There may be a scientific explanation for the vivid near-death experiences, such as seeing a shining light, that some people report after surviving a heart attack, US scientists said Monday.
Apparently, the brain keeps on working for up to 30 seconds after blood flow stops, according to a study published in the Proceedings of the National Academy of Sciences.
University of Michigan scientists did their research on nine lab rats that were anesthetized and then subjected to induced cardiac arrest as part of the experiment.
In the first 30 seconds after their hearts were stopped, they all showed a surge of brain activity, observed in electroencephalograms (EEGs) that indicated highly aroused mental states.
"We were surprised by the high levels of activity," said senior author George Mashour, professor of anesthesiology and neurosurgery at the University of Michigan.
"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."
Similar results in terms of brain activity were seen in rats that were asphyxiated, the researchers said.
"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 lead author Jimo Borjigin.
"It also provides the first scientific framework for the near-death experiences reported by many cardiac arrest survivors."
About 20 percent of people who survive cardiac arrest report having had visions during a period known to doctors as clinical death.
Mainstream science has long considered the brain to be inactive during this period.
Borjigin said she hopes her team's latest study "will form the foundation for future human studies investigating mental experiences occurring in the dying brain, including seeing light during cardiac arrest."