Oscillatory brain activity in vegetative and minimally conscious state during a sentence comprehension task.

Patients with altered states of consciousness continue to constitute a major challenge in terms of clinical assessment, treatment and daily management. Furthermore, the exploration of brain function in severely brain-damaged patients represents a unique lesional approach to the scientific study of consciousness. Electroencephalography is one means of identifying covert behaviour in the absence of motor activity in these critically ill patients. Here we focus on a language processing task which assesses whether vegetative (n=10) and minimally conscious state patients (n=4) (vs control subjects, n=14) understand semantic information on a sentence level ("The opposite of black is ... white/yellow/nice"). Results indicate that only MCS but not VS patients show differential processing of unrelated ("nice") and antonym ("white") words in the form of parietal alpha (10-12Hz) event-related synchronization and desynchronization (ERS/ERD), respectively. Controls show a more typical pattern, characterized by alpha ERD in response to unrelated words and alpha ERS in response to antonyms.