Many people on their deathbeds report seeing a long corridor with a brilliant light at the end of it. Could it be heaven? Probably not. New research shows that these near-death visions may be linked to intense electrical surges that cause "hyper real" thoughts in our brains.
A team of researchers found that during "clinical death," rats exhibit a surge in brain activity, with features similar to a highly aroused human brain.
There are countless tales of people from all walks of life seeing bright lights and other vivid hallucinations when they're at the brink of death. In fact, some estimates say that almost 20 percent of people who survive cardiac arrest — where blood effectively stops flowing and the brain becomes starved of the oxygen it needs — report such near-death experiences.
It's long been assumed that once the brain is cut off from its blood supply, it stops functioning, says Jimo Borjigin, a molecular neurologist at the University of Michigan. And some people reason that if the brain is no longer functioning, it can't possibly be the source of near-death experiences, lending credence to a more supernatural explanation for the phenomenon.
That's why Borjigin decided to look at other sources of activity in the dying brain. She discovered that there's been very little research on electrical signals in the brain immediately after cardiac arrest. "There was some research done in rats a long time ago, where there was this clear blip after the heart stops, but nobody made a big deal about that," Borjigin told io9. "What if that little blip turns out to be something important?"
Borjigin originally became interested in this topic back in 2007, when she was working on a project with her husband, Michael Wang. The couple was trying to figure out what happens to animals' circadian rhythms when they suffer from a stroke, or a disturbance in blood supply to the brain. During their experiments, some of the animals died from the induced strokes. Curiously, brain images showed a huge increase in certain neural chemicals during these animals' deaths.
"After that I started looking into everything that has to do with the dying process," Borjigin said. She dug into the scientific literature for anything that could explain what she and her husband saw — and found herself on the subject of near-death experiences. Though some accounts claimed that the unexplained experiences couldn't stem from brain activity, she wasn't convinced. "If there is that kind of activity happening in the brain after death, it should be measureable."
To investigate the possible neurophysiological basis for near-death experiences, Borjigin, Wang and their colleagues decided to take EEG (electroencephalogram) readings of nine rats while they were awake, under anesthesia and undergoing cardiac arrest. They looked particularly at gamma oscillations, or gamma waves. Neurons in the brain oscillate or fire at different frequencies, with these frequency bands correlating to different types of brain waves (delta, theta, alpha, beta and gamma). Gamma waves, Borjigin explains, occur at the highest of frequencies and therefore carry more information than other brain waves. They are also one of the features of consciousness.
The team found several signs of conscious activity in all nine of the dying rats' brains. First off, within the first 30 seconds after cardiac arrest, there was a sharp increase in gamma frequency power. But it wasn't just random firing — neurons across the brain fired synchronously. Previous research has suggested that this "gamma coherence" underlies conscious perception, such as when you focus all your attention on understanding something.
"But what is really interesting is that the coherence [in the dying rats] is more than two-fold higher than in their waking state," Borjigin said. "This suggests that after cardiac arrest, there is a kind of hyper-consciousness in the brain, with all of the neurons acting together in far more coherence than normal."
Additionally, the team found an increase in "feedback connectivity." Information processing in the brain occurs in two ways: Top-down and bottom-up. Bottom-up processing has to do with sensory awareness, while top-down processing involves your will and intention, such as when you decide to raise your arm. During anesthesia, doctors dampen both kinds of process to make sure that patients aren't aware of what's going on, and don't remember anything about the procedure.
The researchers found that dying rats showed an eight-fold increase in top-down processes and five-fold increase in bottom-up processes following cardiac arrest. Borjigin suggests that anything the rats experienced during this time would likely have seemed "hyper-real." Interestingly, patients have described near-death experiences as being "realer than real."
Finally, the researchers saw cross-frequency coupling — where different electrical waves work together — in the rats' brains after cardiac arrest. They found coupling between low-frequency gamma waves and theta waves, as well as low-gamma waves with alpha waves. When theta waves couple with gamma waves, it represents a conscious control of the brain. Alpha-gamma coupling, on the other hand, is a feature of visual activation or visual awareness, which includes internal visualization (imagination) — Borjigin suggests this particular brain activity could be behind the bright lights some people see during their near-death experience.
Taken together, the evidence suggests that the brain is capable of well-organized electrical activity — specifically conscious processing — immediately following cardiac arrest, despite the fact that the brain experiences a sharp decrease in oxygen, and was previously thought to be non-functional during this time. These neurophysiological changes may very well be the cause of the near-death experiences people often report.
Though the study was conducted on rats, Borjigin believes the basic brain features of cardiac arrest should be conserved in people. And if scientists do a human study, "my prediction is that we are going to find a lot more information than we did in rats," she said.
Read the scientific paper in the journal PNAS.
Top image via _phunkographer_/