出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/01/08 08:23:51」(JST)
An out-of-body experience (OBE or sometimes OOBE) is an experience that typically involves a sensation of floating outside one's body and, in some cases, perceiving one's physical body from a place outside one's body (autoscopy).
The term out-of-body experience was introduced in 1943 by George N. M. Tyrrell in his book Apparitions,[1] and was adopted by researchers such as Celia Green[2] and Robert Monroe[3] as an alternative to belief-centric labels such as "astral projection", "soul travel", or "spirit walking". The researcher Waldo Vieira described the phenomenon as a projection of consciousness.[4][5] OBEs can be induced by brain traumas, sensory deprivation, near-death experiences, dissociative and psychedelic drugs, dehydration, sleep, and electrical stimulation of certain parts the brain[clarify], among others.[6]
Mainstream science considers the OBE a type of hallucination that can be caused by various psychological and neurological factors.[7][8][9] Some parapsychologists and occult writers treat OBEs as evidence that a soul, spirit or subtle body can detach itself from the body and visit distant locations.[10][11]
One in ten people has an OBE once, or more commonly, several times[12] in his or her life.[13] but scientists still know little about the phenomenon.[14]
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Those experiencing OBEs sometimes report (among other types of immediate and spontaneous experience) a preceding and initiating lucid-dream state. In many cases, people who claim to have had an OBE report being on the verge of sleep, or being already asleep shortly before the experience. A large percentage of these cases refer to situations where the sleep was not particularly deep (due to illness, noises in other rooms, emotional stress, exhaustion from overworking, frequent re-awakening, etc.). In most of these cases the subjects then feel themselves awake; about half of them noted a feeling of sleep paralysis.[15]
Another form of spontaneous OBE is the near-death experience (NDE). Some subjects report having had an OBE at times of severe physical trauma such as near-drownings or major surgery.[citation needed]
Along the same lines as an NDE, extreme physical effort during activities such as high-altitude climbing and marathon running can induce OBEs. A sense of bilocation may be apparent, with both ground and air-based perspectives being experienced simultaneously.[16]
Consciously controlled and pre-meditated OBE methods (examples of which are widely available in many popular books on the subject) are also reported.[17][18][19][20][21] Some people have attempted to develop techniques to induce OBEs.
OBEs tend to fall into two types, categorized by Robert Monroe as Locale 1 and Locale 2 experiences.
In Locale 1 experiences the environment is largely consistent with reality; other common labels for this form are etheric, ethereal or RTZ (Real Time Zone) projections. The onset of this type can be frightening as intense physiological sensations may be perceived, such as electrical tingling, full body vibrations and racing heartbeat. Confusion is common in spontaneous Locale 1 experiences; the person can believe he or she has awakened (or died) physically and panic can be caused by the realization that one's limbs appear to be penetrating other objects.
Locale 2 experiences are less overtly physical in nature and have much subjective overlap with lucid dreaming. The subject is immersed in unrealistic worlds, modified forms of reality exhibiting physically impossible or inconsistent features. Bright and vivid colors are a common feature of this form. Robert Bruce considers this type of OBE to be an astral projection.
In surveys, as many as 85% of respondents tell of hearing loud noises, known as "exploding head syndrome" (EHS), during the onset of OBEs.[36][37]
Some who experience OBEs claim to have willed themselves out of their bodies, while others report having found themselves being pulled from their bodies, usually following a feeling of paralysis).
