodes that are often reported to be life-changing and spiritually significant.
"As a scientist, I think there is a biological explanation," he said. "But if there is a deeper meaning for them, then that is a question for philosophers and religious leaders."
All neurologists agreed that there is room for science and belief in the same conversation about near-death experiences.  "You can be a scientist and still have strong faith," said Dexter. "In science you have to have a theory, a hypothesis that you can prove wrong, you can not prove that one's faith is wrong."
"There will always be puzzles that can not be solved," Nelson added. "But it does not hurt the puzzle to know a bit more about it."
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