Consciousness Beyond Life: The Science of the Near-Death Experience (18 page)

Tentative Conclusions About the Occurrence of NDEs

The numerous retrospective and few prospective studies provide conclusive evidence that NDEs can occur under diverse circumstances and not just in life-threatening situations. But no clear medical or psychological indicators have been found that explain why some people do but most people do not experience an NDE. Medication or demographic factors such as gender or standard of education play no role. The NDE occurs in all kinds of circumstances, in all ranks of society, in all sections of the population, in all religions, in all cultures, and in all times. Only a younger age seems to elicit more frequent NDE reports. The younger a person is, the greater the chance of an NDE.

The universal experience of a clear and enhanced consciousness during a period of deep unconsciousness, with lucid thoughts, emotions, and memories from earliest childhood and sometimes with perception from a position outside and above the lifeless body, raises fundamental questions. It resembles neither a dream nor the incoherent stories that are sometimes told upon waking from a coma with brain damage nor a hallucination. It bears no resemblance to the familiar side effects of medication or to memories of birth. But then what is it?

Theories About the Cause and Content of an NDE

Many scientists assume that an NDE is caused by oxygen deficiency in the brain. This used to be my own firm belief. Others believe that psychological reactions such as fear of death play a role or that a combination of physical and psychological factors offer an explanation. It is highly likely that the brain plays some role because certain NDE-like phenomena can be induced by stimulating a particular place in the brains of epileptics. The use of certain hallucinogenic drugs, such as LSD, also produces an altered state of consciousness. However, these actively induced altered states usually consist of fragmented experiences and memories and feature no life review or out-of-body experience. Besides, a drug-induced experience is seldom followed by reports of life changes.

Below, under the headings “Physiological Theories” and “Psychological Theories,” I present a systematic review of most of the hypotheses that have been published in the years following Moody’s first book. These two categories are complementary because the first covers certain physical functions (in this case brain function) and the second covers psychological functions. Each theory will be explained objectively and then appraised. Some NDE elements, specifically the lucid consciousness and verifiable perception during the loss or serious impairment of brain function, challenge the prevailing view of the relationship between consciousness and the brain, which sees consciousness as a product of brain function. This is why so many scientists struggle to understand near-death experience and why research into the subject can be seen as a threat to scientific dogma. Scientists do everything they can to explain the NDE with the help of existing theories and models and often end up giving a rather one-sided and simplified account of the NDE in an attempt to reconcile the comprehensive phenomenon with existing approaches. This has resulted in theories that can account for one or more aspects of the NDE but not for the complex phenomenon in its entirety. Other theories start from unverified and unverifiable assumptions or from speculation based on a few neurochemical studies of animal brains, which disqualifies them as a proper foundation for further debate.
¹⁰

A theory that seeks to consider the special nature of an NDE and, where possible, explain the phenomenon within familiar frameworks will have to

Acknowledge empirically proven elements of the NDE even when these do not conform to commonly accepted views;


Establish a link between NDEs and the circumstances under which they occur in human beings; and


Determine the special nature of NDEs on the basis of similarities and differences with phenomena that bear some resemblance to NDEs.

Our current knowledge appears to preclude an integrated theory of NDEs, forcing us to accept a multifaceted approach that aims to clarify individual aspects of the NDE. Bruce Greyson has produced a fine overview of the various biological aspects of an NDE while the psychologists Edward Kelly and Emily Williams Kelly provide a very well-documented historical overview of the different theories in the chapter on near-death experiences in their recent book,
Irreducible Mind.
¹¹

Physiological Theories

Oxygen Deficiency

When a cardiac arrest disrupts the flow of blood to the brain or asphyxiation causes breathing to stop, the result is unconsciousness due to the
total
cessation of oxygen supply to the brain (anoxia). Breathing stops, all physical and brain-stem reflexes cease, and unless resuscitation is initiated within five to ten minutes, patients will die. However, in the case of oxygen
deficiency
in the brain (hypoxia), as seen in low blood pressure (shock), heart failure, or tightness of the chest, the result is not unconsciousness but confusion and agitation. Brain damage after waking from a coma is also associated with confusion, fear, agitation, memory defects, and muddled speech.

Nonetheless, the most common explanation for NDE is an extremely severe and life-threatening oxygen deficiency in the brain, resulting in a brief spell of abnormal brain activity followed by reduced activity and finally the loss of all brain activity. This results in the blockage of certain receptors in the brain and the release of endorphins, a kind of morphine produced by the body itself, causing hallucinations and a sense of peace and bliss.
¹²

This theory seems inapplicable, however, because an NDE is actually accompanied by an enhanced and lucid consciousness with memories and because it can also be experienced under circumstances such as an imminent traffic accident or a depression, neither of which involves oxygen deficiency. Moreover, a hallucination is an observation that is not rooted in reality, which does not apply to descriptions of out-of-body experiences that are open to verification and corroboration by witnesses. In an out-of-body experience, patients during resuscitation have perceptions from a position outside and above their lifeless body, and doctors, nurses, and relatives can later verify the reported perceptions. They can also corroborate the precise moment the NDE with out-of-body experience occurred during the period of CPR. Besides, one would not expect hallucinations when the brain no longer functions because they require a functioning brain. Hallucinations will be discussed later on in this chapter.

Regarding the tunnel experienced by many NDErs, according to the psychologist (and consulting editor of the
Skeptical Inquirer
) Susan Blackmore, one possible explanation is oxygen deficiency in the (visual) cerebral cortex; others speculate that the tunnel experience is caused by the disruption of oxygen supply to the eye, gradually darkening one’s range of vision and leaving only a short-lived pinprick of light in the middle that would be the tunnel.
¹³
However, a tunnel experience is accompanied by a sense of high speed, meeting deceased relatives, and sometimes by hearing beautiful music. Oxygen deficiency in the eye cannot explain this.

