Contingent negative variation response in chronic pain patients.

The present study assesses central processing of subjective appraisal, expectancy, orientation and reaction time as indexed by Contingent Negative variation (CNV) response in chronic pain patients. Waves N1, P3 and CNV were recorded during a CNV paradigm in a simple reaction time task with a constant interstimulus interval (ISI) of 1 sec. CNV was measured from CZ x FZ in controls and chronic pain patients suffering from cervical spondylosis and low backache due to sciatica. Duration of pain was 5 to 10 years and intensity varied from moderate to severe as adjudged by Visual Analogue Scale. CNV experiment consisted of 32 trials of S1 and S2 motor response sequence. Each trial consisted of warning sound click stimulus (S1) followed by the imperative stimulus in the form of flashes (S2). S2 could be terminated by the subject quickly by pressing a response button with the dominant hand. Cursors were hand set to score the latencies for N1 and P3 potentials to S1, maximal CNV amplitude was scored as the largest negative ongoing potential immediately prior to S2 onset. Similarly Reaction Time (RT), Orientation (O) and Expectancy (E) wave amplitudes and latencies were recorded. There was a significant increase in P3 latency, RT in chronic pain patients, indicating that there is a blunting of cognitive functions and increase in reaction time in patients suffering from chronic pain. These patients also take more time to orient to CNV paradigm.