Investigation of Mnesic Capacities in Patients With a Disorder of Consciousness

Following severe brain damage, some individuals lose partial or total awareness of themselves and their environment, falling into a coma that can evolve towards a Disorder of Consciousness (DoC). Accurately diagnosing the depth of consciousness alteration, and thus characterizing the patient's residual state of consciousness, is a real medical challenge, yet crucial for establishing a neurological prognosis, predicting cognitive outcome, and guiding medical decisions. Clinicians attempt to classify DoC patients into different global states (e.g. coma, Unresponsive Wakefulness Syndrome (UWS), Minimally Conscious State (MCS)) depending on their residual level of arousal and awareness.

In recent years, the improvement of diagnostic tools and the use of a multimodal approach combining clinical, neurophysiological and neuroimaging examinations, have greatly refined this assessment and revealed the existence of possible discrepancies between clinical observation (e.g. poor consciousness state like UWS) and brain activity (richer, MCS+ type, or even conscious) so-called Cognitive-Motor Dissociation, making it essential to search for any 'hidden cognition' not revealed by the clinical behavioral examination. It is therefore essential to have tools that can not only probe consciousness level, but also provide a detailed profile of patients' residual cognitive abilities - such as language, attention or memory - which are essential dimmensions of conscious experience and shape waking cognitive life. This could crucially improve the neurological diagnostic and prognostic' accuracy of these disorders, as well as allowing to infer the eventual subjective experience of these patients. Indeed, The investigator still know very little about the possible conscious 'contents' involved in these states. What does the possible 'mental life' of DoC patients look like? A multidimensional exploration of their cognition is needed, requiring the development of innovative methods capable of probing cognitive functions in the absence of any communication with the patient.

Thus, the general aim of this study lies in the development of tools for the cognitive exploration of DoC patients and their application at patients' bedside in the Intensive Care Unit (ICU). We're particularly interested in assessing memory capacities in these patients, as exploration of memory has immediate clinical implications, since memory encoding during DoC could impact patients' quality of life and be implicated in the occurrence of post-traumatic stress disorder (PTSD) in case of consciousness recovery. More specifically, the investigator want to tackle the following questions: Are patients suffering from a DoC able to form, consolidate and retrieve new memories (anterograde memory)? Are they able to recall memories from their 'past life' (retrograde memory)? Previous research suggests that some DoC patients retain the ability to reactivate old autobiographical memory traces, and to present automatic short-term sensory memory processes, or residual working memory. Nevertheless, DoC patients' memory abilities have been little studied to date, despite their clinical relevance.

The investigator postulate that memory could be differentially preserved between different clinical states of DoC such as UWS and MCS. At the group level, we expect MCS patients to have better learning and memory retrieval abilities than UWS patients. The investigator therefore expect memory functions to be affected by brain lesions and, consequently, by consciousness alteration, although the invenvisage the preservation of unconscious memory processes (e.g. in non-declarative memory subtypes such as perceptual memory) in UWS patients. We hypothesize that the presence of robust markers of memory processes will vary, at the single-patient level, according to the types and stages of memory tested, informing the cognitive profile of the patient suffering from a DoC.

By providing information on the potential presence of memory capacities that cannot be revealed by clinical examination, the physiological tools we are developing in this study will open a crucial window onto non-communicating patients' cognition. Defining DoC patients' memory profile could not only improve their care during and after the disorder (reflection on the quality of life in ICU; better understanding of cognitive and psychological symptoms occurring after a DoC (e.g. amnesia, PTSD); orientation of rehabilitation strategies), but also improve the diagnostic accuracy of these troubles if memory proves to be differentially preserved between different DoC states such as UWS and MCS. Ultimately, we aim to refine the neurological prognosis of these non-responsive patients, by predicting their cognitive outcome thanks to these innovative physiological tools. On a more fundamental level, this project questions the interplay of memory and consciousness, exploring which forms of memory do and do not require a conscious state.