The Physiology of the Tunnel
Susan J. Blackmore
Tom S. Troscianko
University of Bristol
ABSTRACT: Several theories to account for the origin of tunnel hallucina-
tions and tunnel experiences near death are considered: (1) the idea of a "real"
tunnel; (2) representations of transition; (3) reliving birth memories; (4) imag-
ination; and (5) physiological origins. Three different physiological theories are
considered that relate the tunnel form to the structure of the visual cortex. All
can account for much of the phenomenology of the tunnel experience, and all
lead to testable predictions. It is argued that the tunnel experience involves a
change in the mental model of the self in the world. Because of this, an
experience of purely physiological origin, with no implications for other worlds
or for survival, can nevertheless produce lasting changes in the sense of self
and reduce the fear of death.
The tunnel is dark. The light at the end is bright, beautiful, and
alluring. We want to reach the light. It is coming nearer.
The tunnel experience is exciting and somehow mysterious. It gives
the impression of mysteries about to be solved or secrets about to be
revealed. And yet it seems likely that its origin lies in the structure of
the visual cortex. We suggest that these two aspects are not incompat-
ible. We shall explain possible physiological origins of the tunnel and
explore the reasons for its numinous qualities.
Here is an example of a tunnel experience occurring as part of a near-
death experience (NDE). It was reported to us by a 70-year-old widow
and occurred in 1960 when she was operated on for a spinal tumor.
Dr. Blackmore and Dr. Troscianko are at the Perceptual Systems Research Centre
Department of Psychology, University of Bristol. Requests for reprints should be ad-
dressed to Dr. Blackmore at the Department of Psychology, University of Bristol, 8-10
Berkeley Square, Bristol BS8 1HH, England.
Journal of Near-Death Studies, 8(1) Fall 1989
9 1989 Human Sciences Press
16 JOURNAL OF NEAR-DEATH STUDIES
Suddenly amidst all this pain (I was still in the dark) I saw a light
very faint and in the distance. It got nearer to me, and everything was
so quiet; it was warm, I was warm, and all the pain began to go. When
I finally stood out of the dark, and into this light, it was the most
beautiful thing I have ever seen: soft, warm, translucent. I was finally
there, and I felt as if someone had put their arms around me. I was
safe, no more pain, nothing, just this lovely, caring sensation.
Next thing I remembered was a doctor or somebody twisting my
cheek and several people doing things to me.
This happened again (I think once). Then my husband was again
visiting me with my children. I was only vaguely aware of them. I
drifted off. I could again see this light. I couldn't wait to go back down
As early as 1905 Ernest Dunbar collected cases of tunnel experienced
under anesthetics and with other drugs (Dunbar, 1905). The tunnel is
also one of the form constants noted by Heinrich Kluver in the 1930s
(Kluver, 1967). He claimed that almost all hallucinations, regardless
of their cause, took on similar basic forms. The four he listed were
(1) grating, lattice, fretwork, filigree, honeycomb, or chessboard de-
sign; (2) tunnel, funnel, alley, cone, or vessel; (3) spiral; and (4) cobweb.
He also noted that these simple hallucinations were extremely bright
and the colors highly saturated.
These hallucinations can occur in widely different conditions from
hypnagogic imagery when falling asleep (Schachter, 1976); the auras
of epilepsy, migraine, or insulin hypoglycemia (Cowan, 1982); and with
hallucinogenic drugs, such as LSD or mescaline (Siegel, 1977). Need-
less to say, the tunnel also occurs as an important part of the NDE
(Moody, 1975; Ring, 1980). Interestingly, the other forms do not. The
NDE seems to include tunnels, funnels, alleys, cones, and possibly
vessels. It also includes great voids of blackness and space, but no
gratings and cobwebs. The spiral, of course, may form a kind of tunnel,
but we have not come across any examples of a dying person passing
through a cobweb or dancing on a chessboard.
This provides an interesting question. Why is it the tunnel alone that
seems to be so important in NDEs? Should we ignore this difference
and seek one explanation for all the kinds of hallucination; should we
assume that all the forms arise from similar causes and then seek to
explain why NDEs do not include gratings and cobwebs; or should we seek
entirely separate explanations for NDEs and other hallucinations, such
that NDEs provide a glimpse into another world? We shall return to this
question having considered some of the available evidence.
