Reply: Response to ‘Minimally conscious state or cortically mediated state?’

Sir, I read with interest the letter by Bayne and colleagues (2018) on my recent reinterpretation of the minimally conscious state (MCS) as a cortically mediated state (CMS). In their letter, Bayne et al. agreed on my demonstration of MCS being rather a CMS, and on the necessity to create a new classification combining behavioural and functional brain-imaging criteria, but they disagreed on adopting this new CMS label based on several concerns (Naccache, 2017; Bayne et al., 2018). First, they raised the issue that criteria used to label the MCS “also inform us with certainty that the patient is still alive, but no-one would suggest that the MCS should be relabelled the ‘Still Alive State’”. Here, Bayne et al. missed a crucial point that I could have framed more explicitly: the label that we attribute to a given patient corresponds to the richer state we were able to observe with certitude when examining this patient. So, when we say that a patient is in an MCS, we also imply that we couldn’t find reliable evidence in favour of a richer state. Thus describing a patient as being in an MCS also means that there is no evidence that this patient is in a conscious exit-MCS. Likewise diagnosing a patient as being in a vegetative state (VS) also implies that there is no evidence that the patient is in an MCS, even if vegetative functions that are preserved in VS are also obviously preserved in MCS patients. Similarly, stating that a patient is in a CMS means that he/she expresses complex behaviours which necessarily recruit cortical networks (contrarily to what we observe in the behaviour of a VS patient), but without any additional certitude about the conscious versus unconscious type of these cortically-mediated behaviours. Indeed, many cortically mediated behaviours and cognitive processes do occur unconsciously, both during conscious and unconscious states. So the CMS label keeps its relevance to differentiate close but distinct states, in difference with a useless label such as the ‘Still Alive State’ common to all categories at stake. Second, Bayne et al. worried about the absence of EMCS in the new classification I proposed. I reassure them: patients who are in a behavioural EMCS fall, in this proposed new classification, in the conscious 4b category given that functional communication enables to be sure of the existence of subjective reports. Actually, this point was mentioned in my article: ‘At the top of this classification, the label 4b corresponds to the current exit-MCS label’. Bayne et al. then discussed the utility of such a CMS valid label for care-givers and relatives of patients who: ‘are not interested in whether the patient’s behaviours are cortically mediated; instead, they want to know whether these behaviours are accompanied by experiences (and if so, what those experiences are like)’. I fully agree with the premises of this point. But when confronted with these complex situations of patients showing rich behaviours but unable to engage in functional communication, we have no choice but to face and to address this complexity. To do so, our first duty deals with clarity: using words that we can explain and define. I doubt ‘minimally conscious’ is a clear expression, pending the question of what is ‘minimal’ here, and pending the absence of consensus about the definition of ‘consciousness’ (see below). The use of an ambiguous wording opens many misunderstandings. Moreover, my experience with doi:10.1093/brain/awy026 BRAIN 2018: 141; 1–3 | e27