A near-death experience (NDE) is a personal experience associated with death or impending death. Such experiences may encompass a variety of sensations including detachment from the body, feelings of levitation, total serenity, security, warmth, the experience of absolute dissolution, and the presence of a light.
Neuroscience research suggests that an NDE is a subjective phenomenon resulting from "disturbed bodily multisensory integration" that occurs during life-threatening events. NDEs are a recognized part of some transcendental and religious beliefs in an afterlife.
- 1 Etymology
- 2 Characteristics
- 3 Historical reports, incidence and prevalence
- 4 Research
- 5 Explanatory models
- 6 Psychological explanations
- 7 Physiological explanations (organic theories)
- 8 Spiritual explanations - afterlife claims and skeptical responses
- 9 Further reading
- 10 See also
- 11 External links
- 12 References
The equivalent 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. In 1968 Celia Green published an analysis of 400 first-hand accounts of out-of-body experiences. This represented the first attempt to provide a taxonomy of such experiences, viewed simply as anomalous perceptual experiences, or hallucinations. These experiences were popularized by the work of psychiatrist Raymond Moody in 1975 as the near-death experience (NDE).
Researchers have identified the common elements that define near-death experiences. 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. Many common elements have been reported, although the person's interpretation of these events often corresponds with the cultural, philosophical, or religious beliefs of the person experiencing it. For example, in the USA, where 46% of the population believes in guardian angels, they will often be identified as angels or deceased loved ones (or will be unidentified), while Hindus will often identify them as messengers of the god of death.
Although the features of NDEs vary from one case to the next, common traits that have been reported by NDErs are as follows:
- A sense/awareness of being dead.
- A sense of peace, well-being and painlessness. Positive emotions. A sense of removal from the world.
- An out-of-body experience. A perception of one's body from an outside position. Sometimes observing medical professionals performing resuscitation efforts.<
- A "tunnel experience" or entering a darkness. A sense of moving up, or through, a passageway or staircase.
- A rapid movement toward and/or sudden immersion in a powerful light (or "Being of Light") which communicates with the person.
- An intense feeling of unconditional love and acceptance.
- Encountering "Beings of Light", "Beings dressed in white", or similar. Also, the possibility of being reunited with deceased loved ones.
- Receiving a life review, commonly referred to as "seeing one's life flash before one's eyes".
- Receiving knowledge about one's life and the nature of the universe.
- Approaching a border, or a decision by oneself or others to return to one's body, often accompanied by a reluctance to return.
- Suddenly finding oneself back inside one's body.
- Connection to the cultural beliefs held by the individual, which seem to dictate some of the phenomena experienced in the NDE and particularly the later interpretation thereof.
- Body separation
- Entering darkness
- Seeing the light
- Entering the light
He stated that 60% experienced stage 1 (feelings of peace and contentment), but only 10% experienced stage 5 ("entering the light"). According to Alana Karran, the NDE stages resemble the so-called hero's journey.
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. In contrast to common belief, Kenneth Ring argues that attempted suicides do not lead more often to unpleasant NDEs than unintended near-death situations.
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 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.
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 psychopathology, by religious denomination or religiosity, or by experiencers' prior expectations of a pleasant dying process or continued postmortem existence. Greyson (2007) also found that the long term recall of NDE incidents was stable and did not change due to embellishment over time.
Greyson Bush, 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. 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.
NDEs are associated with changes in personality and outlook on life. 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, less concern for acquiring material wealth, 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. However, not all after-effects are beneficial and Greyson describes circumstances where changes in attitudes and behavior can lead to psychosocial and psychospiritual problems. Often the problems are those of the adjustment to ordinary life in the wake of the NDE.
Historical reports, incidence and prevalence
NDEs have been recorded since ancient times. In the 19th century a few studies moved beyond individual cases - one privately done by the Mormons and one in Switzerland. Up to 2005, 95% of world cultures are known to have made some mention of NDEs.
The prevalence of NDEs has been variable in the studies that have been performed. A 1980–1981 survey of the American population showed that 15% described themselves as having had an "unusual experience" when on the verge of death or having a "close call".
