Psychedelic drug

From Wikipedia, the free encyclopedia

Synthetic mescaline. Normally biosynthesized from peyote and some other cacti.^{[citation needed]} Mescaline was the first psychedelic compound to be extracted and isolated.^[1]

 

LSD is widely known as a psychedelic drug and often features psychedelic artwork on its blotters

Psychedelics are a class of drug whose primary action is to trigger psychedelic experiences via serotonin receptor agonism,^[2] causing thought and visual/auditory changes, and altered state of consciousness.^[3] Major psychedelic drugs include mescaline, LSD, psilocybin, and DMT. Studies show that psychedelics are physiologically safe and do not lead to addiction. In fact, two studies conducted using psilocybin in a psychotheraputic setting reveal that psychedelic drugs may assist with treating alcohol and nicotine addiction.^[4]

Differing with other psychoactive drugs, such as stimulants and opioids, psychedelics tend to qualitatively alter ordinary conscious experience. Whereas stimulants cause energized feelings and opioids produce a relaxed euphoric state, the psychedelic experience is often compared to non-ordinary forms of consciousness such as trance, meditation, yoga, religious ecstasy, dreaming and even near-death experiences. Most psychedelic drugs fall into one of the three families of chemical compounds: tryptamines, phenethylamines, or lysergamides.

Many psychedelic drugs are illegal worldwide under the UN conventions, occasionally excepting use in a religious or research context. Despite these controls, recreational use of psychedelics is common.

Origin of term

The term psychedelic is derived from the Greek words ψυχή (psyche, "soul, mind") and δηλείν (delein, "to manifest"), hence "soul-manifesting", the implication being that psychedelics can access the soul and develop unused potentials of the human mind.^[7] The word was coined in 1956 by British psychiatrist, Humphry Osmond, the spelling loathed by American ethnobotanist, Richard Schultes, but championed by the American psychologist, Timothy Leary.^[8]

Aldous Huxley had suggested to Humphry Osmond in 1956 his own coinage phanerothyme (Greek "phaneroein-" visible + Greek "thymos" soul, thus "visible soul").^[9] Recently, the term entheogenic has come into use to denote the use of psychedelic drugs in a religious/spiritual/mystical context.

Traditional use

Psychedelics have a long history of traditional use in medicine and religion, for their perceived ability to promote physical and mental healing. In this context, they are often known as entheogens. Native American practitioners using mescaline-containing cacti (most notably peyote, San Pedro, and Peruvian torch) have reported success against alcoholism, and Mazatec practitioners routinely use psilocybin mushrooms for divination and healing. Ayahuasca, which contains the potent psychedelic DMT, is used in Peru and other parts of South America for spiritual and physical healing as well as in religious festivals.

Examples

Doses of lysergic acid diethylamide (LSD)

Classical or serotonergic psychedelics (agonists for the 5-HT_2A serotonin receptors) include LSD (also known as "acid"), psilocin (the active constituent of psilocybin mushrooms, commonly known as "magic mushrooms" or "shrooms"), mescaline (the active constituent of peyote), and DMT (the active constituent of ayahuasca and an endogenous compound produced in the human body).

Pharmacological classes and effects

Serotonergic psychedelics (5-HT_2A receptor agonists)

This class of psychedelics includes the classical hallucinogens, including the lysergamides like LSD and LSA, tryptamines like psilocybin and DMT, and phenethylamines like mescaline and 2C-B. Many of these psychedelics cause remarkably similar effects, despite their different chemical structure. However, many users report that the three families have subjectively different qualities in the "feel" of the experience, which are difficult to describe. At lower doses, these include sensory alterations, such as the warping of surfaces, shape suggestibility, and color variations. Users often report intense colors that they have not previously experienced, and repetitive geometric shapes are common. Higher doses often cause intense and fundamental alterations of sensory perception, such as synesthesia or the experience of additional spatial or temporal dimensions.^[10] Some compounds, such as 2C-B, have extremely tight "dose curves", meaning the difference between a non-event and an overwhelming disconnection from reality can be very slight.^{[citation needed]} There can be very substantial differences between the drugs, however. For instance, 5-MeO-DMT rarely produces the visual effects typical of other psychedelics and ibogaine (a 'complex tryptamine') is also an NMDA receptor antagonist and κ-opioid receptor agonist in addition to being an agonist for the 5-HT_2A receptors, resulting in dissociative effects as well (see dissociatives below).

