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

Abstract

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.

Narrative Review: Quantitative EEG in Disorders of Consciousness

“…UWS patients were found to have a delayed N400 in incongruous conditions when comparing them to MCS patients. Moreover, there was a correlation between the clinical scales (CNC and DRS) and the peak amplitude as well as latency [107]. The N400 was observed in the UWS group, the MCS group and healthy controls [110].…”

“…The next peak we want to focus on is the negative peak at around 400 ms, i.e., the N400, which was found to have high effectiveness when it comes to examining aspects of language processing [123]. All DOC patients showed a higher N400 peak amplitude in the fronto-central regions as an answer to incongruous words or sentences [103,107]. UWS patients were found to have a delayed N400 in incongruous conditions when comparing them to MCS patients.…”

Managing disorders of consciousness: the role of electroencephalography

“…It does not reliably distinguish VS/UWS from MCS (in three levels: listening, cognition and speech) [ 77 ]. Both MCS and VS/UWS who have a preserved N400 show increased N400 peaks and amplitudes in the middle of the forehead during inconsistent speech stimulation, but the latency of N400 in VS/UWS is longer than that in MCS [ 78 ]. The relationship of N400 with the outcome of DOC patients is noticeable: In a clinical follow-up of 53 VS/UWS and 39 MCS, patients with preserved N400 had a highly significant relationship with the recovery of their communication ability (in MCS: sensitivity = 40%, specificity = 100%; in VS/UWS: sensitivity = 60%, specificity = 97%) [ 79 ].…”

Applied potential of task-free event-related paradigms for assessing neurocognitive functions in disorders of consciousness

“…The N400 has been found in both patients in MCS and with UWS in both active and passive paradigms ( Schoenle and Witzke, 2004 ; Kotchoubey et al , 2005 ; Balconi et al , 2013 ; Steppacher et al , 2013 ; Rohaut et al , 2015 ). The response may be delayed ( Balconi and Arangio, 2015 ; Rohaut et al , 2015 ) or less common ( Schoenle and Witzke, 2004 ; Kotchoubey, 2005 ) in patients with UWS compared to MCS and controls. The nature of the stimuli has been shown to have a significant influence on the probability of detecting an N400, and, in passive auditory paradigms, normatively associated word pairs have been suggested as the most optimal stimuli for eliciting it ( Cruse et al , 2014 ).…”