Barbara Harris Whitfield has heard 22 scientific explanations for near-death experiences like the one she had in 1975. So far, she isn't satisfied by any of them.
"Yes it was brain chemistry that might have fine tuned my ability to pick up this," said Whitfield, 67, an author and therapist in private practice in Atlanta, Ga. "I think the brain is like the radio, and what [science is] explaining is the hardware of the radio, but what we can't explain is the broadcast."
Whitfield doubts science can ever completely explain her experiences when a ventilator malfunctioned as she recovered from spine surgery.
Yet scientists continue to search, and some are intrigued by a small study of cardiac arrest survivors that shows there may be a physical link between carbon dioxide in the blood and the likelihood that someone will wake up remembering floating above their body and moving towards a peaceful light.
The study, published in the journal Critical Care, surveyed 52 people in local hospitals who were revived from clinical death. Eleven people or 21 percent of the group, remembered experiences commonly reported in nearly all near-death experience descriptions. The survivor's religious beliefs, age or sex weren't statistically significant influences on whether they had a near-death experience or not.
But the higher the carbon dioxide level, the more likely the person was to report a near-death experience.
"I think that science can find physical explanations to a lot of questions, but, at the moment, I don't think that near-death experiences are one of them," said Dr. Zalika Klemenc-Ketis, lead author of the study and member of the department of family medicine at the University of Maribor in Slovenia. "They are connected to consciousness -- and the relationship between body and mind is not clear."
Klemenc-Ketis said it is not clear from her research whether the high carbon dioxide levels caused a near-death experience.
"It may simply reflect the fact that higher carbon dioxide levels during resuscitation reflect better blood flow through the brain -- and these people might simply have a better memory of the near-death experience," said Klemenc-Ketis.
Professor Chris French, editor of The Skeptic magazine in the United Kingdom, said three factions have been prying into near-death experiences for years, including scientists looking for physiological explanations.
"Typically people often report a feeling of bliss, an out of body experience as if they are watching the experience from some sort of vantage point... they may report idyllic landscapes or amazing cities -- you can see why people would see thing as some sort of evidence of an afterlife," said French.
"Are these visions of life after death, or are these visions of a dying brain? I would argue that a dying brain is the best approach," said French who is head of the anomalistic psychology research unit at Goldsmiths University of London. "What I like about this physiological work is that it generates testable hypothesis."
Psychologists have also offered explanations, which are much harder to test. French said one popular theory hypothesizes that a near-death experience is a way for the brain to disassociate from the extreme stress of dying and help a person cope.
A third faction, according to French, are theologians who say a near-death experience is a separation of spirit or consciousness from the mind.