Near-death experience, also known as NDE, is the common name for feelings, impressions and out-of-body experiences reported by people who have been resuscitated.
Such reports date back to the time of Plato who wrote about the Myth of Er., but the term near-death experience was coined by a psychologist, Raymond Moody, in his book, Life after Life, first published in 1975. The book was a compilation of the experiences reported by more than 100 people who came close to death. Moody believes in an afterlife, and regards these reports as possible supporting evidence for this, while recognising that there are other explanations. Generally however, scientists consider that NDEs arise from the disordered activity of a brain under extreme stress that is interpreted in a way conditioned by expectations. 
In a later book, Moody wrote: “By the classical definition, death is the state from which you don't return. It is defined as irreversible. Hence, since all of the NDEers returned, they were never really dead. What happened was that various criteria for death were fufilled"   Both adults and children report similar NDE experiences. Similar experiences have been reported by others, including when someone is participating in meditation, under emotional duress or at the bedside of a dying loved one.
Did the NDE experiencer really die?
The immediate reactions to Moody's book were very polarised; some embraced the reports as endorsing their belief in an afterlife, others dismissed the reports as hallucinatory delusions or mere inventions. Moody's book was simply a compilation of anecdotes. However, other researchers since then have consistently found that NDEs are a relatively common occurrence, and follow a quite consistent narrative form in many different cultures and in historical accounts. This suggests that NDEs share a common neurological basis, and various theories have been proposed, for example, that neuronal dysfunction due to anoxia and/or carbon dioxide overload leads to a sequence of disordered brain activity that is subsequently interpreted as an "experience" in a way conditioned by expectations.
Even if the NDE has a relatively prosaic explanation, the impact of an NDE on the lives of those who have experienced one is often considerable. There are many accounts of an NDE changing a person's values, making them less afraid of death, more religious and less materialistic. Conversely, an NDE apparently led Hong Xiuquan to believe that he was the brother of Jesus Christ, and he went on to lead a rebellion that claimed at least 20 million lives. 
In 1980, psychologist Kenneth Ring developed a 10 point interview scale, which he used to interview 102 people who had come close to death. The interview using the scale determined that 48% of Ring's group had had an NDE. Using this information he developed the Weighted Core Experience Index.  This index asked about whether the NDE was peaceful; involved an Out-of-Body Experience (OBE); tunnel or dark area; saw a light; entered the light.
The Greyson Scale was developed by psychiatrist Bruce Greyson after he interviewed 74 people who reported an NDE.   He used the 16 most frequently reported features to develop his questionaire, which sought to establish whether there had been: an experience of altered time; accelerated thought process; a life review; a sense of sudden understanding; feelings of peace/joy/'cosmic oneness'; seeing or feeling the surrounding of light; reporting vivid sensations; extrasensory perception (ESP); experiencing visions; an OBE; a sense being in an 'otherworldly environment', of a mystical entity; of deceased or religious figures; or of a 'border' or point of no return. Each question is rated 0, 1 or 2. The potential maximum score was 32 and a score of 7 was needed to qualify for having an NDE.  There are variances between adults and children in what they may experience and describe concerning the NDE. Cultural variations concerning NDEs have also been reported.
In The Light Beyond, Moody explained that people often reported the following:
- a "sense of peace and painlessness”. Cardiac patients, according to Moody, report the intense pain of a heart attack turns into pleasure.
- an "Out-of-Body Experience" (OBE): Moody reports his study subjects described seeing their body below while retaining a “body” of some sort they can not describe.
- a tunnel. “The descriptions are many, but the sense of what is happening remains the same: the person is going through a passageway toward an intense light” .
- 'People of Light', that glow with intense luminescence that fills the person with love. The light is described as being much brighter than anything found on earth while not hurting the eyes. The person under-going this experience may see friends and relatives who have died.
- Being of Light: The NDE witness will report seeing a holy supreme being of light. When meeting this holy being the person wants to remain but is told by the being of light to return to their earthly body.
