Our increasingly effective methods of reanimation have one advantage that may go overlooked: those who come back to life supply us with more descriptions of what they saw and felt when they were nearly dead. Neurologists are eager to hear such stories.
Heart attack. Pain. Terror. Panic attack. Cardiac arrest. Cerebral hypoxia. Loss of consciousness. Silence. Time stands still, though the hands of the watch keep marking the seconds and minutes. Reanimation. Restoration of the vital functions. Restoration of consciousness.
Research shows that around 20 percent of patients who have experienced clinical death and returned to the world of the living remember the experience. They not only describe their state as conscious but they also claim it was more vivid than waking life. Moreover, they are certain that the experiences they recall are absolutely real. These memories, although they come from a wide range of people, bear an astonishing similarity. These are defined as NDEs, or Near-Death Experiences. This phenomenon was popularized in the 1970s by American doctor and psychologist Raymond Moody, author of Life after Life. Yet similar descriptions can also be found in Plato’s Republic as well as the Bible and the Egyptian Book of the Dead or the Tibetan Book of the Dead. The people around the world who have had near-death experiences number in the millions, and, with advancements in resuscitation techniques and reanimation, this number is only rising. Although most of the testimonies come from people whose state of clinical death came from a heart attack, injury, or stroke, it seems this kind of experience could also happen in moments of mortal danger. It has also been described by those who have had serious, potentially fatal, accidents or victims of crimes who did not quite experience cardiac arrest and never stopped breathing.
The incredible consistency of phenomena experienced by patients in a state of clinical death has served as the basis for charting the most common symptoms, which are used to classify a patient’s experience as near-death. According to psychiatry and neurobehavioral sciences professor Bruce Greyson, these symptoms include: a disrupted sense of time, speeding up of thought processes, life flashing before one’s eyes, a sense of total understanding, peace, pleasure, being united with the universe, the impression of being surrounded by light, unnaturally acute sensory impressions, extrasensory perception, cognitive visions, loss of a sense of physicality, the impression of being outside of the world, the presence of gods, angels, or spirits of the dead, and, finally, hovering on the border between life and death. The American psychologist Kenneth Ring, in turn, has qualified what patients declare to be near-death experiences by such symptoms as: an awareness of being dead, the experience of positive emotions, the impression of being outside of one’s body, a sense of heading through a dark tunnel, colorful visual sensations, the observation of unearthly images of the world, meetings with the dead, recollections from life, and the impression that they are in a point of no return.
Not all patients have experienced all of the above. Almost all of those who remember their near-death experiences describe their state during clinical death as conscious, and 75 percent recall particularly strongly the stirring of cognitive processes. Yet, only around 60 percent declare feeling remarkably pleasant emotions or euphoria and the ebbing of all negative sensations and pain. Still fewer—one half of the subjects—mention a sense of being dead, while 45 percent had a sense of being outside of their body and observing events from some remote perspective. Around 30 percent recall walking through a tunnel toward a light as well as meeting dead people or other creatures, such as gods and angels. Only around 15 percent had memories of their own lives.
The Riddle of Euphoria
In discussions on near-death experiences, the argument is often raised that, although their similarities seem to confirm some shared experience after death, they could come from one person “inspiring” others. Having experienced a state of clinical death, the person then “remembers” impressions like those they heard elsewhere. Yet patient studies seem to eliminate this possibility. First of all, these descriptions include a large number of perceptual details of images, sounds, or smells, which are indicators of real memories; invented stories have none of these details. Secondly, while passing on these memories, we may observe a surge in brainwave activity (theta) in the cortex region, which occurs when we are recalling actual memories.
The remarkable coherence of these stories has prompted neurobiologists to seek the nature of this phenomenon. One of the most convincing arguments inspiring research was that these NDEs were not solely experienced by religious people but also by those who were declared atheists. Furthermore, it was noted that other factors, such as socioeconomic status or gender, played no role in the advent of near-death experiences. All this could indicate that a universal neuronal mechanism is at work. From the moment blood flow stops to the second irreversible changes occur in the brain and the neurons die, a bit of time passes, from a few minutes to almost half an hour, during which, despite the lack of oxygen, the nerve cells remain briefly active. In EEG studies performed during clinical death, the existence of nearly every kind of brainwave has been shown, from slow alpha waves to extremely fast gamma waves. This leads to the hypothesis that near-death experiences originate in brain neuron activity.
Neurobiology gives us many intriguing hypotheses to explain these phenomena, and research on events accompanying death has supplied more fascinating observations, which on one hand reinforce the set premises and on the other stimulate us to ask more questions about the nature of brain death and even its irreversibility.