A study of fighter jet pilots is often cited as a possible explanatory model for NDE. Having been placed in a centrifuge, these pilots experienced momentary oxygen deficiency in the brain when the enormous increase in gravity caused their blood to drop to their feet. Fighter jet pilots can indeed lose consciousness and often experience seizures, like those seen in epilepsy, or tingling around the mouth and in the arms and legs as well as confusion upon waking. Sometimes they also experience elements that are reminiscent of an NDE, such as a kind of tunnel vision, a sensation of light, a peaceful sense of floating, or the observation of brief, fragmented images from the past.
¹⁴
They also see images of living persons but not of deceased people. There are no reports of a life review or out-of-body episodes. Life transformations, such as those often reported after an NDE, are not reported after such an event. In other words, these experiences are not identical to an NDE.

A similar kind of unconsciousness, sometimes accompanied by the experiences reported by pilots, occurs after fainting induced by hyperventilation (forcibly deep breathing) followed by a so-called Valsalva maneuver. The latter involves trying to push air from the body with the mouth and nose closed, which slows the heartbeat and lowers blood pressure and results in a short-lived oxygen deficiency in the brain. The effects of this type of faint have also been wrongly compared to an NDE.
¹⁵

Carbon Dioxide Overload

Oxygen deficiency is accompanied by an increase in carbon dioxide in the body. This increased level of carbon dioxide in the blood has been cited as a possible cause of NDE. Over fifty years ago the Hungarian neurologist Ladislas Meduna, attempting a kind of treatment for his patients, asked people to breathe in carbon dioxide. Some experienced a sense of separation from the body, with occasional reports of a bright light, a tunnel, a sense of peace, or memory flashes. These images were quite rare, were usually extremely fragmented, and never involved a life review or an encounter with deceased persons. No process of life change followed.
¹⁶
In other words, inhaling carbon dioxide does not cause some of the characteristic NDE elements.

One practical problem is that during a frantic resuscitation it is difficult to measure these gases (oxygen and carbon dioxide) in the blood and impossible to measure them in the blood vessels in the brain. On the rare occasion when blood gases have been measured during resuscitation, it was usually only once the heartbeat and blood pressure had been stabilized, with the patient still unconscious on a ventilator and receiving extra oxygen.
¹⁷
In these cases the blood sample was taken from a vein or an artery in the arm or leg, and if the patient had an NDE, the level of oxygen saturation in the blood had been exceptionally high and the level of carbon dioxide extremely low.

Chemical Reactions in the Brain

Ketamine

Because low doses of ketamine, a drug formerly used as an anesthetic, can cause hallucinations, it has been postulated that this kind of substance is released in the brain during a period of stress or oxygen deficiency. Ketamine produces hallucinations because it blocks certain receptors (NMDA) in the brain. A small quantity of ketamine gives some people a sense of detachment from the body or tunnel experiences.
¹⁸
There are no known reports of an encounter with deceased persons or of a life review, nor have there been reports of positive changes. Ketamine usually causes such frightful and bizarre images, which are recognized as hallucinations, that research subjects prefer not to have the substance administered a second time. Because naturally occurring ketaminelike substances have never been found in the brain, this potential explanation must be abandoned. However, we cannot rule out that in some cases the blockade or malfunction of NMDA receptors may play a role in the experience of an NDE.

Endorphins

One of the first attempts at explaining an NDE was based on the fact that stress releases endorphins. These are morphines occurring naturally in the body in small quantities, which function as neurotransmitters. They are released in large quantities during stress. Endorphins can indeed get rid of pain and cause a sense of peace and well-being. However, the effects of endorphins usually last several hours whereas the absence of pain and the sense of peace during an NDE vanish immediately after regaining consciousness. Endorphins also fail to explain other elements of an NDE.

Psychedelics: DMT, LSD, Psilocybin, and Mescaline

The psychoactive substances DMT, psilocybin, and mescaline (but not LSD) are found in large quantities in nature, especially in plants in South America and Mexico but also in mushrooms (“magic” mushrooms).
¹⁹
They have been used for centuries in potions, powders, and inhalants to induce mind-expanding experiences. Dimethyltryptamine, or DMT, is effective only when it is injected into a vein or is being inhaled, but its effect is extremely short-lived because DMT is broken down very rapidly by the body.

All of these psychoactive substances are closely related to the neurotransmitter serotonin, which is found in large amounts in the body, and their chemical structure derives from tryptamine. These psychedelic substances have the same S2 receptor binding site in the brain as serotonin. DMT is produced in the pineal gland, or epiphysis cerebri. The pineal gland, which does not consist of brain tissue, is close to the emotional, visual, and auditory centers of the brain and transmits its substances directly to both the brain and the blood. The substances produced in this gland are responsible for regulating the body’s water balance and sleep–wake rhythm and for developing the sexual glands until puberty. Perhaps they also play a role in dreams. The pineal gland also contains substances that can convert serotonin into DMT and substances capable of blocking the enzymatic breakdown of DMT. The latter also occur in plants, and because it greatly enhances the effect of DMT, the combination is used in ayahuasca in the Amazon.
²⁰

DMT is found not only in various parts of the brain but also in the lungs, the liver, the blood, and the eyes. DMT has an extremely short life span: it is quickly broken down by certain enzymes and is capable of passing the blood-brain barrier. This barrier in the blood vessels of the brain prevents certain substances from leaving the bloodstream, thus protecting the brain from their effects.