A 2005 telephone survey in Australia concluded that 8.9% of the population had had an NDE.
Incidence among cardiac arrest patients
A number of sources report incidences of near death experiences of:
- 17% amongst critically ill patients, in nine prospective studies from 4 different countries.
- between 10-20% from prospective studies with people from different populations who have come close to death
Of these studies, one from 2001 found that 62 patients (18%) had had an NDE, of whom 41 (12%, or 66% of those who had an NDE) described a core experience. Another found an incidence of 6,3% of mental states consistent with NDE.
Contemporary interest in this field of study was originally spurred by the writings of Raymond Moody such as his book Life After Life, which was released in 1975, brought public attention to the topic of NDEs. 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.
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 2,500 self-reported individuals in the US had been reviewed in retrospective studies of the phenomena with an additional 600 outside the US in the West, and 70 in Asia. 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. In all, close to 3,500 individual cases between 1975 and 2005 had been reviewed in one or another study. All these studies were carried out by some 55 researchers or teams of researchers. The medical community has been reluctant to address the phenomenon of NDEs, and grant money for research has been scarce.
Research scales used to classify a near-death experience
Major contributions to the field include Ring's construction of a "Weighted Core Experience Index" to measure the depth of the near-death experience, and Greyson's construction of the "Near-death experience scale" 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 non-specific stress responses. The NDE-scale was later found to fit the Rasch rating scale model. Greyson has also brought attention to the near-death experience as a focus of clinical attention.
Research in animals
Clinical research in cardiac arrest patients
Sam Parnia's 2001 study
In 2001, Parnia and colleagues published the results of a year-long study of cardiac arrest survivors that was conducted at Southampton General Hospital. 63 survivors were interviewed. They had been resuscitated after being clinically dead with no pulse, no respiration, and fixed dilated pupils. These are conditions associated with the cessation of brain function (as confirmed by independent studies). According to Dr. Sam Parnia, a Southampton university clinical research fellow and co-author of the study, "the rapid loss of brainstem activity during cardiac arrest should make it impossible to sustain lucid processes or form lasting memories."
Sam Parnia and colleagues investigated out of body experiences (OBEs) out-of-body claims by placing figures on suspended boards facing the ceiling, not visible from the floor. Parnia wrote "anybody who claimed to have left their body and be near the ceiling during resuscitation attempts would be expected to identify those targets. If, however, such perceptions are psychological, then one would obviously not expect the targets to be identified."
7 patients had memories of the time they were unconscious and 4 had experiences that, according to the study criteria, were NDEs. In other words, six percent of the patients met the strict criteria used to diagnose near-death experiences: they recalled emotions and visions during their unconscious state, including feelings of peace and joy, time speeding up, heightened senses, lost awareness of body, seeing a bright light, entering another world, encountering a mystical being or deceased relative, and coming to a point of no return. According to Dr. Parnia, the recollections, unlike hallucinations, were "highly structured, narrative, easily recalled and clear." No differences were observed on all physiological parameters measured other than oxygen levels. The four patients who met the criteria for a true near-death experience actually had higher oxygen levels—contradicting the notion that lack of oxygen is responsible for the experience. No positive results were reported, and no conclusions could be drawn due to the small number of subjects.
Van Lommel's study
In 2001 Pim van Lommel, a cardiologist from the Netherlands, and his team conducted a study on near-death experiences (NDEs) including 344 cardiac arrest patients who had been successfully resuscitated in 10 Dutch hospitals. Patients not reporting NDEs were used as controls for patients who did, and psychological (e.g. fear before cardiac arrest), demographic (e.g. age, sex), medical (e.g. more than one cardiopulmonary resuscitation (CPR)) and pharmacological data were compared between the 2 groups. The work also included a longitudinal study where the 2 groups (those who had had an NDE and those who had not had one) were compared at 2 and 8 years, for life changes. Van Lommel's prospective study was published in the medical journal The Lancet.