Almost all antidepressant drugs, especially atypical ones like mirtazapine and trazodone, are 5-HT2A antagonists, from moderate to very strong, and thus often totally disrupts psychedelic effects. Furthermore, persons on chronic antidepressive medications virtually can't get any effects from serotonergic psychedelic drugs even after discontinuing antidepressant drugs.

Empathogen-entactogens (serotonin releasers)

The empathogen-entactogens are phenethylamines of the MDxx class such as MDMA, MDEA, and MDA. Their effects are characterized by feelings of openness, euphoria, empathy, love, heightened self-awareness, and by mild audio and visual distortions (an overall enhancement of sensory experience is often reported). Their adoption by the rave subculture is probably due to the enhancement of the overall social and musical experience. MDA is atypical to this experience, often causing hallucinations and psychedelic effects in equal profundity to the chemicals in the 5-HT_2A agonist category, but with substantially less mental involvement, and is both a serotonin releaser and 5-HT_2A receptor agonist.

Dissociatives

NMDA antagonists

Certain dissociative drugs acting via NMDA antagonism are known to produce what some might consider psychedelic effects. The main differences between dissociative psychedelics and serotonergic hallucinogens are that the dissociatives cause more intense derealization and depersonalization.^[11] For example, ketamine produces sensations of being disconnected from one's body and that the surrounding environment is unreal, as well as perceptual alterations seen with other psychedelics.^[12]

Other

Salvia divinorum is a dissociative that is sometimes classified as an atypical psychedelic. The active molecule in the plant, salvinorin A, is a kappa opioid receptor agonist, working on a part of the brain that deals with pain. Activation of this receptor is also linked to the dysphoria sometimes experienced by users of opioids either therapeutically or recreationally. An unusual feature of S. divinorum is its high potency (dosage is in the microgram range) and extremely disorienting effects, which often include "entity contact", complete loss of reality-perception and user's experiencing their consciousness as being housed in different objects e.g. a pane of glass or a pencil. Additionally, ibotenic acid and muscimol, the active constituents of Amanita muscaria, may be regarded as psychedelic, dissociative or deliriant.

Psychedelics and the law

Despite many psychedelic drugs being non-addictive^[13] and there being no evidence to support long term harm on mental health^[14] many of these drugs have been declared illegal under the UN Convention on Psychotropic Substances of 1971. In addition, many countries have analogue acts that automatically forbid any drugs sharing similar chemical structures to common illicit substances regardless of whether they are harmful.

Psychedelic experience

From Wikipedia, the free encyclopedia

A psychedelic experience (or 'trip') is a temporary altered state of consciousness induced by the consumption of psychedelic drugs (such as mescaline, LSD, psilocybin, and DMT). For example, the term acid trip refers to psychedelic experiences brought on by the use of LSD.

The term "psychedelic" derives from Greek words meaning "mind revealing". Psychedelic experiences are interpreted in exploratory, learning, recreational, religious/mystical and therapeutic contexts.

Definition

A psychedelic experience is a temporary altered state of consciousness induced by the consumption of psychedelic drugs (the best known of which are LSD and psilocybin 'magic' mushrooms). The psychedelic altered state of consciousness is commonly characterised as a higher (elevated or transcendent) state relative to ordinary (sober) experience; for example, the psychologist Benny Shanon observed from ayahuasca trip reports: “the assessment, very common with ayahuasca, that what is seen and thought during the course of intoxication defines the real, whereas the world that is ordinarily perceived is actually an illusion.”^[1]

Similarly, psychologist Stanislav Grof described the LSD experience as: “complex revelatory insights into the nature of existence… typically accompanied by a sense of certainty that this knowledge is ultimately more relevant and “real” than the perceptions and beliefs we share in everyday life.”^[2] The philosopher Alan Watts likened psychedelic experiencing to the transformations of consciousness that are undertaken in Taoism and Zen, which he says is, “more like the correction of faulty perception or the curing of a disease… not an acquisitive process of learning more and more facts or greater and greater skills, but rather an unlearning of wrong habits and opinions.”^[3]

The LSD experience was described by Alan Watts as, “revelations of the secret workings of the brain, of the associative and patterning processes, the ordering systems which carry out all our sensing and thinking.”^[4]

Etymology

The term 'psychedelic' was coined in 1953 by the psychiatrist Humphrey Osmond, during written correspondence with Aldous Huxley. 'Psychedelic' derives from two Ancient Greek words, 'psyche' meaning mind or soul and 'delos' meaning reveal or manifest. The psychedelic experience is said to reveal aspects of the mind that are normally hidden.

