出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/08/18 04:59:11」(JST)
A near-death experience (NDE) refers to personal experiences associated with impending death, encompassing multiple possible sensations including detachment from the body, feelings of levitation, total serenity, security, warmth, the experience of absolute dissolution, and the presence of a light. These phenomena are usually reported after an individual has been pronounced clinically dead or has been very close to death. With recent developments in cardiac resuscitation techniques, the number of reported NDEs has increased.[1] The experiences have been hypothesized in medical journals as having the characteristics of hallucinations,[2][3][4] while parapsychologists and a number of scientists have pointed to them as evidence of an afterlife and mind-body dualism.[5][6][7][8] Religious believers tend to be divided on and uncertain about their interpretation of NDEs, given that while they verify some aspects of the faiths, they also explicitly falsify other aspects.[5] According to the 2013 PLOS ONE article by Thonnard et al., "near-death experiences cannot be considered as imagined event memories. On the contrary, their physiological origins could lead them to be really perceived although not lived in the reality."[9]
Popular interest in near-death experiences was initially sparked by Weiss's 1972 The Vestibule,[citation needed] followed by Raymond Moody's 1975 book Life After Life[10][11] and the founding of the International Association for Near-Death Studies (IANDS) in 1981.[12] According to a Gallup poll, approximately eight million Americans claim to have had a near-death experience.[13] Some commentators, such as Simpson,[14] claim that the number of near-death experiencers may be underestimated. People who have had a near-death experience may not be comfortable discussing the experience with others, potentially due in part to some seeing an NDE as a paranormal experience.[12] NDEs are among the phenomena studied in the fields of psychology,[15] psychiatry,[16] and hospital medicine.[17][18]
The earliest accounts of NDE can be traced to the Myth of Er, recorded in the 4th century BC by Plato's The Republic (10.614-10.621), wherein Plato describes a soldier telling of his near-death experiences.[10]:115[19]:96–99
The cognate French term expérience de mort imminente (experience of imminent death) was proposed by the French psychologist and epistemologist Victor Egger as a result of discussions in the 1890s among philosophers and psychologists concerning climbers' stories of the panoramic life review during falls.[21][22] In 1968 Celia Green published an analysis of 400 first-hand accounts of out-of-body experiences.[23] This represented the first attempt to provide a taxonomy of such experiences, viewed simply as anomalous perceptual experiences, or hallucinations. These experiences were popularized with the work of psychiatrist Raymond Moody in 1975 as the Near-Death Experience (NDE). It is uncertain if Moody was aware of the expression earlier used by Egger.[citation needed]
Researchers have identified the common elements that define near-death experiences.[24] Bruce Greyson argues that the general features of the experience include impressions of being outside one's physical body, visions of deceased relatives and religious figures, and transcendence of egotic and spatiotemporal boundaries.[25] Many different elements have been reported, though the exact elements tend to correspond with the cultural, philosophical, or religious beliefs of the person experiencing it:
The traits of a classic NDE are as follows:
Kenneth Ring (1980) subdivided the NDE on a five-stage continuum. The subdivisions were:[29]
He stated that 60% experienced stage 1 (feelings of peace and contentment), but only 10% experienced stage 5 ("entering the light").[30]
Clinical circumstances associated with near-death experiences include cardiac arrest in myocardial infarction (clinical death); shock in postpartum loss of blood or in perioperative complications; septic or anaphylactic shock; electrocution; coma resulting from traumatic brain damage; intracerebral hemorrhage or cerebral infarction; attempted suicide; near-drowning or asphyxia; apnea; and serious depression.[31] In contrast to common belief, Kenneth Ring argues that attempted suicides do not lead more often to unpleasant NDEs than unintended near-death situations.[32]
The distressing aspects of some NDEs are discussed more closely by Greyson and Bush.[33]
| This section requires expansion. (November 2013) |
Karlis Osis and his colleague Erlendur Haraldsson argued that the content of near death experiences does not vary by culture, except for the identity of the figures seen during the experiences. For example, a Christian may see Jesus, while a Hindu may see Yamaraja, the Hindu king of death.[34][35] However, Yoshi Hata and his team reported NDEs with substantially different contents than those described above.[36]