SUSAN J. BLACKMORE AND TOM S. TROSCIANKO 17
Kevin Drab (1981) studied 71 tunnel experiences obtained from 1,112
reports of unusual experiences. He excluded descriptions of voids and
black spaces and defined the tunnel as "the perception of a realistic
enclosed area of space much longer than its diameter" and found
examples occurring in cardiopulmonary arrest; severe stress (from
disease or trauma); mild stress (including minor injuries and pain,
fatigue, fear, mild fever or toxic conditions, and migraines); and normal
conditions (including relaxation, sleep, meditation and hypnosis). Many of
the latter category were associated with out-of-body experiences (OBEs).
He found, among other things, that the tunnel was more frequent in
serious medical conditions than in nonserious conditions. Also, as one
might expect, many of the serious cases involved heart attacks or
mechanical accidents. However, there were no cases with cancer or
stroke. Since those two conditions rank second and third among the
leading causes of death in Americans, this is surprising. It is also
known that patients with cancer do report mood elevations and visions
of other worlds (Osis & Haraldsson, 1977). Drab concluded that tunnel
experiences are more often triggered by a sudden change in physiologi-
cal state such as an abrupt drop in blood pressure or shock.
The tunnels were usually dark or dimly lit (only 10% were brightly
lit), and none of the experiencers reported touching the sides, although
these varied widely and included scintillating darkness, luminous
vapor with fine lines, and bricks with a cobblestone floor. Before my
(SB) own first OBE I went down a tunnel made of leaves (Blackmore,
1982a) and I have often experienced tunnels made of varying textures,
bright lights, or bands of darker and lighter gray.
Nearly half of Drab's cases reported a light at the end of the tunnel.
And 73% of those described it as becoming larger in their field of vision
and described themselves as moving towards it. Many described the
light as extremely bright and some even commented that it did not
seem to hurt their eyes. Almost all of Drab's experiencers described
moving through their tunnels; most went through, some up, and some
down, but only eight cases described coming back through the tunnel.
It is not clear from Drab's description whether they came backwards
through the tunnel or turned around and moved forwards in the oppo-
Explaining the Tunnel Experience
What kind of explanation are we looking for? We think we need to
answer this before considering any offered explanations. Our own
priorities are that first the theory should account well for the phenome-
18 JOURNAL OF NEAR-DEATH STUDIES
nology. This means explaining why there is a tunnel and not some-
thing else, why it is like it is, why there is a light at the end, and so on;
and above all, why it seems so real. Second, the theory should not
multiply other worlds or bodies or vibrations ad hoc. Third, it should
provide testable predictions and the means for changing and improv-
ing the theory by experiment. Applying these criteria means that
untestable occult theories that can '~explain" everything but can never
be refuted are not helpful. No more helpful are dismissive theories of
the kind 'tit's all imagination" or '~It's all in the mind." Of course, it
may all be in the mind, if that phrase means anything, but this is
certainly no explanation. So a successful theory must account for the
phenomena in ways that are economical and testable.
There are generally four types of explanation offered for the tunnel
A "Real" Tunnel
In some occult systems there is said to be an actual tunnel that leads
from one world to the next.
The problems with such theories are many. If the other worlds are
somehow part of this world, then we should be able to measure them or
in some way detect their presence. Attempts to do this have notably
failed (Blackmore, 1982a). On the other hand, most exponents argue
that the higher worlds are in some other dimension or different plane.
If these planes and dimensions are not commensurate with the physi-
cal world then all the problems of any brain-mind dualism are raised.
How can anything be said to pass from one world to another? Positing a
tunnel between them certainly does not help. Such theories can nei-
ther explain the phenomena, except in a purely ad hoc way, nor
provide any predictions by which they might be tested or improved.
Representation of Transition
An alternative is to say that the tunnel is symbolic of the transition
from one state of consciousness to another. Robert Crookall (1964)
wrote that there are at least three ~deaths" as first the physical, then
the soul, and finally the spiritual body are shed to unveil the Eternal
Self. The tunnel is a blacking out of consciousness as it passes from one
state to another. Celia Green (1968) proposed the tunnel as a represen-
tation of a long journey and Kenneth Ring (1980) considered the tunnel
SUSAN J. BLACKMORE AND TOM S. TROSCIANKO 19
a psychological phenomenon through which the mind shifts from its
normal state of consciousness to a holographic or four-dimensional
consciousness of pure frequencies.