The term "trip" was first coined by US Army scientists during the 50s when they were experimenting with LSD. ^[5]

Basic phenomenology

Psychedelic tripping consists of a small number of distinctive phenomenological characteristics. The major identifying characteristics include alterations of visual perception, psychotherapeutic breakthrough experiences leading to personal growth, experiences of religious epiphany/mystical transcendence, and 'bad trips' - negative/unpleasant panic-attack control-loss experiences (note: these four characteristics of psychedelic tripping are not mutually exclusive, there is a wide overlap between them). These four central characteristics of psychedelic experiencing are described in detail in the following sections:

Visual alteration

Probably the most common, widely recognised psychedelic experiential phenomenon is the alteration in visual perception; this includes surfaces in the environment appearing to ripple and undulate; Albert Hoffman, the discoverer of LSD, described how during his bicycle ride home after his first deliberate LSD self-administration: "Everything in my field of vision wavered and was distorted as if seen in a curved mirror". Psychedelic visual alteration also includes spontaneous formation of complex flowing geometric visual patterning in the visual field. When the eyes are open, the visual alteration is overlaid onto the objects and spaces in the physical environment; when the eyes are closed the visual alteration is seen in the 'inner world' behind the eyelids. These visual effects increase in intensity with higher dosages, and also when the eyes are closed.

Psychotherapy/personal development

There is a distinctly gnosis-like quality to psychedelic experiencing; it is a learning experience that elevates consciousness and makes a profound contribution to personal development. For this reason, the plant sources of some psychedelic drugs such as ayahuasca and psilocybin mushrooms are sometimes referred to as "plant teachers".^[6]

Similarly, in a follow-up to the psilocybin and mysticism study at Johns Hopkins, researchers observed that psilocybin: "occasions personally and spiritually significant mystical experiences that predict long-term changes in behaviors, attitudes and values".^[7]

Mystical/religious experience

Psychedelic experience includes the full range of mystical or religious experiential phenomena. Two scientific studies have concluded that psilocybin (a typical psychedelic compound that occurs naturally in psilocybin mushrooms) reliably triggers mystical-type experiences.^[7] The more recent study at Johns Hopkins University identified mystical experiences by means of several questionnaires designed to categorise altered state 'non-ordinary' experiences, including one questionnaire called 'the mysticism scale'.^[7]

Furthermore, psychedelic drugs have a long history of religious use across the world, they are often called entheogens because of their propensity to induce these kinds of experiences.^[8]

Several modern religions exist today that base their religious activities and beliefs around psychedelic experiencing, such as Santo Daime and the Native American Church. In this context, the psychedelic experience is interpreted as a way of communicating with the realm of spirits or ancestors.

Bad trip

A "bad trip" ("drug-induced temporary psychosis" or "psychedelic crisis") is a disturbing, unpleasant, potentially dangerous, and possibly traumatizing psychedelic experience. Bad trips are more common at high doses, where the psychedelic effect is more intense.
The manifestations can range from feelings of mild anxiety and alienation to profoundly disturbing states of unrelieved terror, ultimate entrapment, sheer insanity or cosmic annihilation. This is why a person who plans on taking a psychedelic should be accompanied by a trip sitter.

Bad trips can be exacerbated by the inexperience or irresponsibility of the user or the lack of proper preparation and environment for the trip. At the extreme, the occurrence of bad trips without proper preparation can result in a tripper committing self-harm or harming others, suicide attempts and contact with law enforcement.

Psychedelic specialists in the psychotherapeutic community do not necessarily consider unpleasant experiences as unhealthy or undesirable, focusing instead on their potential for psychological healing, to lead to breakthrough and resolution of unresolved psychic issues.^[9]

Aldous Huxley's concept of the cognitive reducing valve

In his book The Doors of Perception, author and psychonaut Aldous Huxley presents the idea of the mental reducing valve in order to explain the significance of the psychedelic experience. According to Huxley, the central nervous system's main function is to shut out the majority of what we perceive;^[10] the brain filters those perceptions which are useful for survival. Society aids in this filtering by creating a symbolic system which structures our reality and which reduces our awareness.^[10]

Psychedelic experiencing has the effect of reducing the strength of the mind's reducing valve, which allows for a broader spectrum of one's overall experience to enter into conscious experience. A person undergoing a psychedelic trip temporarily possesses a higher level of conscious awareness.

