Mapping "cognitive" event-related potentials in prolonged postcoma unawareness state.

"Cognitive" auditory event-related potentials (ERPs) were mapped to examine the putative conscious responsiveness of eight patients in a postcoma unawareness (PCU) state and of eight matched normal controls. A "passive P3" paradigm was used to evaluate waves N2, P3, and Slow Waves of the ERPs. Results showed that the signal/noise ratio of the patients' waveshapes was poorer than that of the controls. Yet, on the whole, no between-group significant differences were noted for most of the averaged characteristics of the waves. In general, in the patients, the left hemisphere was dominated by negative potentials relative to the right one, whereas in the controls, the opposite asymmetry was apparent. Thirty-eight percent of the patients had passive N2 and P3 waves, and 67% of the responders regained consciousness (versus none of the non-responders). These findings suggest that the presence of intact "cognitive" waves is compatible with a higher probability for improvement, although nondetection of certain waves at the postcoma unawareness state does not necessarily indicate the worst prognosis.