Some cardiac arrest survivors from a range of cultural and religious backgrounds have reported near-death experiences—these might include a sensation of leaving the body, a bright light at the end of a tunnel or memories of past events. Now, researchers are making strides toward a scientific explanation for these events.
In a study published Monday in the Proceedings of the National Academy of Sciences, researchers report that two of four comatose dying patients experienced a surge in brain activity that resembles consciousness after they were taken off ventilators and their hearts had stopped.
The findings indicate scientists have more to learn about how the brain behaves while we’re dying. The study “suggests we are identifying a marker of lucid consciousness,” Sam Parnia, a pulmonologist at New York University who did not contribute to the research, tells Science’s Sara Reardon.
Scientists aren’t sure why near-death experiences occur. These mysterious phenomena “represent a biological paradox that challenges our fundamental understanding of the dying brain, which is widely believed to be nonfunctioning under such conditions,” according to the paper.
But previous work has also shown increased brain activity at the end of life. In a study of rats in 2013, Jimo Borjigin, a co-author of the new study and a neuroscientist at the University of Michigan, found that the rodents’ brains produced surges of gamma waves for 30 seconds after their hearts stopped. Gamma waves are fast brain waves associated with attention, working memory and long-term memory—so they indicate, but do not prove, that the rats might have been conscious, writes Live Science’s Stephanie Pappas. Additionally, a 2022 study found that a person who died of a heart attack while their brain activity was being measured also had gamma wave activity after cardiac arrest.
The new research looked at four patients who had died while their brain activity was being monitored using electroencephalography (EEG). All had been comatose and were considered beyond medical assistance, writes the Guardian’s Hannah Devlin. Their families gave doctors permission to take the patients off life support.
But the brain activity measurements for two of the patients showed surges in gamma waves after they were taken off life support and experienced cardiac arrest. The surges lasted for a couple of minutes and were sometimes very strong. “It was crazy high,” Borjigin tells New Scientist’s Clare Wilson.
Notably, researchers saw intense signals in an area of the brain that can be active when people have out-of-body experiences or dreams. “If this part of the brain lights up, that means the patient is seeing something, can hear something, and they might feel sensations out of the body,” Borjigin tells Issam Ahmed of the Agence France-Presse (AFP).
The findings could lead to further investigation of the dying brain and of consciousness during cardiac arrest, the authors write.
“This paper is really important for the field and the consciousness field more generally,” Charlotte Martial, a biomedical scientist who studies near-death experiences at the University of Liège in Belgium and did not contribute to the study, tells Science.
In the future, Borjigin wants to collect more data on dying brains, per Vice’s Becky Ferreira. The gamma wave activation “needs to be confirmed in more patients,” she tells the publication.
“The more consistent findings we have, the more evidence it is that this likely is a mechanism happening at the time of death,” Ajmal Zemmar, a neurosurgeon at the University of Louisville Health and co-author of the 2022 study, tells Live Science. “If we can pinpoint this down to one location, even better.”