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Near Death Experiences & Brainstem

Near Death Experience-Types

Anesthesia

Pam Reynolds

Cardiac Arrest and Pim van Lommel

Light Experience

Seeing Angels

Tunnel Experience

The Blind Can See

Tunnels and Darkness

© G.M. Woerlee

Many people reporting their deathbed experiences say 'Ah, it's "getting darker"'. Yet other people reporting near death experiences say they "entered darkness into a tunnel through which they passed to enter into the light". These are also descriptions of strange and wondous aspects of these personally profound experiences reported by these people. The fact that observers never see this darkness, these tunnels, or this light, does not mean they are any less real experiences - people reporting these experiences really do undergo them. Now if they are not spiritual experiences, then how can the body generate such experiences of darkness and tunnels? This web page describes how the body is capable of generating such experiences. This article is intended as a supplement to an article of mine published in the Skeptical Inquirer in the beginning of 2004 (1).

The darkness

There are several ways people can experience an experience of darkness without the necessity of invoking a spiritual cause.

1. It really is dark, either because the person is in a dark place, or because the lights were turned off. A person will perceive darkness in these situations.
2. The eyes are closed, and so a person will perceive darkness.
3. The retina fails due to oxygen starvation. Fainting is a good example of this. People faint because the flow of blood to the head suddenly stops for a few seconds. The effect of sudden cessation of blood flow to the head is sudden total oxygen starvation of all organs within the head. Of all these organs and tissues, the tissue most sensitive to oxygen starvation is the retina of the eye. In fact the retina needs mores oxygen to function than does the brain or the brainstem. This means that people lose their vision before they lose consciousness due to fainting. And indeed, this is exactly what happens, because many people report that everything went dark, or black just before they lost consciousness due to fainting - and they must have been conscious in order to have consciously perceived such a sensation. More than 90% of all dying people ultimately lose consciousness and stop breathing due to oxygen starvation (2). This is why many of the dying say, "It's getting dark. Everything is black. etc." More than 90% of all deathbed experiences and other near death experiences are due to oxygen starvation (2), which is why many people unbdergoing and reporting such experiences often tell of a period of darkness.

Tunnel experiences are due to oxygen starvation of the eyes

The cause of the ultimate loss of consciousness of death is oxygen starvation in more than 90% of all dying persons. Such oxygen starvation is usually not sudden, as occurs during fainting, or cessation of heartbeat. Instead it is usually more gradual in onset, and this is where the distribution of blood flow in the retina determines what people see during these periods. It is worth while first looking at the basic anatomy and function of the human eye.

1. Light enters the eye through the cornea (c).
2. Light passes through the pupil and through the lens (le).
3. The lens focusses the light onto the retina (ret), the licht sensitive membrane at the back of the eye.
4. The retina is a light-sensitive membrane which converts the images of light focussed on the retina into nerve signals which are conducted to the brain along the optic nerve (on).

Now we ome to the retina itself. Not only does the retina consume more oxygen than the brainstem, which is why people suffering from oxygen starvation always see darkness before losing consciousness, but the distribution of the flow of blood to the retina means the retina has a structure making it uniquely suited to generating tunnel experiences.

The drawing to the left shows the retina as seen when looking through the cornea into the back of the eye. The retina has a yellowish color, and you see the red colored arteries and the blue clored veins radiating out from the "fovea", which is also the point where the optic nerve enters the eye (see drawing of eye above).

The retina is made up of nerve tissue consuming enormous amounts of oxygen, and this oxygen is supplied to the retina as oxygen chemically bound to to the hemoglobin in the blood flowing through the arteries (the red colored blood vessels). The direction of flow of blood in these arteries is indicated by the green arrows. So the flow of blood in the arteries is from the center of a cricle to the circumference, which means that the supply of blood and oxygen to each square millimeter of the retina decreases with distance from the fovea according to the graph, i.e. flow decreases according to the formula 1/(square of the radius) = inverse square law. This relationship has been demonstrated to be true many times.

Because the oxygen consumption to the retina is more or less similar all over the retina, this means that reducing the supply of oxygen to the retina by any one of the myriad causes of oxygen starvation will cause failure of the outer (peripheral) parts of the retina before causing the cental retina to fail. The result of this is that the affected person will only see a central spot of light surrounded by darkness - "tunnel vision". The diagram below shows how this happens in an oxygen starved retina.

Diagram-A shows the flow of blood from the fovea to the periphery of the retina, and the grey coloration indicates that the degree of oxygen starvation increases with distance from the fovea.

