|
Dr.
Pim van Lommel
Some people who have survived a life-threatening
crisis report an extraordinary experience. Near-death
experience occurs with increasing frequency because
of improved survival rates resulting from modern techniques
of resuscitation.
The content of NDE and the effects on
patients seem similar worldwide, across all cultures and times.
The subjective nature and absence of a frame of reference
for this experience lead to individual, cultural, and religious
factors determining the vocabulary used to describe and interpret
the experience.1
NDE are reported in many circumstances:
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,
and apnea.
Such experiences are also reported by
patients with serious but not immediately life-threatening
diseases, in those with serious depression, or without clear
cause in fully conscious people. Similar experiences to near-death
ones can occur during the terminal phase of illness, and are
called deathbed visions.
Identical experiences to NDE, so-called
fear-death experiences, are mainly reported after situations
in which death seemed unavoidable: serious traffic accidents,
mountaineering accidents, or isolation such as with shipwreck.
Several theories on the origin of NDE
have been proposed. Some think the experience is caused by
physiological changes in the brain, such as brain cells dying
as a result of cerebral anoxia.2-4 Other theories encompass
a psychological reaction to approaching death,5 or a combination
of such reaction and anoxia.6
Such experiences could also be linked
to a changing state of consciousness (transcendence), in which
perception, cognitive functioning, emotion, and sense of identity
function independently from normal body-linked waking consciousness.7
People who have had an NDE are psychologically
healthy; although some show non-pathological signs of dissociation.7
Such people do not differ from controls with respect to age,
sex, ethnic origin, religion, or degree of religious belief.1
Studies on NDE1,3,8,9 have been retrospective
and very selective with respect to patients. In retrospective
studies, 5-10 years can elapse between occurrence of the experience
and its investigation, which often prevents accurate assessment
of physiological and pharmacological factors.
In retrospective studies, about 45%1
of adults and up to 85% of children10 who had a life-threatening
illness were estimated to have had an NDE. A random
investigation of more than 2000 Germans showed 43%
to have had an NDE at a mean age of 22 years.11
Differences in estimates of frequency
and uncertainty as to causes of this experience result from
varying definitions of the phenomenon, and from inadequate
methods of research.12
Patients' transformational processes after
an NDE are very similar1,3,13-16 and encompass life-changing
insight, heightened intuition, and disappearance of fear of
death. Assimilation and acceptance of these changes is thought
to take at least several years.15
The authors defined NDE as the reported
memory of all impressions during a special state of consciousness,
including specific elements such as out-of-body experience,
pleasant feelings, and seeing a tunnel, a light, deceased
relatives, or a life review.
They defined clinical death as a period
of unconsciousness caused by insufficient blood supply to
the brain because of inadequate blood circulation, breathing,
or both. If, in this situation, CPR is not started within
5-10 min, irreparable damage is done to the brain and the
patient will die.
The results show that medical factors
cannot account for occurrence of NDE; although all patients
had been clinically dead, most did not have NDE. Furthermore,
seriousness of the crisis was not related to occurrence or
depth of the experience.
If purely physiological factors resulting
from cerebral anoxia caused NDE, most of the patients should
have had this experience. Patients' medication was also unrelated
to frequency of NDE. Psychological factors are unlikely to
be important as fear was not associated with NDE.
Only 12% of patients had a core NDE, and
this figure might be an overestimate. True frequency of the
experience is likely to be about 10%, or 5% if based on number
of resuscitations rather than number of resuscitated patients.
Patients who survive several CPRs in hospital have a significantly
higher chance of NDE.
Good short-term
memory seems to be essential for remembering NDE.
Patients with memory defects after prolonged
resuscitation reported fewer experiences than other patients
in our study.
Forgetting or repressing such experiences
in the first days after CPR was unlikely to have occurred
in the remaining patients, because no relation was found between
frequency of NDE and date of first interview.
However, at 2-year follow-up, two patients
remembered a core NDE and two an NDE that consisted of only
positive emotions that they had not reported shortly after
CPR, presumably because of memory defects at that time. It
is remarkable that people could recall their NDE almost exactly
after 2 and 8 years.
Our finding that women have deeper experiences
than men has been confirmed in two other studies,1,7 although
in one,7 only in those cases in which women had an NDE resulting
from disease.
Our findings show that the process of
change after NDE tends to take several years to consolidate.
Presumably, besides possible internal psychological processes,
one reason for this has to do with society's negative response
to NDE, which leads individuals to deny or suppress their
experience for fear of rejection or ridicule.
Thus, social conditioning causes NDE to
be traumatic, although in itself it is not a psychotraumatic
experience. As a result, the effects of the experience can
be delayed for years, and only gradually and with difficulty
is an NDE accepted and integrated. Furthermore, the long-lasting
transformational effects of an experience that lasts for only
a few minutes of cardiac arrest is a surprising and unexpected
finding.
Several theories have been proposed to
explain NDE.
We
did not show that psychological, neurophysiological, or physiological
factors caused these experiences after cardiac arrest.
Neurophysiological processes must play
some part in NDE. Similar experiences can be induced through
electrical stimulation of the temporal lobe (and hence of
the hippocampus) during neurosurgery for epilepsy,23 with
high carbon dioxide levels (hypercarbia),24 and in decreased
cerebral perfusion resulting in local cerebral hypoxia as
in rapid acceleration during training of fighter pilots,25
or as in hyperventilation followed by valsalva manoeuvre.4
Ketamine-induced experiences resulting
from blockage of the NMDA receptor,26 and the role of endorphin,
serotonin, and enkephalin have also been mentioned,27 as have
near-death-like experiences after the use of LSD,28 psilocarpine,
and mescaline.21
These induced experiences can consist
of unconsciousness, out-of-body experiences, and perception
of light or flashes of recollection from the past.
These recollections, however, consist
of fragmented and random memories unlike the panoramic life-review
that can occur in NDE. Further, transformational processes
with changing life-insight and disappearance of fear of death
are rarely reported after induced experiences.
Thus, induced experiences are not identical
to NDE, and so, besides age, an unknown mechanism causes NDE
by stimulation of neurophysiological and neurohumoral processes
at a subcellular level in the brain in only a few cases during
a critical situation such as clinical death. These processes
might also determine whether the experience reaches consciousness
and can be recollected.
With lack of evidence for any other theories
for NDE, the thus far assumed, but never proven, concept that
consciousness and memories are localized in the brain should
be discussed.
How could a clear consciousness outside
one's body be experienced at the moment that the brain no
longer functions during a period of clinical death with flat
EEG?22
Also, in cardiac arrest the EEG usually
becomes flat in most cases within about 10 s from onset of
syncope.29,30 Furthermore, blind people have described veridical
perception during out-of-body experiences at the time of this
experience.31 NDE pushes at the limits of medical ideas about
the range of human consciousness and the mind-brain relation.
Another theory holds that NDE might be
a changing state of consciousness (transcendence), in which
identity, cognition, and emotion function independently from
the unconscious body, but retain the possibility of non-sensory
perception.7,8,22,28,31
Lancet December
15, 2001; 358: 2039-45
| 