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

Abstract

Introduction: Behavioral and cerebral dissociation has been now clearly established in some patients with acquired disorders of consciousness (DoC). Altogether, these studies mainly focused on the preservation of high-level cognitive markers in prolonged DoC, but did not specifically investigate lower but key-cognitive functions to consciousness emergence, such as the ability to take a first-person perspective, notably at the acute stage of coma. We made the hypothesis that the preservation of self-recognition (i) is independent of the behavioral impairment of consciousness, and (ii) can reflect the ability to recover consciousness.

Methods: Hence, using bedside Electroencephalography (EEG) recordings, we acquired, in a large cohort of 129 severely brain damaged patients, the brain response to the passive listening of the subject's own name (SON) and unfamiliar other first names (OFN). One hundred and twelve of them (mean age ± SD = 46 ± 18.3 years, sex ratio M/F: 71/41) could be analyzed for the detection of an individual and significant discriminative P3 event-related brain response to the SON as compared to OFN ('SON effect', primary endpoint assessed by temporal clustering permutation tests).

Results: Patients were either coma (n = 38), unresponsive wakefulness syndrome (UWS, n = 30) or minimally conscious state (MCS, n = 44), according to the revised version of the Coma Recovery Scale (CRS-R). Overall, 33 DoC patients (29%) evoked a 'SON effect'. This electrophysiological index was similar between coma (29%), MCS (23%) and UWS (34%) patients (p = 0.61). MCS patients at the time of enrolment were more likely to emerged from MCS (EMCS) at 6 months than coma and UWS patients (p = 0.013 for comparison between groups). Among the 72 survivors' patients with event-related responses recorded within 3 months after brain injury, 75% of the 16 patients with a SON effect were EMCS at 6 months, while 59% of the 56 patients without a SON effect evolved to this favorable behavioral outcome.

Discussion: About 30% of severely brain-damaged patients suffering from DoC are capable to process salient self-referential auditory stimuli, even in case of absence of behavioral detection of self-conscious processing. We suggest that self-recognition covert brain ability could be an index of consciousness recovery, and thus could help to predict good outcome.

Keywords: P300; coma; disorders of consciousness; event-related potentials; self-processing.

Figure 1

Illustrative cases. Event-related potentials (ERP) at Pz and global field power (GFP) from two patients are represented: one COMA patient without SON effect (A), and one COMA patient with SON effect (B). Temporal clustering permutation tests, with one sided t-tests and 10,000 permutations. Significance threshold: alpha cluster was set to 0.01; value of p ≤ 0.05 for SON (orange curve) and OFN (blue curve) comparison at each sample. Abbreviations: SON = subject’s own name; OFN = other first names.

Figure 2

‘Heat maps’ illustrating 6 months behavioral outcome of survivors’ patients with disorders of consciousness according to their behavioral state of consciousness at the time of ERP recording and the absence/presence of a SON effect at the acute stage of brain injury. Background color coding indicates density of patients (%) within a diagnostic category, suggesting clusters of observations. UWS = unresponsive wakefulness syndrome; MCS = minimally conscious state; EMCS = emergence of minimally conscious state; SON = subject’s own name; SON effect −/+ = absence/presence of a SON effect.

Figure 3

Glasgow Outcome Scale of survivors’ patients with disorders of consciousness 6 months after their brain injury according to the absence/presence of a SON effect at the time of ERP recording. GOS = Glasgow outcome scale; SON = subject’s own name; GOS 2/3/4/5: persistent vegetative state/severe disability/moderate disability/good recovery.