What names for covert awareness? A systematic review

Abstract

BackgroundWith the emergence of Brain Computer Interfaces (BCI), clinicians have been facing a new group of patients with severe acquired brain injury who are unable to show any behavioral sign of consciousness but respond to active neuroimaging or electrophysiological paradigms. However, even though well documented, there is still no consensus regarding the nomenclature for this clinical entity.ObjectivesThis systematic review aims to 1) identify the terms used to indicate the presence of this entity through the years, and 2) promote an informed discussion regarding the rationale for these names and the best candidates to name this fascinating disorder.MethodsThe Disorders of Consciousness Special Interest Group (DoC SIG) of the International Brain Injury Association (IBIA) launched a search on Pubmed and Google scholar following PRISMA guidelines to collect peer-reviewed articles and reviews on human adults (>18 years) published in English between 2006 and 2021.ResultsThe search launched in January 2021 identified 4,089 potentially relevant titles. After screening, 1,126 abstracts were found relevant. Finally, 161 manuscripts were included in our analyses. Only 58% of the manuscripts used a specific name to discuss this clinical entity, among which 32% used several names interchangeably throughout the text. We found 25 different names given to this entity. The five following names were the ones the most frequently used: covert awareness, cognitive motor dissociation, functional locked-in, non-behavioral MCS (MCS*) and higher-order cortex motor dissociation.ConclusionSince 2006, there has been no agreement regarding the taxonomy to use for unresponsive patients who are able to respond to active neuroimaging or electrophysiological paradigms. Developing a standard taxonomy is an important goal for future research studies and clinical translation. We recommend a Delphi study in order to build such a consensus.

Proceedings of the First Pediatric Coma and Disorders of Consciousness Symposium by the Curing Coma Campaign, Pediatric Neurocritical Care Research Group, and NINDS: Gearing for Success in Coma Advancements for Children and Neonates

“…A state of MCS+ or eMCS identified when volitional brain activities is detected by task-based fMRI or EEG in individuals who display behavioral features of coma, VS/UWS, or MCS-, and thereby do not show command following at the bedside [10]. Synonymous terms are covert cognition and cognitive motor dissociation (CMD) [1,11,12]. A subtle but key distinction among these terms centers around the possibility of covert awareness and falsely negative task-based test.…”

Functional MRI for Acute Covert Consciousness: Emerging Data and Implementation Case Series

“…These advanced terms have in common a brain state of proven awareness MCS+ or eMCS, which is identified when volitional brain activity is detectable by command-following -based task fMRI or EEG in awake and aware individuals who display behavioral features of coma, VS/UWS, or MCS−, and thereby do not show command-following at the bedside. 30 31 32…”

Self-processing in coma, unresponsive wakefulness syndrome and minimally conscious state

“…The diagnosis of UWS, MCS and EMCS requires the practical use of the revised version of the Coma Recovery Scale (CRS-R), which is now considered as the gold standard ( Giacino et al, 2004 , 2018 ; Schnakers et al, 2008a ; Kondziella et al, 2020 ). However, it is now well known that the behavioral description of these patients does not systematically reflect their residual brain or cognitive functions ( Fernandez-Espejo and Owen, 2013 ; Schnakers et al, 2022 ). Dissociations between behavior and brain activity have been observed repeatedly, both with fMRI and Electroencephalography (EEG) methodologies, in various very simple or complex protocols.…”