There is an article in Trends in Cognitive Sciences for August 2011 titled "Nothing Paranormal About Near Death: How Neurology Can Explain Seeing Bright Lights, Meeting the Dead, or Believing You Are Dead." In this article, the authors tried to explain the most frequent stories of those who returned from "from there".
In this issue I will try to summarize the speculations of scientists on this score.
Death awareness
This is one of the most common sensations reported by people who have experienced clinical death. But a person can feel himself dead not only when he is in this state.
For example, there is a mental disorder called Cotard's Syndrome.
There is a known case of a 24-year-old patient with this syndrome. He was convinced that he had already died of the flu and that he had already gone to heaven. The illusion lasted for several days, after which it began to subside, completely disappearing after a week. Anatomically, this syndrome is associated with the parietal or prefrontal cortex, it occurs as a result of trauma or in the later stages of multiple sclerosis. It is likely that the illusion caused by Cotard syndrome is the result of the brain trying to understand the strange sensations the patient experiences after traumatic events.
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"Exit" from the body
This is not as rare a feeling as it seems. According to statistics, 40% of people experience similar sensations when they are in REM sleep.
But the feeling of being detached from the body can also be caused by artificial means. Olaf Blanke showed that stimulation of the temporo-parietal ganglion in the brain produces such experiences. In their study, "The Neurological Origins of Out-of-Body Experiences and Autoscopy," published in the journal Brain, it was reported that when this area was stimulated, subjects experienced a feeling of weight loss and “pulling away” from bed. Blanquet believes that this condition occurs when the brain stops correctly processing sensory information from the senses.
A light in the end of a tunnel
These sensations can also be induced artificially. Fighter pilots often encounter them when they are exposed to high G-forces (in tight turns or aerobatics).
The appearance of the light tunnel in the immediate vicinity of death can be explained by the lack of blood supply to the retina. The visual cortex contains cells that process images from peripheral and central vision separately. And under certain conditions, this leads to a feeling of high brightness in the central area and dimming in the periphery.
Meeting with deceased relatives
Such sensations sometimes arise in cases of pathological disorders in the brain. This is often reported by patients with Alzheimer's or Parkinson's. Such visions can occur due to over-activation of brain structures in the immediate vicinity of damaged areas of the brain.
Feelings of pleasure and peace
Obviously, this can also be caused artificially. For example, ketamine, given in different doses, can induce many of the sensations that arise in the immediate vicinity of death, from happiness and pleasure to leaving the physical body. Dopamine (the hormone of happiness) also plays a role here.
The fact that more and more researchers are studying the physiological processes that take place in the immediate vicinity of death gives hope that we will soon find answers to the most exciting questions. For example, is consciousness a separate entity from the physical body? Does it continue to exist after our body stops functioning?