I've been skipping around in the impressive (and impressively hefty) new volume Irreducible Mind, by Edward F. Kelly, Emily Williams Kelly, et al. The 800-page book, extensively researched and exhaustively referenced, is a major assault on reductionist or physicalist theories of neurology. The authors cite a vast array of borderline phenomena, including psychic phenomena, in order to build their case that the relationship between brain and mind cannot be reduced to simple terms of cause and effect.
One of the most interesting chapters is Chapter 6, "Unusual Experiences Near Death and Related Phenomena," which was contributed by Emily Williams Kelly, Bruce Greyson, and Edward F. Kelly. I'd like to offer a few excerpts from this chapter, partly to give you the flavor of the book, and partly to address some common criticisms of NDEs. In all these quotes, material in bold font has been emphasized by me, while material in italics has been emphasized by the authors. Also, please note that I have omitted nearly all citations.
Anyone who has studied the subject knows that reductionists like to explain near-death experiences in terms of purely physical causes. The authors show the inadequacy of all such explanations. For instance, there is the claim that oxygen deprivation can bring about an NDE.
One of the earliest and most persistent of the physiological theories proposed for NDEs is that lowered levels of oxygen (hypoxia or anoxia), perhaps accompanied by increased levels of carbon dioxide (hypercarbia), have produced hallucinations.... One study frequently cited is that of Whinnery (1997), who compared NDEs to what he called the "dreamlets" occurring in brief periods of unconsciousness induced in fighter pilots by rapid acceleration in a centrifuge... He claimed that some features common to NDEs are also found in these hypoxic episodes, including tunnel vision, bright lights, brief fragmented visual images, a sense of floating, pleasurable sensations, and, rarely, a sense of leaving the body. The primary features of acceleration-induced hypoxia, however, are myoclonic convulsions (rhythmic jerking of the limbs), impaired memory for events just prior to the onset of unconsciousness, tingling in the extremities and around the mouth, confusion and disorientation upon awakening, and paralysis, symptoms that do not occur in association with NDEs. Moreover, contrary to NDEs, the visual images Whinnery reported frequently included living people, but never deceased people; and no life review or accurate out-of-body perceptions have been reported in acceleration-induced loss of consciousness. [Page 379]
Then there is the ketamine model:
... the suggestion that a ketamine-like endogenous neuroprotective agent may be released in conditions of stress... Ketamine, an anesthetic agent that selectively occupies NMDA receptors, can at subanesthetic doses produce feelings of being out of the body. Moreover, ketamine sometimes produces other features common to NDEs, such as travel through a dark tunnel into light, believing that one has died, or communion with God.
This hypothesis, however, also has problems. First, it is not of all clear that ketamine experiences do in fact resemble NDEs. Unlike the vast majority of NDEs, ketamine experiences are often frightening and involve bizarre imagery, and patients usually express the wish not to repeat the experience. Most ketamine users also recognize the illusory character of their experience, in contrast to the many NDE experiencers who are firmly convinced of the reality of what they experienced and its lack of resemblance to illusions or dreams. Even if ketamine experiences do resemble NDEs in some respects, many important features of NDEs, such as seeing deceased people or a revival of memories, have not been reported with ketamine. Furthermore, ketamine typically exerts its effects in an otherwise more or less normal brain, while many NDEs occur under conditions in which brain function is severely compromised. [Pages 380-381]
The authors further note that a "naturally occurring ketamine-like substance ... has not been identified in humans." (Page 384)
And there is the view, propounded most notably by M.A. Persinger, that electrical stimulation of the brain can reproduce NDEs on demand:
Persinger has also claimed that "a vast clinical and surgical literature ... indicates that floating and rising sensations, OBEs, personally profound mystical and religious encounters, visual and auditory experiences, and dream-like sequences are evoked, usually as single events, by electrical stimulation of deep, mesiobasal temporal lobe structures". His sole reference for this strong claim is a paper by Stevens (1982). That paper, however, is confined entirely to descriptions of certain physiological observations made in studies of epileptic patients, and it contains no mention whatever of any subjective experiences or of electrical stimulation studies, much less of "a vast clinical and surgical literature" supporting Persinger's claim. Persinger goes on to claim that, using weak transcranial magnetic stimulation, he and his colleagues have produced "all of the major components of the NDE, including out-of-body experiences, floating, being pulled towards a light, hearing strange music, and profound meaningful experiences." However, we have been unable to find phenomenological descriptions of the experiences of his subjects adequate to support this claim, and the brief descriptions that he does provide in fact again bear little resemblance to NDEs (e.g., Persinger, 1994, pages 284-285)....
