Originally Posted by Geko45
There are plenty of people that have taken LSD and had similar experiences. If the consciousness (or "soul" if you prefer) is a tangible thing that lies beyond our "physical realm" then why can it so easily be manipulated by psychoactive drugs, neural electrical implants and other sources of stimuli? I would submit that this doctor is simply no longer objective on the topic having experienced powerful hallucinations during a deep coma.
Doctor Alexander considered your hypothesis himself, and rejected it (see Appendix B in his book):
"Endogenous glutamate blockade with excitotoxicity, mimicking the hallucinatory anesthetic, ketamine (occasionally used to explain NDEs in general). I occasionally saw the effects of ketamine used as an anesthetic during the earlier part of my neurosurgical career at Harvard Medical School. The hallucinatory state it induced was most chaotic and unpleasant, and bore no resemblance whatsoever to my experience in coma.
N,N-dimethyltryptamine (DMT) "dump" (from the pineal, or elsewhere in the brain). DMT, a naturally occurring serotonin agonist (specifically at the 5-HT1A, 5-HT2A and 5-HT2C receptors), causes vivid hallucinations and a dreamlike state. I am personally familiar with drug experiences related to serotonin agonist/antagonists (that is, LSD, mescaline) from my teen years in the early 1970s. I have had no personal experience with DMT but have seen patients under its influence. The rich ultra-reality would still require fairly intact auditory and visual neocortex as target regions in which to generate such a rich audiovisual experience as I had in coma. Prolonged coma due to bacterial meningitis had badly damaged my neocortex, which is where all of that serotonin from the raphe nuclei in the brainstem (or DMT, a serotonin agonist) would have had effects on visual/auditory experience. But my cortex was off, and the DMT would have had no place in the brain to act. The DMT hypothesis failed on the basis of the ultra-reality of the audio-visual experience, and lack of cortex on which to act."