What near-death experiences can tell scientists about how the brain works

Floating out of your body and looking down on it. The story of your life flashing by before your eyes. Seeing a bright light at the end of a dark tunnel. These are just two of the most common experiences that people report after a near-death experience (NDE). For some people, NDEs are a transformative spiritual or mystical experience. But what's the source of the phenomena? That's a question that fascinates Dr. Christof Koch is president and chief scientist of the Allen Institute for Brain Science who studies the neuroscience of consciousness. In Scientific American, Koch surveys the science of near-death experiences and what they can tell us about how our brains work under extreme duress. From Scientific American:

Modern death requires irreversible loss of brain function. When the brain is starved of blood flow (ischemia) and oxygen (anoxia), the patient faints in a fraction of a minute and his or her electroencephalogram, or EEG, becomes isoelectric-in other words, flat. This implies that large-scale, spatially distributed electrical activity within the cortex, the outermost layer of the brain, has broken down. Like a town that loses power one neighborhood at a time, local regions of the brain go offline one after another. The mind, whose substrate is whichever neurons remain capable of generating electrical activity, does what it always does: it tells a story shaped by the person's experience, memory and cultural expectations.

Given these power outages, this experience may produce the rather strange and idiosyncratic stories that make up the corpus of NDE reports. To the person undergoing it, the NDE is as real as anything the mind produces during normal waking. When the entire brain has shut down because of complete power loss, the mind is extinguished, along with consciousness. If and when oxygen and blood flow are restored, the brain boots up, and the narrative flow of experience resumes.[...]

Why the mind should experience the struggle to sustain its operations in the face of loss of blood flow and oxygen as positive and blissful rather than as panic-inducing remains mysterious. It is intriguing, though, that the outer limit of the spectrum of human experience encompasses other occasions in which reduced oxygen causes pleasurable feelings of jauntiness, light-headedness and heightened arousal-deepwater diving, high-altitude climbing, flying, the choking or fainting game, and sexual asphyxiation.

"What Near-Death Experiences Reveal about the Brain" (SciAm)

image: detail of "Ascent of the Blessed" by Hieronymus Bosch