It is relatively easy to explain why, in life-threatening situations, a person at risk of a heart attack or severe injury suddenly grows calm, experiences a kind of bliss, and drifts into euphoria right after feeling powerful anxiety and showing all symptoms of a panic response. Research conducted on animals and confirmed in people shows that, at times when we feel powerful stress from fear or anxiety, the brain can initiate a process called stress-induced analgesia, dampening the pain that comes from stress activation. This response also occurs at moments less extreme than clinical death—through injury, for instance, or in cases where pain might limit the ability to take action to overcome and flee the danger. Pain is a signal to stop acting, as we all have surely learned by hurting ourselves during some activity: when we feel pain, we stop what we are doing at once.
The pain-killing effects of stress probably arise from adaptation and, paradoxical as it may seem, a similar mechanism may be engaged in the dying process. This is not at all in order to ease our departure from this world; the stress reaction is simply universal, and its physiological mechanisms are largely divorced from the context.
Reacting to Danger
The stress-induced analgesia mechanism comes in two sorts: dependent or independent of the opioids naturally produced by our bodies. Opioids are neurotransmitters produced and sent by nerve cells. A particularly large amount of opioid neurons are found in parts of the brain connected to the emotional (limbic) system and in the brainstem, the area situated lowest in the brain, attached to the spinal cord. Opioids can block the nerve paths that transmit pain impulses from the body to the brain and process pain through the limbic system. Some monoamines, or neurotransmitters, can serve a similar function, such as noradrenaline and serotonin, which, along with other transmitter systems, are tasked with stress-induced analgesia independent of opioids. Clusters of noradrenergic and serotonergic neurons are found in the brainstem, and their long protrusions (axons) innervate nearly all parts of the brain and the spinal cord. Among the varied functions of these neurotransmitters is blocking the transmission of pain and regulating the functions of the limbic system and the brain cortex.
Studies of the changes occurring in animal brains during clinical death caused by the lack of blood circulation show that there is a significant rise in the concentration of both opioids and noradrenaline and serotonin in the brain. Thus, regardless of what mechanism is directly responsible for pain relief (which is one symptom accompanying a near-death experience), this effect can be compared to a commonplace mechanism that relieves or dampens the sensation of pain at moments of stress tied to mortal danger. Other symptoms also testify to the presence of opioids in effects accompanying near-death incidents. Anxiety can be conquered by the mass spread of opioids and their work smothering neurons localized in the amygdala. The amygdala is one of the most vital structures in the limbic system: its task is to transmit emotional signals to various stimuli, thus creating emotions. Their powerful stimulation through pain or other sensations identified as dangerous triggers powerful fear or anxiety, which is a person’s first feeling in a life-threatening situation.
Opioids not only reduce pain but also the unpleasant emotions that come with it. They calm you down. Opioids also play a crucial function in regulating moods. One of the main systems responsible for moods is the reward system, created by dopamine neurons; opioids are part of the chemical compounds that regulate those neurons’ activities. When the concentration of endogenous (e.g., beta-endorphins) and exogenous opioids (such as morphine) increases in the brain, we observe a major rise of activity in dopamine neurons and a huge rush of dopamine. This brings about an abrupt mood enhancement—a state of euphoria, precisely the same state that could accompany a near-death experience.
Out-of-Body Experience
The out-of-body experience, described by patients in a state of near death as hovering over themselves and, in some cases, observing themselves from above, is a source of special fascination. These phenomena are not the sole domain of near-death experiences—they can also come from taking dissociative drugs, such as ketamine or phencyclidine. With these substances, this effect is probably tied to changes in activity in the brain cortex, owing to how these compounds block vital receptors that facilitate communication between neurons—namely NMDA receptors (N-methyl-D-aspartate) for glutamate, the primary excitatory transmitter. Similar effects can also be generated through transcranial stimulation of the region of the cortex at the intersection of the parietal and occipital lobes. Powerfully stimulating this part of the brain may disrupt the work of neurons and cause the impression of being outside the body. The neurons of the parietal areas of the brain cortex create a cortical representation of the body, receiving information from the cutaneous receptors and interoceptors (located inside the body), as well as the bony labyrinth (responsible for our sense of balance); the disruption of their operations can cause the picture of one’s own body to be distorted. It is possible that the intense activity of monoaminergic neurons of the brainstem, which innervate the cortex, disrupt the latter’s functions. Lack of oxygen can cause a similar effect, resulting in the dysfunction of the cortical neurons. The result of the first, the second, or both mechanisms can be the partial or total loss of sensory information from the body, creating the impression of its separation from the mind.
