What exactly happens in the human brain when a nearly dead person is revived?
A new study of cardiac arrest survivors suggests that nearly 40 percent of people undergoing CPR have memories, dream experiences, or some type of perception even when they are unconscious. Additionally, brain waves show signs of activity that suggest awareness can last as long as an hour before they are brought back to life.
“There is nothing more extreme than cardiac arrest because they are literally teetering between life and death, they are in a deep coma and they are not responding to us physically at all,” said the study’s lead author, Dr. Sam Parnia, an associate professor in the department of medicine at NYU Langone Health. “What we are able to demonstrate is that up to 40% of people actually have the perception that they have been conscious to some extent.”
That perception may just be a vague feeling that something is happening around them. However, six patients in the study reported what the researcher called “transcendental remembered death experiences,” or what many people consider a near-death experience.
“They may have seen their lives again, they may have gone to a place where they felt like home, and so on,” said Parnia, who is also director of critical care and resuscitation research at New York University Langone.
Several patients recalled aspects of medical treatment, such as pain, pressure or hearing. Others recalled dreamlike sensations, such as being chased by the police or being caught in the rain.
Some survivors had positive memories, such as seeing a light, a tunnel, or a family member, or experiencing intense emotions, such as love, tranquility, and peace. Others, however, had a sensation of separation from the body and the recognition of being dead or had delusions about monsters or faceless figures.
In the first-of-its-kind study published Thursday in the journal Resuscitation, Parnia and colleagues in the United States and United Kingdom tracked 567 people undergoing resuscitation for cardiac arrest at 25 different hospitals. Fewer than 10% of patients survived because cardiac arrests are often fatal, even when doctors are prepared to perform CPR. The researchers were able to interview 28 of the 53 survivors.
Eleven of them reported having memories or perceptions that suggested at least some consciousness during resuscitation. The researchers also measured brain oxygen and electrical activity in some patients and found gamma, delta, theta, alpha and beta waves that suggested some mental function during CPR.
“I think it’s incredible,” said Dr. Sheldon Cheskes, a professor of emergency medicine at the University of Toronto, who studies resuscitation for cardiac arrest and was not involved in the research. “You would never have known without being able to monitor brain waves.”
In cardiac arrest, the heart trembles with uncoordinated contractions and blood flow to every part of the body, including the brain, ceases.
Unlike a heart attack, in which the heart continues to beat despite a painful reduction in blood flow, a person suffering cardiac arrest is always unconscious. CPR is the only way to keep a person alive until the heart is brought back to a normal rhythm with a defibrillator or automated external defibrillator or AED. These AED devices can be used by anyone to restart the heart and are often found in public places.
The study was unique in that the researchers also tested whether participants could remember specific images or sounds, known as implicit learning. They put headphones on patients during resuscitation and played three words – apple, pear, banana – and also used a tablet to display 10 images.
When asked if they remembered them, only one of the 28 patients interviewed correctly remembered the three-word sequence, and none could remember the pictures. The research team also analyzed the recalled memories of 126 other cardiac arrest survivors who submitted their experiences by mail or were featured in a community database.
It’s unclear exactly what it means if someone sees a deceased family member, revisits key moments in their life or feels an overwhelming sense of love and peace, but the emotional impact is important, Cheskes said. “I personally wouldn’t read much into these, other than the fact that they’re interesting,” she said. However, the memories could have lingering psychological consequences for survivors, she said.
It was a profound and lasting experience for Mary Curran Hackett of Cincinnati. Hackett, who has been involved in other research with Parnia, suffered cardiac arrest and felt “a sense of complete calm and peace and a sort of being enveloped in love.”
“And then when I came back, I felt the strength of whatever it was come back into me. I can’t explain it otherwise, my whole life has changed since then. I wasn’t afraid of death,” said Hackett, an author who wrote about her experiences. “I had a really profound feeling that I had received a clear message about why we are here.”
The fact that two high-profile people – Buffalo Bills safety Damar Hamlin and Bronny James, son of NBA superstar LeBron James – have survived cardiac arrests in just the last two years brings greater attention to the need for more research into cardiac arrest survivors. cardiac arrest and mental disorders. health impact of resuscitation, Cheskes said.
“That kind of brought him into the public spotlight more than maybe he ever was before,” he said.
Historically, Hamlin and James would not have survived a cardiac arrest at all, said Dr. Lance Becker, chairman of emergency medicine and resuscitation researcher at Northwell Health System in Manhasset, New York. “This would not have happened 10 years ago, and it would never have happened 20 years ago,” said Becker, who was not involved in the research. “We live in a different world and now this study opens up a new perspective and we just need to know more.”
“Hats off to Dr. Parnia because he’s trying to seriously study something that we all wonder about,” he said. “Every one of us takes care of a dying patient – I’ve taken care of thousands – and you wonder, could they be conscious? Could they be having a near-death experience?”
The main point of this study is that survivors may have some memories of CPR, which could be a source of emotional distress for some, said Dr. Katherine Berg, assistant professor of medicine at Harvard Medical School and chair of the group writing for CPR. 2025 American Heart Association Guidelines for Post-Cardiac Arrest Care.
“I hope that studies like this will prompt doctors to ask cardiac arrest survivors about these memories and experiences and to assess for any post-traumatic stress or other psychological symptoms that may need to be addressed,” he said in an email. “I really congratulate the authors on this thoughtful study, which I am sure was very laborious to conduct.”
It’s also a good reminder to perform CPR, call 911 and use an AED if people witness someone go into cardiac arrest, Cheskes said. More than 356,000 people suffer out-of-hospital cardiac arrests each year, according to the American Heart Association, which has this video on how to perform hands-only CPR and use an AED and this guide on when to start CPR.
“A lot of people see the defibrillator and freak out: Am I going to kill the patient?” He said. But a person in cardiac arrest will definitely die, so people should definitely try using an AED, which generally has easy-to-understand instructions, he said. “It’s hard to explain to people that you can’t do anything wrong.”
Cheskes said the patients in the study were not like those suffering from “brain death,” who have an irreversible loss of brain function and are therefore candidates for organ donation.
This article was originally published on NBCNews.com