Effects of distraction on pain-related somatosensory evoked magnetic fields and potentials following painful electrical stimulation

We aimed to compare the effects of distraction on pain-related somatosensor y evoked magnetic fields (pain SEF) following painful electrical stimulatio n with simultaneous recordings of evoked potentials (pain SEP). Painful ele ctrical stimuli were applied to the right index finger of eleven healthy su bjects. A table with 25 random two-digit numbers was shown to the subjects, who were asked to add 5 numbers of each line in their mind (calculation ta sk) or to memorize the numbers (memorization task) during the recording. In the SEF recording, 3 short-latency components within 50 ms of the stimulat ion were generated in the primary sensory cortex (SI) of the hemisphere con tralateral to the stimulated finger. Middle-latency components between 100 and 250 ms after the stimuli were recorded from the secondary somatosensory cortex (SII) in the bilateral hemispheres or the cingulate cortex. No SEF components were significantly affected by either task. In the SEP recording , the middle-latency components (N140 and P230) were identified as being ma ximal around the vertex. Amplitudes of the N140 and P230 were not affected by each task, but the peak-to-peak amplitude (N140-P230) was significantly decreased by both the calculation and memorization tasks, particularly by t he former. Subjective pain rating was decreased in both the calculation and memorization tasks, particularly in the former. We concluded that distract ion tasks reduced activities in the limbic system, in which the middle-late ncy EEG component probably generated, while neither the short-latency SEF c omponents generated in SI nor the primary pain-related SEF components gener ated in SII-insula are affected. (C) 2000 Elsevier Science B.V. All rights reserved.