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.
Whitfield, who said she was an atheist before her near-death experience, takes this particular view.
Whitfield was 32 when a swimming pool accident knocked loose a vertebra in her lower spine. She was in the hospital recovering from major spinal surgery and strapped to a hospital bed when the accident with the ventilator occurred.
"They would come in with a ventilator three times a day," said Whitfield, author of "The Natural Soul."
"The ventilator malfunctioned, it didn't reverse, it just kept flowing," she said.
By the time nurses figured out what happened, air had filled her lungs and her intestinal tract to the point where she looked pregnant. Whitfield remembers she blacked out and when she woke up, she found herself outside of her hospital room in the hallway near the ceiling.
"I thought, 'If I stay out here (I'm) going to be in trouble'," said Whitfield. "That's how innocent I was to this whole thing."
Whitfield said she briefly saw her body below her before a darkness enveloped her. Her dead grandmother soon appeared and she relived, jointly, their history on earth together.
"That alone would have been enough to change me forever," said Whitfield. "I would stop telling people [nurses] because I would get upset and then they'd sedate me. They would tell me it was a hallucination, and I didn't' want to hear it was a hallucination."
A week later, Whitfield faced death again. A nurse positioned her face-down in her hospital bed to prevent bedsores. A nurse was supposed to come back in 20 minutes to move her upright, but nobody showed up. Whitfield was stuck in agony and had no idea how long she waited before she blacked out.
"At this point I saw myself as I was leaving my body. I saw myself in the circle bed. I looked up at the darkness and I saw myself as a baby in a crib," said Whitfield.
Whitfield said a benevolent force enveloped her, bringing an overwhelming sense of peace. She traveled with the force and relived scenes from her entire life up to that point. When she came to, she said the experience changed her life forever, but it took years before she told anyone.
"I agree when they [scientists] explain it on an anatomical way, but they can't explain what we go to when we experience this," said Whitfield.
Dr. Sam Parnia, an intensive care physician who studies near-death experiences, said he too sees the problem with trying to explain near-death experiences with a physiological process.
"One of the things that I've heard being bandied about is because we believe that such and such a chemical has been associated with a near-death experience, therefore NDE is a hallucination," said Parnia. "This is really fraught because every human experience is triggered off by some kind of chemical change in the brain."
Parnia pointed out that aside from one reference to a 1950 text book which is out of print, nothing he's read in the medical literature has been able to mimic a near-death experience with a chemical. He made the analogy of the release of endorphins or hormones with a person who experiences love for their child.
"You can't say your love was a hallucination, because we find the chemical pathways that simulate love," said Parnia, who is based at Weill Cornell Medical Center in New York City and the University of Southampton in England. "If there is a chemical, that doesn't mean that the experience isn't real, it doesn't mean that he experienced a hallucination.
However, Parnia believes science can still test near-death experiences. Parnia leads the multi-institutional AWARE study by the Human Consciousness Project in which different hospitals around the world place "targets" or objects only visible from the ceiling in hospital rooms. When a patient who is resuscitated reports a near-death experience, including floating above the body, researchers check to see if they saw the object.
"We're actually going through the data now and we'll have an answer in a year's time," said Parnia. They have 700 cases to go through."