Preserved Covert Cognition in Non-Communicative Patients With Severe Brain Injury

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Study assessed covert cognition, or the presence of top-down cognitive processing in the absence of discernible motor or verbal responses, in patients in a minimally conscious state (MCS) or vegetative state (VS) using an active event-related potential (ERP) paradigm. Twenty-six patients were included in the analysis: 8 patients diagnosed as MCS+ (those in whom any reproducible response to command was obtained), 8 patients diagnosed as MCS- (no reproducible response to command was obtained), and 10 patients in a VS (no localizing or voluntary response was obtained). There were also 14 healthy controls. The ERP paradigm included a passive condition and an active condition, wherein the participant was instructed to voluntarily focus attention on his/her own name. In each condition, the participant’s own name was presented 100 times (4 blocks of 25 stimuli). In 5 MCS+ patients as well as in 3 MCS- patients and 1 VS patient, an enhanced P3 amplitude was observed in the active versus passive condition. Relative to controls, patients showed a response that was widely distributed over frontoparietal areas and not present in all blocks (3 of 4). In patients with covert cognition, the amplitude of the response was lower in frontocentral electrodes compared with controls but did not differ from that in the MCS+ group. The results indicate that volitional top-down attention is impaired in patients with covert cognition.

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