In a review article B. Greyson refers to Van Lommel's study (as well as other sources) and mentions that there have been "documented and corroborated accurate perceptions by near-death experiencers of incidents that occurred during the time when the brain was fully anesthetized or deprived of blood flow, as during cardiac arrest or respiratory arrest". B. Greyson also mentions that apparently some patients reported events that occurred beyond what their sense organs could perceive and that would have been impossible for them to perceive even in a conscious state.
In the same review article, referring to Van Lommel's study and other works, B. Greyson explains that a process of transformation was observed amongst NDE patients after cardiac arrest. This process was greater with respect to non NDE patients and affected relationship to others, sense of sacredness in life, purpose of life, relationship to others, perception of self and attitude toward life. These changes have been confirmed in long term studies. According to B. Greyson, and referring specifically to Van Lommel's study, changes in attitudes toward life amongst cardiac arrest survivors who experienced NDEs are greater 8 years after the event versus 2 years after.
Another review article reports that 41 (12%) of the cardiac arrest patients interviewed provided accounts similar to the Sam Parnia's 2001 study. Also, the same review article. One patient had a conventional out of body experience where he reported being able to watch and recall events during the time of his cardiac arrest. His claims were confirmed by hospital personnel. “This did not appear consistent with hallucinatory or illusory experiences, as the recollections were compatible with real and verifiable rather than imagined events”.
Awareness during Resuscitation (AWARE) study
While at University of Southampton, Parnia was the principal investigator of the AWARE Study, which was launched in 2008. This study which concluded in 2012 included 33 investigators across 15 medical centers in the UK, Austria and the USA and tested consciousness, memories and awareness during cardiac arrest. The accuracy of claims of visual and auditory awareness was examined using specific tests. One such test consisted in installing shelves, bearing a variety of images and facing the ceiling, hence not visible by hospital staff, in rooms where cardiac-arrest patients were more likely to occur. The results of the study were published in October 2014; both the launch and the study results were widely discussed in the media.
A review article analyzing the results reports that, out of 2060 cardiac arrest events, 101 of 140 cardiac arrest survivors could complete the questionnaires. Of these 101 patients only 9% could be classified as near death experiences. 2 more patients (2% of those completing the questionnaires) described "seeing and hearing actual events related to the period of cardiac arrest". These two patients' cardiac arrests did not occur in areas equipped with ceiling shelves hence no images could be used to objectively test for visual awareness claims. One of the two patients was too sick and the accuracy of her recount could not be verified. For the second patient instead, it was possible to verify the accuracy of the experience and to show that awareness occurred paradoxically some minutes after the heart stopped, at a time when "the brain ordinarily stops functioning and cortical activity becomes isoelectric." The experience was not compatible with an illusion, imaginary event or hallucination since visual (other than of ceiling shelves' images) and auditory awareness could be corroborated.
As of May 2016, a posting at the UK Clinical Trials Gateway website describes plans for AWARE II, a two-year multicenter observational study of 900-1500 patients experiencing cardiac arrest, with subjects being recruited as Aug 1 2014 and a trial end date of May 31, 2017.
In a review article psychologist Chris French, has grouped approaches to explain NDEs in three broad groups which "are not distinct and independent, but instead show considerable overlap": spiritual theories (also called transcendental), psychological theories and physiological theories that provide a physical explanation for NDEs.
Another review article  uses the same approach, although the semantics are slightly different, and also divides explanatory models in 3 groups: psychological, physiological and nonreductionistic explanations (which French calls spiritual theories).
The main argument in support of the psychological theories was that many people who had had a close encounter with death, such as those involved in near-fatal accidents, had described experiencing many of the features of a near death experience just prior to the accident. This had been a feature of the cases described by Albert Heim, the nineteenth-century geologist who had collected over 30 cases of mountaineers who had been involved in near-fatal accidents.
The former of the two review articles, explains that NDE experiencers (NDErs) do not differ from the population at large as far as anxiety, intelligence, neuroticism, extraversion and Rorschach indicators. NDErs have been found to be healthy psychological individuals. However NDErs differ in some respects, namely they “tend to be good hypnotic subjects, remember their dreams more often, and are adept at using mental imagery”. Greyson highlights how it is not possible to tell whether some of these characteristics result from the NDE experience or whether there are traits that have facilitated the occurrence of an NDE.