Some NDEs have elements that bear little resemblance to the "typical" near-death experience. Anywhere from one percent (according to a 1982 Gallup poll) to 20 percent[37] of subjects may have distressing experiences and feel terrified or uneasy as various parts of the NDE occur, they visit or view dark and depressing areas or are accosted by what seem to be hostile or oppositional forces or presences.[38] Persons having bad experiences were not marked by more religiosity or suicidal background. According to one study (Greyson 2006) there is little association between NDEs and prior psychiatric treatment, prior suicidal behavior, or family history of suicidal behavior. There was also little association between NDEs and religiosity, or prior brushes with death, suggesting the occurrence of NDEs is not influenced by psycopathology, by religious denomination or religiosity, or by experiencers' prior expectations of a pleasant dying process or continued postmortem existence.[39] Greyson (2007) also found that the long term recall of NDE incidents was stable and did not change due to embellishment over time.[40]
Bush (2012), a counselor, and board member and former Executive Director to the International Association for Near-Death Studies, holds that not all negative NDE accounts are reported by people with a religious background.[41] Suicide attempters, who should be expected to have a higher rate of psychopathology according to Greyson (1991) did not show much difference from non-suicides in the frequency of NDEs.[42] Bush (2012), holds that frightening NDEs have been ignored too long, in favor of only positive reports: "In fact, because contemporary metaphysical thought has so strongly emphasized the belief (or certainly the hope) that only the light is real and has value, it has by and large denied or ignored the 'dark night' aspects of spirituality."[43]
Lindley, Bryan and Conley (1981) in a study of 55 near-death encounters found eleven (20 percent) to be "partially negative or Hellish." They defined a "negative" near death experience as one that contains extreme fear, panic or anger. It may also contain descriptions of demonic creatures or embittered human-like voices that mock or taunt the subjects. Such negatives may only form part of the overall NDE incident. Margot Grey's study of NDEs in England (Grey 1985) reports that distressing experiences tend to follow 5 phases: fear and panic, out of body experience, entering a black void, sensing an evil force and entering a hellish environment. These 5 phases parallel the more typical "standard" NDEs of peace, out of body experience, tunnel travel, seeing the light, and entrance to the paradise environment. Distressing experiences were more likely to be reported shortly after the NDE incident than the positive experiences.[44]
Grey's comparative study of British and American near-death experiencers indicates that negative features, while a small minority, definitely exist. Typical negative experiences described by subjects include feelings of panic, anguish, desperation, intense loneliness and desolation. Subjects described environments as either dark and gloomy or barren and hostile; some subjects reported being on the brink of a pit or abyss, or sensing evil or malevolent forces or creatures. Such environments were sometimes conceived of by subjects as intensely hot or cold and often included sounds of despair or mourning. Atwater (1988) also noted patterns parallel to peaceful NDEs in her study including lifeless apparitions, barren expanses, threats or silence, a seeming danger of violence, a sense of hell and coldness. Flynn (1986) notes a general pattern to distressing experiences in which evil or darkness is experienced as a distinct dimension or entity separate from the positively experienced light.[45] Atwater (1992) reports that only adults in her sample experienced distressing NDEs, not children.[46]
Three patterns of distressing NDEs. Greyson and Bush's (2013) analysis of 50 distressing NDEs, report the following 3 patterns:[47]
Moral dimensions of distressing NDEs. A number of writers on Near Death Experiences identify a dark zone or "void" in association with negative or malignant spiritual beings, or a zone of despair, depression or despondency connected with the actions persons have committed in earthly life or their moral character.[49] These negative elements may not be isolated but may blend with other standard NDE features. NDErs who have viewed a "dark" void of depressed or trapped "souls" for example, may still go on to have a Life Review, feeling of warmth and love, and other such elements. The Life Review NDE accounts detail is usually a time of searching exposure and affirmation, having moral implications that the NDE traveler had to confront, including his or her actions and the negative or positive impact they had on others.[50] Some New Age writers like Edgar Cacye[51] and Emmanuel Swedenborg[52] also identify a dark or negative area brought about by the dead person's own behavior, state or obsessions in their earthly physical life. According to Swedenborg: "All who are in the Hells are in evils and in falsities therefrom derived from the loves of self and of the world" (n. 551-565).[53]
