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 say.
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 anaesthetised and 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 George Mashour, professor of anaesthesiology 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-organised 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," lead author Jimo Borjigin said. "It also provides the first scientific framework for the near-death experiences reported by many cardiac arrest survivors."
About 20 per cent of people who survive cardiac arrest report having had visions during a period called clinical death.
Borjigin hopes the study will lead to "human studies investigating mental experiences occurring in the dying brain, including seeing light".