Near-death experiences

Abstract

In his Dec 15 Commentary, C C French1French CC Dying to know the truth: visions of a dying brain, or false memories?.Lancet. 2001; 358: 2010-2011Summary Full Text Full Text PDF PubMed Scopus (33) Google Scholar states that any report of veridical perception during out-of-body experiences would represent a strong challenge to any non-paranormal explanation of the near-death experience. Another context in which out-of-body experiences have been described is the dissociated rapid-eye-movement (REM) sleep state, defined as sleep paralysis. Cheyne and colleagues2Cheyne JA Rueffer SD Newby-Clark IR Hypnagogic and hypnopompic hallucinations during sleep paralysis: neurological and cultural construction of the night-mare.Conscious Cogn. 1999; 8: 319-337Crossref PubMed Scopus (161) Google Scholar reported 17 cases of autoscopic experiences associated with sleep paralysis, in which the individuals viewed themselves lying on the bed, generally from a location above the bed. I previously reported the results of a survey of people experiencing sleep paralysis.3Buzzi G Cirignotta F Isolated sleep paralysis: a web survey.http://www.sro.org/2000/Buzzi/61/Google Scholar Of 264 participants, 28 (11%) had had some kind of out-of-body experiences. Some of them reported recurrent episodes of such experiences. I invited these people to do the following simple reality tests: trying to identify objects put in unusual places; checking the time on the clock; and focusing on a detail of the scene, and comparing it with reality. I received a feedback from five individuals (unpublished data). Objects put in unusual places (eg, on top of the wardrobe) were never identified during out-of-body experiences. Clocks also proved to be unreliable: a woman with nightly episodes of sleep paralysis had two out-of-body experiences in the same night, and for each the clock indicated an impossible time. Another participant stated “I look at my alarm clock to check, and if the bright green LED is not there, then I immediately know that it is a sleep disorder experience…my bedroom seems the same as it is during waking, only the lights don't work”. Finally, in all cases but one, some slight but important differences in the details were noted: “I looked at ‘me’ sleeping peacefully in the bed while I wandered about. Trouble is the ‘me’ in the bed was wearing long johns…I have never worn such a thing”. On the whole, out-of-body experiences in people who experience sleep paralysis seem not to pass reality tests. Therefore, what is seen should be thought of as a recollection of information stored in the person's memory of his or her surroundings. A clue about the origin of such experiences may come from neuroimaging studies of brain activation during REM sleep. By use of positron emission tomography, Maquet and colleagues4Maquet P Péters JM Aerts J et al.Functional neuroanatomy of human rapideye-movement sleep and dreaming.Nature. 1996; 383: 163-166Crossref PubMed Scopus (961) Google Scholar noted a significant negative correlation between regional cerebral blood flow (rCBF) and REM sleep in a large area of the dorsolateral prefrontal cortex and the parietal cortex, and a significant positive correlation between rCBF and REM sleep in limbic-system structures implicated in the formation and consolidation of memories. In dissociated REM sleep states, activation of such limbic structures during inhibition of the neocortex may lead to an oneiric recollection of images concerning the individual's sleeping environment. Likewise, in near-death experiences, out-of-body visions, and possibly other phenomena, such as flashes of recollection from the past, and even life reviews reported by some patients, may represent a disinhibition of limbicsystem structures due to hypoxic suppression of the neocortex,5Lempert T Bauer M Schmidt D Syncope and near-death experience.Lancet. 1994; 334: 829-830Abstract Scopus (55) Google Scholar rather than paranormal phenomena or false memories.