I will first deal with Ketamine. Let’s take it one piece at a time.
NDEs are quantified by using Greyson's NDE Scale and Ring’s Weighted Core Experience Index. No such NDE measures are known to have been taken by the subjects involved in drug-related experiments in order to make a valid comparison. Scientists in the new field of neurotheology are researching psilocybin and its mystic state-inducing capabilities for its possible therapeutic effectiveness.”The International Association for Near-Death Studies (IANDS) provides a quick criticism of the Ketamine model by stating:
“Ketamine and psilocybin are two drugs that have reportedly triggered mystical experiences that appear to be different than hallucinations and have similar elements to NDEs. Karl Jansen, who has written more than anyone else on NDE-like ketamine experiences, says the following.
“After 12 years of studying ketamine, I now believe that there most definitely is a soul that is independent of experience. It exists when we begin, and may persist when we end. Ketamine is a door to a place we cannot normally get to; it is definitely not evidence that such a place does not exist.” Jansen, Karl. (1997). Response to Commentaries on “The Ketamine Model of the Near-Death Experience.” Journal of Near-Death Studies. 16, 79-95.
The above analysis is being very friendly to the Ketamine model. There are additional criticisms that can be provided.
The ketamine model/hypothesis is an argument of a relationship between human biology and the transcendental experience. One can easily come to the conclusion that the mind is an entryway between the physical and spiritual worlds and therefore ketamine is should not be used as a tool to demystify the nde.
Also, during cardiac arrest there is a loss of all functions of the brain and therefore whether on ketamine or not the person is unconscious yet they feel fully conscious and even occasionally state they felt more real and alive than when in our current realm.
Also, it is not very clear whether ketamine experiences actually replicate ndes. In fact, most nders suggest this is not the case at all. NDErs mostly report positive feelings from the experience whereas ketamine experiences more often report differently. I cannot recall one person who had a non-drug affiliated genuine greyson scale nde and also experienced drug use, such as LSD, Ketamine, etc that say they are similar in anyway, just researchers.
In addition, Ketamine does not explain away the accuracies of out-of-body perceptions in people who lacked any brain activity whatsoever.
There is one additional analysis accessible on the web (I am doing my best to find obtainable sources instead of sources requiring subscriptions, e.g. journal articles). Dr. Fenwick discusses similarities and provides an example:
One of the major models we have of the NDE at the moment is the ketamine model. During cerebral anoxia, when the heart stops and there is no oxygen supply to the brain, there is widespread release of a chemical called glutamate, an NMDA agonist which leads to high nerve cell stimulation rates and chaotic firing in the brain. Ketamine is an anesthetic drug that acts like glutamate and is sometimes used as a street drug because of its pleasant subjective effects. Experimentally, ketamine leads to some NDE phenomena. Evgeny Krupitzky and Alexander Grinenko (1997) used ketamine in psychotherapy with alcoholics and found that it resulted in the same sorts of changes that people have with NDEs. Their patients became more social, more creative; more concerned with self-perfection and with achievement in life; more spiritually content; more interested in family, education, and social values; and more individually independent – many of the changes that NDErs have. Does that mean that the experiences are the same? Is it the NMDA stimulation that produces the NDE?
Well, look at this example of a ketamine experience, taken from Karl Jansen’s 2001 book, Ketamine:
... I found myself as a bodiless point of awareness and energy floating in the midst of a vast vaulted chamber. There was a sense of presence all around, as though I was surrounded by millions of others, although no one else could be seen. In the center of the chamber was a huge, pulsing, krishna-blue mass of seething energy that was shaped in a geometric, mandalic form ... . Then suddenly, I was back in my body, lying on my bed. ‘‘Wow,’’ I thought, ‘‘it’s over. How abrupt!’’ I tried to sit up. Suddenly, my body was gone again and the room dissolved into blackness of the void, my reality being quickly pulled out from underneath my feet, like a hyperspatial magician’s tablecloth trick. (p. 243)
NDErs, is that like your experience? No, it is not. There are some similar features, but there are other features that are very different.
So although the ketamine model is the best scientific candidate so far to account for the NDE in cardiac arrest, it cannot explain every feature of NDEs. And I am not sure that even if we say that the NDE is a ketamine-like experience, we can, in fact, completely understand the whole of the NDE during cardiac arrest. Because we are left with the problem of exactly when does the NDE occur? And the only way you can get an answer to this is through out-of-body experiences (http://iands.org/research/important-res ... ml?start=3 ).
Please note Dr. Gregory Stone provides a full critique of Susan Blackmore’s Dying to Live and this is published on IANDS for additionally criticisms.