Psychedelic psychotherapy

Psychedelic therapy refers to therapeutic practices involving the use of psychedelic drugs to facilitate beneficial emotional processing and exploration of the psyche. In contrast to conventional psychiatric medication which is taken by the patient regularly or as-needed, in psychedelic therapy, patients remain in an extended psychotherapy session during the acute activity of the drug and spend the night at the facility. In the sessions with the drug, therapists are nondirective and support the patient in exploring their inner experience. Patients participate in psychotherapy before the drug psychotherapy sessions to prepare them and after the drug psychotherapy to help them integrate their experiences with the drug.^{[11] [12]}
An early practitioner of psychedelic drug based psychiatry was Humphrey Osmond, a British psychiatrist who was responsible for coining the word 'psychedelic' in the first place. Osmond claimed that his own personal use of LSD had helped him to understand the inner mental states of his schizophrenic patients.^[13]

Another important practitioner in this field is Stanislav Grof, who pioneered the use of LSD in psychotherapy.^[14] Grof characterised psychedelic experiencing as "non-specific amplification of unconscious mental processes", and he analysed the phenomenology of the LSD experience (particularly the experience of psychospiritual death and rebirth) in terms of Otto Rank's theory of the unresolved memory of the primal birth trauma.^[15]

The use of psychedelic drugs can allow terminally ill patients (e.g. those with end-stage cancer) to deal with the difficult emotions (fear and anxiety) resulting from their illness. Trials have demonstrated that psychedelic experiencing is capable of causing the pains associated with imminent, unavoidable death to become manageable and understandable; realizing that the passage from life to death is simply another step in living.

Near-death experience

From Wikipedia, the free encyclopedia

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.^[1] NDEs are a recognized part of some transcendental and religious beliefs in an afterlife.
Different models have been described to explain NDEs.^[5] Neuroscience research suggests that an NDE is a subjective phenomenon resulting from "disturbed bodily multisensory integration" that occurs during life-threatening events.^[6]

Etymology

Ascent of the Blessed by Hieronymus Bosch is associated by some NDE researchers with aspects of the NDE.^[7][8]

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.^[9][10] In 1892 a series of subjective observations by workers falling from scaffolds, war soldiers who suffered injuries, climbers who had fallen from heights or other individuals who had come close to death (near drownings, accidents) was reported by Albert Heim. This was also the first time the phenomenon was described as clinical syndrome.^[11] In 1968 Celia Green published an analysis of 400 first-hand accounts of out-of-body experiences.^[12] 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 who coined the term "near-death experience" (NDE).^[11]

Characteristics

Common elements

Researchers have identified the common elements that define near-death experiences.^[3] 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.^[13] 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.^[14][15]

Common traits that have been reported by NDErs are as follows:

• A sense/awareness of being dead.^[3]
• A sense of peace, well-being and painlessness. Positive emotions. A sense of removal from the world.^[3]
• An out-of-body experience. A perception of one's body from an outside position, sometimes observing medical professionals performing resuscitation efforts.^[3][16]
• A "tunnel experience" or entering a darkness. A sense of moving up, or through, a passageway or staircase.^[3][16]
• A rapid movement toward and/or sudden immersion in a powerful light (or "Being of Light") which communicates with the person.^[17]
• An intense feeling of unconditional love and acceptance.^[18]
• Encountering "Beings of Light", "Beings dressed in white", or similar. Also, the possibility of being reunited with deceased loved ones.^[3][16]
• Receiving a life review, commonly referred to as "seeing one's life flash before one's eyes".^[3]
• Approaching a border or a decision by oneself or others to return to one's body, often accompanied by a reluctance to return.^[3][16]
• Suddenly finding oneself back inside one's body.^[19]
• 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.

Stages

Kenneth Ring (1980) subdivided the NDE on a five-stage continuum. The subdivisions were:^[20]

1. Peace
2. Body separation
3. Entering darkness
4. Seeing the light
5. Entering the light

He stated that 60% experienced stage 1 (feelings of peace and contentment), but only 10% experienced stage 5 ("entering the light").^[21] According to Alana Karran, the NDE stages resemble the so-called hero's journey.^[22]

Clinical circumstances

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.^{[citation needed]} In contrast to common belief, Kenneth Ring argues that attempted suicides do not lead more often to unpleasant NDEs than unintended near-death situations.

