One in ten cardiac-arrest patients report 'near-death experiences'. Now a large-scale study aims to find out what's going on

When Jeanette Atkinson was 18 years old she was admitted to hospital with deep-vein thrombosis and seven pulmonary embolisms (blood clots on the lungs). At 9pm, Jeanette remembers the light changing, and she had the sensation of floating out of her body, down the ward and past the nurse station. The light changed again, and she found herself entering a long black tunnel. "It was turning like a corkscrew and at the bottom of this tunnel were these most fantastic lights, just like a child's kaleidoscope," she recalls. "I was going towards these lights and it was wonderful, it was peaceful, and then all of a sudden, a voice said to me: 'Come on you silly old cow, it's not your turn yet.' And I was back in my body. Back in pain, with a crash team round me. I don't remember anything else after that."

Jeanette had a strange but by no means unique experience. As many as one in 10 patients who recover from cardiac-arrest report a near-death experience (NDE), a term that came into common use in 1975 after the American physician, Raymond Moody, published the seminal book on NDE, Life after Life. It sold more than 13 million copies. Everyone wanted proof of eternity, and Moody seemed to supply it. Since then, much of the excitement has waned. People have made up their minds: either they believe NDE to be real, or they think it's just New Age mumbo jumbo; opinions have become entrenched. Nevertheless, serious scientific research has been going on in the USA, the UK and Holland.

In the UK, Dr Sam Parnia, of Southampton University, and Dr Peter Fenwick, a neuropsychiatrist, are about to embark on a large-scale study that will, among other things, look at the phenomenon of out-of-body experience (or, to use the medical parlance, "veridical perception"). They will place objects out of the line of sight of cardiac patients and ask them to report on what they saw during their out-of-body experience. Smaller studies have so far proved inconclusive. Dr Parnia and Dr Fenwick's study will cover at least a dozen hospitals in the UK.

Many people who have an NDE have reported similar experiences: a feeling of floating out of the body; a journey through a dark tunnel; a light at the end of the tunnel; feelings of indescribable joy, love and peace. Sometimes they meet a supernatural being, maybe Jesus or Buddha. There may be a reunion with deceased relatives or friends. There is often a review of their life. At some point on this journey, they get a strong pull to go back, because it's not their time yet. These experiences are fairly consistent, regardless of culture, age or religious conviction.

These people have all been dead, in a clinical sense - in other words, they have no pulse, and their pupils are fixed and don't react to strong light. Of course, they're not brain dead. There's no coming back from brain death. So are they really dead? This has been a bone of contention throughout the whole NDE field. Surely this is just a dream? An hallucination caused by a brain starved of oxygen and sugar? But Dr Parnia points to studies that have shown that during cardiac arrest and advanced cardiac life support, global brain function ceases. EEG studies have shown that electrical activity in the brain ceases at least 10 seconds prior to the heart stopping, and doesn't show any activity for up to two hours after the heart has been started again.

Of course, there's nothing to say that these experiences don't happen during the recovery phase. This is one of the arguments Dr Parnia wants to verify, by hiding his test objects in places that are only visible from above. "The key to solving this mystery lies in the accurate timing of the experiences," he says. "If it can be proven that this period of consciousness has indeed taken place during cardiac arrest, it will have huge implications."

But not everyone in the scientific world is prepared to accept that the mind and the brain might be separate entities. After a near-death experience of her own, Dr Susan Blackmore began studying the phenomenon, but the more she examined NDE, the less convinced she became of a transcendental explanation for it.

Meanwhile, the researchers Stanislav Grof and Joan Halifax have claimed that NDEs are simply the patient reliving their birth experience. Bright light at the end of the tunnel - the opening of the womb. An ineffable being suffused in white light - the midwife. Others have claimed that the experiences are mere hallucination. But why would everyone share the same hallucination on their deathbed?

As Moody says in Life after Life: "[People] will regard their own orientations as sources of explanations that are intuitively obvious, even when cases are brought up that seem to weigh against that particular explanation. Those who espouse the theories of Freud delight in seeing the being of light as a projection of the subject's father, while Jungians see archetypes of the collective unconsciousness, and so on."

But Dr Blackmore has examined all the arguments and believes she knows what causes these NDE visions. Firstly, the light at the end of the tunnel is simply "noise" in the visual cortex. It is often experienced by epileptics, migraine sufferers and those who meditate. It is not unique to NDE. The out-of-body experience? Well, if you think about the last time you walked along a beach, for example, where do you see yourself? Probably not through your eyes, but from a vantage point above or to the side of you. Most people have a bird's-eye view of themselves when remembering past events. What Blackmore found in her own studies is that people who dream from a bird's-eye perspective are more likely to have out-of-body experiences.

The American cardiologist Michael Sebom, said that some of his patients reported the exact behaviour of needles on monitoring apparatus, even though their eyes had been shut and they had been unconscious. But Dr Blackmore reminds us that the last sense to be lost is our hearing. Isn't it possible that these cardiac-arrest survivors are remembering conversations between medical staff? If Dr Parnia's study shows results, this is exactly the sort of thing that could be ruled out. An unconscious patient, even with their hearing still functioning, couldn't know that there is a red triangle taped to the top of a medical cabinet.

As for the survivors' lives flashing in front of their eyes, Dr Blackmore says that people who suffer from temporal lobe epilepsy have similar experiences. In fact, "life reviews" have been artificially induced in subjects by stimulating their temporal lobes. And the feel-good factor could simply be a release of endogenous endorphins into the brain during the trauma.

However, Dr Parnia says that these are only theories. Whether these experiences are transcendental, psychological or physiological is still open to debate. What is certain, however, is that NDEs are life- changing. "I don't fear death any more," says Jeanette. "For me, death is a progression of life. You go on to somewhere better."

"My first near-death experience was more real than ordinary life," says Dr Blackmore. "You feel as though you've woken up for the first time and that this is real and ordinary life isn't. But good science will explain those experiences to people and help them to value them, without making false leaps into paranormal belief."

So Dr Parnia and Dr Fenwick may never prove that the mind is separate from the brain, but even if they don't, their study could provide other benefits: "We may also be able to discover the biochemical pathways that convey the sense of joy that accompanies NDEs, and in so doing harness their power to treat patients with severe depression," says Dr Parnia.