In 1969 during my rotating internship a patient was successfully resuscitated in the cardiac ward by electrical defibrillation. The patient regained consciousness, and was very, very disappointed. He told me about a tunnel, beautiful colours, a light and beautiful music. I have never forgotten this event, but I did not do anything with it. Years later, in 1976 Raymond Moody first described the so-called “near-death experiences”, and only in 1986 I read about these experiences in the book by George Ritchieentitled “Return from Tomorrow,” which relates what he experienced during a period of clinical death of 6-minutes duration in 1943 during his medical study.4 After reading his book I started to interview my patients who had survived a cardiac arrest. To my great surprise, within two years about fifty patients told me about their NDE.

My scientific curiosity started to grow, because according to our current medical concepts, it is not possible to experience consciousness during a cardiac arrest, when circulation and breathing have ceased.

Several theories on the origin of an NDE have been proposed. Some think the experience is caused by physiological changes in the brain such as brain cells dying as a result of cerebral anoxia, and possibly also caused by release of endorphins, or NMDA receptor blockade.5 Other theories encompass a psychological reaction to approaching death6 or a combination of such reaction and anoxia.7 But until now there was no prospective, meticulous and scientifically designed study to explain the cause and content of an NDE. All studies had been retrospective and very selective with respect to patients. In retrospective studies 5-30 years can elapse between occurrence of the experience and its investigation, which often prevents accurate assessment of medical and pharmacological factors. We wanted to know if there could be a physiological, pharmacological, psychological or demographic explanation why people experience consciousness during a period of clinical death. The definition of clinical death was used for the period of unconsciousness caused by anoxia of the brain due to the arrest of circulation and breathing that happens during ventricular fibrillation in patients with acute myocardial infarction.

We studied patients who survived cardiac arrest, because this is a well-described life threatening medical situation, where patients will ultimately die from irreversible damage to the brain if cardio-pulmonary resuscitation (CPR) is not initiated within 5 to 10 minutes. It is the closest model of the process of dying.

So, in 1988 we started a prospective study of 344 consecutive survivors of cardiac arrest in ten Dutch hospitals with the aim of investigating the frequency, the cause and the content of an NDE.1 We did a short standardised interview with sufficiently recovered patients within a few days of resuscitation, and asked whether they could remember the period of unconsciousness, and what they recalled. In cases where memories were reported, we coded the experiences according to a weighted core experience index. In this system the depth of the NDE was measured according to the reported elements of the content of the NDE. The more elements were reported, the deeper the experience was and the higher the resulting score was.

Results: 62 patients (18%) reported some recollection of the time of clinical death. Of these patients 41 (12%) had a core experience with a score of 6 or higher, and 21 (6%) had a superficial NDE. In the core group 23 patients (7%) reported a deep or very deep experience with a score of 10 or higher. And 282 patients (82%) had no recollection of the period of cardiac arrest.

In the American prospective study of 116 survivors of cardiac arrest 11 patients (10%) reported an NDE with a score of 6 or higher; the investigators did not specify the number of patients with a superficial NDE with a low score.2 In the British prospective study of 63 survivors of cardiac arrest only 4 patients (6.3%) reported an NDE with a score of 6 or higher, and 3 patients (4.8%) had a superficial NDE, a total of 7 patients (11%) with memories from the period of cardiac arrest.3

In our study about 50% of the patients with an NDE reported awareness of being dead, or had positive emotions, 30% reported moving through a tunnel, had an observation of a celestial landscape, or had a meeting with deceased relatives. About 25% of the patients with an NDE had an out-of-body experience, had communication with “the light,” or observed colours, 13% experienced a life review, and 8% experienced a border.

What might distinguish the small percentage of patients who report an NDE from those who do not? We found that neither the duration of cardiac arrest nor the duration of unconsciousness, nor the need for intubation in complicated CPR, nor induced cardiac arrest in electrophysiological stimulation (EPS) had any influence on the frequency of NDE. Neither could we find any relationship between the frequency of NDE and administered drugs, fear of death before the arrest, foreknowledge of NDE, religion or education. An NDE was more frequently reported at ages lower than 60 years, and also by patients who had had more than one CPR during their hospital stay, and by patients who had experienced an NDE previously. Patients with memory defects induced by lengthy CPR reported an NDE less frequently. Good short-term memory seems to be essential for remembering an NDE. Unexpectedly, we found that significantly more patients who had an NDE, especially a deep experience, died within 30 days of CPR (p<0.0001).