Those who have experienced OBEs sometimes claim to have observed details which were unknown to them beforehand.[38]
An archetypal, classical OBE unfolds through perceptually distinct stages.[39][40]
In practice, the absence of one or more of the classical stages is not unusual. Some (notably Robert Monroe) have claimed these stages become considerably less applicable with extreme familiarity with OBE, eventually finding just a deliberate mental shift to the feeling of the state equivalent.[46] Monroe likened this to tuning a radio away from one station to another into a different focus level of attention.[47]
The phenomenology of an NDE usually includes additional physiological, psychological and transcendental factors beyond those of typical OBEs (Parnia, Waller, Yeates & Fenwick, 2001). Near-death experiences may include subjective impressions of being outside the physical body, visions of deceased relatives and religious figures, and transcendence of ego and spatiotemporal boundaries.[48] Typically the experience includes such factors as: a sense of being dead; a feeling of peace and painlessness; hearing of various non-physical sounds, an out-of-body experience; a tunnel experience (the sense of moving up or through a narrow passageway); encountering people of Light; God-like figures, helpers, spiritual guides, or similar forces; being given a "Life review", and a reluctance to return to life.[49]
The accepted explanation for the OBE in the fields of cognitive science and psychology is that the OBE is a hallucinatory construct that arises from different psychological factors.[6][7][8][9]
An early researcher Edmund Gurney proposed that out-body-body experiences were hallucinations of the pathological type.[50] Charles Richet held that OBEs are created by the subject's memory and imagination processes and are no different than dreams.[51][52] James H. Hyslop wrote that OBEs occur when the activity of the subconscious mind dramatizes certain images to give the impression the subject is in a different physical location.[53] Eugèn Osty considered OBEs to be nothing more than the product of imagination.[54] Other early researchers such as (Schmeing, 1938) supported psychophysiological theories.[55] G. N. M. Tyrrell interpreted OBEs as hallucinatory constructs relating to subconscious levels of personality.[56]
Rawcliffe (1959) connected the OBE experience with psychosis and hysteria.[57] Other researchers have discussed the phenomena of the OBE in terms of a distortion of the body image (Horowitz, 1970) and depersonalization (Whitlock, 1978). Some psychologists (Fordor, 1959; Ehrenwald, 1974) proposed that an OBE is a defense mechanism designed to deal with the threat of death.[58][59] According to (Irin and Watt, 2007) Jan Ehrenwald had described the out-of-body experience (OBE) "as an imaginal con- firmation of the question for immortality, a delusory attempt to assure ourselves that we possess a soul that exists independently of the physical body.[60] The psychophysiologist Stephen Laberge has written that the explanation for OBEs can be found in lucid dreaming.[61] There are several other scientists, however, who challenge this approach, and argue that psychophysiological studies do not support the idea that the person is dreaming during an OBE [62][63] For example, Frederick Aardema (2012), a clinical researcher, argues that dreaming is just one of the many different modes of consciousness a person may enter during an OBE.[62] In other words, lucid dreaming does not define the OBE. Rather, lucid dreaming is defined by the OBE as an experience during which you find yourself in a location other than that of the physical body.
Some scientists suspect that OBEs are the result of a mismatch between visual and tactile signals.[64][65]
Some parapsychologists and occult writers have written that OBEs are not psychological and that a soul, spirit or subtle body can detach itself out of the body and visit distant locations. Muldoon (1936) embraced the concept of an etheric body to explain OBEs.[10] This view was also supported by occult writers and Theosophists of the early 20th century such as Ralph Shirley and Arthur E. Powell. The psychical researcher Ernesto Bozzano (1938) had also supported a similar view describing the phenomena of the OBE experience in terms of bilocation in which an "etheric body" can release itself from the physical body in rare circumstances.[66] Robert Crookall in many publications supported the subtle body theory of OBEs.[67][68] Hart (1967), and other writers such as (De Boni, 1960) also speculated on the existence of a subtle body to explain the OBE experience.[69][70]
The first extensive scientific study of OBEs was made by Celia Green (1968).[71] She collected written, first-hand accounts from a total of 400 subjects, recruited by means of appeals in the mainstream media, and followed up by questionnaires. Her purpose was to provide a taxonomy of the different types of OBE, viewed simply as an anomalous perceptual experience or hallucination, while leaving open the question of whether some of the cases might incorporate information derived by extrasensory perception.
Previous collections of cases had been made by Dr Ernesto Bozzano (Italy) and Dr. Robert Crookall (UK). Crookall approached the subject from a spiritualistic position, and collected his cases predominantly from spiritualist newspapers such as the Psychic News, which appears to have biased his results in various ways. For example, the majority of his subjects reported seeing a cord connecting the physical body and its observing counterpart; whereas Green found that less than 4% of her subjects noticed anything of this sort, and some 80% reported feeling they were a "disembodied consciousness", with no external body at all.
In 1981, Brazilian Physician and medium Dr. Waldo Vieira proposed a new field in parapsychology called projectiology,[72] in which researchers study the subjective dynamics of the OBE directly through systematic self-experimentation rather than through verbal reports. He also formed an institution called the CCC - Center of Continued Consciousness (later IIPC - International Institute of Conscientiology), to promote discussions about the subject.[73]
In 1999, at the 1st International Forum of Consciousness Research in Barcelona, International Academy of Consciousness research-practitioners Wagner Alegretti and Nanci Trivellato presented preliminary findings[74] of an online survey on the out-of-body experience answered by internet users interested in the subject; therefore, not a sample representative of the general population.