Neurologist Ernst Rodin stated bluntly: "In spite of having seen hundreds of patients with temporal lobe seizures during three decades of professional life, I have never come across that symptomatology [of NDEs] as part of the seizure." [Pages 382-383]
As the authors explain, the similarities between hallucinations produced by electrical stimulation of the brain and NDEs have been greatly exaggerated:
As we mentioned earlier, research frequently cited in support of a model in which abnormal temporal lobe electrical activity produces an OBE is that of neurosurgeon Wilder Penfield. Penfield is widely reported as having produced OBEs and other NDE-like phenomena in the course of stimulating various points in the exposed brains of awake epileptic patients being prepared for surgery. Only two out of his 1132 patients, however, reported anything that might be said to resemble an OBE: One patient said: "Oh God! I am leaving my body". Another patient said only: "I have a queer sensation as if I am not here... As though I were half here and half there". In later studies at the Montréal Neurological Institute (where Penfield had conducted the study's), only one of 29 patients with temporal lobe epilepsy reported "a 'floating sensation' which the patient likened at one time to the excitement felt when watching a football game and at another time to a startle" (Gloor et al., 1982, pages 131-132). Such experiences hardly qualify as phenomenologically equivalent to OBEs. [Page 396]
Having disposed of the various physicalistic theories for NDEs, the authors go on to say:
NDEs seem instead to provide direct evidence for a type of mental functioning that varies "inversely, rather than directly, with the observable activity of the nervous system" (Myers, 1891d., p. 638). Such evidence, we believe, fundamentally conflicts with the conventional doctrine that brain processes produce consciousness, and supports the alternative view that brain activity normally serves as a kind of filter, which somehow constrains the material that emerges into waking consciousness. On this latter view, the "relaxation" of the filter under certain still poorly understood circumstances may lead to drastic alterations of the normal mind-brain relation and to an associated enhancement or enlargement of consciousness. [Page 385]
In their discussion of anesthesia, they consider the claim that some aspects of NDEs can be explained by the anesthetized patient being partially awake and hearing or feeling what is being done to him. They point out that such awakenings are exceedingly rare and different in kind from reported NDEs.
The expression "adequately anesthetized" is intended here to exclude cases of literal awakening, or partial awakening, during surgical procedures. Such awakening is known to occur, even using present-day techniques, in something on the order of 0.1-0.3% of all general-surgery procedures. Higher rates occur, as might be expected, when muscle relaxants are used in combination with low levels of anesthetic agents.... The phenomenology of such awakenings, however, is altogether different from that of NDEs, and often extremely unpleasant, frightening, and even painful. The experiences are typically brief and fragmentary, and primarily auditory or tactile, and not visual. [Footnote, page 387]
In their discussion of the celebrated and controversial Pam Reynolds case, they address the objection that the heavily anesthetized patient might still have been able to hear what was going on around her:
The experience also included some verifiable features: First, despite having speakers in her ears that blocked all external sounds with 95 dB clicks, the experience began when she heard the sound of the special saw used to cut into her skull... She also noted the unexpected (to her) way in which her head had been shaved, and she heard a female voice commenting that her veins and arteries were small....
Her description of the unusual saw was verified by the neurosurgeon and by photographs of it obtained by Sabom. Also, as the patient had heard, at the time the cardiopulmonary bypass procedure was being started, the cardiac surgeon (a female) had commented that the right femoral vessels were too small to support the bypass, so that she had to prepare the left leg. Although at the time this comment was made the patient's brainstem auditory evoked potentials had not yet disappeared, the molded speakers in her ears themselves, let alone the 95 dB clicks, would have made it impossible for her to hear the comment in the ordinary way, even had she been fully conscious at the moment....
