Common reports of near-death experiences include encountering a bright light, meeting deceased loved ones, and seeing and hearing "real" events from another perspective - often known as an out-of-body experience.
The researchers - led by Dr. Sam Parnia, who was an honorary research fellow at the University of Southampton in the UK when he began this study - publish their findings in the journal Resuscitation.
According to Dr. Parnia, death is a potentially reversible process that happens after a severe injury or illness causes the heart, lung or brain to stop functioning. "If attempts are made to reverse this process, it is referred to as 'cardiac arrest.' However, if these attempts do not succeed it is called 'death,'" he explains.
Patients who experience cardiac arrest and are resuscitated often report a near-death experience (NDE) - described as a lucid experience of perceived consciousness that occurs during impending death.
Although NDEs differ from person to person, common reports of these experiences include encountering a bright light, meeting deceased loved ones, and seeing and hearing "real" events from another perspective - often known as an out-of-body experience.
The researchers note that NDEs are often perceived to be hallucinatory, but that such experiences have not been studied systemically.
"In this study we wanted to go beyond the emotionally charged yet poorly defined term of NDEs to explore objectively what happens when we die, " says Dr. Parnia, now an assistant professor of critical care medicine and director of resuscitation research at the State University of New York, NY.
Mental experiences linked to death may reach further than previously thought
In 2008, Dr. Parnia and his team began the AWAreness during REsuscitation (AWARE) study. The researchers identified 2,060 cardiac arrest survivors from 15 hospitals in the UK, US and Australia.
Of the survivors who underwent an interview about any mental experiences related to death and reported some sense of awareness during resuscitation, 39% were unable to recall any specific details.
"This suggests more people may have mental activity initially but then lose their memories after recovery, either due to the effects of brain injury or sedative drugs on memory recall," says Dr. Parnia.
Some of the survivors who reported a sense of awareness during resuscitation completed another interview.
The team notes that only 9% of survivors reported mental experiences compatible with NDEs, while 46% reported experiencing an array of death-related mental recollections that were not consistent with the traditional definition of NDE. Some survivors reported fearful and violent experiences, for example, while others reported remembering events prior to cardiac arrest or family members.
Dr. Parnia and his team note that this finding suggests the mental experiences associated with death may reach further than those traditionally linked to NDEs.
3-minute out-of-body experience validated in one patient
Complete awareness consistent with out-of-body experiences, such as "seeing" and "hearing" events linked to resuscitation, was reported in 2% of patients.
One survivor's experience of this was monitored and timed via auditory stimuli during cardiac arrest.
"This is significant," Dr. Parnia notes, "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."
It is believed that the brain stops functioning within 20-30 seconds of the heart stopping. But the monitored patient appeared to see and hear surrounding events for up to 3 minutes after their heart had stopped beating. When the patient awoke, the events and sounds they described in this 3-minute window were consistent with what actually occurred.
Commenting on their findings, Dr. Parnia says:
"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 of explicit recall of visual awareness or so-called out-of-body experiences), 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."
The researchers add that further research is warranted to determine if awareness during cardiac arrest could lead to long-term psychological issues, such as post-traumatic stress disorder (PTSD).
Last year, Medical News Today reported on a study by researchers from the University of Michigan claiming NDEs are electrical surges in the brain.