Near-death experiences may be explained by brain activity
After
cardiac arrest, a rat’s brain showed a surge of activity that had
features associated with consciousness and visual activation,
researchers found.
It could be the afterlife, as many people who have come close to dying have asserted. But a new study says it might well be a show created by the brain, which is still very much alive. When the heart stops, neurons in the brain appeared to communicate at an even higher level than normal, perhaps setting off the last picture show, packed with special effects.
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Scientists from the University of Michigan recorded electroencephalogram (EEG) signals in nine anesthetized rats after inducing cardiac arrest. Within the first 30 seconds after the heart had stopped, all the mammals displayed a surge of highly synchronized brain activity that had features associated with consciousness and visual activation. The burst of electrical patterns even exceeded levels seen during a normal, awake state.
In other words, they may have been having the rodent version of a near-death experience.
“On a fundamental level, this study makes us think about the neurobiology of the dying brain,” said senior author and anesthesiologist George A. Mashour. It was published Monday online by the Proceedings of the National Academy of Sciences.
Near-death experiences have been reported by many who have faced death, worldwide and across cultures. About 20 percent of cardiac arrest survivors report visions or perceptions during clinical death, with features such as a bright light, life playback or an out-of-body feeling.
“There’s hundreds of thousands of people reporting these experiences,” Borjigin said. “If that experience comes from the brain, there has to be a fingerprint of that.”
An unanswered question from a previous experiment set her down the path of exploring the phenomenon. In 2007, Borjigin had been monitoring neurotransmitter secretion in rats when, in the middle of the night, two of her animals unexpectedly died. Upon reviewing the overnight data, she saw several unknown peaks near the time of death.
This got her thinking: What kinds of changes does the brain go through at the moment of death?
Then last year, Borjigin turned to Mashour, a colleague with expertise in EEG and consciousness, for help conducting the first experiment to systematically investigate the brain after cardiac arrest. EEG uses electrodes to measure voltage fluctuations in the brain caused by many neurons firing at once. A normal, awake brain should show spikes depending on what types of processing are going on; in a completely dead brain, it flat-lines.
When the heart suddenly stops, blood flow to the brain stops and causes death in a human within minutes. A likely assumption would be that, without a fresh supply of oxygen, any sort of brain activity would go flat. But after the rats went into cardiac arrest, Mashour and his colleagues observed the opposite happening.
“We saw a window of activity with certain signatures typically associated with conscious processing,” he said.
Those signatures include heightened communication among the different parts of the brain, actively seen in an awake state. Mashour speculates this could be a marker of consciousness — in which the brain integrates disparate aspects of the world, like visual in one area and auditory in another.
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In the rats, this connectivity went above and beyond the levels seen during the awake state — which could possibly explain the hypervivid, “realer-than-real” perceptions reported close to death, Borjigin said.
Scientists are still trying to pin down a clear-cut electrical marker of consciousness because there are many gray areas — for instance, being under anesthesia or in a vegetative state or having a seizure.
“We don’t have any rough and ready way to take a measurement and assign a meaning to it with regards to conscious content,” said neurologist Nicholas D. Schiff of the Weill Cornell Medical College, who was not involved in the study.
Borjigin also noted an increase in a certain type of EEG pattern that has been tied to visual stimulation in humans that could possibly explain the very bright light that survivors describe.
“My hypothesis would be that during the near-death process, the visual process is highly activated,” she said.
The researchers also confirmed the effect using another form of death, asphyxiation via carbon dioxide inhalation. The same highly aroused features were seen in a nearly identical pattern.
Schiff finds the study “very interesting” and novel but is skeptical about any near-death interpretations.
“There’s no intrinsic reason to believe that these rats are in some heightened state of awareness,” he said. He believes the spike in activity is simply a shock-to-the-system response by the brain cells to a major change in physiology.
“The majority of near-death experiences cannot be explained by such a study,” said radiation oncologist and near-death researcher Jeffrey Long, who thinks it is another in a long line of possible scientific explanations that haven’t panned out.
The EEG surge fails to explain the out-of-body feeling and reuniting with long-lost loved ones reported by many, he said.
Long, a skeptic-turned-believer, has been researching near-death moments for more than 14 years. He set up the Near Death Experience Research Foundation, which has collected more than 3,000 accounts from survivors around the world.
Borjigin and Mashour hesitate to state a direct connection between their findings and near-death experiences. The links are merely speculative at this point and provide a framework for a human study, Borjigin said.
Even if the EEG patterns after cardiac arrest appear similar to the those of the awake state, Schiff cautioned that the same interpretation may not be possible because the brain’s playing field has changed drastically because of lack of blood flow. He does think that this surge in activity recorded in rat brains would probably be similar in humans.
Some case reports by doctors describe similar EEG sequences in their patients at the point of death, but no systematic study has been done.
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