Scholars point out that perceiving one’s own mind from the perspective of a being hovering above could be the result of the prefrontal cortex’s automatic process of anticipating reality when there is a lack of sensory data. Combined with information from short-term memory concerning events that precede the moment in question—an accident, injury, sudden deterioration of one’s health, etc. that the memory associates with death—the prefrontal cortex could, in a logical way, generate a narrative about being dead. This would seem all the more probable because lack of oxygen disrupts the cognitive processes, which significantly reduces the odds of “common sense” verifying the automatically generated prediction of reality as the result of death. In normal conditions, the side prefrontal cortex, responsible for common sense and monitoring functions, generally “strikes out” erroneous predictions, replacing them in the consciousness with an image of the situation that better fits the reality.
Interestingly enough, and partly in support of the above hypothesis, with Cotard’s syndrome, an illness in which the sufferer is convinced of their own death, scholars have confirmed irregularities in the function and communication of several regions of the brain cortex (including all the above parts: prefrontal, temporal, and parietal lobes) responsible for creating an image of one’s own body, anticipating reality, and verifying its predictions.
A similar mechanism could explain the presence of dead people and divine beings. On the one hand, these images could be automatically “culled” from memory as associated with death; on the other, they could result from characteristic hallucinations or distortions of perceptions and consciousness called up by the powerful stimulation of neurons of the cortex by serotonin. As mentioned above, the stress accompanying a life-and-death situation greatly stimulates the serotonin neurons, producing a state like that of being on psychedelics, such as LSD or DMT, which activate serotonin receptors. These substances often create the impression that the boundary between the self and the surrounding world has been blurred, along with a sense of a deep connection to everything all around. They can also give us the impression that supernatural beings are present. As such, feeling as though we are outside the body and traveling to the world of the dead, figures may be summoned up which fill two criteria at once: they are beings with whom we feel a bond and who belong to a world that is not of this earth.
Dopamine may also account for these hallucinations, as, like the other monoamines, its excretions dramatically increase in situations when life is in peril. Various kinds of substances stimulating dopamine brain receptors are known for their potential to cause hallucinations. An indirect mechanism generating images divorced from our reality could be lack of oxygen, which causes neurons to “shut down,” leading to partial or total sensory deprivation. Reducing the quantity of mental information or removing it entirely from the brain cortex can paradoxically activate its vast sphere of associations, which begin independently generating visions of strange worlds.
An example of this mechanism leading to hallucinations, sometimes including complex objects, is the Charles Bonnet syndrome. In this disorder, sensory deprivation caused by damage to the retina makes gaps in the sufferer’s field of vision, which are filled by neuron-generated images from visual associative fields of the cortex that would normally be suppressed by the ones processing real sensory data. It is not unreasonable to suppose that, in significant deprivation, as can occur during a clinical death, the gap in the depiction of the world can even cover 100 percent of perception; this is filled in by the cortex, which creates its own visions. This is why these people’s experiences can be not only unearthly and detailed but also believable, because data that might bring them down to earth does not get through to the brain.
Where the Tunnel Comes From
The credibility of near-death experiences related by those who have experienced clinical death as absolutely true may also be tied to dopamine. This neurotransmitter is responsible for giving significance, both to particular objects analyzed by the brain and to whole situations. Small wonder, then, that, after a massive surge of dopamine, not only do patients have no doubt when it comes to a vision but also it sinks deep into their memory and is regarded as a life-changing experience.
Another characteristic symptom accompanying near-death experiences is the impression of being in a dark tunnel and sometimes moving toward a bright light. As with the out-of-body experience, this effect also often occurs after having taken large doses of dissociatives, such as ketamine. Users of these drugs often have visions of being in a deep well; from the bottom the world up above seems quite remote and beyond their grasp.
It is not quite clear what mechanism could be responsible for this state, but, when it comes to dissociatives, it probably goes hand-in-hand with blocking receptors for glutamate, the main neurotransmitter that stimulates the cortex. This could inhibit the stream of consciousness, which could create the feeling that the distal parts of the field of vision, including attention and consciousness, are left blank (and thus, black). A similar narrowing of consciousness, with a sense of the world being distant, is described by patients given general anesthetic. There have been other attempts to explain this phenomenon, such as the hypothesis that the neurons of the visual cortex corresponding to the retinal area responsible for the central field of vision have better circulation than the neurons that “service” its distal parts and thus stay active longer, generating centered images; this is impossible with the peripheral regions of vision, which remain black.
The mechanisms probably responsible for the experiences mentioned by survivors are based on the premise that in clinical death, when circulation stops, the brain neurons are active enough not only to generate all these symptoms but also to produce and support a state of consciousness to register and remember them. Neurobiologists do not agree, however, when it comes to a basic question: Does the brain, and the cortex in particular, remain strong and active long enough to produce near-death experiences?