This idea escapes the obvious problems of positing ~real" tunnels and
allows for more flexibility. But in the process we suggest that it loses
all power as an explanation. It simply begs the question ~'Why the
tunnel?" Why shouldn't something else be used as a symbol of transi-
tion? There could be gates, doorways, arches, chasms, or the great river
Styx. In fact these other forms do occur later on in NDEs, in the stage
of worlds beyond, but it is the tunnel that appears regularly, in predict-
able forms, and, as we have seen, in numerous different circumstances.
We understand this ubiquitous tunnel no better by saying that it is
symbolic of something else.
Reliving Birth Memories
One of the most popular theories is that the NDE is a reliving of one's
birth and that the tunnel is really the birth canal (Honegger, 1983;
Sagan, 1977). This theory has been roundly criticized already (Becker,
1982). The main problems are that it is implausible to suppose that the
infant would perceive the world in a form that could later be recalled
by an adult with totally different perceptual capabilities. Also the
birth canal is nothing like a tunnel with a light at the end, and in any
case the fetus is pushed along it with the top of its head usually
emerging first, not its eyes. It takes a vast leap of the imagination to
make the two comparable, and yet this theory has produced a welter of
New Age ideas and techniques.
One virtue of this kind of theory is that, at least in some forms, it is
testable. If the tunnel experience is reliving birth memories, then the
kind of birth should make a difference. In particular, people born by
Cesarean section have never been along the birth canal and so, pre-
sumably, should not be able to relive it. One of us carried out a survey
of 254 people, of whom 36 had been born by cesarean section. These 36
did not report more or fewer tunnel experiences than the others; 36% of
each group reported tunnel experiences (Blackmore, 1982b).
To circumvent this difficulty, Scott Rogo (1982) has argued that the
tunnel is not actually reliving one's birth but is a kind of symbolic
representation of birth in general. Indeed Carl Sagan's theory can be
interpreted in this way. If so, this theory is equivalent to the previous
kind of theory and suffers from the same weakness.
Rogo did, however, suggest that people who had a difficult birth
20 JOURNAL OF NEAR-DEATH STUDIES
would have more negative associations with later OBEs than people
who had an easy birth. As far as we know this has not yet been tested.
A lot of commentators seem to like the idea that the tunnel, the OBE,
and many other experiences are ~'just imagination." We refer to this
approach as a dismissive nonexplanation (Blackmore, 1988). The expe-
riences almost certainly are, or include, the imagination, but this
alone is no explanation. If specific similarities between imagination
and the tunnel experience can be found, then this is helpful, but we
must remember the criteria for a useful theory. The ~'just imagination"
theory neither accounts for the phenomenology (why the dark tunnel
with a light at the end, and not a green gate with a ditch in front of it,
and so on), nor is it really testable. It can, we suppose, be refuted by the
demonstration of something else being involved, but it cannot be im-
proved on by progressive tests or positive predictions. It is, by its very
nature, a contentless explanation. For that reason we want a theory
that, even if it says the tunnel is imaginary, explains why one should
imagine tunnels rather than anything else.
If we suppose that the hallucinatory form constants are generated by
some physiological process, where should we look for it? There is good
reason to think they are generated in the cortex. First, according to
Cowan (1982) they do not move with the eyes and are therefore not
afterimages or other retinal effects. Second, they can be produced by
pressure on the eyes. In this case they do move with the eyes but can
only be produced by binocular pressure, which again points to the
cortex as the site of origin. There are now a number of theories that
relate the tunnel form to the structure of the visual cortex.
John Cowan (1982) argued that because we know the appearance of
the hallucinations and also the way images on the retina are mapped
onto the cortex (Daniel & Whitteridge, 1961), we should be able to
calculate the cortical form that corresponds to any hallucination.
Using this mapping he showed that concentric rings on the retina or in
the visual world correspond to straight lines parallel to one axis in the
visual cortex. Straight lines at right angles to those are mapped in the
visual cortex as radiating lines; straight lines at other angles are
SUSAN J. BLACKMORE AND TOM S. TROSCIANKO 21
mapped as spirals. If the lines move, the spirals or rings expand and
contract. Expanding concentric rings could produce the impression of
moving through a tunnel.
But why should there be moving stripes across the visual cortex?
