Paper: Neuro-functional modeling of near-death experiences in contexts of altered states of consciousness.
Author(s): Raymond Romand and Gunter Ehret
Journal: Frontiers in Psychology
Link to full article.

In this paper, Romand and Ehret look at the phenomenon of RED or near-death experience as simply an epiphenomenon due to the neuro-functioning of the brain at the time of death.
As Romand writes: “Such a neuro-functional approach may offer valuable ideas for psychiatric and psychologic learning- and/or medication-based treatment of persons who suffer from their experiences.

The authors begin by reviewing the current definitions of RED and defining the difference between clinical death (no heart function, no reflexes, not breathing etc) and brain death (diagnosed with EEG etc) which may occur some minutes later. “Therefore, one has to understand that clinical death is not death, but brain death implies the termination of a human’s life.”

The underlying physiological differences between hypoxia-sensitive and less sensitive neurons are not yet clear.
What is clear, however, is the fact that neurons of the brain do not become irreversibly damaged or dead immediately after assessment of clinical death. There is a time window of roughly 5 min of progression toward irreversible damage ending with brain death.

The authors of the paper go on to suggest possible explanations for the commonly described RED or NDE:

Electrical activity:

The latest EEG technologies and their use on dying patients have revealed an initial decline in EEG activity (rated on the so-called Bispectral Index or BIS) followed by an unexpected increased BIS. The authors speculate that this activity might lead to patients experiencing memories and images that are later recalled.

Other studies have also reported a secondary wave of increased electrical activity (especially gamma waves) in response to hypoxia (cells being starved of oxygen). This activity does not appear to be disorganised or erratic but shows “phases of coordinated coupling and oscillatory activity resembling memory recall and sensory and sensory-motor associations”.

Drugs:

Near-death experiences and perceptions may result from the actions of drugs and/or anaesthetics administered. In particular, the drug Ketamine, used in anaesthetic procedures, has been found to produce similar experiences to those commonly described in RED. Another drug DMT (N, N-dimethyltryptamine) produces similar experiences and has been found to occur naturally in the brain.

Deranged blood gasses in the brain:

A reduction in blood flow to the brain during cardiac arrest results in disturbed levels of oxygen, carbon dioxide and potassium. Previous studies have shown this can lead to experiences of euphoria, clarity and happiness (low oxygen) or an excited lambic system (high carbon dioxide) that may mimic RED.

The authors go on to conclude:

Neuroactive substances such as anesthetics and other drugs, epileptic seizures and brain stimulation and, especially, ischemic stress (hypoxia, anoxia) of the brain, all these modifications of brain functioning have been shown to generate subjective perceptions closely covering those of NDEs including OBEs [Out of Body Experiences]. Therefore, neuro-functional models of NDE including OBE generation offer scientifically appropriate causal explanations for the occurrence of NDEs, possibly as hallucinations of a brain in ASCs. Such alterations are very likely expressions of physiological changes in a brain under ischemic stress as has been shown mainly after cardiac arrest in persons attested to be clinically dead. Neuro-functional NDE models may be used in further well-controlled clinical/laboratory settings to gain more insight into NDE-specific questions such as the generation of specific NDE themes by local cortical activity, or which actual state of consciousness may allow NDE memory content to be saved. In general, the study of NDE models will contribute to the understanding of how brain activity can generate and represent subjective experiences at all. NDEs actually seem to be promising gates to the study of brain functions, especially in situations in which states of altered consciousness may be traced back to defined measures or sets of measures of brain activity.