Flashes from Life
A step toward acquiring data that will allow us to respond more unambiguously is, firstly, the research conducted on terminal patients, capturing the moment of death and accompanying phenomena, and, secondly, research on animals whose brains were deprived of oxygen by stopping their circulation. (The latter may seem to be pointless apart from satisfying our curiosity, but it has been done to gather data that will allow us to reanimate people more effectively in the future.)
EEG studies measuring the brain’s electrical activity show that, with a lack of oxygen, there is a model of neuronal activity very close to a holding state (and unlike a state of narcosis), with nearly all the types of brain waves, including those of the highest frequency (gamma), pointing to high cognitive activity, including consciousness. The data that concerns communication between the prefrontal cortex and the regions of the parietal cortex or the cortex situated between the parietal and the temporal lobes could testify to patients remaining conscious as they die. It seems the neurons in these areas create mutual links, and their reciprocal stimulation is the basis for attention and consciousness. The capacity not only for producing and supporting consciousness but also the remarkably strong activation of attention processes might be demonstrated by heightened noradrenergic and dopaminergic activity. Both noradrenaline and dopamine are among the more important neurotransmitters activating and maintaining attention.
One of the most fascinating phenomena occurring in the brain during clinical death was discovered through research on animals and then partly confirmed in people. When circulation stops, there is a fairly swift and constant reduction of neuronal activity caused by lack of oxygen (lasting from several seconds to a few minutes), which leads, of course, to the death of neurons, then of the brain, and finally to biological death. Yet, before this occurs, there is a sudden and remarkably strong surge in neuronal activity encompassing major parts of the brain. This can last up to several seconds, after which the brain’s activity again takes the form of a straight line. This brief, but clear and powerful, surge of bioelectric brain activity is called “the wave of death”; according to some, it could explain impressions described as near-death experiences. It could also be a scientific explanation for why, before death, “your whole life flashes before your eyes.”
Other scholars believe that this surge in brain activity is too brief to “hold” all these sensations, even considering the fact that patients can misjudge the time of the events they describe, owing to the significant disruption of their sense of time that comes with disturbing the work of the brain.
Animal research has also pointed to a second wave of the surge of brain activity—one that is similar but weaker and more drawn out in time—that occurs after the heartbeat is restored and the oxygenated blood begins flowing once more to the brain. This is called the “wave of resuscitation,” and it is connected with the slow return of brain activity. Some researchers see this phenomenon as causing the experiences of people who have managed to return to the world of the living from a state of clinical death.
Proof of the Existence of the Soul?
The mysterious “wave of death” fascinates us, prompting a shudder of excitement or terror. Those who seek proof of transcendence in science see a moment of the soul (or spirit) separating from the body, yet brain scholars provide a down-to-earth and prosaic explanation. From a scientific point of view, it seems this violent burst of activity in a vast number of neurons comes from their incapacity to produce and support “resting potential.” This is tied to the uneven distribution of the load between the inside of the cell and its surroundings, causing the cell’s stimulation, or a capacity to generate active potential, commonly known as a nerve impulse. Unlike the active potential—which, despite its name, is a passive process, transpiring with the opening of channels through which ions freely balance the concentration between the two sides of the cell membrane—resting potential requires considerable energy output. It comes from ATP hydrolysis (a compound commonly known as an energy carrier) and is used against diffusion to cause uneven disintegration of ions on both sides of the membrane. ATP is produced in oxygen metabolism, at a point when there is a lack of oxygen and its supply to the neurons drops to nothing, the nerve cells lose their resting potential en masse, active potential is generated, the neuronal activity of the whole brain explodes, and this is registered as the wave of death.
We cannot be fully sure what is responsible for all the sensations described as near-death experiences. Our neurobiological hypotheses are confirmed by growing numbers of analyses. Perhaps more research and the development of knowledge about the mechanisms behind the brain’s functions will give us the ultimate scientific explanation of this phenomenon. For now, the final stage of life still holds many mysteries.
For some, the extremely evocative and extraordinary sensations that occur when dying prove the existence of the afterlife, the immortality of the soul, paradise, and God; for others, they are the remarkable effect of changes occurring in the brain due to lack of oxygen and the disruption of its physiology. Yet, regardless of the nature of these experiences on the verge of death, they are worth exploring by both scientists and religious thinkers. They doubtless change the lives of those they touch.
And those who have not known them can be absolutely certain that sooner or later (let us hope it is later) they too will have the chance to find out what is at the end of the tunnel: a light or darkness.
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