1,007 (85%) of the first 1,185 respondents reported having had an OBE. 37% claimed to have had between two and ten OBEs. 5.5% claimed more than 100 such experiences. 45% of those who reported an OBE said they successfully induced at least one OBE by using a specific technique. 62% of participants claiming to have had an OBE also reported having enjoyed nonphysical flight; 40% reported experiencing the phenomenon of self-bilocation (i.e. seeing one's own physical body whilst outside the body); and 38% claimed having experienced self-permeability (passing through physical objects such as walls). The most commonly reported sensations experienced in connection with the OBE were falling, floating, repercussions e.g. myoclonia (the jerking of limbs, jerking awake), sinking, torpidity (numbness), intracranial sounds, tingling, clairvoyance, oscillation and serenity.
Another reported common sensation related to OBE was temporary or projective catalepsy, a more common feature of sleep paralysis. The sleep paralysis and OBE correlation was later corroborated by the Out-of-Body Experience and Arousal study published in Neurology [75] by Kevin Nelson et al. (2007). Also noteworthy, is the Waterloo Unusual Sleep Experiences Questionnaire [76] that further illustrates the correlation.
William Buhlman, an author on the subject, has conducted an informal but informative online survey [77] as well.
There are several possible physiological explanations for parts of the OBE. OBE-like experiences have been induced by stimulation of the brain. OBE-like experience has also been induced through stimulation of the posterior part of the right superior temporal gyrus in a patient.[78] Positron-emission tomography was also used in this study to identify brain regions affected by this stimulation. The term OBE-like is used above because the experiences described in these experiments either lacked some of the clarity or details of normal OBEs, or were described by subjects who had never experienced an OBE before. Such subjects were therefore not qualified to make claims about the authenticity of the experimentally-induced OBE.
English psychologist Susan Blackmore and others suggest that an OBE begins when a person loses contact with sensory input from the body while remaining conscious.[62][63] The person retains the illusion of having a body, but that perception is no longer derived from the senses. The perceived world may resemble the world he or she generally inhabits while awake, but this perception does not come from the senses either. The vivid body and world is made by our brain's ability to create fully convincing realms, even in the absence of sensory information. This process is witnessed by each of us every night in our dreams, though OBEs are claimed to be far more vivid than even a lucid dream.
Irwin[79] pointed out that OBEs appear to occur under conditions of either very high or very low arousal. For example, Green[80] found that three quarters of a group of 176 subjects reporting a single OBE were lying down at the time of the experience, and of these 12% considered they had been asleep when it started. By contrast, a substantial minority of her cases occurred under conditions of maximum arousal, such as a rock-climbing fall, a traffic accident, or childbirth. McCreery[81][82] has suggested that this paradox may be explained by reference to the fact that sleep can supervene as a reaction to extreme stress or hyper-arousal.[83] He proposes that OBEs under both conditions, relaxation and hyper-arousal, represent a form of "waking dream", or the intrusion of Stage 1 sleep processes into waking consciousness.
Research by Olaf Blanke in Switzerland found that it is possible to reliably elicit experiences somewhat similar to the OBE by stimulating regions of the brain called the right temporal-parietal junction (TPJ; a region where the temporal lobe and parietal lobe of the brain come together). Blanke and his collaborators in Switzerland have explored the neural basis of OBEs by showing that they are reliably associated with lesions in the right TPJ region[84] and that they can be reliably elicited with electrical stimulation of this region in a patient with epilepsy.[85] These elicited experiences may include perceptions of transformations of the patient's arms and legs (complex somatosensory responses) and whole-body displacements (vestibular responses).[86][87]
In neurologically normal subjects, Blanke and colleagues then showed that the conscious experience of the self and body being in the same location depends on multisensory integration in the TPJ. Using event-related potentials, Blanke and colleagues showed the selective activation of the TPJ 330–400 ms after stimulus onset when healthy volunteers imagined themselves in the position and visual perspective that generally are reported by people experiencing spontaneous OBEs. Transcranial magnetic stimulation in the same subjects impaired mental transformation of the participant's own body. No such effects were found with stimulation of another site or for imagined spatial transformations of external objects, suggesting the selective implication of the TPJ in mental imagery of one's own body.[88]
In a follow up study, Arzy et al. showed that the location and timing of brain activation depended on whether mental imagery is performed with mentally embodied or disembodied self location. When subjects performed mental imagery with an embodied location, there was increased activation of a region called the "extrastriate body area" (EBA), but when subjects performed mental imagery with a disembodied location, as reported in OBEs, there was increased activation in the region of the TPJ. This leads Arzy et al. to argue that "these data show that distributed brain activity at the EBA and TPJ as well as their timing are crucial for the coding of the self as embodied and as spatially situated within the human body."[89]