Cowan offered an analogy with thermodynamics. In its normal stable
state, cortical activity is inhibited by many inhibitory neurons. When
these neurons are disrupted, as they are known to be by drugs such as
LSD and by anoxia, the disinhibition destabilizes the uniform state,
and stripes of activity pass across the cortex. The analogy is with a
fluid heated from below, in which either hexagonal patterns or stripes
of rising and falling fluid are produced. Cowan concluded that a simi-
lar process takes place in the cortex and gives rise to the four form
This theory seems to have some problems. First, it does not account
for the fact that NDEs include tunnels but not cobwebs and lattices. It
does not explain why people seem to move forwards through tunnels
but rarely backwards. Nor does it explain just what those stripes are
and why and how they move as they do.
One of us (SB) therefore suggested a far simpler theory. Perhaps no
stripes are needed at all. When the brain is starved of oxygen, inhibi-
tion is first suppressed, which creates a state of hyperactivity. The cells
in the visual cortex will be firing randomly, or noisily. Using the same
retinocortical mapping, we can see that there will be far more cells
firing that represent the center of the visual field and far fewer at the
edges. The effect will appear like a flickering speckled world that gets
brighter and brighter towards the center. It is known that the visual
system is biased towards movements in an outward direction (George-
son and Harris, 1978). In addition, visually perceived movement, espe-
cially in the absence of any reference, is easily interpreted as self
movement; the classic example of this is the feeling that your train is
moving backwards when another train pulls out of the station. In other
words, this scintillating speckled world of electrical noise could appear
to expand outwards from a brighter center. Could this be the tunnel?
Tom Troscianko then made a further suggestion (Blackmore & Tros-
cianko, 1988). Perhaps this process would not be enough to produce the
tunnel effect. However, if you started with very little noise and it
gradually increased, the effect would be of a light at the center getting
bigger and bigger and hence closer and closer. The tunnel would occur
as the noise levels increased and would stop either when they de-
creased again or when the whole cortex was so noisy that the light
enveloped it all. In other words, one would have entered the light. It
could get no brighter.
22 JOURNAL OF NEAR-DEATH STUDIES
All these theories have some advantages in common. They explain
why there is a tunnel rather than any other symbol of passage to
another world. They explain how the light can be extremely bright but
does not hurt the eyes: the eyes are not involved at all. The stimulation
in the cortex may be as bright, or even brighter, than any real stimula-
tion could actually produce. They all explain Drab's findings that the
tunnel occurs with more serious medical conditions, and that it does
not occur with slow progressive disease.
Predictions from the Theories
All the physiological theories provide testable predictions. For exam-
ple, they imply that an intact visual cortex is required, and if this were
damaged, as in some kinds of blindness or stroke, then the tunnel could
not be produced.
In other ways they differ. Primarily, Cowan's theory requires that
there be stripes of activity passing across the cortex. This might be
related to cortical spreading depression, which is thought to be impli-
cated in migraine. This spreads at a rate of 2 to 3 mm per min (Leao,
1944). By contrast, Cowan claimed that tunnel hallucinations fill up
the visual field in about 2.5 msec, corresponding to a propagation
velocity of 1 or 2 cm per sec. However, he gave no data or reference for
his claim, and that is clearly something to be investigated further.
Whether or not the mechanism is similar to cortical spreading depres-
sion, it would be expected to have a rate dependent on the neural
mechanisms underlying it. In this case, we should expect, according to
Cowan's theory, that the tunnel would always be travelled at roughly
the same speed. This appears not to be the case. Some people claim to
float gently down tunnels, while others rush at a tremendous rate.
Drab (1981) reported 67 cases describing movement, of which 12 said
they were moving at a slow to moderate speed and 24 were moving
By comparison, Blackmore's theory makes no stipulation about
speed. If the movement is induced merely by the speckly noise, then it
depends on the amount of noise: the more noise, the greater the speed.
But this in turn implies that faster movement is associated with a
larger central white area. As far as we know, this has not been tested.
The final theory makes a clear prediction. If the movement is created
by the expansion of the central white area, then speed is not restricted,
but the overall change in the tunnel is. In other words, you can only
move from a tiny white light to a completely enveloping one. The faster
SUSAN J. BLACKMORE AND TOM S. TROSCIANKO 23
you move through the tunnel, the quicker the experience will end. This
also has not been tested. So these differences provide a way of testing
the various theories, which could be done by collecting appropriate
descriptions from people who have experienced the tunnel.
