Dark tunnels, bright light and encounters with divine beings – to prestigious Harvard neuroscientist Eben Alexander these were all fantasies and imaginings that he often heard from his patients – until at the end of 2008 he himself had a near death experience. Early in the morning he was suffering from severe headache, after which an epileptic seizure followed. Alexander lost consciousness and fell into a coma. His colleagues at the hospital diagnosed a practically unknown adult form of meningitis.
As E. coli bacteria attacked the neurosurgeon’s brain, his percentage likelihood of survival sat in single digits. The doctor spent seven days in a coma, while high doses of antibiotics aimed to kill the harmful bacteria in his body. The neocortex, the sensory processing part of the cerebral cortex, no longer showed any kind of reaction. And yet Alexander could later remember exactly what he had felt over those days. He described his near-death experience in a book entitled “Proof of Heaven”, which was published in German under the title “Blick in die Ewigkeit” in March this year. In his experiences at the borderline between life and death there existed both a rather bad sounding “underworld”, and also a world of bright light, flowers, music and angels. His near-death experiences are very similar to those that about one in five people – regardless of age, gender, and cultural background – have after a cardiac arrest.
Realer than real life
Time and again, “returnees” report profound feelings of peace, love and happiness in their transition from life to death. Other patterns, such as looking into a “tunnel” with a blazing light at the end, leaving one’s body, encounters with dead or supernatural beings, or a reshowing of one’s life, are among those often had with near-death experiences. Only occasionally those concerned also report negative images and feelings. Often these experiences at the threshold between life and death are portrayed as extremely lively, clear and unusually real. Among scientists, these experiences are, however, controversial because many dismiss the possibility of a conscious perception in the human brain at this time.
No nutrients, no brain activity
After a cardiac arrest, brain activity ends, since the brain is no longer supplied with nutrients, so the argument goes. In this state, coordinated processes are no longer possible. The proponents of these assumptions trace near-death experiences back to oxygen deficiency, stress-related over-excitation of certain brain areas and the dispersal of natural substances that have a similar effect to drugs. A recent study that for the first time examined in animals what goes on within a dying brain could now bring more clarity to the heated debate about near-death experiences.
What happens in the brain shortly after a cardiac arrest?
In their current publication in the journal Proceedings of the National Academy of Sciences, scientists at the University of Michigan write: “If near death experiences are the result of brain activity, they should be detectable in the brain shortly before the supplying of blood ends”. Brain researcher Jimo Borjigin and his colleagues from the University of Michigan examined their idea using as their basis brain activity of nine rats in a waking state, under anaesthesia, and after a cardiac arrest, because in their basic structures the brain activities of rats and humans are quite comparable. The occurance of conscious experience and thought, in rats as in people, can be read via certain characteristics of brain waves in an electroencephalogram (EEG), these waves originating when brain signals are exchanged between different brain areas. Findings such as synchronised and enhanced gamma waves, slower theta waves, often coupled with gamma waves, point to such an event.
Using electrodes which the scientists implanted in the skulls of the nine rats, they first observed brain activity during normal waking periods of the animals. This was followed by measurements made of anaesthetised animals. The researchers obtained key measurements from the animals using a potassium chloride injected solution that triggers a cardiac arrest. The researchers recorded the brain activity of dying rats for a further 30 minutes after interruption in blood supply to the brain in the animals.
Surprising burst of activity
To the great surprise of the scientists, the intensity of some gamma waves increased sharply about 10 seconds after the animals’ cardiac arrest. After another 20 seconds, the animals showed a brain wave profile that suggests a very active brain: for example, brain waves at values between 25 and 55 hertz were indicated, which were higher than those in the animals’ waking state. In addition, the synchronicity of the gamma waves increased at this time – a state which lasted more than 15 seconds and in which the slower theta waves tuned in to the gamma waves. Only after this wave activity did brain waves subside slowly and finally fade out completely. Some signals of the brain were thus even more active in near-death phase than in the waking state. Is this a possible explanation for near-death experiences? “Absolutely”, say the researchers, as their measurements suggest that the electrical activity in the rat’s brain does not simply ebb away after cardiac arrest, but still seems for a short time to be able to reach a state of organised activity. “This strong burst of activity could be the trigger for experiences perceived as highly lifelike and genuine in the transition from life to death”, write the scientists.
Explanation, but no evidence
Neurologist Michael Schroeter of the University Hospital of Cologne likewise sees in the study an attractive explanation for near-death experiences. To him the rapid increase in activity can be explained by the lack of input from the outside, like an engine revving at idle. The absence of external stimuli would also give the brain waves more rhythm. Proof that the hyperactivity of the brain is the cause of near-death experiences nonetheless he says has not been delivered by the results.