This aspect of the Life Review is sometimes described as humbling with inward character, thoughts and outward actions laid bare, and the subject invited to examine how wrong (or right) they were through the eyes of the Divine/Light Being, and how others were affected. While the exposure was felt as distressing in some aspects, the Review is generally in a larger context of being unconditionally loved, though regret and guilt may be experienced. NDErs under the full moral exposure of the Review almost always agreed with the Divine Being as to rightness or wrongness of their actions, as seen through the Being's moral perspective, and the rightness of that perspective.[50] The Being of Light or others may later make clear to the NDE that they are in a temporary transitional not permanent state and must choose to "go back" or "stay". Sometimes the NDEr is told that a "work" or life must be completed. The final moral destiny or fate of the "returning" NDEr is thus pushed back to some future time.[54]
In the 1990s a literature on distressing near-death experiences emerged. One cardiologist (Maurice Rawlins) describes a patient fading in and out of consciousness screaming "I am in hell." The patient later described near-death phenomena but without recalling the hellish aspect. Both doctor and patient were transformed by the experience, each becoming religious. Medical patients appear more likely to forget such frightening experiences than pleasant ones, or may be more reluctant to share negative self-images and memories than positive ones with researchers.[55] According to one study of NDEs- most contemporary near-death experiencers recount that they, not the Light Being perform the moral judgment, their own consciences holding them accountable. The "Figure of Light" serves to provide the standard of judgment. A recurring theme in Life Reviews is that each person is responsible for every thought, word and deed of his or her life.[56] Bush (2012) holds that the notion of being prepared may apply if consciousness is not strictly in the human brain:
Distressing NDE patterns and outcomes. Rommer (2001) found that NDE suicide attempters made up 55% of people in her research who reported a Type II Eternal Void experience, 18% who reported a Type III Hellish experience, and most of those who reported a Type IV Negative Judgment experience, but cautions against jumping to conclusions about suicides since some suicide NDEs are pleasurable, and the emotional turmoil surrounding the suicide event, and/or guilt or fear about the negative consequences for suicides on the other side may play a part in influencing the pattern of these experiences.[58] NDErs who experience distressing experiences may often turn around their lives in a positive way, or attempt to do so. Rommer 2001[59] suggests that distressing NDErs almost always come to see their experiences as blessings in disguise. Bush (2002) holds that "returning" NDErs have a more mixed pattern of post-event edjustment- with those who interpret the experience as a warning to correct previous behaviors healing most quickly and thoroughly. Others may attempt to dismiss the experience as less valid than pleasurable NDEs, or may take a long view, sometimes lasting years, to draw lessons and conclusions from the NDE experience.[60]
A small percentage of NDE subjects report a prophetic vision that reveals to them the fate of earth and humanity. This is generally an apocalyptic vision showing the end times, but some report visions of humanity evolving into higher beings. Although some claim to have specific forecasts such as the time of a big natural disaster, most NDErs who allege messages or prophecies do not proffer specific information on future world events, save in a general way: such as warning mankind that it is accountable on the other side, a vague coming period of war and chaos, or to turn from environmental destruction or mistreatment of one another, or the vast new realm of light and love beyond physical death.[61] Some prophecies are of a personal nature, such as children that will be born in the future, or the pending death of a relative.[62] Other prophecies are limited to the personal testimony of the NDE, as to the felt reality of the experience, the future of light and hope, or the ethical, moral or religious lessons to be drawn, rather than sweeping claims as to specific future historical incidents.[63]
Messages said to be given sometimes occur during the Life Review, where the NDEr is given a detailed "playback" exposing all thoughts, actions and motives and their impact, as seen through the moral and spiritual lens of the Being of Light. The personal future or outcome of the temporary NDE sojorner is sometimes left ambiguous. A Life Review may confirm personal safety, protection or salvation upon future death, or may leave the future open until the normal termination of earthly life. Some NDE travelers may conceive of Life Reviews as a "reprieve" or a "second chance" to put things right in their lives, before they cross over the other side of death, since all actions and thoughts are to be accountable there.[64] NDErs generally are changed by their experience, becoming less ego-centric, more empathetic, and having less interest in status symbols and material possessions.[39]
