Neurochemical models of near-death experiences: A large-scale study based on the semantic similarity of written reports

Abstract

The real or perceived proximity to death often results in a non-ordinary state of consciousness characterized by phenomenological features such as the perception of leaving the body boundaries, feelings of peace, bliss and timelessness, life review, the sensation of traveling through a tunnel and an irreversible threshold. Near-death experiences (NDEs) are comparable among individuals of different cultures, suggesting an underlying neurobiological mechanism. Anecdotal accounts of the similarity between NDEs and certain drug-induced altered states of consciousness prompted us to perform a large-scale comparative analysis of these experiences. After assessing the semantic similarity between ≈15,000 reports linked to the use of 165 psychoactive substances and 625 NDE narratives, we determined that the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine consistently resulted in reports most similar to those associated with NDEs. Ketamine was followed by Salvia divinorum (a plant containing a potent and selective κ receptor agonist) and a series of serotonergic psychedelics, including the endogenous serotonin 2A receptor agonist N,N-Dimethyltryptamine (DMT). This similarity was driven by semantic concepts related to consciousness of the self and the environment, but also by those associated with the therapeutic, ceremonial and religious aspects of drug use. Our analysis sheds light on the longstanding link between certain drugs and the experience of "dying", suggests that ketamine could be used as a safe and reversible experimental model for NDE phenomenology, and supports the speculation that endogenous NMDA antagonists with neuroprotective properties may be released in the proximity of death.

An encounter with death: a comparative thematic and content analysis of naturalistic DMT experiences and the near-death experience

“…The themes are arranged in ascending order of proximity score, meaning the higher the point on the plot, the more dissimilar the prevalence of themes between DMT and NDE. This visualisation is comparable to that of Figure 3 by Martial et al (2019) , which graphically plotted similarity scores between various psychoactive substance experience reports and a corpus of NDE reports based on semantic analyses against a class of psychoactive substances. A tabular version of this, including proximity scores, is provided in Supplementary material (see SM 15) .…”

An encounter with death: a comparative thematic and content analysis of naturalistic DMT experiences and the near-death experience

“…The themes are arranged in ascending order of proximity score, meaning the higher the point on the plot, the more dissimilar the prevalence of themes between DMT and NDE. This visualisation is comparable to that of Figure 3 by Martial et al (2019) , which graphically plotted similarity scores between various psychoactive substance experience reports and a corpus of NDE reports based on semantic analyses against a class of psychoactive substances. A tabular version of this, including proximity scores, is provided in Supplementary material (see SM 15) .…”

The Near-Death Experience Content (NDE-C) scale: Development and psychometric validation

“…Interestingly, in Study 3, no item was found to distinguish between NDEs and NDEs-like. This is consistent with the possibility that NDE neurophysiological mechanisms can be activated spontaneously or in non-life-threatening situations where the threat is only apparent or even absent (Jansen, 1997;Martial & Cassol, et al, 2019). This newly developed NDE-C scale was developed with the aim of identifying "classical" NDEs; however, it was found that the scale also allows for the objective quantification and identification of NDEs-like.…”

The Emergent Post-Loss Experience (EPLE) in Grief Therapy: A Mixed-Method Study

“…Previous research on NDEs has consistently highlighted core experiential features such as heightened perceptual clarity, altered temporality, intense affective states-often characterized by peace and well-being)-and a profound sense of meaning or insight (Greyson, 2000;Martial et al, 2020). Notably, several of these elements were also prominent in the phenomenological profile of EPLEs observed in the present sample, including vivid perceptual qualities, experiences of temporal suspension, and meaning-related transformations.…”

An encounter with death: a comparative thematic and content analysis of naturalistic DMT experiences and the near-death experience

“…The themes are arranged in ascending order of proximity score, meaning the higher the point on the plot, the more dissimilar the prevalence of themes between DMT and NDE. This visualisation is comparable to that of Figure 3 by Martial et al (2019) , which graphically plotted similarity scores between various psychoactive substance experience reports and a corpus of NDE reports based on semantic analyses against a class of psychoactive substances. A tabular version of this, including proximity scores, is provided in Supplementary material (see SM 15) .…”

The Near-Death Experience Content (NDE-C) scale: Development and psychometric validation

“…Interestingly, in Study 3, no item was found to distinguish between NDEs and NDEs-like. This is consistent with the possibility that NDE neurophysiological mechanisms can be activated spontaneously or in non-life-threatening situations where the threat is only apparent or even absent (Jansen, 1997;Martial & Cassol, et al, 2019). This newly developed NDE-C scale was developed with the aim of identifying "classical" NDEs; however, it was found that the scale also allows for the objective quantification and identification of NDEs-like.…”

The Emergent Post-Loss Experience (EPLE) in Grief Therapy: A Mixed-Method Study

“…Previous research on NDEs has consistently highlighted core experiential features such as heightened perceptual clarity, altered temporality, intense affective states-often characterized by peace and well-being)-and a profound sense of meaning or insight (Greyson, 2000;Martial et al, 2020). Notably, several of these elements were also prominent in the phenomenological profile of EPLEs observed in the present sample, including vivid perceptual qualities, experiences of temporal suspension, and meaning-related transformations.…”

An encounter with death: a comparative thematic and content analysis of naturalistic DMT experiences and the near-death experience

“…The themes are arranged in ascending order of proximity score, meaning the higher the point on the plot, the more dissimilar the prevalence of themes between DMT and NDE. This visualisation is comparable to that of Figure 3 by Martial et al (2019) , which graphically plotted similarity scores between various psychoactive substance experience reports and a corpus of NDE reports based on semantic analyses against a class of psychoactive substances. A tabular version of this, including proximity scores, is provided in Supplementary material (see SM 15) .…”

The Near-Death Experience Content (NDE-C) scale: Development and psychometric validation

“…Interestingly, in Study 3, no item was found to distinguish between NDEs and NDEs-like. This is consistent with the possibility that NDE neurophysiological mechanisms can be activated spontaneously or in non-life-threatening situations where the threat is only apparent or even absent (Jansen, 1997;Martial & Cassol, et al, 2019). This newly developed NDE-C scale was developed with the aim of identifying "classical" NDEs; however, it was found that the scale also allows for the objective quantification and identification of NDEs-like.…”

The Emergent Post-Loss Experience (EPLE) in Grief Therapy: A Mixed-Method Study

“…Previous research on NDEs has consistently highlighted core experiential features such as heightened perceptual clarity, altered temporality, intense affective states-often characterized by peace and well-being)-and a profound sense of meaning or insight (Greyson, 2000;Martial et al, 2020). Notably, several of these elements were also prominent in the phenomenological profile of EPLEs observed in the present sample, including vivid perceptual qualities, experiences of temporal suspension, and meaning-related transformations.…”