According to the two preceding review articles, one of the oldest one, proposed in the 1970s by professor of psychiatry Russell Noyes and clinical psychologist Roy Kletti, suggested the NDE is a form of depersonalization experienced under emotional conditions such as life-threatening danger, potentially inescapable danger and that the NDE can best be understood as a fantasy based hallucination. The two medical researchers acknowledged that their psychological model could be used to explain those near death experiences where the patient was psychologically, but not physiologically, near death. According to this theory, the subject forms a fantasy that replaces the terrifying experience with a pleasurable dream-like scenario that is more bearable. The subject depersonalizes, in other words abandons all sense of his/her own identity, detaches himself (herself) and completely separates from the frightening perception by engaging in pleasant fantasies. "One’s thoughts and feelings seem unreal and one loses all sense of identity."
According to the two above review articles, the main shortcoming of this theory is that NDErs never lose the feeling of their identity, on the contrary (!), and always report their experiences as being very real to them. Some studies showed results in favour of the depersonalization model, such as the observation "of both higher absorption and fantasy proneness scores amongst NDErs". The model supports "reasonably well for the OBE component of the NDE". However, the sense of more real than real, characterizing NDEs, is totally unlike any form of depersonalization. It has indeed been pointed out that what is altered is not one's own sense of identity but rather "the association of this identity with bodily sensations." Also, near death experiences, unlike depersonalization, may also be unpleasant.
Another psychological theory discussed in the two preceding review articles is called the expectancy model. It has been suggested that although these experiences could appear very real, they had actually been constructed in the mind, either consciously or subconsciously, in response to the stress of an encounter with death (or perceived encounter with death), and did not correspond to a real event. In a way, they are similar to wish-fulfillment: because someone thought they were about to die, they experienced certain things in accordance with what they expected or wanted to occur. Imagining a heavenly place was in effect a way for them to soothe themselves through the stress of knowing that they were close to death. The ‘psychological comfort’ theory proposed including not just the heavenly component of near death experiences, such as seeing a bright light and entering a new domain, but also the resuscitation attempts that some people had claimed to have been able to watch while supposedly out of body. It had been suggested that the brain might simply be constructing that experience from previously stored memories. Most people are now quite familiar with what happens in hospitals through the many medical programs on television. The two review articles highlight the shortcomings of this model, namely:
- the central features of near death experiences have been recorded throughout history and across numerous cultures. Also individuals "often report experiences that conflict with their specific religious and personal expectations regarding death".
- Children who have no knowledge and thus no expectations about death, report similar near death experiences features as adults. Also, some have reported experiences that occurred during their first year of life (although the experiences were reported later).
- Also, societal beliefs do not influence near death experiences: despite the influence of Moody’s book (published in 1975), defining the prevailing Western model of a NDE, near death experiences reports from before and after the publication did not differ except for the more frequent descriptions of a tunnel.
The two preceding review articles also describe another psychological model called dissociation. This is a form of withdrawal to protect an individual from a stressful event. Under extreme circumstances some people may detach from certain unwanted feelings in order to avoid experiencing their emotional impact and suffering associated with them. The person also detaches from one's immediate surroundings. One trigger for such a sensation could be a situation that may appear potentially fatal. According to this theory, near death experiences could be an unconscious defense mechanism in which individuals separate themselves from specific activities or emotions in order to avoid their reality. Findings are contradictory as to whether near death experiences are (or are not) more prone to dissociate than the general population.
Another psychological theory mentioned in the two preceding review articles is that near death experiences could be a form of reliving the trauma of birth. Since a baby travels from the darkness of the womb to light and is greeted by the love and warmth of the nursing and medical staff, and so, it was proposed, the dying brain could be recreating the passage through a tunnel to light, warmth and affection.