In the process of clinical death, the heart stops working and pumping blood to the brain, thereby cutting the brain's essential supply of oxygen and of other less urgent nutrients. In dogs, measurable brain activity ends within 20 to 40 seconds.[65] And during brain death, all brain function halts permanently. As characteristic of all biological cells, brain cells die once deprived of oxygenated blood, destroying the brain. According to the current mainstream neuroscientific view, the mind fails to survive brain death and ceases to exist.[66][67]
Because the study of NDEs is a topic that addressed multiple possible feelings, sensations and their origins, research on NDE should be conducted primarily by researchers with credentials in cognitive neuroscience. Cognitive neuroscience addresses the questions of how psychological functions (for example, human feelings and sensations) are produced by neural circuitry (including the human brain). Modern contributions to the research on near-death experiences, however, have come from several academic disciplines that generally do not include neuroscience.[68] There are multiple reasons for this trend.[68] For example, brain activity scans are not typically performed when a patient is undergoing attempts at emergency resuscitation.[69] Claiming that there is no measurable brain activity without having a variety of different EEG, catSCAN, FMRI, etc. is not considered a good scientific practice.[68][69] Existing research is mainly in the disciplines of medicine, psychology and psychiatry. Heightened brain activity has been recorded in experimental rats directly following cardiac arrest though there has been no similar research in humans.[70]
Individual cases of NDEs in literature have been identified into ancient times.[71] In the 19th century a few efforts moved beyond studying individual cases - one privately done by Mormons and one in Switzerland. Up to 2005, 95% of world cultures have been documented making some mention of NDEs.[71]
Contemporary interest in this field of study was originally spurred by the writings of Jess Weiss (popular literature author), Elisabeth Kübler-Ross (psychiatrist), George Ritchie (psychiatrist), and Raymond Moody Jr. (psychologist and M.D.). Moody's book Life After Life, which was released in 1975, brought public attention to the topic of NDEs.[24] This was soon to be followed by the establishment of the International Association for Near-death Studies (IANDS) in 1981. IANDS is an international organization that encourages scientific research and education on the physical, psychological, social, and spiritual nature and ramifications of near-death experiences. Among its publications are the peer-reviewed Journal of Near-Death Studies and the quarterly newsletter Vital Signs.[12]
Bruce Greyson (psychiatrist), Kenneth Ring (psychologist), and Michael Sabom (cardiologist), helped to launch the field of Near-Death Studies and introduced the study of near-death experiences to the academic setting. From 1975 to 2005, some 2500 self reported individuals in the US had been reviewed in retrospective studies of the phenomena[71] with an additional 600 outside the US in the West,[71] and 70 in Asia.[71] Prospective studies, reviewing groups of individuals and then finding who had an NDE after some time and costing more to do, had identified 270 individuals.[71] In all close to 3500 individual cases between 1975 and 2005 had been reviewed in one or another study. And all these studies were carried out by some 55 researchers or teams of researchers.[71] The medical community has been reluctant to address the phenomenon of NDEs, and grant money for research has been scarce.[12] Nevertheless, both Greyson and Ring developed tools usable in a clinical setting. Major contributions to the field include Ring's construction of a "Weighted Core Experience Index"[72] to measure the depth of the near-death experience, and Greyson's construction of the "Near-death experience scale"[73] to differentiate between subjects that are more or less likely to have experienced an NDE. The latter scale is also, according to its author, clinically useful in differentiating NDEs from organic brain syndromes and nonspecific stress responses.[73] The NDE-scale was later found to fit the Rasch rating scale model.[15] Greyson[74] has also brought attention to the near-death experience as a focus of clinical attention, while Melvin Morse, head of the Institute for the Scientific Study of Consciousness, and colleagues[28][75] have investigated near-death experiences in a pediatric population.
