A new study suggests that some patients who are declared clinically dead may retain signs of brain activity longer than previously believed.
Dr. Sam Parnia, a physician at NYU Langone Medical Center, led research examining brain function in patients who suffered cardiac arrest and were later revived. Cardiac arrest occurs when the heart stops beating, and patients are often declared clinically dead when circulation and breathing cease.
The findings, published in the journal Resuscitation, indicate that measurable brain activity can continue during resuscitation efforts. In some cases, patients who had been considered clinically dead reported awareness of events taking place around them while medical teams were attempting to revive them.
The study analyzed 53 cardiac arrest survivors treated at 25 hospitals, primarily in the United States and the United Kingdom. Researchers monitored brain activity using electroencephalograms (EEGs), which measure electrical signals in the brain. They detected patterns of gamma, delta, theta, alpha, and beta waves—signals typically associated with higher cognitive functions—up to 35 to 60 minutes after the heart had stopped.
Approximately 40% of participants reported memories or conscious experiences during the period in which they were clinically dead. Some said they felt separated from their bodies but were still aware of their surroundings, including conversations and medical procedures in the hospital room.
Dr. Parnia said the findings challenge longstanding assumptions that the brain suffers irreversible damage within 10 minutes of losing oxygen. Instead, the research suggests that the brain may show signs of electrical recovery during prolonged cardiopulmonary resuscitation (CPR).
Researchers believe that as blood flow decreases, certain inhibitory systems in the brain shut down. This process, known as disinhibition, may trigger heightened mental clarity or vivid recollections. Some survivors described experiencing a review of their lives or intense awareness during the period they were considered clinically dead.
The study’s authors emphasize that more research is needed to fully understand the relationship between cardiac arrest, brain activity, and consciousness. However, the findings could influence future approaches to resuscitation and the treatment of brain injuries following cardiac arrest.