A growing body of evidence suggests that the loss of consciousness after death is much less immediate than previously thought. 

Nearly 20% of people who were revived after being declared clinically dead reported that they remained alert, though they were unable to move. Some of them even heard their own time of death announced.

These findings challenge long-held beliefs about the nature of death, and lend credence to claims of “out-of-body” or “life-after-death” experiences.

Though the heart stops, senses continue

Over the last decade, Dr. Sam Parnia of NYU’s Langone School of Medicine has tracked the brain activity of thousands of subjects in the United States and Europe, charting what happens to the brain in the minutes and hours after cardiac arrest — when the heart ceases to beat.

The American Heart Association defines cardiac arrest as the interruption of the electronic impulses which cause the heart muscle to expand and contract. Death shortly follows.

And conventionally, that is how doctors have always determined a person’s time of death, Parnia told LiveScience — based on the moment the heart stops. 

A surprising number of patients who were brought back to life said they had the capacity to see or hear even after being officially declared dead.

He said that following the loss of heartbeat, brain function ceases “almost instantaneously” and the body stops producing basic reflexes such as gag reflex or pupil dilation.

Because the heart isn’t beating and the body has seemingly stopped responding to outside stimuli, it has always been assumed that following cardiac arrest, the final stage of death has been reached.

However, Parnia said, a surprising number of patients who have been brought back to life report having had the capacity to see or hear even after being officially declared dead. 

Some clinically dead patients who have been revived, he said, describe “watching doctors and nurses working… having awareness of full conversations, of visual things that were going on, that would otherwise not be known to them.”

What happens when you die

Parnia told LiveScience that within seconds after cardiac arrest, the cerebral cortex — the part of the brain responsible for what we consider thinking — slows down and then stops, and electronic monitors are no longer able to pick up brain activity.

This sets the death of brain cells into motion, though the process can take hours.

 It is possible to prolong this window by continuing to perform CPR, which provides the brain with about 15% of the blood that it normally requires, he said. This can slow the process of brain death, but is still short of what it takes to restart brain function, which is why performing CPR doesn’t cause reflexes to resume.

“If you manage to restart the heart, which is what CPR attempts to do, you’ll gradually start to get the brain functioning again,” Parnia told Live Science. “[But it’s] happening at a slightly slower rate.”

The white light

Parnia said that medical staff reviving people who suffered cardiac arrest were surprised to hear their patients describe what had been going on around them, even though they were technically dead. He said the staff were able to verify details described by the patients as accurate.

In The Telegraph, Parnia spoke about an earlier study of 2,000 patients that he and fellow researchers conducted between 2010 and 2014, which said that 39% of people who were brought back to life had some memory of the minutes after their hearts stopped beating.

Out of 2,060 people studied, 330 were successfully revived, and 140 participated in a survey. 

The study was published in the journal Resuscitation. In it, one man recalled leaving his body and watching medical staff revive him from the corner of the room — minutes after the 20-30 second span in which scientists believe the brain usually shuts down.

While these near-death experiences may not be quite what Hollywood promised, some people who lived through them came back profoundly changed.

Others reported seeing lights, or what appeared to be the sun shining, while some felt extreme fear or the feeling of being dragged through deep water. Thirteen percent felt time slow down or speed up, and another 13% said they felt that their senses were heightened.  

Parnia told LiveScience that while these experiences may not be quite as spectacular as the kind of stuff you may find in a Hollywood movie, some people who have lived through them come back profoundly changed. And he estimates that millions of people could be going through similar things — far fewer than actually reported.

“What tends to happen is that people who’ve had these very profound experiences may come back positively transformed — they become more altruistic, more engaged with helping others. They find a new meaning to life having had an encounter with death,” Parnia said.

Of mice and men

Parnia’s later research picked up with real human subjects where a 2013 University of Michigan study of nine anesthetized rats left off. 

Results of the U-M study seemed to corroborate anecdotal reports of near-death experiences from humans who were successfully revived: scientists found that during the first 30 seconds of artificially induced cardiac arrest, the rats displayed a surge of brain activity associated with a highly aroused brain.

The effects were almost identically reproduced when the rats underwent asphyxiation.

The researchers, who analyzed recordings of the rats’ brain activity called electroencephalograms (EEGs), did hypothesize that they would find some conscious activity in the brain during cardiac arrest.

“But we were surprised by the high levels of activity,” George Mashour, a professor of anesthesiology and neurosurgery, and the study’s senior author, told Kurzweil Networks.

The study’s authors said it was the first of its kind, telling Kurzweil that it would form the basis for future studies of the human experience during cardiac arrest — including the phenomenon of seeing flashes of light.

The paper, published in PNAS, the official journal of the National Academy of Sciences, said near-death experiences have been used as evidence for unknowable claims, such as the existence of life after death and the human soul. 

But, write the authors, those assumptions are based on the belief that post-death experiences can’t be taking place naturally within the human brain. 

They say that with the evidence provided in their study, they now “provide a scientific framework to begin to explain the highly lucid and realer-than-real mental experiences reported by near-death survivors.”

In other words, they believe they’ve discovered a scientific explanation for the supernatural experiences that have been raising questions among humankind for millennia. 

Nothing to prove

Parnia said his research is mostly focused on finding better ways to resuscitate people following cardiac arrest and minimizing brain injury as doctors work to restart the heart. The study of post-death consciousness is not his primary question.

But, he said, even while monitoring things such as how much oxygen the brain is receiving at different stages during cardiac arrest and revival, there is still the opportunity for other existential observations.

“At the same time, we also study the human mind and consciousness in the context of death, to understand whether consciousness becomes annihilated or whether it continues after you’ve died for some period of time — and how that relates to what’s happening inside the brain in real time,” Parnia said.

As Parnia told The Telegraph: “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 correspond to actual events.”