The mystery of why people 'brought back from the dead' report powerful spiritual experiences may have a biological explanation, according to experts.
Researchers who studied brainwaves of dying patients, found there was a surge of electrical activity in their brains just moments before their lives ended.
The doctors from George Washington University medical centre in Washington believe this surge may be the cause of near-death experiences, where patients see themselves walking towards a bright light or floating outside their bodies.
Many patients who experience these sensations believe they are having a religious vision and treat it as confirmation of an afterlife.
Some revived patients even reported seeing religious figures such as Jesus, Muhammad or Krishna. Others said they felt suffused with a sense of peace as they start to walk into a light-filled tunnel.
However, the intensive care doctors at George Washington have an alternative biological explanation, which has been published in the Journal of Palliative Medicine.
A team led by Dr Lakhmir Chawla used an electroencephalograph (EEG), a device that measures brain activity, in seven terminally ill people to provide pain-relieving sedation.
Dr Chawla noticed moments before death patients experienced a burst of brainwave activity that lasted from 30 seconds to three minutes.
The activity was similar to that measured in fully conscious people. Soon after the surge the patients were declared dead.
'We think the near-death experiences could be caused by a surge of electrical energy released as the brain runs out of oxygen,' Dr Chawla told The Times.
'As blood flow slows down and oxygen levels fall, the brain cells fire one last electrical impulse. It starts in one part of the brain and spreads in a cascade and this may give people vivid mental sensations.'
He added that he had seen the same phenomenon in around 50 other patients.
However, Sam Parnia, leader of the Awareness During Resusciation study in the UK, said Dr Chawla's conclusions should be treated with caution.
Dr Parnia said there was no proof that the electrical surge is linked to near death experiences as all the patients died.
His team are currently interviewing 700 Britons who have been brought back to life after cardiac arrests to study the mental consequences of the experience.
'We see death as a moment, but actually it is a process and one which modern medicine can often reverse,' he said.
Near death experiences have been found to have a positive effect on the majority of patients, whatever their cause.
A Dutch study published in The Lancet in 2001 found around one in five cardiac arrest victims underwent a near-death experience. They found these patients tended to feel happier, more altruistic and less afraid of death later on.