- Life Review: “The closest description I've heard of it is that the whole person's life is there at once,” writes Moody. Moody states the NDE experiencer comes away from the experience realizing the most important things in life are love followed by knowledge.
- Return: NDE experiencers want to remain in the heavenly place and often experience short-term anger when they are brought back from death states.
In 1982, a Gallup poll survey in the United States, where most people believe in an afterlife, estimated that approximately 8 million people had had an NDE. Of those, 26% described an OBE; 23% felt that they had experienced accurate visual perception; 17% heard sounds or voices; 32% feelings of peace or painlessness ; 14% saw light phenomena; 32% described having a life review ;32% being in another world ;23% encountering other beings; 9% described a tunnel experience; and 6% described a sense of precognition .
In 2011, the journal Trends in Cognitive Sciences published a paper entitled 'There is nothing paranormal about near-death experiences: how neuroscience can explain seeing bright lights, meeting the dead, or being convinced you are one of them'. The paper, by neuroscientists Dean Mobbs and Caroline Watt, summarised the results of various scientific studies of NDEs. 
A commonly reported features of NDEs is an awareness of being dead - but these feelings are not limited to NDEs. A condition called "Cotard" - or "walking corpse" syndrome, where a person believes they are dead, has been seen after trauma and during the advanced stages of typhoid and multiple sclerosis. Out-of-body experiences can be artificially induced by stimulating the right temporoparietal junction in the brain, an area that has a role in perception and awareness. The "tunnel of light" sensation can also be artificially induced: pilots flying at G-force can experience "hypertensive syncope" which causes tunnel-like vision for up to eight seconds , and one study suggests that the light at the end of the tunnel is explained by poor blood and oxygen supply to the eye. The feelings of bliss and euphoria, meanwhile, can be recreated with drugs such as ketamine and amphetamine.
"I died, as you know. I seemed to leave my body and stand beside it, looking down on what was me. The me that was standing there looked like the form I was looking at, only, I was alive and the other was dead. I gazed at my body for a few minutes, then turned and walked away. I left the house and village, and walked on and on to the next village, and there I found crowds of people,—Oh, so many people! The place which I knew as a small village of a few houses was a very large place, with hundreds of houses and thousands of men, women, and children. Some of them I knew and they spoke to me,—although that seemed strange, for I knew they were dead,—but nearly all were strangers. They were all so happy! They seemed not to have a care; nothing to trouble them. Joy was in every face, and happy laughter and bright, loving words were on every tongue." From Hawaiian Folk Tales (1907) 
The Handbook of Near-Death Experiences summarises reports collated in 16 refereed journal articles describing more than 275 non-Western NDEs, gathered since 2005. Experiences from Asia, Pacific area and hunter-gatherer cultures, and show many similarities .
Pediatrician Melvin Morse became interested in NDEs after one of his patients told about her NDE. She was resuscitated after nearly drowning. Katie spent three days near the brink of death and was kept in a deep coma. On the third day she awoke as if from a deep sleep and by the next day was visiting with family. She showed no signs of brain damage. Morse interviewed the girl about what she remembered from the experience and was told about her visit to heaven. Morse reports a person actually needs to be near death to have a near-death experience. He also reports the ara in the brain near the right temporal lobe is genetically coded for near-death experiences, forward to the book Closer to the Light. 
Morse created the Seattle Study to determine if someone needed to be near death in order to have an NDE. The control group of 121 seriously ill children had a less than five percent chance of dying but were ill. Morse interviewed children based on the psychological experience of being in an intensive care unit with no mention of NDEs. Interviews lasted approximately two hours and asked questions such as what the patient remembered while being sick, dreams and hospital experiences. 118 of the children who were seriously ill, but not close to death, did not remember their hospital experience.
The experimental group, the cardiac survivors or ones who awoke from deep comas, most of the children did report at least one feature of the NDE. Morse states the child would often start telling of their experience with a puzzled look. He gave the example of “Well, I kind of remember a really funny thing that I can't exactly telly. I was looking at myself and going somewhere, but I didn't exactly know where,” p. 23 Closer to the Light. Morse said the children would go onto tell about their NDE. Some of the children were not affected by the experience while others were profoundly affected. 