Neurobiological factors in the experience have been investigated by researchers in the field of medical science and psychiatry.[76] Among the researchers and commentators who tend to emphasize a naturalistic and neurological base for the experience are the British psychologist Susan Blackmore (1993), with her "dying brain hypothesis",[77] and the founding publisher of Skeptic magazine, Michael Shermer (1998). More recently, cognitive neuroscientists Jason Braithwaite (2008)[78] from the University of Birmingham and Sebastian Dieguez (2008)[79] and Olaf Blanke (2009)[80] from the Ecole Polytechnique Fédérale de Lausanne, Switzerland have published accounts presenting evidence for the brain-based nature of near death experiences.
In September 2008, it was announced that 25 U.K. and U.S. hospitals would examine near-death studies in 1,500 heart attack patient-survivors. The three-year study, coordinated by Sam Parnia at Southampton University, hopes to determine if people without heartbeat or brain activity can have an out-of-body experience with veridical visual perceptions.[81] This study follows on from an earlier 18-month pilot project.[82] On a July 28, 2010 interview about a recent lecture at Goldsmiths,[83] Parnia (internal medicine physician by training with specialty in pulmonology, critical care, and sleep medicine) asserts that "evidence is now suggesting that mental and cognitive processes may continue for a period of time after a death has started" and describes the process of death as "essentially a global stroke of the brain. Therefore like any stroke process one would not expect the entity of mind / consciousness to be lost immediately". He also expresses his disagreement with the term 'near death experiences' because "the patients that we study are not near death, they have actually died and moreover it conjures up a lot of imprecise scientific notions, due to the fact that [death] itself is a very imprecise term".[84]
Researcher Lakhmir Chawla, an Associate Professor of Anesthesiology and Critical Care Medicine and Medicine at George Washington University medical centre in Washington D.C. argues that near-death experiences are caused by a surge of electrical activity as the brain runs out of oxygen before death. Levels were similar to those seen in fully conscious people, even though blood pressure was so low as to be undetectable, and could generate vivid images and feelings. The gradual loss of brain activity had occurred in the approximate hour before death, and was interrupted by a brief spurt of action, lasting from 30 seconds to three minutes. Sam Parnia disputed this explanation, claiming that Lakhmir Chawla had not provided proof that the electrical surges he recorded were linked to near-death experiences, saying: "Since all the patients died, we cannot tell what they were experiencing".[85]
The top peer-reviewed journals in neuroscience, such as Nature Reviews Neuroscience, Brain Research Reviews, Biological Psychiatry, Journal of Cognitive Neuroscience are generally not publishing research on NDEs. Among the scientific and academic journals that have published, or are regularly publishing, new research on the subject of NDEs are Journal of Near-Death Studies, Journal of Nervous and Mental Disease, British Journal of Psychology, American Journal of Disease of Children, Resuscitation, The Lancet, Death Studies, and the Journal of Advanced Nursing.