There are other predictions made by these theories. If the key to the
tunnel is cortical disinhibition, then the drugs that produce tunnels
should all be those that reduce inhibition. This certainly appears to be
the case, the major hallucinogens being the best example. On the other
hand, some drugs increase inhibition, such as the minor tranquilizers
like Valium, which act by potentiating the neurotransmitter gamma-
aminobutyric acid. We should therefore not expect to find tunnel expe-
riences in people taking these drugs. In particular, if they approach
death by an overdose of such drugs they should not have the tradi-
tional near-death tunnel. Again, this prediction has not been tested.
We would like now to return to the question of why tunnels occur
when they do. With the major hallucinogenic drugs tunnels are com-
mon, but so are lattices, spirals, cobwebs, and other simple forms. The
tunnel seems to have a special place in the NDE. Why is this?
As far as we can tell, Cowan's theory provides no answer. If the
disinhibition is the same regardless of its immediate cause, then the
patterns produced should be the same. On the other hand, both the
other theories can only produce tunnel forms, and not the other form
constants. In particular, Troscianko's theory suggests that the tunnel
can only occur when there is a fairly rapid increase in cortical noise, as
would be expected in cardiopulmonary failure or an accident or sudden
In addition, all these theories can account for Drab's apparently odd
finding that there were no tunnels reported by stroke victims. They all
require an intact visual cortex, and if that were damaged by a stroke
the tunnel could not be seen. A further prediction is related to this. If
the tunnel is of cortical origin, then anyone with a damaged visual
cortex should not experience it. So, for example, people blind through
retinal disease or other damage in the eye should have tunnel experi-
ences just like anyone else, but those suffering from cortical blindness
should not. This too awaits testing.
The first way to test these theories should be to find out just what
kind of visual stimulation is necessary to induce the impression of
moving through a tunnel. Obviously, we cannot open up someone's
cortex and apply the hypothesized stimulation that way. We can,
however, mimic that stimulation by presenting visual forms to people.
Using retinocortical mapping we can construct the visual equivalent of
the different kinds of cortical stimulation. In Cowan's case this would
24 JOURNAL OF NEAR-DEATH STUDIES
be concentric rings or spirals. In Blackmore's case it would be ran-
domly flickering specks of light distributed like the cells in the visual
system, with many in the center and fewer towards the periphery. In
Troscianko's case it would mean having brightness at any spot scaled
according to the same mapping, with the brightest in the center fading
out to the edges, and the brightness of the whole picture gradually
So far we have only tried the latter. Troscianko and his colleagues
wrote a program to display this on a monitor and it does indeed appear
like a tunnel with a bright light at the end that gets gradually brighter
(and apparently nearer) (Blackmore & Troscianko, 1988). This re-
search is still underway, and the next stage is to produce the other
forms and to get people who have had tunnel experiences to compare
them with their experienced tunnels. This might give some further
clue as to the precise origin of the tunnel.
It can be seen that these physiological approaches to the tunnel
experience already account for many of the previous findings, and they
provide numerous ways of testing them for the future. In this respect
they are quite different from all the previous theories I have
Why Is the Tunnel So Real?
This is a question most physiological theories leave untouched. Nev-
ertheless, the experience cannot be fully understood without consider-
When tunnels appear in drug-induced states, they are usually consid-
ered to be hallucinatory or illusory (Siegel, 1977); but near death, and
in some other OBEs, they seem to be as real as anything in normal
perception. Why? To answer this we have to step back to the question
of why anything ever seems real. It seems implausible to suppose that
the perceptual system can easily discriminate input from recalled
information when the two are mixed almost from the very periphery.
Therefore the system must, at some level, make a decision about which
of its representations, or mental models, are ~real" and which imagin-
ary. We suggest that it does this at a high level, comparing representa-
tions of the world and choosing the most stable as the outside world;
i.e. attributing reality to it (Blackmore, 1984, 1988).
Normally, of course, the model chosen is that which is constructed on
the basis of input. This is the only one that is stable and predicts future
SUSAN J. BLACKMORE AND TOM S. TROSCIANKO 25
input as it goes along. Other models, by comparison, are fleeting and
unstable. However, the conditions that give rise to tunnel experiences,
as well as OBEs, are precisely those in which input is disrupted, either
because of damage to the nervous system or because of deep relaxation,
meditation, or sensory isolation. In these conditions the input model is
no longer the most stable, and therefore, according to my hypothesis,
whichever model is most stable will take over as '~reality."
