PAIN-RELATED AND COGNITIVE COMPONENTS OF SOMATOSENSORY-EVOKED POTENTIALS FOLLOWING CO2-LASER STIMULATION IN MAN

We recorded cortical potentials evoked by painful CO, laser stimulatio n (pain SEP), employing an oddball paradigm in an effort to demonstrat e event-related potentials (ERP) associated with pain. In 12 healthy s ubjects, frequent (standard) pain stimuli (probability 0.8) were deliv ered to one side of the dorsum of the left hand while rare (target) pa in stimuli (probability 0.2) were delivered to the other side of the s ame hand, Subjects were instructed to perform either a mental count or button press in response to the target stimuli. Two early components (N2 and P2) of the pain SEP demonstrated a Ct maximal distribution, an d showed no difference in latency, amplitude or scalp topography betwe en the oddball conditions or between response tasks. In addition, anot her positive component (P3) following the P2 was recorded maximally at Pt only in response to the target stimuli with a peak latency of 593 msec for the count task and 560 msec for the button press task. Its sc alp topography was the same as that for electric and auditory P3. The longer latency of pain P3 can be explained not only by its slower impu lse conduction but also by the effects of task difficulty in the oddba ll paradigm employing the pain stimulus compared with electric and aud itory stimulus paradigms. It is concluded that the P3 for the pain mod ality is mainly related to a cognitive process and corresponds to the P3 of electric and auditory evoked responses, whereas both N2 and P2 a re mainly pain-related components.