You feel yourself float up and out of your physical body. You glide toward the entrance of a tunnel, and a searing bright light envelops your field of vision.
Rather than an ascent into the afterlife, a new study says these features of a near-death experience may just be a bunch of neurons in your brain going nuts.
"A lot of people believed that what they saw was heaven," said lead researcher and neurologist Jimo Borjigin. "Science hadn't given them a convincing alternative."
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 brain activity that had features associated with consciousness and visual activation. The burst of electrical activity even exceeded levels 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 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 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 [near-death] experiences," said Borjigin. "If that experience comes from the brain, there has to be a fingerprint of that."
An unanswered question from a previous experiment bothered her. In 2007, Borjigin had been monitoring neurotransmitter secretion in rats when, in the middle of the night, two of the 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?
Last year, Borjigin turned to Mashour, a colleague with expertise in EEG and consciousness, for help conducting the first experiment to systematically investigate electrical brain activity 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 of activity depending on what types of processing are going on; in a completely dead brain, it flat-lines.
When the heart suddenly stops, ongoing 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 saw the opposite.
"We saw a window of activity with certain signatures typically associated with conscious processing," said Mashour.
Those signatures include heightened communication among the different parts of the brain, actively seen in an awake state, but often lost during anesthesia. 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, said Borjigin.
Mashour speculates this integration coincides with consciousness while we work to process aspects of the world in different areas of the brain, like visual in one area and auditory in another.
"The brain kind of gets it all together so we have this unified, seamless experience," he said.
But there are many gray areas of consciousness — for instance, being under anesthesia or in a vegetative state or seizing — and scientists are still trying to pin down a clear-cut electrical marker of consciousness.
"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 Schiff of the Weill Cornell Medical College, who was not involved in the study.
Borjigin also noted an increase in EEG activity that has been tied to visual stimulation in humans that could possibly explain the very bright light that survivors describe.
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 find the study "very interesting" and novel, but is very 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.
While the study does look at the data within the context of near-death experiences, both Borjigin and Mashour hesitate to state a direct connection between the two. The links are merely speculative at this point and provide a framework for a human study, said Borjigin.
Even if the EEG patterns after cardiac arrest appear similar to the those of the awake state, Schiff cautioned that the same rules may not apply when the brain's playing field has changed drastically due to lack of blood flow. He does think that a similar surge in activity, if seen in rat brain, would translate to human brain as well.
There are some case reports by doctors who have witnessed a surge in EEG activity in their patients at the point of death, but no systematic study has been done.