The prevalence of NDEs has been variable in the studies that have been performed. According to the Gallup and Proctor survey in 1980-1981, of a representative sample of the American population, data showed that 15% had an NDE.[86] Knoblauch in 2001 performed a more selective study in Germany and found that 4% of the sample population had an NDE.[87] The information gathered from these studies may nevertheless be subject to the broad timeframe and location of the investigation.
Perera et al., in 2005, conducted a telephone survey of a representative sample of the Australian population, as part of the Roy Morgan Catibus Survey, and concluded that 8.9% of the population had an NDE.[88] In a more clinical setting, van Lommel et al. (2001), a cardiologist from Netherlands, studied a group of patients who had suffered cardiac arrests and who were successfully revived. They found that 62 patients (18%) had an NDE, of whom 41 (12%, or 66% of those who had an NDE) described a core experience.
According to Martens[89] the only satisfying method to address the NDE-issue would be an international multicentric data collection within the framework for standardized reporting of cardiac arrest events. The use of cardiac-arrest criteria as a basis for NDE research has been a common approach among the European branch of the research field.[18][90]
The first formal neurobiological model for NDE was presented in 1987 by Chilean scientists Juan Sebastián Gómez-Jeria (who holds a PhD in Molecular Physical Chemistry) and Juan Carlos Saavedra-Aguilar (M.D.) from the University of Chile.[91] In the 1990s, Rick Strassman conducted research on the psychedelic drug dimethyltryptamine (DMT) at the University of New Mexico.[92][93][94] Strassman advanced the hypothesis that a massive release of DMT from the pineal gland prior to death or near-death was the cause of the near-death experience phenomenon. Only two of his test subjects reported NDE-like aural or visual hallucinations, although many reported feeling as though they had entered a state similar to the classical NDE. His explanation for this was the possible lack of panic involved in the clinical setting and possible dosage differences between those administered and those encountered in actual NDE cases. All subjects in the study were also very experienced users of DMT and/or other psychedelic/entheogenic agents. Some speculators consider that if subjects without prior knowledge on the effects of DMT had been used during the experiment, more volunteers would have reported NDE. Critics have argued that neurobiological models often fail to explain NDEs that result from close brushes with death, where the brain does not actually suffer physical trauma, such as a near-miss automobile accident. Such events may however have neurobiological effects caused by stress.[citation needed]
Whether or not these experiences are hallucinatory, they have a profound impact on the observer. Many psychologists not necessarily pursuing the paranormal, such as Susan Blackmore, have recognized this, and seek its biological cause.[95]
According to Engmann (medical doctor),[96] near-death experiences of people who are clinically dead are psychopathological symptoms caused by a severe malfunction of the brain resulting from the cessation of cerebral blood circulation. An important question is whether it is possible to "translate" the bloomy experiences of the reanimated survivors into psychopathologically basic phenomena, e.g. acoasms, central narrowing of the visual field, autoscopia, visual hallucinations, activation of limbic and memory structures according to Moody's stages. The symptoms suppose a primary affliction of the occipital and temporal cortices under clinical death. This basis could be congruent with the thesis of pathoclisis—the inclination of special parts of the brain to be the first to be damaged in case of disease, lack of oxygen, or malnutrition—established eighty years ago by Cécile and Oskar Vogt.[97] According to that thesis, the basic phenomena should be similar in all patients with near-death experiences. But a crucial problem is to distinguish these basic psychopathological symptoms from the secondary mental associated experiences which may result from a reprocessing of the basic symptoms under the influence of the person's cultural and religious views.
