Lately I've been reading The Supreme Adventure: Analysis of Psychic Communications, by Robert Crookall. In it, Crookall collects many accounts of the dying process from a variety of sources and examines them to see if they tell a more or less consistent story. His idea is that if the details of the story are consistent and cannot credibly be explained by collusion or coincidence, then there's good reason to believe that these details are true.
One particularly interesting detail is the well-known "tunnel" through which the spirit is said to travel after leaving the body. This imagery became famous in the 1970s when the term near-death experiences was coined by Raymond Moody, but Crookall's book precedes Moody's by 14 years and contains the same imagery.
A common symbol used in describing the act of shedding ... the Physical Body is that of passing through a 'tunnel' (or a 'door', 'passage', 'tube', 'shaft', 'hole', 'funnel', etc.): this is clearly related to the 'momentary coma' [experienced upon separating from the body], though lasting somewhat longer and, perhaps, with some dim consciousness, of existence if not of environment. There are many considerations which strongly suggest that in this symbol a genuine experience of a surviving soul is indicated.
He then lists a number of statements "by people who left the body other than by death and who use identical symbols" -- that is, by people who had out-of-body experiences (astral projection) or, in some cases, what we would now call near-death experiences. (Where possible, I have given the date of the published account.)
"I seemed to float in a long tunnel. It appeared very narrow at first but gradually expanded into unlimited space." (1952)
"Suddenly there appeared an opening, like a tunnel, and, at the far end, a light. I moved nearer to it and was drawn up the passage." (1950)
"A constant preliminary to the loss of consciousness is the symbolic passing through a pitch-black tunnel." (1953)
"I was falling ... down a dark, narrow tunnel or shaft ... Sometimes the speed is so tremendous that one gets the effect of tumbling through a hole into a new sphere."
"I find myself going down a long dim tunnel ... At the far end is a tiny speck of light which grows, as I approach, into a large square, and I am there!"
"In one of my own experiences I seemed to pass through a tunnel in a dream-like state and emerged through the opening at the end into a scene of bright sunlight." (1956)
"I was hurried off at great speed. Have you ever looked through a very long tunnel and seen the tiny speck of light at the far end?... Well, I found myself... hurrying along just such a tunnel or passage." (1935 near-death experience)
Crookall includes a 1946 mystical experience:
"I closed my eyes and watched a silver glow which shaped itself into a circle with a central focus brighter than the rest. The circle became a tunnel of light proceeding from some distance on in the heart of the Self. Swiftly and smoothly I was borne through the tunnel."
And a number of statements from people who had an out-of-body experience under anesthesia:
"I was in a long tunnel with a light at the end... I knew that if I could only get to the light at the end I should understand everything." (1935)
"I seemed to float down a dark tunnel, moving towards a half-moon of light that was miles away."
"On being given ether I was moving, at a terrific rate, through what seemed to be a tunnel."
"I found myself in an avenue of trees, slowly moving farther and farther from my body... I continue to advance along the avenue towards a brilliant light at the end of it." (1955)
"I found myself proceeding along a straight black tube with hardly any room to move." (1894)
What is most interesting is that these statements agree with communications through mediums.
"I remember a curious opening, as if one had passed through subterranean passages and found oneself near the mouth of the cave... The light was much stronger outside."
An alleged discarnate who said he helped people make the transition said he tried "to make this passage through the tunnel as happy as possible." (1931)
Another communicator said he traveled through a "dark tunnel" while leaving his body. Yet another spoke of "traveling down a tunnel".
A 1926 communicator said: "I saw in front of me a dark tunnel. I stepped out of the tunnel into a new world."
These ostensible communicators also seem to agree that returning to the physical body can require going through a tunnel. This is true even if the discarnate entity is trying to temporarily enter the body of a medium.
"Do not look at me too critically: to try to transmit through the organism of a medium is like trying to crawl through a hollow log." (George Pelham, communicating through Mrs. Piper to Richard Hodgson)
Another discarnate compared entering a medium's body to getting into "a sort of funnel" (1948).
One would-be communicator failed to get through: "He was able to see the light in the darkness of a long funnel. But he doubted so much that it went out. He was frightened for fear he would never find his way back." (1936)
Interestingly, Crookall notes that the tunnel symbol "is also used for describing the experience of reentering the Physical Body" in what we would today call near-death experiences. "This also is felt as a brief coma, 'blackout', or passage through a 'tunnel' (depending on the duration of the experience)."
One NDEr said, "I turned away from the bright light... and entered a gloomy tunnel. I fought my way back to a tiny light in the distance... When I got back to the light, I found myself back in bed."
Crookall even quotes an account given by Plutarch in A.D 79 (On the Delay of Divine Justice) in which a certain Aridaeus suffered a severe fall and was momentarily startled out of his body. Surviving the fall, he felt himself reenter his physical shell. "Then, as though he were suddenly sucked through a tube ... he lit [i.e. alit] in his body."
However, Crookall notes that most people appear to have only a momentary blackout, rather than the full tunnel experience, when they reenter their bodies. He cites a 1923 study of out-of-body experiences in support of this statement. Modern studies of NDEs also find that the tunnel phenomenon is more commonly remembered when leaving the body than when returning, and that the return is often much more rapid.
It appears, then, that the tunnel phenomenon is not easily explained as a neurological quirk. Neurology might explain the experience of the tunnel in NDEs, when the brain is presumably shutting down. It does not explain the tunnel imagery in more routine out-of-body experiences, such as astral projection experiments, when there is no physical damage to the brain. Nor does it explain the persistence of this imagery in mediumistic communications ostensibly originating from the deceased, who are describing their own passage - either their passage out of the body upon death, or their passage into the medium's body for purposes of the séance.
And remember that all of the above quotes were collected prior to 1961, the publication date of The Supreme Adventure. This rules out the conjecture that the tunnel with a bright light at the end is merely a "meme" originating in Raymond Moody's 1975 bestseller Life after Life and popularized by the media.