For several years, the Coma science Group has been working with the Association du locked-in syndrome (ALIS), in France. Vanessa Charland-Verville carried out the Greyson test on 40 LIS patients belonging to this association, as well as asking several extra questions such as, “Do you remember anything about your coma?” or “Did you have the feeling of dying?” “Fourteen LIS patients said they remembered the period around their coma and eight of them had scores on the Greyson scale allowing them to be considered as experiencers", the FNRS research fellow points out. The answers of these eight patients to the Greyson scale were compared to the answers of 23 non-LIS patients known to have had a classic NDE. The frequency of the phenomena they reported (OBE, tunnel of light, etc.) and the feelings experienced were relatively similar. However, the crucial point is that LIS patients reported having experienced significantly less positive feelings and emotions (well-being, peace, joy, harmony) than the ‘classic’ experiencers. Furthermore, the richness of their autobiographical memories (specifically, memories focused on the impression of having seen one’s life flash by in a fraction of a second) was much greater.

What's the reason behind these differences? According to the authors of the article in Consciousness and Cognition, there are two possible hypotheses. The first one is neuroanatomical. In LIS patients, the lesions are subtentorial, i.e. they are situated at the level of the cerebellum and the brainstem. On the other hand, in so-called ‘classic’ NDE, the lesions are supratentorial, i.e. located at the level of the encephalon(3). Could the location of the lesions explain why LIS patients have a less positive view of their NDE, which is filled with autobiographical details? It’s possible. “The brainstem has connections with the limbic system and the mesencephalon”, says Vanessa Charland-Verville. “Because of the influence on the amygdalae, which are known for their involvement in the emotion of fear, and on other structures in the limbic system, the alteration of these connections, which cause locked-in syndrome, could lead to feelings of panic or, at least, to far less well-being in the case of cortical lesions characteristic of classic NDE.”

The second hypothesis put forward to explain the differences observed between LIS patients who have experienced an NDE and other experiencers, relates to the context of emotional distress in which the former are plunged owing to the fact that their consciousness is intact in a paralysed body.  “It's difficult to draw a conclusion, but I think it's likely that both neuroanatomy and the context play a role and that therefore, the two hypotheses aren't mutually exclusive", the Coma Science Group researcher points out.

Lexical analysis

Continuing her exploration of NDE, Vanessa Charland-Verville is coordinating a project that follows on from the article published in 2013 in PLoS One. It involves the lexical analysis of NDE accounts using software. What words do experiencers most commonly use? And how are they associated? For instance, what are the chances that the word ‘light’ will be used in combination with the word ‘tunnel’? As a result, it should be possible to draw up a map of the correlations between the words. Ultimately, the goal is to determine how NDE accounts are organised and, in order to define their true meaning, to compare this organisation with those of accounts of dreams, striking events (flashbulb memories) or hallucinations caused by anaesthesia or ketamine administered to volunteers.

Moreover, Vanessa Charland-Verville offers a different outlook: “The lexical analysis must also allow us to establish a comparison between NDE accounts of different etiologies, bearing in mind that last year, we showed that the Greyson scale scores were very similar among near-death experiences caused by anoxia, a head injury or a haemorrhage. The same was true when an NDE (but, here, the term isn’t really appropriate) occurred in circumstances where the subject wasn’t in a life-threatening situation - syncope, meditation, sleep, anaesthesia, etc."

Nevertheless, we’re far from having completely untangled the phenomenological expression of near-death experiences. For the time being, the Coma Science Group researchers are using neuroimaging (fMRI, PET scans, EEG) to try to better define the cerebral correlates that may underpin – according to their hypothesis – the expression of the various components of NDE (OBE, tunnel of light, feeling of completeness, etc.). To bring the programme to a successful conclusion, they are particularly focusing on the brain function in volunteers who have had these odd experiences during a spontaneous and transitory loss of consciousness.

(3) The existence of subtentorial lesions in LIS patients doesn’t exclude the presence of other brain lesions that are potentially characteristic of components of NDE (OBE, tunnel of light, etc.) or damage affecting the connectivity of these regions. For their study, the Coma Science Group researchers didn’t have the MRI images for the patients concerned.