A new study has offered more insight into what a person is experiencing when they nearly die during resuscitation.

Research shared on Resuscitation journal last week suggests nearly 40% of people undergoing CPR show examples of being conscious. Whether it’s memories or dreamlike episodes, the study finds people experience some form of perception even while appearing completely unconscious.

“Although doctors have long thought that the brain suffers permanent damage about ten 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,” study author Dr. Sam Parnia, an associate professor at NYU’s Department of Medicine, said in a press release.

“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.”

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The study also found brain waves of cardiac arrest survivors showing signs of awareness activity for up to an hour during resuscitation. For some patients, the study also measured brain oxygen and electrical activity where they found gamma, delta, theta, alpha and beta waves.

The “AWAreness during REsuscitation (AWARE)-II” study monitored 567 people who experienced cardiac arrest resuscitation at 25 hospitals where less than 10% of the patients survived.

Researchers interviewed 28 of the 53 people who lived to tell about their near death experience and four in 10 of those that survived recalled memories or perceptions of consciousness.

Other forms of perception the survivors reported included “separation from the body, observing events without pain or distress and a meaningful evaluation of their actions and relationships.” The study clarified these experiences of death differ from hallucinations, illusions, delusions dreams, or CPR-induced consciousness.

The study authors hypothesize that natural inhibitory, or breaking systems, are removed from a “flatlined” brain, according to the press release. These processes can sometimes open “new dimensions of reality” such as lucid recollection of early childhood memories from a moral perspective. The study added that the evolutionary purpose for this process is unknown but that it could allow for a better understanding of what happens when someone dies.

The authors also added that the study contradicts the idea that the brain always suffers permanent damage when the heart stops.

Parnia said the research “may also guide the design of new ways to restart the heart or prevent brain injuries and hold implications for transplantation.”

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This article originally appeared on USA TODAY: Cardiac arrest survivors describe near death experiences in new study