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- 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
- Dean Mobbs1 and Caroline Watt2
- 1 Medical Research Council, Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge, CB2 7EF, UK
- 2 University of Edinburgh, Department of Psychology, 7 George Square, Edinburgh, EH8 9JZ, UK
- Approximately 3% of Americans declare to have had a
- near-death experience [1]. These experiences classically
- involve the feeling that one’s soul has left the body,
- approaches a bright light and goes to another reality,
- where love and bliss are all encompassing. Contrary to
- popular belief, research suggests that there is nothing
- paranormal about these experiences. Instead, neardeath
- experiences are the manifestation of normal brain
- function gone awry, during a traumatic, and sometimes
- harmless, event.
- The notion that death represents a new beginning, a
- passing to an afterlife, where we are reunited with loved
- ones and live eternally in a utopian paradise, is common
- across most theological doctrines. The theological case is
- solidified by the anecdotal reports of people who have
- encountered near-death experiences. These experiences
- leave an indelible mark on the individual’s life, often
- reducing any pre-existing fear of death. Such experiences
- have been observed across cultures and can be found in
- literature dating back to ancient Greece, but are placed
- firmly in the contemporary conscience by books, such as
- Raymond Moody’s Life after Life, which document many
- cases of near-death experiences. This and other bestseller
- books have largely omitted discussion of any physiological
- basis for these experiences, and instead appear to prefer
- paranormal explanations over and above scientific enlightenment.
- Yet, a handful of scientific studies of near-death experiences
- do exist. One example is a case study in which a
- patient with diabetes reported a near-death experience
- during an episode of hypoglycaemia (too low blood sugar).
- During this episode, the patient was in a sleep-like state
- with rapid eye-movement (REM) – a common marker of
- dreaming and thought to underlie the consolidation of
- memories, a process that may explain life reviews during
- near-death experiences (e.g. where the individual reexperiences
- or relives events from their life). Despite not
- being in danger of dying, upon resuscitation, the patient
- recounted many of the classic features of the near-death
- experience [2]. Indeed, Owen and colleagues reported that
- 30 out of 58 patients (51.7%) who recounted near-death
- experiences were not in medical danger, and hence death
- was not so near [3] (Figure 1).
- Basic features of near-death experiences
- There are a number of common features across near-death
- experiences. In one study [2], of those who had had a neardeath
- experience, 50% reported an awareness of being
- dead, 24% said that they had had an out-of-body experience,
- 31% remembered moving through a tunnel, and 32%
- reported meeting with deceased people. Moreover, while it
- is a common anecdote that near-death experiences are
- associated with feelings of euphoria and bliss, only 56%
- associated the experience with such positive emotions, and
- some even reported negative experiences.
- An awareness of being dead
- One of the most frequently reported features of near-death
- experiences is an awareness of being dead [2]. These feelings,
- however, are not limited to near-death experiences.
- For example, an intriguing syndrome, which can also help
- to explain the sensations relating to near-death experiences,
- is ‘Cotard’ or ‘walking corpse’ syndrome. This syndrome
- was named after the French neurologist Jules
- Cotard and results in ‘le de´lire de negation’ – a feeling
- that one is dead. McKay and Cipolotti published recently a
- case report on a 24-year old patient called LU with Cotard
- delusions [4]. LU repeatedly thought that she was in
- heaven (although actually in National Hospital, Queen
- Square, London) and that she might have died of flu.
- The delusions diminished over a few days and were gone
- after a week. Anatomically, Cotard syndrome has been
- associated with the parietal cortex, as well as the prefrontal
- cortex [5], and has been described following trauma,
- during advanced stages of typhoid and multiple sclerosis.
- Still, why delusions such as Cotard syndrome occur is
- unknown. One explanation is that they may simply be
- an attempt to make sense of the strange experiences that
- the patient is having.
- Out-of-body experiences
- Out-of-body experiences are often described as feelings
- that one is floating outside of the body and in some cases
- involve ‘autoscopy’ or seeing one’s body from above. The
- celebrated Canadian neurosurgeon Wilder Penfield argued
- that the veridical perception during out-of-body experiences
- is brain-based. These experiences are also common during
- interrupted sleep patterns that occur just prior to sleep or
- waking. For example, sleep paralysis, which is a natural
- part of REM sleep and results in paralysis when the person
- is still aware of the external world, is reported in up to 40% of
- the population and is associated with hypnagogia (i.e. vivid
- dreamlike auditory, visual, or tactile hallucinations associated
- with the wake-sleep cycle), which can result in the
- sensation of floating above one’s body [6]. Recently, Olaf
- Blanke and colleagues demonstrated that out-of-body
- experiences can be artificially induced by stimulating the
- right temporoparietal junction [7]. Upon stimulation, the
- patient would say things like ‘‘I see myself lying in bed. . .’’.
- Other stimulations resulted in the patient feeling as if
- they were ‘floating’. The authors of the study suggested that
- out-of-body experiences result from a failure to integrate
- multisensory information from one’s body, which results
- in the disruption of the phenomenological elements of
- self-representation.
- A tunnel of light
- Near-death experiences are also associated with the perception
- that one is moving down a dark tunnel and surfacing
- into a ‘world of light’. These experiences can also be
- artificially induced: pilots flying at G-force can sometimes
- experience a phenomenon known as hypotensive syncope,
- which usually causes tunnel-like peripheral to central
- visual loss to develop over 5-8 seconds [8]. Although in
- the case of actual near-death experiences the mechanisms
- are still unclear, a review by Nelson and colleagues suggested
- that the light at the end of the tunnel can be
- explained by visual activity during retinal ischemia [9],
- which occurs when the blood and oxygen supply to the eye
- is depleted. A visual disorder, such as glaucoma, can also
- result in loss of peripheral vision leading to tunnel vision.
