New Delhi, Aug. 12: Scientists have observed a dramatic, paradoxical rise in the brain’s electrical activity in rats placed on death’s door that they say could explain the near-death experiences among people revived after cardiac arrest.
A team of researchers in the US said today the bursts of electrical activity indicate an aroused brain engaged in internal information processing in a near-death state where, conventional wisdom says, the brain should have been turning deathly silent.
Relying on anecdotal accounts, doctors have over the past several decades documented unusual experiences — from flying through a dark tunnel or moving towards a bright light to out-of-body sensations — among some survivors of cardiac arrest. Medical studies suggest that such near-death experiences are reported by one in five people revived after cardiac arrest.
The new findings emerged when anaesthesiologist George Mashour and his colleagues at the University of Michigan, Ann Arbor, examined the brain activity of rats first while the animals were awake, then while they were under anaesthesia, and finally after they had suffered cardiac arrest.
The researchers spotted a surge of widespread, highly synchronised brain activity, some of which lasted 30 seconds to 60 seconds. The findings were published today in the US journal Proceedings of the National Academy of Sciences.
“The high level of activity was a huge surprise,” said Mashour, director of neuro-anaesthesiology at the University of Michigan. “Some patterns were even more prominent after cardiac arrest than in the normal waking state.”
A cardiac arrest stops blood circulation and the resulting loss of oxygen to the brain leads to loss of consciousness. But cardiopulmonary resuscitation through chest compressions, electric shocks delivered through defibrillators, or medications may help revive the heart’s activity. Irreversible brain injury and eventually brain death occurs if the cardiac arrest is not reversed in about five minutes.
The patterns of activity the scientists observed in the rats suggest that the visual cortex — the zone of the brain that processes vision — may be highly activated during cardiac arrest.
Scientists believe this might help explain the visions reported by people during near-death experiences, which have remained controversial because they are not universal and are paradoxical.
“These are intriguing results. Instead of going silent, the dying brain seems to be screaming,” said Sumantra Chattarji, a senior neurobiologist at the National Centre for Biological Sciences, Bangalore, who was not associated with the study.
“What is also interesting is that this massive surge in synchronised and coherent activity occurs in frequencies known to be involved in the conscious processing of information across the brain.”
The US team detected a surge in a type of the electrical activity called gamma oscillations in the brains of all the nine rats in whom cardiac arrest had been induced after anaesthesia.
“The increase in coherence and communication across the brain may mean heightened cognitive processing in the near-death state,” said Dinesh Pal, an Indian neurobiologist and research team member.
“This study has brought the subject of (the) near-death state into the realm of science,” said Pal, who specialises in electroencephalograph recordings, which were used to measure the brain activity of the rats.
Some have used examples of near-death experiences to advocate the existence of life after death and to argue that consciousness, while centred in the brain, may also have a non-biological basis.
But others have suggested that near-death experiences may be mere manifestations of normal brain functions gone awry during severely traumatic or, at times, even harmless events.
“There may not be a single explanation for near-death experiences,” Caroline Watt, a senior lecturer in psychology at the University of Edinburgh, told The Telegraph.
Watt and Dean Mobbs, a psychologist at Columbia University, had pointed out in the journal Trends in Cognitive Sciences two years ago that many different physiological and psychological processes may produce experiences similar to near-death experiences.
“Air force pilots experiencing extremely high accelerations have reported tunnel-like visual loss for five to eight seconds,” Watt said.
“A lot of people resuscitated after cardiac arrest do not report such experiences. It is possible (that) there is a psychological component to near-death experiences — some experience it; others do not.”
Mashour cautioned that the findings’ implications for humans were still unclear. “But some of the analyses we performed in rats have counterparts in humans.”
Neurophysiologists Jimo Borjigin and Michael Wang at the University of Michigan conceived the idea for the research study, while Borjigin and Mashour designed the experiments. The other team members were UnCheol Lee, Tiecheng Liu, Sean Huff, Daniel Klarr, Jennifer Sloboda, and Jason Hernandez.