14 August 2013

EEG explained the phenomenon of "light at the end of the tunnel"

Between life and death

Tatiana Shcheglova, Copper NewsNeurology specialists from the University of Michigan do not exclude that they have come closer to solving the phenomenon of the same type of sensations and experiences reported by people who have experienced a state of clinical death.

During experiments on rats, the authors managed to record a surge of unusual electrical activity of the brain moments after cardiac arrest, similar to the clearest state of consciousness in humans. The work was published in the journal Proceedings of the National Academy of Sciences (Borjigin et al., Surge of neurophysiological coherence and connectivity in the dying brain).

Approximately 20 percent of patients who survived cardiac arrest describe what they had to go through as incredibly realistic sensations, perceived more vividly and acutely than in ordinary life. We are talking, as a rule, about such mystical adventures as, for example, leaving your body shell and watching from somewhere from the side or from above the attempts of doctors to resuscitate the body stretched out below, flying through some dark tunnel towards an incredibly bright light source, a feeling of unearthly bliss, meeting with deceased relatives.

The uniformity of these visions, which is difficult not to notice, poses a key metaphysical question to the interested persons, to whom, in fact, all living people belong: are these impressions an exclusively specific product of brain activity or is it a kind of reflection of the soul's life after death, outside the body?

A definite answer to it, perhaps fortunately, still does not exist, but scientists have been trying for a long time to debunk the mystical nature of near-death experiences. For example, in the autumn of 2011, psychologists from the University of Edinburgh and the Medical Research Council at the University of Cambridge conducted a detailed analysis of existing descriptions and studies of the visions in question, and found nothing in these sensations that could not be explained by physiological reasons. "Our brain is perfectly able to fool us," is the main summary of their research.

The results obtained by Jimo Borjigin and her colleagues from the University of Michigan also speak in favor of this materialistic hypothesis. Initially, they were engaged in another project – they measured the change in hormonal levels in rats after a stroke. Some of the animals died unexpectedly, and the researchers recorded a powerful release of neurochemicals into the blood in the interval between the last contraction of the heart muscle and the cessation of electrical activity of the brain. This prompted Borjigin to take a closer look at these last seconds between life and death.

Borjigin and her colleagues implanted electrodes into the brains of nine rats to measure the electrical activity of six different parts of it. Then the rats were put into an unconscious state and an injection of potassium chloride caused cardiac arrest. In the interval of about 30 seconds between the last heartbeat and the moment when the brain completely stopped producing electrical signals, a surge of oscillations in the low-frequency gamma range (ranging from 25 to 55 Hertz) was recorded against the background of a general decrease in the level of electrical activity of the brain.

Previous electroencephalographic studies conducted on humans have shown that the gamma rhythm, one of the main rhythms of the brain, prevails in the most active state of consciousness, for example, when performing tasks requiring maximum concentration, as well as during meditation and in the rem sleep phase, characterized by increased brain activity.

As Borjigin and her colleagues noted, in the near-death state, gamma oscillations were synchronized in all parts of the rat brain to an even greater extent than is normal when animals are just awake. In addition, an eightfold increase in the number of so-called descending fronts of gamma-theta and alpha waves associated with sensory perception and information processing was recorded compared to the norm.

If we put all the data together, Borjigin believes, quoted by the journal Science (Probing the Brain's Final Moments), it can be assumed that the dying brain in its last seconds shows even greater neurophysiological activity than in the state of the clearest consciousness.

The results obtained by the Borjigin group, meanwhile, have raised doubts among experts who believe that the reactions of the rat brain cannot be adequately transferred to the human one. "The data obtained by the Borjigin group raises more questions than it answers," says neuroscientist Christof Koch of the Allen Institute for Brain Science (Seattle, Washington). According to Koch, who in the early 1980s worked together with Francis Crick on the hypothesis of the connection between the gamma rhythm and the work of consciousness, a near-death burst of gamma oscillations does not mean at all that rats are in a hyper-conscious state at the same time. It is impossible to project mental experiences inherent in humans on these animals, the expert believes. In addition, he believes that the indicators of brain activity of rats could be affected by the anesthesia applied before.

Koch's opinion is shared by other experts. "It is impossible to use an animal model to assess near–death experiences," says intensive care physician Sam Parnia from Stony Brook University School of Medicine (New York). "We will never be able to find out what animals feel at the moment of death." At the same time, Parnia believes that the results of the Borjigin group's work are important for clinical practice, as they give a clearer idea of the behavior of the brain immediately before death.

Borjigin herself, however, believes that the results obtained by her group are very promising and provide good grounds for continuing the study of the electrical activity of the brain in the near-death state now in humans. As Borjigin suggested, this can be done with operations on the brain, including cooling it and reducing blood supply. This procedure, as there is evidence in the scientific literature, also causes near-death visions similar to those reported by survivors of clinical death, and makes it possible to systematically study this phenomenon.

Portal "Eternal youth" http://vechnayamolodost.ru14.08.2013

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