The Relationship Between Coma Near Coma, Disability Ratings, and Event-Related Potentials in Patients with Disorders of Consciousness: A Semantic Association Task

The present research explored the relationship between different measures of disorders of consciousness (DOC), that is electrophysiological measures (ERP N400, event-related potentials) and clinical measures (Coma Near Coma, CNC; Disability Rating Scale, DRS). This analysis aimed to verify the preservation of semantic linguistic processes in eighteen patients with DOC. Patients in minimally conscious state (MCS) and in vegetative state (VS) were compared with respect of N400 amplitude and latency measures. They were submitted to an associative auditory task that included congruous (related final words) or incongruous (unrelated final words) word sequences. Firstly, an increased N400 peak amplitude within the fronto-central cortical areas was revealed in response to incongruous sequences for all patients. Moreover, this peak was temporally delayed in response to incongruous conditions in these cortical sites. In addition, patients in VS showed a delayed N400 in comparison with patients in MCS in incongruous condition. Secondly, a direct correlation was found between the clinical scales and the ERP modulation, in terms of peak amplitude and latency. Thus the present results were discussed taking into account the significance of N400 as a marker of semantic processes in patients with DOC. Secondly it was underlined that this cognitive covert process may be demonstrated also in patients who show significant impairment in overt behavior (as in VS or MCS). Finally it was suggested to use ERP measure to improve the diagnostic profile in cases of DOC.