Up to an hour after their hearts had stopped, some patients revived by cardiopulmonary resuscitation (CPR) had clear memories afterward of experiencing death and had brain patterns while unconscious linked to thought and memory.

This is the finding of a study led by researchers at NYU Grossman School of Medicine, in cooperation with 25 mostly United States and British hospitals, in which some survivors of cardiac arrest described lucid death experiences that occurred while they were seemingly unconscious. The research is published in Resuscitation

Despite immediate treatment, fewer than 10% of the 567 patients studied who received CPR in the hospital recovered sufficiently to be discharged. Four in 10 of those that survived, however, recalled some degree of consciousness during CPR not captured by standard measures.

The study also found that in these patients, nearly 40% had brain activity that returned to normal, or nearly normal, at points even an hour into CPR. As captured by EEG, the patients saw spikes in the gamma, delta, theta, alpha, and beta waves associated with higher mental function.

Survivors have long reported having heightened awareness and powerful, lucid experiences, say the study authors. These have included a perception of separation from the body, observing events without pain or distress, and a meaningful evaluation of their actions and relationships. The new work found these experiences of death to be different from hallucinations, delusions, illusions, dreams, or CPR-induced consciousness.

The study authors hypothesize that the “flatlined,” dying brain removes natural inhibitory systems. These processes, known collectively as disinhibition, may open access to “new dimensions of reality,” they say, including lucid recall of all stored memories from early childhood to death, evaluated from the perspective of morality. While no one knows the evolutionary purpose of this phenomenon, it “opens the door to a systematic exploration of what happens when a person dies.”

“Although doctors have long thought that the brain suffers permanent damage about 10 minutes after the heart stops supplying it with oxygen, our work found that the brain can show signs of electrical recovery long into ongoing CPR,” says senior study author Sam Parnia, MD, PhD, an associate professor in the department of medicine at NYU Langone Health. “This is the first large study to show that these recollections and brain wave changes may be signs of universal, shared elements of so-called near-death experiences.”

These experiences provide a glimpse into a real, yet little-understood dimension of human consciousness that becomes uncovered with death, adds Parnia, who is also director of critical care and resuscitation research at NYU Langone. The findings “may also guide the design of new ways to restart the heart or prevent brain injuries and hold implications for transplantation.”

Called the AWAreness during REsuscitation (AWARE)-II study, it followed 567 men and women who experienced cardiac arrest during hospital stays between May 2017 and March 2020 in the United States and United Kingdom. Of the 567 patients, only 85 were monitored via EEG to measure brain waves during their experiences. 

Only hospitalized patients were enrolled to standardize the CPR and resuscitation methods used, as well as recording methods for brain activity. Additional testimonies from 126 community survivors of cardiac arrest with self-reported memories were also examined to provide greater understanding of the themes related to the recalled experience of death.

The study authors conclude that research to date has neither proved nor disproved the reality or meaning of patients’ experiences and claims of awareness in relation to death. They say the recalled experience surrounding death merits further empirical investigation, and they plan to conduct studies that more precisely define biomarkers of clinical consciousness and that monitor the long-term psychological effects of resuscitation after cardiac arrest.