Unmasking of an early laser evoked potential by a point localization task

Objectives: The investigation of the CO2 laser evoked potential (LEP) modif ications following a point localization task. Methods: LEPs were recorded from 10 healthy subjects in two different condi tions. (1) Task condition: laser stimuli were shifted among 3 different loc ations on the right hand dorsum, and the subjects were asked to identify th e stimulated area. The mean error rate in point localization was 4.5%. (2) Non-task condition: laser pulses were delivered on the first intermetacarpa l space, and the subject was asked to count the number of stimuli. The mean error rate in counting was 5.8%. Results: In the task condition, the temporal traces contralateral to the st imulation showed an early positive component (eP, mean peak latency 83 ms) preceding the N1 negativity (mean peak latency 144 ms). At the eP peak late ncy, topographic maps showed a positivity highly focused on the contralater al temporal region. In the non-task recordings no reliable response was ide ntifiable before the N1 potential. Conclusions: While no LEP component earlier than the middle-latency N1 pote ntial can be recorded in the non-task condition, a positive response (eP) p receding the N1 component is identifiable in the contralateral temporal reg ion during the spatial localization of painful stimuli. The eP scalp distri bution is compatible with its origin from a radial source in the second som atosensory (or insular) area, thus suggesting that the opercular cortex is involved not only in the middle-latency (N1 potential), but also in early p ain processing. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.