Many people worldwide have reported 'near-death experiences' - particularly following a heart attack. But what causes the visions and perceptions that these survivors report after their brush with death? Scientists from the University of Michigan believe they have found the answer.
A near-death experience (NDE) is defined as a psychological event that occurs when a person is close to death.
Reported circumstances of a NDE, from the educational nonprofit the International Association for Near-Death Studies, include vivid perceptions of movement, light, darkness, encounters with deceased loved ones, encounters with spiritual presences or entities, and some people talk of an "out-of-body experience."
According to the researchers in the Michigan study, around 20% of cardiac arrest survivors have reported a NDE. However, they add that although these experiences have been described as "realer than real," it has been unclear as to whether the brain is able to produce these senses during clinical death.
Jimo Borjigin, who holds associate professorships in molecular and integrative psychology, and in neurology at the University of Michigan Medical School, says:
"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 researchers analyzed the recordings of brain activity, electroencephalograms (EEGs), of nine anesthetized rats as they were in the midst of induced cardiac arrest.
Researchers found that during near-death experiences, there is an electrical surge of brain activity
The study, published in the journal Proceedings of the National Academy of Sciences, revealed that following clinical death - when the heart stops beating and blood stops flowing to the brain, the rats showed brain activity patterns similar to "conscious perception."Within the first 30 seconds of a cardiac arrest, all rats showed a widespread electrical surge of transient brain activity, which had characteristics similar to a fully active brain.
Additionally, when the rats were undergoing asphyxiation - death from lack of oxygen, they showed almost identical brain patterns.
George Mashour, assistant professor of anesthesiology and neurosurgery at the University of Michigan, explains:
"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-organized electrical activity during the early stage of clinical death."
Borjigin adds: "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."
Challenge to ideas on brain activity during heart attacks
The study authors say that previously, it was assumed the brain was inactive during cardiac arrest, but this is the first time the neurophysiological state of the brain has been systemically investigated.
The researchers say their findings provide the first scientific framework for the near-death experiences reported by many cardiac arrest survivors.
"This study, performed in animals, is the first dealing with what happens to the neurophysiological state of the dying brain," Borjigin says.
"It will form the foundation for future human studies investigating mental experiences occurring in the dying brain, including seeing light during cardiac arrest."
There have been previous reports from neurologists looking into near death experiences. Researchers from the University of Kentucky wrote in 2006 that when a person is experiencing clinical death, the same parts of the brain are activated as when a person is having a dream.