Research released in 2010 by University of Maribor, Slovenia had put near-death experiences down to high levels of carbon dioxide in the blood altering the chemical balance of the brain and tricking it into 'seeing' things.[85] Of the 52 patients, 11 reported NDEs.[98][99] Neuropsychiatrist Peter Fenwick of the Institute of Psychiatry at Kings College London responded to this study with "in cardiac arrests, everybody has high CO2 but only 10 percent have NDEs," and "What's more, in heart attack patients, Fenwick said, "there is no coherent cerebral activity which could support consciousness, let alone an experience with the clarity of an NDE."[99]
An article by Dutch cardiologist Pim van Lommel et al., argues, "With a purely physiological explanation such as cerebral anoxia for the experience, most patients who have been clinically dead should report one."[18] Accordingly, a lack of predictable experiences should cast doubt on wholesale explanations of NDEs. According to Southampton University researcher Sam Parnia (critical care doctor), "Death starts when the heart stops beating, but we can intervene and bring people back to life, sometimes even after three to four hours when they are kept very cold. It could be that a far higher proportion of people have near-death experiences but don't remember them."[85]
Psychologist Christopher C. French has summarized psychological and organic theories that provide an existing scientific explanation for NDEs. Psychological include the proposal that the NDE is a dissociative defense mechanism that occurs in times of extreme danger. A wide range of organic theories of the NDE has been put forward including those based upon cerebral hypoxia, anoxia, and hypercarbia; endorphins and other neurotransmitters; and abnormal activity in the temporal lobes.[100] NDE subjects have increased activity in the left temporal lobe.[3] In an experiment with one patient, electrical stimulation at the left temporoparietal junction lead to an illusion of another person close to her.[101][102]
A 2012 study led by neuroradiologist Renemane reached the conclusion that the NDE is considered as a state of unconsciousness resembling oneiroid syndrome.[103]
It is suggested that the extreme stress caused by a life-threatening situation triggers brain states similar to REM sleep and that part of the near death experience is a state similar to dreaming while awake.[104] People who have experienced times when their brains behaved as if they were dreaming while awake are more likely to develop the near death experience.[citation needed]
Some sleep researchers, such as Timothy J. Green, Lynne Levitan and Stephen LaBerge, have noted that NDE experiences are similar to many reports of lucid dreaming, in which the individual realizes he is in a dream. Often these states are so realistic as to be barely distinguishable from reality.
In a study of fourteen lucid dreamers performed in 1991, people who perform wake-initiated lucid dreams (WILD) reported experiences consistent with aspects of out-of-body experiences such as floating above their beds and the feeling of leaving their bodies.[105] Due to the phenomenological overlap between lucid dreams, near-death experiences, and out-of-body experiences, researchers say they believe a protocol could be developed to induce a lucid dream similar to a near-death experience in the laboratory.[106]
Other similarities include seeing oneself from the outside (an out of body experience), floating or flying, heightened awareness, and feelings of joy or peace. Some researchers believe this is caused when the mind is deprived of the majority of its senses and relies on the expectational processing. In this regard one experiences what one would expect to happen in their current circumstance. This could explain experiences caused by mental trauma such as a near miss accident in which the mind may close itself off at least partially to the senses and ones caused by physical trauma in which again the mind closes itself off to the world.[citation needed] At present, there exists no clear physiological or psychological basis for any relationship between lucid dreaming and NDEs.
Modeling of NDEs by S. L. Thaler in 1993 [107] using artificial neural networks has shown that many aspects of the core near-death experience can be achieved through simulated neuron death.[108][109][110][111] In the course of such simulations, the essential features of the NDE—life review, novel scenarios (i.e., heaven or hell), and OBE—are observed through the generation of confabulations or false memories, as discussed in Confabulation (neural networks). The key feature contributing to the generation of such confabulatory states are a neural network's inability to differentiate dead from silent neurons.[112] Memories, whether related to direct experience, or not, can be seeded upon arrays of such inactive brain cells.
