Seeing a white light, feeling yourself leave your body, and sensing the presence of some sort of supernatural entity are all hallmarks of near-death experiences (NDEs), and scientists think they may now be able to explain these strange conscious phenomena. Often reported by cardiac arrest sufferers after resuscitation, these stereotypical visions and sensations may actually represent an evolutionary response to mortal danger, according to the authors of a new study.
Describing NDEs as “episodes of disconnected consciousness” that occur in the face of “actual or potential physical threat,” the researchers go on to review the existing scientific literature regarding the psychological and neurological underpinnings of these experiences. Tying all of this data together, they propose a “comprehensive model” that incorporates previously suggested theories.
Dubbed the Neurophysiological Evolutionary Psychological Theory Understanding Near-death Experience (NEPTUNE), the model suggests that NDEs begin when oxygen levels drop in the brain while carbon dioxide concentrations skyrocket, resulting in “cerebral acidosis”. This then “sets off a chain reaction that leads to increased neuronal excitability in key brain regions, including the temporoparietal junction and the occipital lobe, accompanied by massive release of endogenous neurotransmitters.”
For instance, increased serotonin signaling may be responsible for the “vivid visual hallucinations” that typify NDEs, while spikes in endorphin and GABA levels are theorized to generate “a feeling of deep peace”. At the same time, the researchers say a flood of dopamine could explain the “profound feelings of hyper-reality associated with these hallucinations.”
Seeking an evolutionary basis for this mechanism, the study authors suggest that NDEs “might form part of a defence cascade” triggered by “neurophysiological responses to threats when fight-or-flight behavioral responses are no longer possible”. In such situations, they say, “people could enter a state of mental dissociation, allowing attention to be focused on internally oriented fantasies, to help them cope with and survive life-threatening situations.”
This may explain why certain individuals appear more prone to NDEs than others, with those displaying a higher propensity for dissociation or daydreaming also being more likely to see the white light when faced with existential threats. On top of this, the researchers note that NDEs are also more common in people who are particularly predisposed to REM intrusion, whereby brain activity linked to dreaming occurs while awake.
This particular trait “has the potential to contribute key NDE features, including unusual light perception, [loss of normal muscle tone], euphoria and out-of-body sensations,” write the researchers.
And yet, the study authors go on to concede that “despite our efforts to develop a comprehensive model, some questions remain: for example, what combinations of the above-mentioned processes are necessary and/or sufficient to trigger an NDE?” Additionally, while the NEPTUNE model may help to demystify certain aspects of NDEs, it does not explain other elements like “precognition”, whereby those who undergo such an experience are left with a sense of knowledge about the future.
The study is published in the journal Nature Reviews Neurology.
