A number of neurological theories have also been put forward to explain NDEs. "Not all of them are plausible," says Steven Laureys. "One of them ascribes these subjective experiences to hallucinations resulting from drugs administered during the resuscitation. Yet NDEs can occur outside of a medical context, when someone nearly drowns, for example." Currently, as previously mentioned, the most relevant neurological theories associate diverse NDE elements with dysfunctions in brain-damaged areas, especially following head injuries or a lack of oxygen due to cardiac arrest.

We have mentioned OBEs, which can be caused by a malfunction in the right temporoparietal area. It has also been well documented that the left temporoparietal area, which is easily damaged in the event of poor oxygenation, has been implicated in the sensation of a nearby presence. "The temporoparietal region is a multimodal association area which integrates different sensory information (visual, auditory, proprioceptive, and others) and which consequently plays a critical role in distinguishing between one's self and others," explains the head of the Coma Science Group.

We also know that epileptic patients whose epileptogenic focus is situated in the hippocampus (which is known to play an important role in memorisation) can also see their life flash before their eyes, as occurs in certain NDEs. And the hippocampus is very sensitive to a lack of oxygen.

The posterior parietal cortex is also greatly affected during anoxia. It was identified as the source of spiritual experiences or the sensation of being at one with the cosmos. This was evidence by fMRI studies conducted on religious participants by University of California researchers in 2009.

"In cases of cardiac arrest or head injuries, the entire brain suffers, but most particularly certain areas that are only irrigated by small arterioles and are therefore the most vulnerable to a lack of oxygen," notes Steven Laureys. "We suspect that these are the areas involved in NDE phenomena."

The exploration of memories

Before using neuroimaging to confirm this presumption and conducting systematic investigations to better explain the neural correlations of different NDE elements, the Coma Science Group and ULg's Cognitive Psychology Unit joined forces to identify the characteristics of NDE memories, using accepted psychological methods. Were NDE accounts pure imaginary creations, or rather memories with the same characteristics as memories of real events? "The description of the phenomenological characteristics of memories recounted by the affected people could help to orient our research into neuronal correlates for NDEs," indicates Marie Thonnard.

Other than determining plausibility, how did they differentiate between real and imagined memories?  "Generally, real memories are richer in sensory detail (visual, auditory, etc.), self-referential (relating to the subject), and emotional," explains Hedwige Dehon, PhD in Psychological Sciences and assistant at ULg's Cognitive Psychology Unit. Therefore the phenomenological characteristics of these two types of memories are usually different.