NDE variants

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. For instance, they may visit or view dark and depressing areas or are accosted by what seem to be hostile or oppositional forces or presences.^[24]

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.^[25] Greyson (2007) also found that the long term recall of NDE incidents was stable and did not change due to embellishment over time.^[26]

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.^[27] 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.^[28]

After-effects

NDEs are associated with changes in personality and outlook on life.^[3] 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 a need for being alone more often, increased physical sensitivity; diminished tolerance of light, sound, alcohol, or 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.^[3] However, not all after-effects are beneficial^[29] and Greyson describes circumstances where changes in attitudes and behavior can lead to psychosocial and psychospiritual problems.^[30]

Historical reports, incidence and prevalence

NDEs have been recorded since ancient times.^[31] 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.^[31]

A number of more contemporary sources report incidences of near death experiences of:

• 17% amongst critically ill patients, in nine prospective studies from 4 different countries.^[32]
• 10-20% of people who have come close to death.^[11]

Research

Near-death studies

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^[31] with an additional 600 outside the US in the West,^[31] and 70 in Asia.^[31] Additionally, prospective studies had identified 270 individuals. Prospective studies review groups of individuals (e.g., selected emergency room patients) and then find who had an NDE during the study's time; such studies cost more to perform.^[31] 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.^[31]

Melvin Morse, head of the Institute for the Scientific Study of Consciousness, and colleagues^[16][33] have investigated near-death experiences in a pediatric population.

Research scales used to classify a near-death experience

Major contributions to the field include Ring's construction of a "Weighted Core Experience Index"^[34] to measure the depth of the near-death experience, and Greyson's construction of the "Near-death experience scale"^[35] 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.^[35] The NDE-scale was later found to fit the Rasch rating scale model.^[36]

Research in animals

Heightened brain activity has been recorded in experimental rats directly following cardiac arrest, though there has been no similar research in humans.

Clinical research in cardiac arrest patients

Parnia 2001 study

In 2001, Sam 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. Parnia and colleagues investigated out-of-body experience claims by placing figures on suspended boards facing the ceiling, not visible from the floor. Four had experiences that, according to the study criteria, were NDEs but none of them experienced the out-of-body experience. Thus, they were not able to identify the figures.^[41][5][42]

Psychologist Chris French wrote regarding the study "unfortunately, and somewhat atypically, none of the survivors in this sample experienced an OBE".^[5]

Van Lommel's study

Pim van Lommel

In 2001 Pim van Lommel, a cardiologist from the Netherlands, and his team conducted a study on 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. One patient had a conventional out of body experience. 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".^[42][43]

Awareness during Resuscitation (AWARE) study

While at University of Southampton, Parnia was the principal investigator of the AWARE Study, which was launched in 2008.^[13] 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.^[44] 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.^[45][46]

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 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.^[42]

AWARE II

As of May 2016, a posting at the UK Clinical Trials Gateway website described plans for AWARE II, a two-year multicenter observational study of 900-1500 patients experiencing cardiac arrest, which said that subject recruitment had started on 1 August 2014 and that the scheduled end date was 31 May 2017.^[47]

Explanatory models

In a review article, psychologist Chris French^[5] 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.

Spiritual or transcendental theories

French summarizes this model by saying : "the most popular interpretation is that the NDE is exactly what it appears to be to the person having the experience".^[5] The NDE would then represent evidence of the supposedly immaterial existence of a soul or mind, which would leave the body upon death. An NDE would then provide information about an immaterial world where the soul would journey upon ending its physical existence on earth.^[5]

According to Greyson^[11] some NDE phenomena cannot be easily explained with our current knowledge of human physiology and psychology. For instance, at a time when they were unconscious patients could accurately describe events as well as report being able to view their bodies "from an out-of-body spatial perspective". In two different studies of patients who had survived a cardiac arrest, those who had reported leaving their bodies could describe accurately their resuscitation procedures or unexpected events, whereas others "described incorrect equipment and procedures".^[11] Sam Parnia also refers to two cardiac arrest studies and one deep hypothermic circulatory arrest study where patients reported visual and/or auditory awareness occurring when their brain function had ceased. These reports "were corroborated with actual and real events".^[48][42]

