Researchers conducting the largest ever study into near-death experiences have discovered that awareness may continue even after the brain has shut down, revealing more about what happens when we die.
Scientists at the University of Southampton studied more than 2,000 people who suffered cardiac arrests at 15 hospitals across Britain, Austria and the United States.
Around 40% of patients who survived described "awareness" during the time before their hearts were restarted, when they were clinically dead.
One 57-year-old man, a social worker from Southampton, described the noise of the machines and what the medical staff were doing during this time.
Dr Sam Parnia, who led the study, told the Daily Telegraph: "We know the brain can't function when the heart has stopped beating. But in this case, conscious awareness appears to have continued for up to three minutes into the period when the heart wasn't beating, even though the brain typically shuts down within 20 to 30 seconds after the heart has stopped."
"The man described everything that had happened in the room, but importantly, he heard two bleeps from a machine that makes a noise at three minute intervals. So we could time how long the experience lasted for," he added.
"He seemed very credible and everything that he said had happened to him had actually happened."
For the study, the scientists examined 2,060 cardiac arrest patients. Of the 330 that survived, 140 said they had experienced some kind of awareness while being resuscitated.
One in five said they felt a sense of peacefulness. Some said they saw a bright light and felt time had sped up or slowed down, while others described the feeling as drowning or being submerged in deep water.
Parnia suggested more people may have similar experiences when close to death, but medication used in resuscitation may prevent them from remembering.
"Estimates have suggested that millions of people have had vivid experiences in relation to death but the scientific evidence has been ambiguous at best. Many people have assumed that these were hallucinations or illusions but they do seem to have corresponded to actual events."
"And a higher proportion of people may have vivid death experiences, but do not recall them due to the effects of brain injury or sedative drugs on memory circuits," Parnia said, adding that further research was needed.
Parnia is the principal investigator of the Aware study (Awareness during Resuscitation), which was launched in 2008 to examine near-death experiences during cardiac arrest with methods aimed at measuring the quality of oxygen delivered to the brain.
"When you think about it, most people out there think of death as a moment, you're either dead or you're not," Parnia told US news programme Today in 2009. "But what we've found is there is no moment of death; it begins when your heart stops, and it goes on for a period of time."
The research was published in the journal Resuscitation.