The first clinical study of near-death experiences (NDEs) in cardiac arrest patients was by Pim van Lommel, a cardiologist from the Netherlands, and his team (The Lancet, 2001).[18] Of 344 patients who were successfully resuscitated after suffering cardiac arrest, 62 (18%) expressed an intraoperative memory and among these, 41 (12%) experienced core NDEs, which included out-of-body experiences. According to Lommel, the patients remembered details of their conditions during their cardiac arrest despite being clinically dead with flatlined brain stem activity. Van Lommel concluded that his findings supported the theory that consciousness continued despite lack of neuronal activity in the brain. Van Lommel conjectured that continuity of consciousness may be achievable if the brain acted as a receiver for the information generated by memories and consciousness, which existed independently of the brain, just as radio, television and internet information existed independently of the instruments that received it.[17]
Van Lommel et al., reported that 62 of the 344 patients with cardiac arrest reported some recollection. Of these 62, 50% reported an awareness or sense of being dead, 24% said that they had had an out-of-body experience, 31% recalled moving through a tunnel, whilst 32% described meeting with deceased people. Moreover, while near-death experiencers commonly report feelings of peace and bliss, only 56% associated the experience with such positive emotions. No patients reported a distressing or frightening NDE.[26]
NDEs are also associated with changes in personality and outlook on life.[24] Kenneth Ring (professor of psychology) has identified a consistent set of value and belief changes associated with people who have had a near-death experience. Among these changes one finds a greater appreciation for life, higher self-esteem, greater compassion for others, a heightened sense of purpose and self-understanding, desire to learn, elevated spirituality, greater ecological sensitivity and planetary concern, and a feeling of being more intuitive. Changes may also include increased physical sensitivity; diminished tolerance of light, alcohol, and drugs; a feeling that the brain has been "altered" to encompass more; and a feeling that one is now using the "whole brain" rather than a small part.[24] However, not all after-effects are beneficial[113] and Greyson[114] describes circumstances where changes in attitudes and behavior can lead to psychosocial and psychospiritual problems.[115] Often the problems are those of the adjustment to ordinary life in the wake of the NDE.
Recent research into afterlife conceptions across cultures by religious studies scholar Gregory Shushan [116] analyzes the afterlife beliefs of five ancient civilizations (Old and Middle Kingdom Egypt, Sumerian and Old Babylonian Mesopotamia, Vedic India, pre-Buddhist China, and pre-Columbian Mesoamerica) in light of historical and contemporary reports of near-death experiences, and shamanic afterlife "journeys". It was found that despite numerous culture-specific differences, the nine most frequently recurring NDE elements also recur on a general structural level cross-culturally, as if to suggest that the authors of these ancient religious texts were familiar with NDE or similar. Cross-cultural similarity, however, can be used to support both religious and physiological theories, for both rely on demonstrating that the phenomenon is universal. Others dispute in favor of cultural similarities;[117] and others suggest that the experience is essentially universal, but altered in detail by cultural bias.[118]
Many individuals who experience an NDE see it as a verification of the existence of an afterlife.[18][119][120][121][122][123][124][125][126]
According to Sam Parnia, "Arch sceptics will always attack our work. I'm content with that. That's how science progresses. What is clear is that something profound is happening. The mind – the thing that is 'you' – your 'soul' if you will - carries on after conventional science says it should have drifted into nothingness."[127] However, Belgian neurologist Dr. Steven Laureys disagrees, stating in his study that: "Many individuals having had NDEs were not physically in danger of death suggesting that the perception, on its own, of the risk of death seems to be important in eliciting NDEs."[128]
Skeptics argue against the false deduction that the brain of a patient is inactive. In fact there is no way to verify the timing of memory formation relative to brain scans when the patient is not conscious.[129] Most brain activity tests are not typically performed when a patient is undergoing attempts at emergency resuscitation. It is entirely possible, for example, that a patient showing no activity on an EEG scan could still have brain activity that would appear on an FMRI, PET, or catSCAN. Also, the experiences reported by NDE subjects have also been reported by other patients whose experiences had known triggers (mostly chemicals of a psychedelic nature.) The chemical processes that happen in a brain under oxygen deprivation are known to share some characteristics with the effects of psychoactive substances.
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| リンク元 | 「cardiac death」「determination of death」「臨死体験」 |
| 関連記事 | 「experience」「near」「death」 |