We performed a longitudinal study with taped interviews of all late survivors with NDE 2 and 8 years following the cardiac arrest, along with a matched control group of survivors of cardiac arrest who did not report an NDE.1 This study was designed to assess whether the transformation in attitude toward life and death following an NDE is the result of having an NDE or the result of the cardiac arrest itself. In this follow-up research into transformational processes after NDE, we found a significant difference between patients with and without an NDE. The process of transformation took several years to consolidate. Patients with an NDE did not show any fear of death, they strongly believed in an afterlife, and their insight in what is important in life had changed: love and compassion for oneself, for others, and for nature. They now understood the cosmic law that everything one does to others will ultimately be returned to oneself: hatred and violence as well as love and compassion. Remarkably, there was often evidence of increased intuitive feelings. Furthermore, the long lasting transformational effects of an experience that lasts only a few minutes was a surprising and unexpected finding.

Several theories have been proposed to explain NDE. However, in our prospective study we did not show that psychological, physiological or pharmacological factors caused these experiences after cardiac arrest. With a purely physiological explanation such as cerebral anoxia, most patients who had been clinically dead should report an NDE. All 344 patients had been unconscious because of anoxia of the brain resulting from their cardiac arrest. Why should only 18% of the survivors of cardiac arrest report an NDE?

And yet, neurophysiological processes must play some part in NDE, because NDE-like experiences can be induced through electrical “stimulation” of some parts of the cortex in patients with epilepsy,8 with high carbon dioxide levels (hypercarbia)9 and in decreased cerebral perfusion resulting in local cerebral hypoxia, as in rapid acceleration during training of fighter pilots,10 or as in hyperventilation followed by Valsalva maneuver.11 Also NDE-like experiences have been reported after the use of drugs like ketamine,12 LSD,13 or mushrooms.14 These induced experiences can sometimes result in a period of unconsciousness, but can at the same time also consist of out-of-body experiences, perception of sound, light or flashes of recollections from the past. These recollections, however, consist of fragmented and random memories unlike the panoramic life-review that can occur in NDE. Further, transformational processes are rarely reported after induced experiences. Thus, induced experiences are not identical to NDE.

Another theory holds that NDE might be a changing state of consciousness (transcendence, or the theory of continuity), in which memories, identity, and cognition, with emotion, function independently from the unconscious body, and retain the possibility of non-sensory perception. Obviously, consciousness during NDE was experienced independently from the normal body-linked waking consciousness.

With lack of evidence for any other theories for NDE, the concept thus far assumed but never scientifically proven, that consciousness and memories are localized in the brain should be discussed. Traditionally, it has been argued that thoughts or consciousness are produced by large groups of neurons or neuronal networks. How could a clear consciousness outside one’s body be experienced at the moment that the brain no longer functions during a period of clinical death, with flat EEG?15 Furthermore, blind people have also described veridical perceptions during out-of-body experiences at the time of their NDE.16 Scientific study of NDE pushes us to the limits of our medical and neurophysiological ideas about the range of human consciousness and relationship of consciousness and memories to the brain.

Also Greyson2 writes in his discussion: “No one physiological or psychological model by itself explains all the common features of NDE. The paradoxical occurrence of heightened, lucid awareness and logical thought processes during a period of impaired cerebral perfusion raises particular perplexing questions for our current understanding of consciousness and its relation to brain function. A clear sensorium and complex perceptual processes during a period of apparent clinical death challenge the concept that consciousness is localized exclusively in the brain.” And Parnia and Fenwick3 write in their discussion: “The data suggest that the NDE arises during unconsciousness. This is a surprising conclusion, because when the brain is so dysfunctional that the patient is deeply comatose, the cerebral structures, which underpin subjective experience and memory, must be severely impaired. Complex experiences such as are reported in the NDE should not arise or be retained in memory. Such patients would be expected to have no subjective experience [as was the case in the vast majority of patients who survive cardiac arrest in the three published prospective studies1-3 or at best a confusional state if some brain function is retained. Even if the unconscious brain is flooded by neurotransmitters this should not produce clear, lucid remembered experiences, as those cerebral modules, which generate conscious experience, are impaired by cerebral anoxia. The fact that in a cardiac arrest loss of cortical function precedes the rapid loss of brainstem activity lends further support to this view. An alternative explanation would be that the observed experiences arise during the loss of, or on regaining consciousness. The transition from consciousness to unconsciousness is rapid, with the EEG showing changes within a few seconds, and appearing immediate to the subject. Experiences which occur during the recovery of consciousness are confusional, which these were not”. In fact, memory is a very sensitive indicator of brain injury and the length of amnesia before and after unconsciousness is an indicator of the severity of the injury. Therefore, events that occur just prior to or just after loss of consciousness would not be expected to be recalled. And as stated before, in our study1 patients with loss of memory induced by lengthy CPR reported significantly fewer NDE. Good short-term memory seems to be essential for remembering NDE.