Blanke and colleagues thus propose that the right temporal-parietal junction is important for the sense of spatial location of the self, and that when these normal processes go awry, an OBE arises.[90]
In August 2007 Blanke's lab published research in Science demonstrating that conflicting visual-somatosensory input in virtual reality could disrupt the spatial unity between the self and the body. During multisensory conflict, participants felt as if a virtual body seen in front of them was their own body and mislocalized themselves toward the virtual body, to a position outside their bodily borders. This indicates that spatial unity and bodily self-consciousness can be studied experimentally and is based on multisensory and cognitive processing of bodily information.[91]
Michael Persinger has undertaken similar research to Olaf Blanke using magnetic stimulation applied to the right temporal lobe of the brain, which is known to be involved in visuo-spatial functions, multi-sensory integration and the construction of the sense of the body in space.[92] Persinger's research also found evidence for objective neural differences between periods of remote viewing in two individuals thought to have psychic abilities. Persinger undertook his research on Sean Harribance and Ingo Swann, a renowned remote viewer who has taken part in numerous studies.[93] Examination of Harribance showed enhanced EEG activity within the alpha band (8–12 Hz) over Harribance's right parieto-occipital region, consistent with neuropsychological evidence of early brain trauma in these regions. In a second study, Ingo Swann was asked to draw images of pictures hidden in envelopes in another room. Individuals with no knowledge of the nature of the study rated Swann's comments and drawings as congruent with the remotely viewed stimulus at better than chance levels. Additionally, on trials in which Swann was correct, the duration of 7 Hz (alpha band) paroxysmal discharges over the right occipital lobe was longer. Subsequent anatomical MRI examination showed anomalous subcortical white matter signals focused in the perieto-occipital interface of the right hemisphere that were not expected for his age or history.
In August 2007, Henrik Ehrsson, then at the Institute of Neurology at University College of London (now at the Karolinska Institute in Sweden), published research in Science demonstrating the first experimental method that, according to the scientist's claims in the publication, induced an out-of-body experience in healthy participants.[94] The experiment was conducted in the following way:
The study participant sits in a chair wearing a pair of head-mounted video displays. These have two small screens over each eye, which show a live film recorded by two video cameras placed beside each other two metres behind the participant's head. The image from the left video camera is presented on the left-eye display and the image from the right camera on the right-eye display. The participant sees these as one "stereoscopic" (3D) image, so they see their own back displayed from the perspective of someone sitting behind them.The researcher then stands just beside the participant (in their view) and uses two plastic rods to simultaneously touch the participant's actual chest out-of-view and the chest of the illusory body, moving this second rod towards where the illusory chest would be located, just below the camera's view.
The participants confirmed that they had experienced sitting behind their physical body and looking at it from that location.[64][95]
Both critics and the experimenter himself note that the study fell short of replicating "full-blown" OBEs. As with previous experiments which induced sensations of floating outside of the body, Ehrsson's s work does not explain how a brain malfunction might cause an OBE. Essentially, Ehrsson created an illusion that fits a definition of an OBE in which "a person who is awake sees his or her body from a location outside the physical body."[96]
In the autumn of 2008, 25 UK and US hospitals began participation in a 3 year study, coordinated by Dr. Sam Parnia and Southampton University. Following on from the work of Pim van Lommel in the Netherlands, the study aims to examine near-death experiences in 1,500 cardiac arrest survivors and so determine whether people without a heartbeat or brain activity can have documentable out-of-body experiences.[97]
The Monroe Institute's Nancy Penn Center is the oldest and most established facility specializing in out-of-body experience induction.[citation needed] The Center for Higher Studies of the Consciousness in Brazil is another large OBE training facility. The International Academy of Consciousness in southern Portugal features the Projectarium,[98] a spherical structure dedicated exclusively for practice and research on out-of-body experience.
Olaf Blanke's Laboratory of Cognitive Neuroscience has become a well-known laboratory for OBE research.[citation needed]
Astral projection is a paranormal interpretation of out-of-body experiences that assumes the existence of one or more non-physical planes of existence and an associated body beyond the physical. Commonly such planes are called astral, etheric, or spiritual. Astral projection is often experienced as the spirit or astral body leaving the physical body to travel in the spirit world or astral plane.[99]
Evidence for objective reality of projection on to the etheric plane (a near-copy of the physical plane) is sometimes suggested when people, such as patients during surgery, describe OBEs in which they see or hear events or objects outside their sensory range (for instance, Pam Reynolds reported experiencing an OBE during brain surgery and described a surgical instrument she had not seen previously, as well as conversation that occurred while she was under anesthesia).[100]
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