Near-Death-Like experiences that are not
One view of NDEs is to include them in the large group of phenomena in which changes in the body seem related to mental or spiritual experiences. There are many of these, from mediation and fasting to ceremonial intoxicants to forty days in the wilderness. In any of them, the effects have been interpreted as anything from madness to divine inspiration. Morse  rejects this view, and considers none of the following to be NDEs:
- LSD – People who use this drug may feel like they've left their bodies. They also know they are not experiencing reality.
- Morphine and Heroin – People using these drugs usually do not perceive this experience as real, nor does it usually involve seeing the tunnel of light, seeing the light, or having visions of heaven.
- Recreational drugs such as marijuana, cocaine, amphetamines and barbituates tend to cause paranoia, speech disturbances, loss of control of thought processes, poor memory, depression and fear, but not NDE-like experiences.
- Anesthetic Agents – halothane, surital, nitrous oxide, narcotics, and nembutal do not cause hallucinations, although the patient may hear conversations while under the influence of one of these agents and become confused.
- Ketamine – Another anesthetic agent no longer used. When used, patients reported frightening OBEs and they may have seen mirror images of themselves (autoscopic) when under the influence of this agent. Patients also know they are under the influence of drugs during this experience.
- Transient Depersonalization – The person becomes emotionally detached from their bodies during a near-fatal experience. Morse found no evidence of this in the children he interviewed after their NDE.
Causes of NDEs
NDEs seem to be relatively common in cardiac arrest patients after successful resuscitation, with an estimated incidence of 11 to 23%.One prospective study of 52 patients with out-of-hospital cardiac arrest reported that 11 had experienced an NDE, and that this was connected to higher initial partial pressures of end-tidal CO2, higher arterial blood CO2 levels, and previous NDEs. Higher serum levels of potassium might also play a role. During cardiac arrest, the end-tidal CO2 falls to very low levels, reflecting the very low cardiac output achieved with cardiopulmonary resuscitation. CO2 levels affect the acid-base equilibrium in the brain, and this can provoke unusual experiences in the form of bright light, visions, and out-of-body experiences 
In 2007, the New England Journal of Medicine published a report of a patient, in whom electrodes had been implanted to suppress tinnitus, who repeatedly experienced an out-of-body experience during stimulation of part of the superior temporal gyrus. Positron-emission tomographic scanning showed brain activation at specific brain sites following stimulation, and the authors suggested that the experience of disembodiment is mediated by coactivation of a small area at the junction of the angular and supramarginal gyrus, which affects vestibular–somatosensory integration of body orientation in space, and the posterior part of the superior temporal cortex, which is believed to be involved in processing an internal map of self-perception. They suggest that these same regions may be activated in patients who report disembodiment as part of an NDE.
Neuroscientist Mario Beauregard and colleagues measured brain activity (using functional magnetic resonance imaging (fMRI) and electroencephalography (EEG)) while they meditated; participants were asked to mentally visualize and emotionally connect with the "being of light" allegedly encountered during their "near-death experience". The meditative state was associated with hemodynamic and neuroelectric changes in brain regions known to be involved either in positive emotions, visual mental imagery, attention or spiritual experiences.
Neurologist Kevin Nelson attributes NDEs to Rapid Eye Movement (REM) state, and believes that the NDE bright light is caused by visual stimulation in the brain due to the REM, while the 'tunnel' is caused by a decrease of blood flow to theeye. Mark Mahowald, director of the Minnesota Regional Sleep Disorders Center similarly attributes NDEs to oxygen starvation in the brain.
Morse writes in Closer to the Light that electrical stimulation of the right temporal lobe has caused patients to report 'seeing God'. He first came up with this theory after discussing NDEs with Art Ward who was the chairman of neurosurgery at the University of Washington. Ward recalled one patient who experienced every trait of the NDE experience after an area of his brain was examined with an electric probe (by Wilder Penfield).
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