Using virtual reality, volunteers mimicked the near-death phenomenon
THURSDAY, Aug. 23 (HealthDay News) -- European scientists have come close to replicating the mysterious "out-of-body" experience that trauma survivors sometimes report feeling as death nears.
The results of two experiments on healthy volunteers, reported in the Aug. 24 issue of Science, offer what experts call a plausible neurological explanation for these uncanny events.
An "out-of-body" experience is the feeling of corporal detachment and of looking at your own body from some distance, and it may arise when various sensory systems or "modalities" -- vision, touch and the sense of being in your body, called proprioception -- become disconnected under stress.
The new research "shows that the integration of various sensory modalities is important for retaining our sense of where our body is, of where our self is in that body," explained Dr. Kevin Nelson, a leading researcher on near-death phenomena who was not involved in either of the new studies.
Far from being a rare occurrence, the "out-of-body" experience is actually quite common, as Nelson's own work has shown. "In fact, one of 20 people have had 'out-of -body' experiences," said Nelson, who is a neurology professor at the University of Kentucky in Lexington. "In our study of 55 normal, everyday people, 3 -- about 6 percent -- had had an 'out-of-body 'experience."
Still, it has been tough to fully investigate "out-of-body" experiences, because they are so uncontrolled and spontaneous.
So, in the two Science studies, researchers tried to recreate them for healthy volunteers.
In one case, volunteers in London were equipped with high-tech 3-D goggles with which they viewed a real-time 3-D film of their own bodies, taken from a perspective of about six feet behind them.
At the same time, a researcher used two plastic rods to simultaneously touch the volunteer's real chest (out of his or her view) and the filmed -- but distant -- version of their chest in exactly the same spot.
The result, according to the participants, was the sensation of sitting behind their physical body and looking at it from that six-foot distance.
"This was a bizarre, fascinating experience for the participants -- it felt absolutely real for them and was not scary," the author the study, Dr. Henrik Ehrsson of the University College London's Institute of Neurology, said in a prepared statement.
Ehrsson even used a hammer to create the illusion that the distant, illusory body was going to be hit. When that happened, sensors on the volunteers' skin showed increased sweating, indicating that they felt the threat was real.
Another team, this time led by Olaf Blanke of the Ecole Polytechnique Federal de Lausanne, in Switzerland, tried a slightly different experiment. In this case, the participants watched one of three 3-D holographic projections: of their own body, the body of a dummy, or a square block placed directly in front of them.
In each instance, the image's "back" was stroked with a brush, sometimes in sync with a brush being stroked on the volunteer's own back. Immediately afterwards, the person was blindfolded and backed up, then told to return to where he believed he had been standing before.
If the participants had viewed either the dummy body or the block, they invariably returned to the correct spot, suggesting that they had not lost the notion of their actual body's position. However, participants who had viewed the 3-D likeness of themselves typically overshot the mark and advanced to where the illusory duplicate had been.
One expert called the findings "intriguing."
"You are feeling this touch as if you are watching it -- like you are somewhere else," said Paul Sanberg, director of the Center of Excellence for Aging and Brain Repair at the University of South Florida College of Medicine in Tampa.
"It's like those video games where you are driving a car, but the car is in front of you," he reasoned. "You aren't actually in the car, but, in essence, I think some people think they are in the car."
While Ehrsson claims to have recreated a true "out-of-body" experience in the lab, Blanke's group doesn't go so far. They noted that the participants said they understand that the video "them" was just an illusion -- whereas people who typically have "out-of-body" experience believe they are observing their own body. "We have only induced some aspects of 'out-of-body' experience," the Swiss team concluded.
Nelson believes that neither team fully replicated the "out-of-body" state but did create a convincing "illusion."
"I think these are very clever and interesting experiments," he added. "And I think they show the importance of the visual system in how we integrate our identity of self in space."
In other words, the two experiments create a visual illusion that is so convincing to the brain that it somehow disrupts the usually seamless integration between the eyes, touch and proprioception, Nelson said. The result -- which might also occur during sleep-wake transitions, as the brain is put under stress near death, or in certain medical conditions -- is that sensation of temporarily losing contact with the body.
None of this means that vision is the key component, Nelson said. "If we were able to manipulate another [sense] in such a comprehensive or complete fashion, maybe we'd get similar results," he added.
"There's a simple way of proving that," he said. "Close your eyes. Can you still tell where you are or where your body is? You can. You have no visual input, yet you still retain that sense of self and where you are in space."
He agreed with Blanke that your close identification with your own body was essential to the illusion, since viewing a dummy body had no effect.
"Full body consciousness seems to require not just the 'bottom up' process of correlating sensory information but also the 'top down' knowledge about human bodies," Blanke said in a statement.
The new findings have implications beyond neuroscience, he added. They might lead to better and more "real" video gaming technologies, or even surgeries where doctors conduct procedures from a distance.
Blanke's research team even included one philosopher -- because the connection between the body and consciousness runs to the heart of much of theology and philosophy.
Nelson said it's tempting -- but probably erroneous -- to infer any higher spiritual meaning from these scientific findings, however.
"Does this ultimately prove a certain duality or spiritual, Platonic kind of existence?" he said. "No, these are totally separate [investigations], and people get them muddled and confused."
For more on the human brain, head to the BrainExplorer.
SOURCES: Kevin Nelson, M.D., professor, neurology, University of Kentucky, Lexington; Paul Sanberg, Ph.D., distinguished university professor and director, Center of Excellence for Aging and Brain Repair, University of South Florida School of Medicine, Tampa; Aug. 23, 2007, statement, Ecole Polytechnique Federale de Lausanne; Aug. 23, 2007, statement, University College London; Aug. 24, 2007, Science
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