It is estimated that as many as 18 percent of people who have been resuscitated after cardiac arrest have reported a near-death experience. ­Courtesy StockXchng­

In 1991, Atlanta, Ga. resident Pam Reynolds had a near-death experience (NDE). Reynolds underwent surgery for a brain aneurysm, and the procedure required doctors to drain all the blood from her brain. Reynolds was kept literally brain-dead by the surgical team for a full 45 minutes. Despite being clinically dead, when Reynolds was resuscitated, she described some amazing things. She recounted experiences she had while dead -- like interacting with deceased relatives. Even more amazing is that Reynolds was able to describe aspects of the surgical procedure, down to the bone saw that was used to remove part of her skull [source: Parker].

What's remarkable (although not unique) about Reynolds' experience is that it is the combination of an NDE and an out-of-body-experience (OBE). HowStuffWorks has braved this territory on the edge of reality, explaining how near-death experiences work and how a person can have an out-of-body experience. Science, too, has made its own headway toward explaining these weird phenomena. Two studies on the separate aspects of Reynolds' experience were conducted in 2007. Each seems to explain how a person can have an OBE or a NDE, but do they hold up in explaining experiences like Reynolds'? ­­



­As many as 18 percent of people brought back from death after a heart attack said they'd had a NDE [source: Time]. While many religious adherents might not be surprised by these accounts, the idea that human consciousness and the body exist distinctly from each other flies in the face of science. A brain-dead person should not be able to form new memories -- he shouldn't have any consciousness at all, really. So how can anything but a metaphysical explanation cover NDEs?

A study from the University of Kentucky has quickly gained ground among scientists as possibly the best explanation for NDEs. Researchers there theorize that the mysterious phenomenon is really an instance of the sleep disorder rapid eye movement (REM) intrusion. In this disorder, a person's mind can wake up before his body, and hallucinations and the feeling of being physically detached from his body can occur.

The Kentucky researchers believe that NDEs are actually REM intrusions triggered in the brain by traumatic events like cardiac arrest. If this is true, then this means the experiences of some people following near-death are confusion from suddenly and unexpectedly entering a dream-like state.

This theory helps explain what has always been a tantalizing aspect of the mystery of NDEs: how people can experience sights and sounds after confirmed brain death. The area where REM intrusion is triggered is found in the brain stem -- the region that controls the most basic functions of the body -- and it can operate virtually independent from the higher brain. So even after the higher regions of the brain are dead, the brain stem can conceivably continue to function, and REM intrusion could still occur [source: BBC].

This sounds like a good explanation for NDEs, but what about OBEs? Are they the same thing? Read the next page to discover the distinctions between near-death and out-of-body experiences.