The case is not perfect. The details were not published for several years after the experience occurred. More importantly, the verifiable events that she reported observing in the operating room occurred when she was anesthetized and sensorially isolated but before and after the period of time in which she was clinically "dead."... Even so, the extremity of her condition and her heavily anesthetized state throughout the entire procedure casts serious doubt on any view of mind or consciousness as unilaterally and totally dependent on intact physiological functioning. [Pages 392-394]
There is also a brief but fascinating discussion of an "even rarer kind of deathbed experience, but one that like NDEs calls into question the absolute dependence of mental functioning on the state of the brain":
There are scattered reports of people apparently recovering from dementia shortly before death. The eminent physician Benjamin Rush, author of the first American treatise on mental illness, observed that "most of mad people discover a greater or less degree of reason in the last days or hours of their lives". Similarly, in his classic study of hallucinations, Brierre de Boismont noted that "at the approach of death we observe that ... the intellect, which may have been obscured or extinguished during many years, is again restored in all its integrity". Flournoy mentioned that French psychiatrists had recently published cases of mentally ill persons who showed sudden improvement in their condition shortly before death....
[Other examples of more recent vintage follow. Then:]
Such cases are few in number and not adequately documented, but the persistence of such reports suggest that they may represent a real phenomenon that could potentially be substantiated by further in traditions. If so, they would seriously undermine the assumption that in such diseases as Alzheimer's the mind itself is destroyed in lockstep with the brain. Like many of the experiences discussed in this chapter, such cases would suggest that in some conditions, consciousness may be enhanced, not destroyed, when constraints normally supplied by the brain are sufficiently loosened. [Pages 410-411]
I might note that Nancy Reagan reported seeing a sudden return of awareness and recognition in her husband's eyes in the last moments before his passing. At the time of President Reagan's death, some commentators observed that this phenomenon was not unusual.
And the authors observe that while awakening during anesthesia is rare and usually traumatic, there are cases in which people remember what transpired while they were anesthetized. These cases involve hypnosis:
The most impressive reports of explicit (or conscious) awareness of events during anesthesia have been elicited by hypnosis. The historically important Levinson study, for example, involved 10 highly hypnotizable subjects undergoing very similar surgical procedures carry out under a deliberately deep and uniform anesthesia regime monitored with EEG. A month later -- but only under hypnosis -- four of these patients recalled nearly verbatim, and four others recalled partially, standardized remarks made by the anesthetist in conjunction with a staged "crisis" in the procedure. These studies have never, to our knowledge, been adequately followed up, but they should be, because such results, if applicable, suggest, like NDEs, that mind is still somehow able to operate when the brain is disabled by anesthesia. Moreover, they suggest, as Myers argued, that hypnosis is a method particularly conducive to loosening the "barrier" [between ordinary consciousness and subliminal consciousness] and thus accessing subliminal levels of consciousness. [Pages 414-415]
The authors are at pains to point out that these phenomena are not merely fringe issues that can be safely ignored. Instead NDEs, OBEs, and similar events pose a paradigm-shattering challenge to reductionist orthodoxy:
How might scientists intent upon defending the conventional view respond to the challenge presented by cases occurring under conditions like [the Pam Reynolds case]? First, it will undoubtedly be objected that even in the presence of a flat-lined EEG there still could be undetected brain activity going on....
[The authors concede as much, but go on to say:]
This first objection, however, completely misses the mark. The issue is not whether there is brain activity of any kind whatsoever, but whether there is brain activity of the specific form a regarded by contemporary neuroscience as the necessary condition of conscious experience. Activity of this form is eminently detectable by current EEG technology, and as we have already shown, it is abolished both by adequate general anesthesia and by cardiac arrest. [Pages 418-419]
In a footnote, the authors add: "Representative of people who have completely missed the mark here is Woerlee (2004)." An interesting debate between Dr. Gerald Woerlee and Kevin Williams is found here.
After considering a few other objections, the authors conclude as follows:
In sum, the central challenge of NDEs lies in asking how these complex states of consciousness, including vivid mentation, sensory perception, and memory, can occur under conditions in which current neurophysiological models of the production of mind by brain deem such states impossible. This conflict between current neuroscientific orthodoxy and the occurrence of NDEs under conditions of general anesthesia and/or cardiac arrest is head-on, profound, and inescapable. [Page 421]