However, many near death experiences do not contain the features of a tunnel or a light, and the birth canal would appear very dark and constrained. The reports of travelling through a tunnel do not differ between near death experiencers born by Caesarean versus those delivered naturally, contradicting what the model predicts. Finally, "newborns lack the visual acuity, spatial stability of their visual images, mental alertness, and brain coding capacity to register memories of the birth experiences.
Two review articles also mention that near death experiences could be more frequent amongst subjects with higher fantasy proness, in other words subjects who are likely to experience sensations intensely, who have a rich fantasy life and a capacity to create images in their minds. However, results from studies show contradictory findings: tendency toward fantasy proneness among near-death experiencers has not been shown to be consistently greater than that observed in control groups.
Posttraumatic stress disorder
Posttraumatic stress disorder is a mental disorder resulting from exposure to traumatic events and characterized "by recurrent, intrusive thoughts of the traumatic event and by efforts to avoid thinking about it". Near death experiencers (NDErs) who had a close brush with death, tend to report intrusive memories of the event. This is similar to PSTD patients and different to those who, despite coming close to death, did not have a near death experience. However, NDErs differ from PTSD subjects since the former “do not report greater efforts to avoid reminders of the event”.
Physiological explanations (organic theories)
Physiological theories attempt to explain near death experiences as a result of "normal or abnormal functions of the brain". A wide range of physiological theories of the NDE have been put forward including those based upon cerebral hypoxia, anoxia, and hypercarbia; endorphins and other neurotransmitters; and abnormal activity in the temporal lobes.
Neurobiological factors in the experience have been investigated by researchers in the field of medical science and psychiatry. 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". More recently, cognitive neuroscientist Olaf Blanke (2009), from the Ecole Polytechnique Fédérale de Lausanne, Switzerland, has published a review article presenting evidence for a brain-based explanation of near-death experiences.
In the early 1980s the neuropsychologist Daniel Carr proposed that the NDE has characteristics suggestive of a limbic lobe syndrome and that the NDE can be explained by the release of endorphins and enkephalins in the brain. Judson and Wiltshaw (1983) noted how the release of endorphins can lead to blissful or emotional NDEs, whilst naloxone can produce "hellish" NDEs. 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. Their model included endorphins, neurotransmitters of the limbic system, the temporal lobe and other parts of the brain. Extensions and variations of their model came from other scientists such as Louis Appleby (1989) and Karl Jansen (1990).
The research of Karl Jansen has revealed how the effects of an NDE can be induced by ketamine. In 1996 he published a paper on the subject which concluded "mounting evidence suggests that the reproduction/induction of NDE's by ketamine is not simply an interesting coincidence... ketamine administered by intravenous injection, in appropriate dosage, is capable of reproducing all of the features of the NDE which have been commonly described in the most cited works in this field."
In the 1990s Rick Strassman conducted research on the psychedelic drug dimethyltryptamine (DMT) at the University of New Mexico. 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 or other psychedelic/entheogenic agents.
According to Engmann (2008) 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 (nonverbal auditory hallucinations), 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.
Professor of neurology Terence Hines (2003) claimed that near-death experiences are hallucinations caused by cerebral anoxia, drugs, or brain damage. A 2006 study by Lempert et al. induced syncopes in 42 healthy subjects using cardiovascular manipulations. They found that the subjects reported NDE experiences such as seeing lights, tunnels, meeting deceased family members and visiting other worlds.
Neuroscientists Olaf Blanke and Sebastian Dieguez (2009) have written that NDE experiences can best be explained by different brain functions and mechanisms without recourse to the paranormal. They suggest that damage to the bilateral occipital cortex and the optic radiation may lead to visual features of NDEs such as seeing a tunnel or lights, and interference with the hippocampus may lead to emotional experiences, memory flashbacks or a life review. They concluded that future neuroscientific studies are likely to reveal the neuroanatomical basis of the NDE which will lead to the demystification of the subject.
Vanhaudenhuyse et al. 2009 reported that recent studies employing deep brain stimulation and neuroimaging have demonstrated that out-of-body experiences result from a deficient multisensory integration at the temporoparietal junction and that ongoing studies aim to further identify the functional neuroanatomy of near-death experiences by means of standardized EEG recordings.
