P3 event related cerebral evoked potential in chronic pain patients.

P3 component of event related cerebral evoked potentials has been applied as an index of information processing in a wide variety of normal and cognition impaired subjects. The present study was undertaken to examine possible changes in central nervous system processing and subjective appraisal, indexed by cerebral evoked potentials (N200 & P300), in 20 pain free controls and 20 subjects suffering from chronic pain (cervical spondylosis and low backache, sciatica). Standard auditory 'Odd ball' paradigm involving simple discrimination task of concentrating on infrequent (target) stimulus and ignoring the frequent stimulus (non-target) was employed. Evoked response trial of discriminating 32 target stimuli out of 160 total presented (20% target and 80% non target, randomly) were replicated and analysed by computer. There was significant increase in P3 latency in patients suffering from pain as compared to age and sex matched controls, suggesting change in cognitive functions.