Near-death experiences, in which people claim to encounter a variety of unusual phenomena, including moving through a tunnel toward light, feeling lightweight, feeling peace and joy, and profoundly spiritual moments, have often been classified by scientific researchers as a function of anoxia, or oxygen deprivation in the brain.

For many people, and the religious in particular, the phenomenon of near-death experience — assuming it’s real and not simply a result of a dying brain’s hallucinatory interpretation of a flood of brain chemicals — validates their belief in the afterlife and heaven. Many books have been written by people who claim to have come back from the brink of death and seen God and heaven (though earlier this year the best-selling memoir “The Boy Who Came Back From Heaven” was admitted by its author to have been faked).

Scientific evidence, however, suggests that the experience is not a spiritual or metaphysical one, but instead a chemical one.

VIDEO: Why We See the White Light Near Death

A new study in which researchers induced anoxia in rats offers more support for near-death experiences (NDEs) as happening inside the dying brain and being interpreted as an out-of-body or spiritual experience.

The researchers examined neurotransmitters, changes in brain and heart electrical activity and brain-heart connectivity. They concluded, “Asphyxia stimulates a robust and sustained increase of functional and effective cortical connectivity, an immediate increase in cortical release of a large set of neurotransmitters… . These results demonstrate that asphyxia activates a brainstorm, which accelerates premature death of the heart and the brain.”

According to an article at MedicalDaily.com, the researchers found that “the brain is much more active during the dying process than in the waking state… In the 30-second period after the animal’s hearts stopped beating, the researchers observed an immediate release of more than a dozen neurochemicals, while high-frequency brainwaves called gamma oscillations increased.

10 Crazy Things to Do When You're Dead

“This activity seemed to trigger a connection between the brain and the heart… . [Lead author Jimo] Borjigin believes a similar, elevated level of brain activity may also happen during the human experience of ‘near death’ and it is this that gives rise to a heightened state of consciousness, including the visions experienced by survivors of cardiac arrest.”

This “brainstorm,” or cascade of neurotransmitter chemicals, can cause benign hallucinations such as those reported in NDEs. This new study joins several others implicating anoxia as a contributing (if not causative) factor to near-death experiences. Researcher Borjigin had conducted previous research with similar findings in 2013, published in the Proceedings of the National Academy of Sciences.

Causes of Near-Death Experiences

When examining near-death experiences, it’s important to understand that no one has survived true clinical death (which is why the experiences are called “near-death”).

Service Lets You Video Chat With Dead People

Many people have been revived after their heart stopped beating for short periods of time — around 20 minutes or more — but no one has actually come back from the dead. Anyone revived from true brain death would be permanently and irreparably brain damaged and unable to report their experiences.

Researcher Susan Blackmore, author of “Dying to Live: Near-Death Experiences” (Prometheus Books, 1993), notes that many NDEs (such as euphoria and the feeling of moving toward a tunnel of white light) are common symptoms of oxygen deprivation in the brain.

A 2001 article published in Trends in Cognitive Sciences by neuroscientist Dean Mobbs, of the University of Cambridge’s Medical Research Council Cognition and Brain Sciences Unit, and Caroline Watt, of the University of Edinburgh, found that “contrary to popular belief, research suggests that there is nothing paranormal about these experiences. Instead, near-death experiences are the manifestation of normal brain function gone awry, during a traumatic, and sometimes harmless, event.”

Near-death Experiences Explained

In fact, the researchers noted that many classic NDE symptoms are reported by people who were never actually in danger of dying and thus are not necessarily correlated with near-fatal trauma.

A 2010 study in the journal Critical Care found that of 52 heart attack patients, 11 reported having NDEs. Between one in four and one in ten heart attack survivors report some form of near-death experience.

Surprisingly, only a minority of people who are actually near death report near-death experiences; they are the exception, not the rule. This may be because not all circumstances that may bring a person near death necessarily involve conditions under which anoxia would be expected. A near-drowning victim, for example, would be more likely to experience an NDE than someone whose lung functions were normal but whose injury or condition involved the brain or another major organ.

Awareness After Death? Study Hints It Exists

Additional evidence for an earthly explanation for near-death experiences can be found in the fact that the phenomena can be chemically induced. The drug ketamine, for example, sometimes used in anesthesia, is similar to PCP and can create visual and auditory hallucinations such as those reported in NDEs.

The new study, “Asphyxia-activated corticocardiac signaling accelerates onset of cardiac arrest,” was conducted by the University of Michigan Medical School and published in Proceedings of the National Academy of Sciences.