Some people whose brains flatline but survive can recall lucid 'experiences of death'

Nurse checks patient's pulse. — Normally, the brain has "braking systems" in place that filter most elements of brain function out of our experience of consciousness.

(Image credit: Henry King via Getty Images)

What happens when we actually die — when our heart stops and all electrical activity "flatlines" in our brain?

Humans have been asking this question since time immemorial. It's a tough one because the dead do not normally ping back to us about the nature of their experiences. Religious texts are capable of supplying a multitude of explanations. But scientists have not given up on providing their own set of answers, and they are making some strides in better understanding the brain's process of transitioning from life to death.

Most recently, this has become possible because of research that has monitored the brains of people who have been in the throes of actually dying. Some of these individuals have been able to report back about what they experienced. According to findings published on Sept. 14 in the journal Resuscitation, the flatlined brains of some cardiac arrest patients burst into a flurry of activity during CPR, even though their heart stopped beating up to an hour. A small subset of study participants who survived were able to recall the experience, and one person was able to identify an audio stimulus that was played while doctors were trying to resuscitate them.

The researchers interpret the brain recordings they made of these patients as markers of "lucid, recalled experiences of death" — an observation that has "never been possible before," says lead author Dr. Sam Parnia, an associate professor of medicine at NYU Langone Health and a longtime researcher of what happens to people as they die. "We've also been able to put forward a coherent, mechanistic explanation for why this occurs."

"Recalled experiences of death" — a term Parnia prefers over "near-death experiences" for accuracy — have been reported across diverse cultures throughout recorded history. Some Western scientists previously dismissed such stories as hallucinations or dreams, but recently a few research teams have begun to pay more serious attention to the phenomena as a means to investigate consciousness and shine light on the mysteries of death.

In the new study, Parnia and his colleagues sought to find a biological signature of recalled experiences of death. They teamed up with 25 hospitals, primarily in the U.S. and the U.K. Medical personnel used portable devices that could be placed on the heads of patients who were having a cardiac emergency to measure their brain oxygen levels and electrical activity without interfering with their medical treatment. The researchers also tested for conscious and unconscious perceptions by placing headphones on patients that played a repeated recording of the names of three fruits: banana, pear and apple. In terms of unconscious learning, a person who does not remember hearing these fruit names but is asked to "randomly think of three fruits" may still give the right answer, Parnia says. Past research has shown, for example, that even people in a deep coma can unconsciously learn the names of fruits or cities if those words are whispered in their ear.

Between May 2017 and March 2020, 567 people suffered cardiac arrests at participating hospitals. Medical staff managed to gather usable brain oxygen and activity data from 53 of these patients, most of whom showed an electrical flatline state on electroencephalographic (EEG) brain monitors. But about 40% then experienced electrical activity that reemerged at some point with normal to near-normal brain waves that were consistent with consciousness. This activity was sometimes restored up to 60 minutes into CPR.

Of the 567 total patients, just 53 survived. The researchers conducted interviews with 28 of the survivors. They also interviewed 126 people from the community who had gone through cardiac arrests because the sample size of survivors from the new study was so small. Nearly 40% reported some perceived awareness of the event without specific memories attached, and 20% seemed to have had a recalled experience of death. Many in the latter group described the event as a "moral evaluation" of "their entire life and how they’ve conducted themselves," Parnia says.

He and his colleagues have developed a working hypothesis to explain their findings. Normally, the brain has "braking systems" in place that filter most elements of brain function out of our experience of consciousness. This enables people to efficiently operate in the world, because under regular circumstances, "you couldn't function with access to your whole brain’s activity being in the realm of consciousness," he says.

In the dying brain, however, the researchers hypothesize that the braking system is removed. Parts that are normally dormant become active, and the dying person gains access to their entire consciousness — "all your thoughts, all your memories, everything that's been stored before," Parnia says. "We don't know the evolutionary benefit of this, but it seems to prepare people for their transition from life into death."

The findings also raise questions about the brain’s resiliency to oxygen deprivation. It could be, Parnia says, that some people who have conventionally been thought to be beyond the point of saving could in fact be revived. "The traditional thinking among doctors is that the brain, once deprived of oxygen for five to 10 minutes, dies," he says. "We were able to show that the brain is quite robust in terms of its ability to resist oxygen deprivation for prolonged periods of time, which opens up new pathways for finding treatments for brain damage in the future."

The new study "represents a Herculean effort to understand as objectively as possible the nature of brain function as it may apply to consciousness and near-death experiences during cardiac arrest," says Dr. Lakhmir Chawla, an intensive care unit physician at Jennifer Moreno Department of Veterans Affairs Medical Center in San Diego, California, who was not involved in the research but has published papers on spikes of EEG activity at the time of death in some patients.

Rachel Nuwer is a freelance science journalist and author who regularly contributes to Scientific American, the New York Times and National Geographic, among other publications.