If there is noise in the visual cortex producing a tunnel form, and if
the input-driven model is also unstable, then the tunnel form will be
the most stable model in the system and hence will be chosen as '~real."
This is why tunnels near death, but not in the milder drug-induced
experiences, seem real. Indeed they are '~real" in just the same sense as
anything ever is real; because they are the most stable model the
system has at the time.
We would take one further step from this, although it is not neces-
sary to understanding the tunnel experience. That is to say that these
mental models are not something we construct. Rather ~we" are the
mental models constructed by the brain. One of us has argued else-
where (Blackmore, 1989) that consciousness is simply what it is like
being a mental model, and the sense of a separate self arises from the
construction of a model of a separate self. In other words, the whole
system produces a mass of models, and we are just one of them. The
normal state of consciousness is dominated by a stable model of self in
the world. In the tunnel experience, the tunnel replaces the model of
the outside world. It does not necessarily obliterate the model of self.
However, when the tunnel occurs as part of the NDE, it may also
involve the dissolution of the self model.
Why the Sense of Mystery?
More than 80 years ago Dunbar gave a marvelous account of the
effects of anesthetics, which were then primarily ether and chloroform.
He wrote first:
I have made a point of asking patients in the surgical wards how they
felt when they were being anaesthetised. The common experience
(eighty per cent of cases) is that of rushing into a dark tunnel. There is
singing in the ears and a flashing of lights in the eyes. (Dunbar, 1905,
26 JOURNAL OF NEAR-DEATH STUDIES
He also described experiments with ether:
Next comes the sensation that the body is just as much a part of the
environment as anything else, and it is perhaps this sensation which,
together with the wide-awake intelligence, compels the individual to
adopt the standpoint of subjective idealism; which, in its turn, drives
him to think that at last the solution of the mystery is dawning upon
him. (p. 73)
Isn't this how it is in some drug experiences, in OBEs, and near
death? In these states it seems as though the mystery is less impene-
trable than before.
This may not be mere delusion. Rather, given what we have said
about mental models and consciousness, we think something quite
important has happened. Our usual assumption, that the input-based
model is a true picture of a ~real" world ~out there" and that we are a
separate individual inhabiting that world and our bodies, is chal-
lenged. It becomes obvious that there are other ways of being aware.
Any model can seem real. Our assumptions about the real world are
shaken. It is this, we suggest, that gives rise both to the impression
that ~the light is dawning" and to the aftereffects of the experiences on
It is misleading that this metaphorical light is often equated with the
physiologically induced light. The light at the end of the tunnel is
induced by randomly firing neurons. It is not just imagination. It has a
very definite physiological origin. This is no reason, however, to dis-
miss the often claimed insights as worthless. The physiologically in-
duced tunnel can be one way of realizing something important about
ourselves, a realization that can change our lives: that is, that we are
mental models and nothing more. Frightening as this is to our sober
everyday selves, it is not the least frightening when directly experi-
enced. The extent to which this insight can be maintained when the
experience is over may be the extent to which fear of death is reduced.
Finally, we have hinted that the dissolution of the self model is
possible. All this means is that a biological system that is designed to
build a model of self ceases to do so. It isn't an easy state to achieve.
Strong biological pressures are against it, but it can happen either
through long years of training or in extremis. Afterwards the self
model appears again. It is hard for ~you" (the self model) to remember
what it was like not being; so these states are not easily recalled.
Nevertheless there can be a lasting effect on the system. The self never
seems quite so solid again and the idea of its death is not so frightening.
SUSAN J. BLACKMORE AND TOM S. TROSCIANKO 27
We have presented several theories of the tunnel experience. The
various physiological theories seem by far the best able to explain the
phenomenology of the experience, to provide testable predictions, and
to contribute to our understanding of altered states of consciousness. A
great deal of work now needs to be done to determine which, if any, of
these is correct.
These theories entail no other worlds and hold out no hope for
survival of death. Nevertheless, far from denigrating the tunnel expe-
rience, we think they provide a stepping stone to understanding its
numinous and life-changing qualities.
Tom Troscianko was funded by the Medical Research Council (UK).
We thank Patrick Bougant and Marni Stewart for programming
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