Diagram-B shows the situation of looking at a man through such an oxygen starved eye. In the normally functioning eye, the image of the man is projected upon the retina from N to NN, and the person can see the figure of the whole man. But when a sufficient degree of oxygen starvation causes failure of the peripheral retina, a situation arises where the areas of the retina from N to H, and from HH to NN no longer function. This means that nerve signals generated by the retina in response to the image of this man only arise from the still functioning area of retina H to HH. The effect is that the image of his upper and lower body disappear - it is like looking at the man through a tube, or a tunnel. And because only the region of retina from H to HH functions, the partial image of the man is seen to be surrounded by darkness. This is how the oygen starved retina generates the perception of looking through a tunnel.

Simulating the "tunnel experience"

I made some photgraphs in a garden to demonstrate the effects of tunnel vision in the oxygen starved eye.

1 -Normal situation.

2 -Pupils widen due to oxygen starvation, fear, medicines, etc. More light enters the eyes, so that the light that is seen is perceived as bright.

3 -The outer edges of the retina fail, causing tunnel vision, and "bright light" pours in through the "tunnel"

This is how the functioning of the eyes generates the sensations of "darkness", of "tunnels", and of "bright light pouring into the tunnel" in people with opened eyes during oxygen starvation. Resuscitaion will restore normal retina function, restoring normal sight, so generating the perception of "leaving the tunnel to enter the light" in people who still have widened pupils when their retina function is restored. Even so, some people do undergo tunnel and light experiences while in darkness, or while their eyes are definitely closed.

Other mechanisms by which the body generates tunnel experiences

Sometimes people undergo "tunnel experiences" when their eyes are closed, or while they are in darkness. There are two possible mechanisms by which the body can generate such sensations.

1. Malfunction of the optical cortex. I discussed this in the page on The Light. Dr. Blackmore and colleagues found that when the optical, or visual cortex of the brain is increasingly stimulated, as can occur during epileptic nervous activity such as due to oxygen starvation, the effects of drugs and medicines, or migraine, a truly wonderful sensation of moving through a tunnel to "enter the light" sensation can arise (3).
2. Hallucination. The hallucination of moving through a tunnel to enter light can be generated by the functioning of other bodily mechanisms such as those generating out-of-body experiences (2), combined with the expectation of entering a brightly lit heaven, paradise, or life after death. After all, for many people, deathbed and near death experiences are determined to a large degree by their expectations and socio-cultural upbringing (2, and also see Near Death Experience-Types). The fact that these experiences are hallucinations does not in any way diminish their reality and impact upon those undergoing them.

Conclusions and remarks

These are several of the mechanisms by which the body can generat sensations of "darkness", of "tunnels", and of "light pouring into the tunnel". No supernatural explanations are required.

Even so, some people say these explanations are all very well, but they do not explain the serenity and wondrous ineffability experienced by those reporting these sensations. Accordingly they then proceed to say that these explanations do not explain these sensations of light, of darkness, and of tunnels, because they do not explain these sensations.

Unfortunately these people make no disctinction between a perception and an associated emotion. Look at the situations of people undergoing deathbed, or near death experiences. These people are near to death, or actually dying, and this means their brains are also influenced by the causes of their dying, or their near death experiences. Af ter all, if they were not dying, or near to death, they would not undergo these experiences. All causes of death affect brain function, and this causes typical manifestations. The abnormal brain function of these people causes them to feel calm, serene, ineffable, even joyous, while removing the sensation of pain and discomfort. They even feel their mental function is normal, or even better than normal. Yet an observer sees something quite different; observers see a sick, dying, or apparently unconscious person with abnormal brain and body function (see chapters 15, 16, 17, and 18 of "Mortal Minds" for detailed explanations).This this is the cause of the differences between the perceptions of experiences undergone by healthy and dying persons. And this explains the differences in associated sensations. So when the eyes or the brain of a dying person generate tunnel and light experiences, it is not at all surprising that they also report associated sensations and emotions of serenity, ineffiability, etc, etc.

So the body is capable of generating all the emotions, sensations, and the perceptions of "the light", of "darkness", of "tunnels", and of "passing through a tunnel to enter light". No unknown immaterial forces or powers need to be invoked to explain these sensations and perceptions.

References

1. Woerlee, G.M. (2004). Darkness, tunnels, and light.Skeptical Inquirer,28: 28-32.
2. Mortal Minds, by G.M. Woerlee.
3. Blackmore S, (1991), Near-Death Experiences: In or out of the body.Skeptical Inquirer, 16: 34-45.