Event-related brain potential modulation in patients with severe brain damage

ObjectiveThe limited evidence and inconsistency of purposeful behaviors in patients in a minimally conscious state (MCS) asks for objective electrophysiological marker of the level of consciousness. Here, a comparison between event-related potentials (ERPs) was investigated using different level of stimulus complexity.MethodsERPs were recorded in seventeen patients, 6 of which in vegetative state (VS), 11 in MCS, and 10 controls. Three oddball paradigms with different level of complexity were applied: sine tones, the subject's own name versus sine tones and other first names. Latencies and amplitudes of N1 and P3 waves were compared.ResultsCortical responses were found in all MCS patients, and in 6 of 11 patients in VS. Healthy controls and MCS patients showed a progressive increase of P3 latency in relation to the level of stimulus complexity. No modulation of P3 latency was observed in the vegetative patients.ConclusionsThese results suggest that the modulation of P3 latency related to stimulus complexity may represent an objective index of higher-order processing integration that predicts the recovery of consciousness from VS to MCS when clinical manifestations are inconsistent.SignificanceModulation of P3 latency related to stimulus complexity could provide valuable information about the cognitive capabilities of unresponsive patients.

► The chance to observe more robust and reliable ERP responses in patients with altered state of consciousness seems to be increased by the use of complex salient stimuli. ► The lack of a P3 latency modulation in VS may reflect an impairment of higher cognitive resources that involve semantic processes and language comprehension which are partially or completely preserved in the MCS. ► The presence of a modulation of P3 latency could provide valuable information about the cognitive capabilities of unresponsive patients and help in differential diagnosis.