Chemical "causes" of NDEs? Greyson's analysis.

Bruce Greyson writes: “I was recently part of a multinational research team that analyzed language usage and language structure in 625 accounts of near-death experiences and compared them to almost fifteen thousand accounts of unusual experiences of people taking any of 166 different drugs. We found that the drug states most similar to near-death experiences were those associated with ketamine. However, we were careful to note that other common effects of ketamine don’t appear in near-death experiences, which suggests that near-death experiences are not simply an effect of the drug. In a similar vein, Karl Jansen, the neuroscientist who has most fiercely promoted the ketamine model for near-death experiences, concluded after twelve years of research that he viewed ketamine as ‘just another door’ to near-death experiences, and not as actually producing them.”

Other scientists argue that “near-death experiences might be connected to serotonin, adrenaline, vasopressin, and glutamate, all of which are chemicals that transmit signals between nerve cells. But in spite of the theoretical reasons for thinking that brain chemicals might be involved in near-death experiences, there has been no research looking into this possibility.” Greyson says, “I don’t expect any such research to be done in the near future. Bursts of these chemicals in the brain tend to be very short-lived and localized, so to find them, we’d have to look at exactly the right time at exactly the right place in the brain—and as I discovered, we don’t even know where in the brain to look.”

Bruce Greyson, After: A Doctor Explores What Near-Death Experiences Reveal about Life and Beyond, 109-110.