THE EFFECT OF TONIC PAIN ON PROCESSING THE NONPAINFUL STIMULI INDEXEDBY LATE COMPONENTS OF EVENT-RELATED POTENTIALS

Event-related potentials (ERPs) evoked by light flashes and auditory t ones in a standard odd-ball procedure were recorded from Fz, Cz and Pz scalp sites. Tonic pain was evoked by immersion of the hand in cold w ater (5 degrees C). Significant effects of pain were found in response s to target stimuli but not in responses to non-target stimuli. P300 w ave was affected more than the earlier P200 component. The reduction o f P300 amplitude was the strongest effect, both in auditory and visual tests. P300 latency was not significantly affected. Difference curves (target minus non-target ERPs) showed the additional effects: latency of P200 component was elongated and its amplitude enlarged but only i n auditory experiments. In control experiments with warm water stimula tion no significant alterations of P300 or P200 components were found. The results show that the effect of tonic pain is specific: it predom inantly affects the processes that manifest themselves as amplitude ch anges of P300 components in responses to target stimuli.