Lakhmir Chawla, an Associate Professor of Anesthesiology and Critical Care Medicine and Medicine at George Washington University medical centre argued that near-death experiences are caused by a surge of electrical activity as the brain runs out of oxygen before death. Levels of brain activity were similar to those seen in fully conscious people, even though blood pressure was so low as to be undetectable. 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. Chawla and colleagues from a case series of seven patients wrote "increase in electrical activity occurred when there was no discernable blood pressure, patients who suffer 'near death' experiences may be recalling the aggregate memory of the synaptic activity associated with this terminal but potentially reversible hypoxemia."
Chris French has written that the "temporal lobe is almost certain to be involved in NDEs, given that both damage to and direct cortical stimulation of this area are known to produce a number of experiences corresponding to those of the NDE, including OBEs, hallucinations, and memory flashbacks."
In 2011 Alexander Wutzler and his colleagues at the Charité University of Medicine in Berlin, Germany suggested that near-death experiences may be triggered by an increase of serotonin in the brain. Charles Q. Choi in an article for the Scientific American concluded "scientific evidence suggests that all features of the near-death experience have some basis in normal brain function gone awry."
In a 2013 study, Marie Thonnard and colleagues suggested that the memories of NDEs are flashbulb memories of hallucinations. The findings were in accordance with a 2014 study published in Frontiers in Human Neuroscience.
In 2013 Jimo Borjigin found four states of brainwaves including γ neural oscillation in dying rats. The γ neural oscillation was similar to a previous human study, which speculated that "patients who suffer 'near death' experiences may be recalling the aggregate memory of the synaptic activity associated with this terminal but potentially reversible hypoxemia." The human γ neural oscillations ranged 60–100 Hz,which were also similar to 80–130 Hz found in long-term meditators.
A recent study in 2015 by Duan Li and colleagues suggested there is evidence that the "brain possesses a high capacity for producing well-organized neurophysiological and neurochemical activities and for generation of internal states of consciousness at near-death."
Low oxygen levels in the blood (hypoxia or anoxia) have been hypothesized to induce hallucinations and hence possibly explain NDEs. This is because low oxygen levels characterize life-threatening situations and also by the apparent similarities between NDEs and G-LOC (G-force induced Loss Of Consciousness) episodes. These episodes are observed with fighter pilots experiencing very rapid and intense acceleration that result in lack of sufficient blood supply to the brain. Whinnery studied almost 1000 cases and noted how the experiences often involved "tunnel vision and bright lights, floating sensations, automatic movement, autoscopy, OBEs, not wanting to be disturbed, paralysis, vivid dreamlets of beautiful places, pleasurable sensations, psychological alterations of euphoria and dissociation, inclusion of friends and family, inclusion of prior memories and thoughts, the experience being very memorable (when it can be remembered), confabulation, and a strong urge to understand the experience." However, hypoxia-induced acceleration's primary characteristics are "rythmic jerking of the limbs, compromised memory of events just prior to the onset of unconsciousness, tingling of extremities ..." that are not observed during NDEs. Also G-LOC episodes do not feature life reviews, mystical experiences and "long-lasting transformational aftereffects". Although this may be due to the fact that subjects have no expectation of dying.
Another reason why low oxygen levels are unlikely to be associated with near death experiences is that hypoxia is a very distressing experience where subjects report "perceptual distortions and hallucinations" and confused thinking. These experiences differ significantly from NDEs which are generally "recalled as peaceful and positive experiences" and where subjects experience great clarifty of thought.
Altered blood gas levels
Some investigators have studied whether hypercarbia or higher than normal carbion dioxide levels, could explain the occurrence of NDEs. However, studies are difficult to interpret since NDEs have been observed both with increased levels as well as decreased levels of carbion dioxide, and finally some other studies have observed NDEs when levels had not changed. According to another secondary source features resembling NDEs that are observed in patients with hypercarbia are "comparatively rare an isolated".
