After facing a life-threatening situation (e.g., cardiac arrest), or a situation perceived as such, some people will report peculiar life-changing events known as “near-death experiences” (NDEs). These experiences, that typically include transcendental and mystical features (e.g., out-of-body experiences, meeting with deceased relatives), have aroused curiosity among lay people and scientists. To date, the mechanisms that underlie the emergence of the phenomenon and its rich memory remain ill-described. Consequently, by exploring NDE accounts, the aims of this thesis were three-fold: i) to contribute to a better description of the NDE phenomenology; ii) to examine how its memory is stored in autobiographical memory; and iii) to explore its potential neurochemical models.
Study 1: By means of an exploratory qualitative thematic analysis, we extracted the common features reported in written NDE accounts. We identified ten “time-bounded” (i.e., isolated features experienced during the NDE) and one “transversal” theme (i.e., a feature that shapes the whole experience and does not correspond to a defined point in time). Time-bounded themes were the following: “light”, “return”, “meeting”, “hyperlucidity”, “description of scenes”, “darkness”, “out-of-body experience”, “awareness of death”, “life events” and “entrance in the NDE”. The “altered time perception” was identified as the only transversal theme.
Study 2: NDEs are typically associated with positive affect; however, some distressing NDEs have also been described. Empirical investigations about these phenomena are still lacking. Our goal was therefore to examine their prevalence, content and possible precipitating factors. Results showed that they represent 14% of our sample and that they are as phenomenologically detailed as “classical” NDEs. Besides, they seem to follow suicidal attempts more often. These findings support the possible implication of “top-down” processes in the emergence of NDEs: when sensory inputs are degraded (i.e., altered states of consciousness), the content of the conscious experience produced by our brain could be influenced by one’s state of mind and/or prior knowledge in order to mentally “fill in the gap”.
Study 3: Given the reported impact of NDE memories on experiencers’ lives, we assessed to what extent they could meet the definition of “self-defining
memories” (SDMs; i.e., vivid memories that strongly contribute to our sense of self). NDE experiencers described their two main SDMs and completed the Centrality of Event Scale (i.e., to assess how central an event is to one’s identity). The NDE memory was reported by a majority of participants. Moreovoer, it was considered more “central” compared to other SDMs. Findings confirm the strong impact of NDEs and reveal the importance for clinicians to facilitate their integration within the self.
Study 4: Given their emotionality and consequentiality, NDE memories are often compared with flashbulb memories (i.e., a vivid memory of the circumstances in which a surprising piece of news was heard). We therefore examined the phenomenological characteristics, centrality and amount of episodic and non-episodic information provided in verbal recalls of NDE, flashbulb and control autobiographical memories. Analyses revealed that NDE memories comprise more episodic details than control autobiographical and flashbulb memories, and more non-episodic details than flashbulb memories. Besides, flashbulb memories are considered less central, and are associated to a lower intensity of feelings while remembering and a lower personal importance. Overall, even though NDE and flashbulb memories seem to be similar at first glance, our findings highlight that NDE memories are unrivaled and particularly rich in details.
Study 5: Several neurochemical models have been suggested to reproduce NDE features in a laboratory setting, notably endorphins, DMT and ketamine. To further investigate potential neurochemical models for NDEs, we assessed the semantic similarity between NDE narratives and thousands of reports linked to the use of 165 psychoactive substances. Analyses indicated that the accounts of experiences under ketamine were the most similar to those associated with NDEs. Altogether, results indicate that ketamine could be used as a safe pharmacological model to study the NDE phenomenology in a laboratory setting.
To conclude, we believe that NDE memories can be regarded as SDMs with flashbulb-like components. Their important impact on experiencers’ lives highlights the importance of developing psychological interventions to foster their integration into their life story, especially since some of them are particularly distressing. Besides, if the neural correlates of NDEs have not been identified yet, research has made significant progress in that direction.