Limitations of spiritual or transcendental theories

Five prospective studies have been carried out, to test the accuracy of out of body perceptions by placing "unusual targets in locations likely to be seen by persons having NDEs, such as in an upper corner of a room in the emergency department, the coronary care unit, or the intensive care unit of a hospital." Twelve patients reported leaving their bodies, but unfortunately none could describe the hidden visual targets. Although this is a small sample, the failure of purported out-of-body experiencers to describe the hidden targets raises questions about the accuracy of the anecdotal reports described above.^[11]

Psychologist James Alcock has described the afterlife claims of NDE researchers as pseudoscientific. Alcock has written the spiritual or transcendental interpretation "is based on belief in search of data rather than observation in search of explanation."^[49] Chris French has noted that "the survivalist approach does not appear to generate clear and testable hypotheses. Because of the vagueness and imprecision of the survivalist account, it can be made to explain any possible set of findings and is therefore unfalsifiable and unscientific."^[50]

Psychological explanations

French summarises the main psychological explanations which include: the depersonalization, the expectancy and the dissociation models.^[5]

Depersonalization model

A depersonalization model was proposed in the 1970s by professor of psychiatry Russell Noyes and clinical psychologist Roy Kletti, which suggested that 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 an hallucination. According to this model, those who face their impending death become detached from the surroundings and their own bodies, no longer feel emotions, and experience time distortions.^[11]

Limitations of the depersonalization model

This model suffers from a number of limitations to explain NDEs for subjects who do not experience a sensation of being out of their bodies; unlike NDEs, experiences are dreamlike, unpleasant and characterized by "anxiety, panic and emptiness".^[11] Also, during NDEs subjects remain very lucid of their identities, their sense of identify is not changed unlike those experiencing depersonalization.^[11]

Expectancy model

Another psychological theory 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.^[5] Subjects use their own personal and cultural expectations to imagine a scenario that would protect them against an imminent threat to their lives.^[11]

Limitations of the expectancy model

Subjects' accounts often differed from their own "religious and personal expectations regarding death" which contradicts the hypothesis they may have imagined a scenario based on their cultural and personal background.^[11]

Although the term NDE was first coined in 1975 and the experience first described then, recent descriptions of NDEs do not differ from those reported earlier than 1975. The only exception is the more frequent description of a tunnel. Hence, the fact that information about these experiences could be more easily obtained after 1975, did not influence people's reports of the experiences.^[11]

Another flaw of this model can be found in children's accounts of NDEs. These are similar to adults', and this despite children being less affected by religious or cultural influences about death.^[11]

Dissociation model

The dissociation model proposes that NDE 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.^[5]

Birth model

The birth model suggests 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.^[5]

Limitations of the birth model

Reports of leaving the body through a tunnel are equally frequent among subjects who were born by cesarean section and natural birth. Also, newborns do not possess "the visual acuity, spatial stability of their visual images, mental alertness, and cortical coding capacity to register memories of the birth experience".^[11]

Physiological explanations (organic theories)

A wide range of physiological theories of the NDE have been put forward including those based upon cerebral hypoxia, anoxia, and hypercapnia; endorphins and other neurotransmitters; and abnormal activity in the temporal lobes.^[5]

Neurobiological factors in the experience have been investigated by researchers in the field of medical science and psychiatry.^[55] 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".^[56]

Neuroanatomical models

Neuroscientists Olaf Blanke and Sebastian Dieguez (2009),^[57] from the Ecole Polytechnique Fédérale de Lausanne, Switzerland, propose a brain based model with two types of NDEs :

• "type 1 NDEs are due to bilateral frontal and occipital, but predominantly right hemispheric brain damage affecting the right temporal parietal junction and characterized by out of body experiences, altered sense of time, sensations of flying, lightness vection and flying" ^[6]
• "type 2 NDEs are also due to bilateral frontal and occipital, but predominantly left hemispheric brain damage affecting the left temporal parietal junction and characterized by feeling of a presence, meeting and communication with spirits, seeing of glowing bodies, as well as voices, sounds, and music without vection" ^[6]

They suggest that damage to the bilateral occipital cortex may lead to visual features of NDEs such as seeing a tunnel or lights, and "damage to unilateral or bilateral temporal lobe structures such as the hippocampus and amygdala" 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 without needing paranormal explanations.^[6]

Animation of the human left temporal lobe

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".^[5]

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.^[58]

According to Greyson^[11] multiple neuroanatomical models have been proposed where NDEs have been hypothesized to originate from different anatomical areas of the brain, namely: the limbic system, the hippocampus, the left temporal lobe, Reissen's fiber in the central canal of the spinal cord, the prefrontal cortex, the right temporal lobe.

