The 'light at the end of the tunnel' reported by many people during near-death experiences is caused by a surge in brain activity, scientists have said.

New research sheds light on the hitherto unexplained phenomena reported by those who narrowly avoid death, including out-of-body experiences, feelings of levitation and a white light which draws the person towards it.

Around one in five cardiac arrest survivors report near-death experiences, with most reporting visions they believe to be "realer than real". For centuries these accounts been used to support a belief in the after-life.

However researchers at the University of Michigan say they have the first scientific evidence that the brain is actually responsible for these sensations.

The team found that shortly after clinical death - where the heart stops beating and blood stops flowing to the brain - the brain shows activity patterns similar to those witnessed during conscious perception.

They analysed the brain activity of nine anesthetised rats undergoing induced cardiac arrest. For 30 seconds after cardiac arrest, all the rats displayed a surge of highly synchronised brain activity consistent with features associated with a highly aroused brain.

Foundation of human studies

Jimo Borjigin, lead author of the study, said: This study, performed in animals, is the first dealing with what happens to the neurophysiological state of the dying brain

"It will form the foundation for future human studies investigating mental experiences occurring in the dying brain, including seeing light during cardiac arrest.

"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."

The study authors also found that the same brain activity was recorded in rats dying from asphyxiation.

"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," says Borjigin. "It also provides the first scientific framework for the near-death experiences reported by many cardiac arrest survivors.

"The prediction that we would find some signs of conscious activity in the brain during cardiac arrest was confirmed with the data."

George Mashour, senior anaesthesiologist for the study, added: "We were surprised by the high levels of activity. 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.­­­"