- Indeed, such tunnel vision is associated with extreme fear
- and hypoxia (i.e. oxygen loss), two processes common to
- dying. As Blackmore points out, the visual cortex is organized
- by cells that process peripheral and fovea (i.e. central)
- vision and excitation of the these cells will result in a
- central bright light and dark periphery, that is, a tunnel
- effect [10].
- Meeting deceased people
- Prevalent in fiction and celluloid is the notion that, when
- we die, we are surrounded by the souls of the dead, angels
- or a religious figure in a peaceful transcendental place.
- Many neuroscientific studies have shown that brain pathology
- can lead to similar visions. For example, patients
- with Alzheimer’s or progressive Parkinson’s disease can
- have vivid hallucinations of ghosts or even monsters.
- Patients have also been noted as seeing headless corpses
- and dead relatives in the house, which has been linked to
- pallidotomy lesions, suggesting that this result from abnormal
- dopamine functioning, a neurochemical that can
- evoke hallucinations[11]. Intriguingly, electrical stimulation
- of the adjacent region of the angular gyrus can result
- in a sense of presence (i.e. someone is standing behind
- us[12]). Macular degeneration (i.e. damage to the center, or
- macula, of the visual field) can also result in vivid visual
- hallucinations of ghosts and fairytale characters. Such an
- example is Charles-Bonnet syndrome, which mostly occurs
- in the elderly populations. One theory is that hallucinations
- occur due to compensatory over-activation in brain
- structures nearby the damaged area or making sense of
- noise coming from the damaged areas. Thus, hallucinations
- might be derived from internal sources which are
- appraised incorrectly.
- Figure 1. Large scale studies showing the number of people who report near-death experiences (NDEs). The far left bars show that a large proportion (82%) of near-death
- survivors do not report near-death experiences [2]. The central bars represent a retrospective, or historic, study [15]. Crucially, the far right bars show that around half of the
- people who reported near-death experiences in this study were not in danger of dying [3].
- Update Trends in Cognitive Sciences October 2011, Vol. 15, No. 10
- 448
- FIGURE FOUND AT: http://imgur.com/YHVFt
- Positive emotions
- Another commonly reported feature of near-death experiences
- is a feeling of pure bliss, euphoria and an acceptance
- of death. Many medicinal and recreational drugs, however,
- can mirror the positive emotions and visions reported in
- near-death experiences. At varying doses, the administration
- of ketamine can mimic these experiences including
- hallucinations, out-of-body experiences, positive emotions
- such as euphoria, dissociation, and spiritual experiences.
- Ketamine is sometimes used as an anesthetic through its
- binding with opioid mu- receptors and hallucinations may
- occur through inhibiting N-methyl-D-aspartate (NMDA)
- receptors, the same receptors that are evoked during the
- administration of recreational drugs like amphetamine.
- Thus, the neurochemical processes that ketamine evokes
- may be similar to some of the positive emotional experiences
- and visions during near-death experiences, through
- evoking the rewarding properties of the opioid system and
- misattribution of events due to disruption of the prefrontal
- cortex [13]. Such processes may occur naturally and similar
- systems are evoked when animals are under extreme
- danger. For example, dopamine and opioid systems become
- active when an animal is under predatory attack. Thus,
- these endogenous systems come into play during highly
- traumatic events and have likely evolved to aid in the
- survival of the organism.
- Understanding the neurobiological mechanisms of
- near-death experiences
- The near-death experience is a complex set of phenomena
- and a single account will not capture all its components.
- One recent theory is that the basic arousal systems beginning
- in the midbrain may account for many of the components
- of the near-death experience [10]. Of interest is the
- locus coeruleus, a midbrain region involved in the release
- of noradrenaline. Noradrenaline is known to be involved in
- arousal related to fear, stress, and hypercarbia [10], and is
- highly connected to regions that mediate emotion and
- memory, including the amygdala and hippocampus. Indeed,
- stimulation of the noradrenaline system has been
- shown to enhance and consolidate memory, and plays a
- critical role in the sleep-wake cycle, including REM sleep.
- Along with basic midbrain systems, such as the periaqueductal
- gray, a region involved in opioid analgesia and basic
- fear responses, and the ventral tegmental area, which is a
- core dopamine reward area, the noradrenaline system may
- be part of a basic set of systems that directly or indirectly
- evoke positive emotions, hallucinations and other features
- of the near-death experience.
- Taken together, the scientific evidence suggests that all
- aspects of the near-death experience have a neurophysiological
- or psychological basis: the vivid pleasure frequently
- experienced in near-death experiences may be the result of
- fear-elicited opioid release, while the life review and REM
- components of the near-death experience could be attributed
- to the action of the locus coeruleus- noradrenaline
- system. Out-of-body experiences and feelings of disconnection
- with the physical body could arise because of a breakdown
- in multisensory processes, and the bright lights and
- tunneling could be the result of a peripheral to fovea
- breakdown of the visual system through oxygen deprivation.
- A priori expectations, where the individual makes
- sense of the situation by believing they will experience the
- archetypal near-death experience package, may also play a
- crucial role [14]. If one challenge of science is to demystify
- the world, then research should begin to test these and
- other hypotheses. Only then will discussion of near-death
- experiences move beyond theological dialogue and into the
- lawful realm of empirical neurobiology.
- Acknowledgements
- We wish to thank Chris Frith, Bernhard Staresina, Donna Harris and
- Michael Ewbank for helpful comments. The paper was supported by the
- UK Medical Research Council.
- References
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