Limits of neuroanatomical models

Blanke et al.^[6] admit that their model remains speculative to the lack of data. Likewise Greyson^[11] writes that although some or any of the neuroanatomical models proposed may serve to explain NDEs and pathways through which they are expressed, they remain speculative at this stage since they have not been tested in empirical studies.^[11]

Neurochemical models

Some theories hypothesize that drugs used during resuscitation induced NDEs, for example, ketamine or as resulting from endogeneous chemicals that transmit signals between brain cells, neurotransmitters:^[5]

• In the early eighties, Daniel Carr wrote that NDE has characteristics are suggestive of a limbic lobe syndrome and that the NDE can be explained by the release of endorphins and enkephalins in the brain.^[59][60] Endorphins are endogenous molecules "released in times of stress and lead to a reduction in pain perception and a pleasant, even blissful, emotional state." ^[5]
• Judson and Wiltshaw (1983) noted how the administration of endorphin-blocking agents such as naloxone had been occasionally reported to produce "hellish" NDEs.^[61] This would be coherent with endorphins' role in causing a "positive emotional tone of most NDEs".^[5]
• Morse et al. 1989 proposed a model arguing that serotonin played a more important role than endorphins in generating NDEs ^[62] "at least with respect to mystical hallucinations and OBEs".^[5]

Limits of neurochemical models

According to Parnia, neurochemical models are not backed by data. This is true for "NMDA receptor activation, serotonin, and endorphin release" models.^[42] Parnia writes that no data has been collected via thorough and careful experimentation to back "a possible causal relationship or even an association" between neurochemical agents and NDE experiences.^[48]

Multi-factorial models

The first formal neurobiological model for NDE, included endorphins, neurotransmitters of the limbic system, the temporal lobe and other parts of the brain.^[63] Extensions and variations of their model came from other scientists such as Louis Appleby (1989).^[64]

Other authors suggest that all components of near-death experiences can be explained in their entirety via psychological or neurophysiological mechanisms, although the authors admit that these hypotheses have to be tested by science.^[65]

Low oxygen levels (and G-LOC) model

Low oxygen levels in the blood (hypoxia or anoxia) have been hypothesized to induce hallucinations and hence possibly explain NDEs.^[14][5] This is because low oxygen levels characterize life-threatening situations and also by the apparent similarities between NDEs and G-force induced loss of consciousness (G-LOC) 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^[66] 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."^[5][66]

Limitations of low oxygen levels (and G-LOC) model

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.^[14] 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.^[5]

Also, hypoxic hallucinations are characterized by "distress and agitation" and this is very different from near death experiences which subjects report as being pleasent.^[11]

Altered blood gas levels models and their limitations

Some investigators have studied whether hypercarbia or higher than normal carbon 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 carbon dioxide, and finally some other studies have observed NDEs when levels had not changed, and there is little data.^[14]

Other models

French said that at least some reports of NDEs might be based upon false memories.^[67]

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.^[68] 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.^[69]

Professor of neurology Terence Hines (2003) claimed that near-death experiences are hallucinations caused by cerebral anoxia, drugs, or brain damage.^[70]

Cross-cultural aspects

Gregory Shushan published an analysis of 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) and compared them with historical and contemporary reports of near-death experiences, and shamanic afterlife "journeys". Shushan found similarities across time, place, and culture that he found could not be explained by coincidence; he also found elements that were specific to cultures; Shushan concludes that some form of mutual influence between experiences of an afterlife and culture probably influence one another and that this inheritance in turn influences individual NDEs.^[71]

According to Parnia, near death experiences' interpretations are influenced by religious, social, cultural backgrounds. However, the core elements appear to transcend borders and can be considered universal. In fact, some of these core elements have even been reported by children <3 age="" an="" and="" at="" been="" by="" children="" class="reference" communicated="" culture="" have="" id="cite_ref-Parnia2014rev_42-5" in="" influenced="" language="" many="" months="" not="" occurred="" old="" or="" other="" over="" playing="" s="" should="" sup="" they="" this="" tradition.="" using="" where="" whilst="" words="" years="">[42]

Also, according to Greyson,^[11] the central features of NDEs are universal and have not been influenced by time. These have been observed throughout history and in different cultures. This notwithstanding, cultural influences have probably played a role in some NDEs' reported descriptions.