Semantic processes in disorders of consciousness. The role of ERP measures in a linguistic task

Disorders of consciousness (DOC) were amply studied in the recent years. At this regards new methodologies and technologies were applied to explore the diagnostic and prognostic criteria that may be applied to the DOC patients. Recently, ERPs (event-related potentials) were adopted to integrate the classical neuroimaging measures. We may distinguish different planes of analysis related to ERP profile. Sensory ERPs generally appear in response to perceptual features of a stimulus. Contrarily, cognitive ERPs are used to evaluate higher level functions like attention, memory, and language. These long-latency potentials are considered well-suited to assess functions of consciousness.Specifically long-latency ERPs were used in the present research to verify the maintenance of semantic processes in vegetative states (VS)/minimal consciousness state. A specific ERP marker, the N400 deflection was previously observed following sentences that end with semantically inappropriate words or, more generally, significant stimuli. In this case the semantic violation may be used to assess language comprehension.N400 ERP effect was measured in DOC patients in response to a semantic task, consisting in an implicit comprehension of auditory words that may be inserted into a congruent or incongruent context (semantically related or unrelated words). An ampler negative deflection was registered in DOC patients similar to the N400 peak previously found in control subjects. Moreover, the N400 marker appears to be ampler on specific cortical sites, that is frontal (mainly Fz) areas. The morphological resemblance of the ERP measure between control subjects and DOC patients may suggests that also in case of invasive disturbs of consciousness some important cognitive processes are preserved, and that the semantic level may be partially active in response to linguistic comprehension.