It is suggested that the extreme stress caused by a life-threatening situation triggers brain states similar to REM sleep and that a part of the near death experience is a state similar to dreaming while awake. 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.
Some sleep researchers, such as Timothy J. Green, Lynne Levitan and Stephen LaBerge, have noted that NDEs 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. 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.
Modeling of NDEs by S. L. Thaler in 1993 using artificial neural networks has shown that many aspects of the core near-death experience can be achieved through simulated neuron death. 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. Memories, whether related to direct experience, or not, can be seeded upon arrays of such inactive brain cells.
Spiritual explanations - afterlife claims and skeptical responses
Many individuals who experience an NDE see it as a verification of the existence of an afterlife, and some researchers in the field of near-death studies see the NDE as evidence that human consciousness may continue to exist after death. The transcendental (or survivalist) interpretation of the NDE contends that the experience is exactly what it appears to be to the persons having the experience. According to this interpretation, consciousness can become separated from the brain under certain conditions and glimpse the spiritual realm to which souls travel after death.
The transcendental model is in some friction with the dominant view from mainstream neuroscience; that consciousness is a product of, and dependent on, the brain. According to the mainstream neuroscientific view, once the brain stops functioning at brain death, consciousness fails to survive and ceases to exist.
Several NDE researchers have argued that the NDE poses a major challenge to current scientific thinking regarding the relationship between consciousness and the brain, as argued by Van Lommel:
|“||How could a clear consciousness outside one's body be experienced at the moment that the brain no longer functions during a period of clinical death with flat EEG?... (the) NDE pushes at the limits of medical ideas about the range of human consciousness and the mind-brain relation.||”|
These arguments raised by several researchers have been criticized by some scientific skeptics and scientists on several grounds. Chris French (2005, 2009) noted that, "it is clear that the argument that recent findings present a major challenge to modern neuroscience hinges upon the claim that the NDE is actually experienced "during a period of clinical death with flat EEG" as claimed". With respect to the former point he pointed out that it is not at all clear that NDEs actually do occur during a period of flat EEG. Assuming that the patients in question entered a period of flat EEG, French argued that the NDE may have occurred as they entered that state or as they slowly recovered from it. Parnia and Fenwick (2001) had rejected the idea that the NDE may have occurred as the patient is becoming unconscious because they argued that this happens too quickly. But French points out that it is unclear how much time would be required to experience an NDE and that a common feature of altered states of consciousness is time distortion. He argued that this is well illustrated by the life review component of the NDE itself which, although involving a review of a person's entire life, only seems to last a very brief time. And that therefore, "who can say, therefore, that the few seconds of remaining consciousness as an individual enters the state of clinical death is insufficient for the experiences that form the basis of the NDE?".
Parnia and Fenwick (2001) also claimed that the NDE could not occur as a person slowly regains consciousness as this period is characterized by delirium and not by the lucid consciousness reported by NDErs. French again argued that the attribution of confusion is typically made by an outside observer. The subjects themselves may not subjectively feel confused at all. He quoted from an article by Liere and Stickney where they noted that, "Hypoxia quickly affects the higher centers, causing a blunting of the finer sensibilities and a loss of sense of judgment and of self-criticism. The subject feels, however, that his mind is not only quite clear, but unusually keen", and that the subjective claim of great clarity of thought may therefore well be an illusion. French (2005) also noted that "it should be borne in mind that we are always dealing with reports of experiences rather than with the experiences themselves. Memory is a reconstructive process. It is highly likely the final narrative will be much more coherent after the individual has reflected upon it before telling it to others, given the inherently ineffable nature of the experience itself".
And with respect to the latter point, the survivalists have also been criticized by scientists like French and Braithwaite of placing undue confidence in EEG measures. French (2005, 2009) and Braithwaite (2008) claimed that survivalists generally appear to assume that a flat EEG is indicative of total brain inactivity and that therefore the experience of an NDE during such a flatline period would completely undermine the core assumption of modern neuroscience that any complex experience must be based upon a functioning neural substrate.
