Do we need a theory-based assessment of consciousness in the field of disorders of consciousness?

Adequate assessment of (un)consciousness is not only of theoretical interest but also has a practical and ethical importance, especially when it comes to disorders of consciousness (DOC). Accurately determining the presence or absence of consciousness in patients with DOC allows informed decisions to be made about long-term care support, referral for rehabilitation, pain management and withdrawal of life support. In spite of significant progress in neuroimaging and the introduction of clear-cut clinical diagnostic criteria, determining the (un)consciousness still presents an important clinical problem: errors are common and have been shown to be as high as 37–43% (Tresch et al., 1991; Childs et al., 1993; Andrews et al., 1996; Schnakers et al., 2006). Assessment errors arise because the evaluation of patients with DOC is based mostly on clinical observation of subjectively interpreted behavioral responses, while conscious experience often occurs without any behavioral signs. Additionally behavioral responses of such patients are usually limited by their cognitive dysfunctions and/or by their frequent motor impairment. Therefore, determining if a non-communicative or minimally communicative patient is phenomenally conscious poses a major clinical and ethical challenge. For this reason, there is a need for paraclinical diagnostic markers for the presence or absence of consciousness. We believe that a theoretical account of what conscious experience is and how it emerges within the brain will advance the search for appropriate neuromarkers of the presence or absence of consciousness in non-communicative brain-damaged patients. In our view, several important considerations need to be kept in mind: