The "near-death experience" reported by cardiac arrest survivors worldwide may be grounded in science, according to research at the University of Michigan. (Agencies)
The study shows shortly after clinical death, in which the heart stops beating and blood stops flowing to the brain, rats display brain activity patterns characteristic of conscious perception.
"This study, performed in animals, is the first dealing with what happens to the neurophysiological state of the dying brain," said lead study author Jimo Borjigin.
"It will form the foundation for future human studies investigating mental experiences occurring in the dying brain, including seeing light during cardiac arrest," she said.
Approximately 20 percent of cardiac arrest survivors report having had a near-death experience during clinical death. These visions and perceptions have been called "realer than real," researchers said.
"We reasoned that if near-death experience stems from brain activity, neural correlates of consciousness should be identifiable in humans or animals even after the cessation of cerebral blood flow," she said.
Researchers analyzed the recordings of brain activity called electroencephalograms (EEGs) from nine anaesthetized rats undergoing experimentally induced cardiac arrest.
Within the first 30 seconds after cardiac arrest, all of the rats displayed a widespread, transient surge of highly synchronized brain activity that had features associated with a highly aroused brain. Furthermore, the authors observed nearly identical patterns in the dying brains of rats undergoing asphyxiation.
"The prediction that we would find some signs of conscious activity in the brain during cardiac arrest was confirmed with the data," said Borjigin.
"But, we were surprised by the high levels of activity," adds study senior author anaesthesiologist George Mashour.
In fact, at near-death, many known electrical signatures of consciousness exceeded levels found in the waking state, suggesting that the brain is capable of well-organized electrical activity during the early stage of clinical death.
The brain is assumed to be inactive during cardiac arrest. However the neurophysiological state of the brain immediately following cardiac arrest had not been systemically investigated until now.
"This study tells us that reduction of oxygen or both oxygen and glucose during cardiac arrest can stimulate brain activity that is characteristic of conscious processing," said Borjigin.
The "near-death experience" reported by cardiac arrest survivors worldwide may be grounded in science, according to research at the University of Michigan.