Even assuming that NDEs actually occur during such periods, the assumption that isoelectric surface EEG recordings are always indicative of total brain inactivity is according to Braithwaite and French wrong. Braithwaite noted that "unless surgically implanted into the brain directly, the EEG principally measures surface cortical activity. The waveforms seen in cortical EEG are largely regarded to come from the synchronistic firing of cortical pyramidal neurons. As such, it is entirely conceivable that deep sub-cortical brain structures could be firing, and even in seizure, in the absence of any cortical signs of this activity." Braithwaite also noted that Gloor (1986) reviewed evidence indicating that inter-ictal discharges in the hippocampus or amygdala can produce complex meaningful hallucinations without the involvement of the cerebral cortex.
Another argument which, according to Braithwaite (2008), relies upon misplaced confidence in surface EEG measurement was put forward by Fenwick P. and Fenwick E. (1995). They argued that, in cases where the surface EEG recording was not flat, if the NDE was a hallucinatory experience based upon disinhibition, evidence of this disinhibition should be visible in the surface EEG recorded at the time. However, Braithwaite argued that data from a recent study comparing EEG recorded at the scalp with EEG recorded from electrodes surgically implanted in deep sub-cortical regions show conclusively that high-amplitude seizure activity can be occurring in deep brain regions and yet be completely undetectable in the surface EEG. Even more so, a study comparing surface EEG recordings with the fMRI blood-oxygen-level dependent (BOLD) response showed that the surface EEG could fail to detect seizure activity at the level of the cortex that was detected by the BOLD response.
Another argument made by several NDE researchers such as Parnia and Fenwick (2001) for the transcendental model is that the occurrence of anecdotal reports of patients being able to see and recall detailed events occurring during the cardiac arrest that are afterwards verified by hospital staff supports the argument that such perception sometimes do occur during periods of clinical death. NDE researcher Janice Miner Holden found 107 such anecdotal reports in the NDE literature as of 2009, out of which approximately 91% were accurate.
According to French (2005) and Blackmore (1993), when serious attempts at corroboration are attempted, the evidence often turns out to be nowhere near as impressive as it initially appeared. And such cases can possibly (since they had not been ruled out) be accounted for in terms of non-paranormal factors including, "information available at the time, prior knowledge, fantasy or dreams, lucky guesses, and information from the remaining senses. Then there is selective memory for correct details, incorporation of details learned between the end of the NDE and giving an account of it, and the tendency to tell a good story."
According to French (2005) a similar claim to the argument from veridical perceptions are the cases of blind people that during NDEs are able to see even though, in some cases, they may have been blind from birth. According to French (2005), "initial readings of such accounts often give the impression that the experience involves seeing events and surroundings in the same way that sighted people do, but closer reflection upon these cases suggests otherwise." French quoted from an article by NDE researcher Ring where he noted that, "as this kind of testimony builds, it seems more and more difficult to claim that the blind simply see what they report. Rather, it is beginning to appear it is more a matter of their knowing, through a still poorly understood mode of generalized awareness, based on a variety of sensory impressions, especially tactile ones, what is happening around them." French (2005) concluded that, "NDEs in the blind are certainly worthy of study but do not merit any special status in terms of evidential support for spiritual explanations of the phenomenon."
Nevertheless, according to French (2005) future research in the near-death experience should focus on devising ways to distinguish between the two main hypotheses relating to when the NDE is occurring. If it really is occurring when some NDE researchers claim that it is, during a period of flat EEG with no cortical activity, then modern neuroscience would require serious revision. This would also be the case if the OBE, either within the NDE or not, could be shown to be veridical. Attempts to test the veridicality of OBEs using hidden targets (e.g., Parnia and Fenwick (2001)) should be welcomed.
Recent research into afterlife conceptions across cultures by religious studies scholar Gregory Shushan 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, which tends to suggest that the authors of these ancient religious texts were familiar with NDEs or similar experiences. Cross-cultural similarity, however, can be used to support both religious and physiological theories, for both rely on demonstrating that the phenomenon is universal.
Studies that have investigated cultural differences in NDEs have argued that the content of the experiences do 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.
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