You must have heard of the instances where people declared dead come back to life and claim that they have experienced and seen the other world or  their soul traveled away from their body or they saw a light,etc. These instances are indeed interesting and science has tried to explain this phenomenon by means of various theories and researches. We will try to find out what exactly is Near Death Experience (NDE) and why does it happen?

tunnel experience
Near Death Experience (NDE) includes a variety of experiences in which a person who is close to death or has been pronounced clinically dead (but resuscitated back to life) experiences various types of sensations like detachment from body or out of body experience, sense of peace, serenity and painlessness,  tunnel experience (sense of moving through a tunnel towards a light), presence of a light, awareness of being dead, retrospective life review, perception of a border, conscious return of the body, etc. 
out of body experience
People remember NDEs very vividly and clearly and are able to tell what happened to them even years after the incidence though science would tell us they shouldn't be able to perceive and form memories when their brain is not functioning well and sometimes not functioning at all. 
  
Let us try to understand NDE through some incidences or examples.
  
  Al Sullivan (studied by Dr. Greyson), a 55 year old farmer while undergoing a bypass surgery had a NDE in which his deceased mother and brother-in-law told him to tell his neighbours that their son who has lymphoma will be fine. Sullivan even remembered while having NDE that surgeon was flapping his arms in a particular unusual manner.

  In another case a woman was dying due to a heart condition while her sister was in coma in the same hospital. The woman was resuscitated and when she woke up, she told that she had a conversation with her sister and reported that her sister died when doctors were resuscitating her. Doctor denied the information but sister confirmed that her sister died exactly during the time mentioned by woman.

  Olga Gearhardt, 63 year old woman, was undergoing a heart transplant. At 2:15 am her heart stopped beating and it took three hours to revive her. When the son-in-law of the woman (who was at home) was called to give him the good news, he said that he knew it already as his mother-in-law had come to him at 2:15 am and told him not to worry and that she will be all right. When Olga regained her consciousness, she confirmed that she traveled to her son-in-law to communicate the message.

 Shared death experiences is another phenomenon related to NDEs in which a person who is close to the dying person experiences the same things like NDE.
A doctor(woman) was resuscitating her mother who had a cardiac arrest. While resuscitating, she felt herself leaving her body and saw her body resuscitating her mother. As her mother died, she saw her mother in spirit form, the spirit met some beings some of whom her mother had known and all of them were sucked into a tunnel!

  Some blind people (some of them blind from birth) were able to see during the time they were dead and they were able to tell everything about how doctors resuscitated them.

  Some scientists are trying to find out whether mind continues to function when the brain has died or ceased to function. If mind is produced by brain, then it should not function after the the brain is dead. Science claims that death is the end of consciousness like a television signal. But shutting off the TV does not affect the TV signal. Some scientists propose that cosmic energy and input that once made our conscious mind is free to expand and this expansion manifest in the form of various types of mental visions. If it is proved that mind (consciousness) continue to function even after brain is dead, it will prove by default that 'soul'  exists even after the body is dead!

    It is apt at this point to discuss the various theories that have been proposed to explain NDE.

  Depersonalization theory(1930) argued that people replace their unpleasant reality of death and illness with pleasant fantasies to protect themselves. But this theory is criticized on the basis that some features like increased alertness, awareness and strong spiritual experiences does not fit in depersonalization mode.

  Afterlife hypothesis suggest that soul freed away from the body travels through the tunnel into the heaven(bright light is the light of heaven) to spend the time till eternity with others who have died before.

  Memories of Birth theory suggest that NDEs are nothing but the memories of birth and what happened when life began. A baby leaves the womb, travels through a tunnel and what waits for him in the light is a world full of love and warmth. But this theory does not explain why people with NDEs meet relatives and other people who have died before. Also new born's mental processes are not developed enough to store the memories of the birth process.

  Dying Brain Hypothesis (Susan Blackmore) suggest that all the experiences related with NDEs are nothing but the products of the dying brain and an artifact of the brain chemistry. It says that there is nothin like a spirit that survives after the body is dead.

 Temporal Lobe Theory suggest that stress associated with being close to death stimulates temporal lobe of the brain that causes NDEs. Researchers found that they were able to mimic some features of NDE by stimulating this lobe. Also there is support to the theory by the fact that there is lower incidence of NDE in people who have stroke or tumour in temporal lobe.
But this theory has been criticized on the basis that temporal lobe stimulation causes emotions of fear, sadness, loneliness and not calmness, serenity and love like in NDEs.

  Hallucination Theory suggest that dying secretes endorphins and hormones that act on the central nervous system, suppresses pain and gives a high. But endorphins do not cause hallucinations. They may relieve pain but they can not account for the every feature of NDEs.

Lack of Oxygen Theory suggest that NDEs are due to hallucinations caused by the lack of oxygen to the brain when the person is dying. However hallucinations almost always occur when the person is conscious while NDEs occur during unconsciousness. Also most hallucinations are chaotic while NDEs are serene and calm.

  Rick Strassman advanced a theory in the 90s that suggest that a massive release of DMTs(dimethyl tryptamine) from the pineal gland prior to death causes NDEs. 

  Some scientists suggest that ketamine (anesthetic) like substances may be released by the body during NDEs and cause various features of the phenomenon esp. out of body experiences.

  Richard Kinseher proposed a new theory in 2006 that looming death causes the brain to scan the entire episodic memory. All the scanned and retrieved data is analysed by the brain to cope with the potentially fatal situation. Brain transforms the retrieved data into a dream like state.

  A research released by University of  Maribor in 2010 has suggested that NDEs may be due to high level of carbon dioxide in the blood that alters the chemical balance of the brain and causes it to see things.

  However Pim Van Lommel argues that if NDEs are due to physiological imbalance, then most patients who have been declared clinically dead should report NDEs which is not the case.

  Researcher Lakhmir Chawla suggest that there is surge in electrical energy as brains runs out of oxygen  which spreads from one part of the brain to the other, causes vivid sensations and manifest as NDEs. Patients who are revived may recall the memories caused by these cascading impulses of electrical energy.

  We can see that there are a lot of theories and researches to explain the mysterious phenomenon. However scientists are not unanimous about the exact reason behind NDEs. Scientists suggest that NDEs can be completely explained by biological, chemical and mental processes while there are some who see a spiritual and paranormal dimension to it. However people who have experienced the phenomenon are unfazed by these questions  because they have the answers!









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