Arousal modulation in disturb of consciousness: how about the semantic meaning process?

Objective: One common question regarding Disturb Of Consciousness patients (DOC) is about the preservation of their linguistic ability. The present study aimed to explore the DOC semantic skills by monitoring their autonomic correlates, in terms of arousal (Skin Conductance Response, SCR; and Heart Rate, HR), during an auditory linguistic task. Since arousal is modulated by enhanced cognitive effort we expected significant autonomic activity in response to semantic congruence violations for patients with partially preserved linguistic skills. Participants and Methods: The sample included 24 patients and 20 control subjects. According to Coma-Near Coma and Disability Rating Scale scorings, DOC patients were subdivided into two subgroups: Vegetative State (VS) and Minimally Conscious patients (MCS). The participants were required to implicitly process congruous vs. incongruous auditory word sequences, each composed of four words with a semantic related or unrelated final word. Results: Two sets of ANOVA were applied to SCR and HR with two independent factors: group (2) and congruence (2). It was found a significant increasing in the autonomic activity (SCR and HR) for both patient and control groups in response to incongruous than congruous condition. Moreover, the comparison between VS and MCS revealed an even stronger autonomic activity for MCS as compared with VS. On the contrary, no difference was observed for congruous condition across the two groups. Conclusions: The similarity of behavior revealed by patient and control subjects in the detection of semantic incongruence may underline that some relevant cognitive linguistic functions were preserved in DOC. However VS appear generally less responsive to incongruence than MCS, a difference which may be considered more “quantitative” than “qualitative”. This fact goes against the general supposition on the poor conceptual skills of VS patients. Finally, the present contribution indicates the autonomic measure as an important tool for explore consciousness.