People may still have consciousness after "death" according to a new study.
A large-scale study involving 2,060 patients from 15 hospitals in the UK, USA and Austria has found that patients experience real events for up to a three-minute period after their heart has stopped beating.
Dr Sam Parnia, assistant professor of critical care medicine and director of resuscitation research at the State University of New York and a former research fellow at the University of Southampton, explained that it was previously thought that only hallucinatory events were experienced in these circumstances.
These are normally described as out-of-body experiences (OBEs) or near-death experiences (NDEs).
The Awareness during Resuscitation (Aware) study, sponsored by the University of Southampton in the UK, used objective markers to establish whether the experiences were real or hallucinatory.
The results showed that 39% of patients who survived cardiac arrest described a perception of awareness but did not have explicit recall.
A total of 46% experienced a broad range of mental recollections 9% had experiences compatible with NDEs and 2% exhibited full awareness compatible with OBEs with explicit recall of "seeing" and "hearing" events.
And one case was validated and timed using auditory stimuli during cardiac arrest.
Dr Parnia said: "This is significant, since it has often been assumed that experiences in relation to death are likely hallucinations or illusions, occurring either before the heart stops or after the heart has been successfully restarted, but not an experience corresponding with 'real' events when the heart isn't beating.
"In this case, consciousness and awareness appeared to occur during a three-minute period when there was no heartbeat.
"This is paradoxical, since the brain typically ceases functioning within 20-30 seconds of the heart stopping and doesn't resume again until the heart has been restarted.
"Furthermore, the detailed recollections of visual awareness in this case were consistent with verified events.
"Thus, while it was not possible to absolutely prove the reality or meaning of patients' experiences and claims of awareness, (due to the very low incidence - 2% - of explicit recall of visual awareness or so called OBEs), it was impossible to disclaim them either and more work is needed in this area.
"Clearly, the recalled experience surrounding death now merits further genuine investigation without prejudice."
Dr Jerry Nolan, editor-in-chief of the journal Resuscitation which has published the research, said: "The Aware study researchers are to be congratulated on the completion of a fascinating study that will open the door to more extensive research into what happens when we die."