Pain-related cerebral potential (pain-related P250) of patients in a persistent vegetative state

It is well-established that in normal subjects a large positive wave with a latency of approximately 250 ms can be reliably recorded when painful stimuli are applied. This pain-related cerebral potential (pain-related P250) has been interpreted as a reflection of cortical activation in response to the painful stimuli, presumably in relation to cognitive processing of painful information. The pain-related P250 is unique in terms of its ability to reflect the cortical responsiveness to painful stimuli directly and quantitatively without involving the function of the motor system. In the present study, we undertook an electrophysiological examination based on the pain-related P250 of patients in a persistent vegetative slate (PVS). The results revealed that the amplitude of the pain-related P250 was variably depressed in such patients. The depressed pain-related P250 strongly suggested deficits of cognitive function of painful information that may underlie a reduced responsiveness. However, the present study also demonstrated that the pain-related P250 in a few patients increased spontaneously after 6 months, and a significant association was noted between the increase in amplitude of the pain-related P250 and improvement in the level of consciousness. Based on our assessments of the pain-related P250, there appeared to be a large variability of cognitive function in PVS patients.