Experiences you have in the here and now could hint at whether you'll see a light at the end of the tunnel when you're close to the hereafter.
A new study finds that people who have had near-death experiences are generally more likely to have difficulty separating sleep from wakefulness.
Researchers surveyed 55 people who'd had a near-death experience (NDE) and 55 who had not. The experience was defined as a life-threatening episode such as a car accident or heart attack when the person experienced a variety of feelings, including:
For 60 percent of those who had been through an NDE, the rapid-eye movement (REM) state of sleep intrudes into their regular consciousness while awake, the study found. Both before and after their traumatic event, these people had experiences that include waking up and not being able to move, sudden muscle weakness in their legs, and hearing sounds that no one else hears upon waking or falling asleep.
Only 24 percent of people who had not had an NDE report this REM intrusion.
Inside your mind
The human arousal system is activated from the brain stem, a primordial control system that manages other vital functions like heartbeat and breathing. We all have a switch there that regulates between REM sleep and being awake, explained study leader Kevin Nelson, a neurologist at the University of Kentucky in Lexington. In people who have had an NDE, the switch is more likely to blend those two states.
"These findings suggest that REM-state intrusion contributes to near-death experiences," Nelson said. "People who have near-death experiences may have an arousal system that predisposes them to REM intrusion."
The results are detailed in the April 11 issue of the journal Neurology.
Near-death experiences are seen by some as evidence for the paranormal, as a link to the world beyond. Not everyone who recovers from being near death or declared clinically dead describes the same eerie sensations, however. Nelson says that about 10 percent of cardiac arrest patients who survive had an NDE during the event.
In a Dutch study of 344 cardiac patients who had been resuscitated after clinical death, 62 of them, or 18 percent, reported an NDE.
What's going on
During REM sleep, many body functions are known to change. Muscles lose their tone, for example.
In a crisis, if the REM-state intrudes on an otherwise awake person, the 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 during danger and brain impairment from lack of blood flow or oxygen could contribute to the experience of near death."
The intrusion might also explain the vivid scenes described by some NDE survivors, such as seeing their own bodies from above during surgery.
"One of the basic features of REM state is activation of the visual system," Nelson said. "REM-state intrusion could promote the prominent visual phenomena of near-death experience."
NDEs appear not to be dreams (http://www.livescience.com/humanbiology/041028_Lost_Dreams.html), however.
"Most dreaming occurs in REM sleep and despite the possible contribution to NDE by REM-intrusion, NDE and dreams fundamentally differ," Nelson explains. "Near-death experiences are recalled with an intense sense of realness that contrasts sharply to dreams. Furthermore, NDEs lack the bizarre characteristics of dreams."
The new study does not answer the question of whether near-death experiences have a biological rather than paranormal basis, Nelson told LiveScience, but he plans further research in an effort to settle that issue.
For now, there are hints that biology and the paranormal might converge. Our emotions are controlled by the brain's limbic system, which is strongly active during REM sleep.
"REM-state intrusion provides a mechanism for robust activation of the limbic system, which is expected to underlie many of the paranormal, transcendental and emotional aspects of NDE," Nelson said.