Jennie Dear in The Atlantic:
For many dying people, “the brain does the same thing that the body does in that it starts to sacrifice areas which are less critical to survival,” says David Hovda, director of the UCLA Brain Injury Research Center. He compares the breakdown to what happens in aging: People tend to lose their abilities for complex or executive planning, learning motor skills—and, in what turns out to be a very important function, inhibition. “As the brain begins to change and start to die, different parts become excited, and one of the parts that becomes excited is the visual system,” Hovda explains. “And so that’s where people begin to see light.”
Recent research points to evidence that the sharpening of the senses some people report also seems to match what we know about the brain’s response to dying. Jimo Borjigin, a neuroscientist at the University of Michigan, first became intrigued by this subject when she noticed something strange in the brains of animals in another experiment: Just before the animals died, neurochemicals in the brain suddenly surged. While scientists had known that brain neurons continued to fire after a person died, this was different. The neurons were secreting new chemicals, and in large amounts. “A lot of cardiac-arrest survivors describe that during their unconscious period, they have this amazing experience in their brain,” she says. “They see lights and then they describe the experience as ‘realer than real.’” She realized the sudden release of neurochemicals might help to explain this feeling.Borjigin and her research team tried an experiment. They anesthetized eight rats, and then stopped their hearts. “Suddenly, all the different regions of the brain became synchronized,” she says. The rats’ brains showed higher power in different frequency waves, and also what is known as coherence—the electrical activity from different parts of the brain working together.