Differential effects on the laser evoked potential of selectively attending to pain localisation versus pain unpleasantness.

Abstract Objective : To determine the effects on the laser evoked potential (LEP) of selectively attending to affective (unpleasantness) versus sensory-discriminative (localisation) components of pain. Methods : LEPs, elicited by painful CO 2 laser stimulation of two areas of the right forearm, were recorded from 62 electrodes in 21 healthy volunteers, during three tasks that were matched for generalised attention: Localisation (report stimulus location), Unpleasantness (report stimulus unpleasantness), Control (report pain detection). LEP components are named by polarity, latency, and electrode. Results : N300-T7 peak amplitude was significantly greater during Localisation than Unpleasantness. The difference in N300-T7 amplitude between Localisation and Control approached significance, suggesting an increased amplitude in Localisation compared with Control, rather than a reduced amplitude in Unpleasantness. Peak amplitude, latency, and topography of N300-FCz, P450, P600–800 (early P3) and P800–1000 (late P3) did not differ significantly between tasks. Conclusions : These results suggest that the N300-T7 LEP peak reflects the activity of cerebral generators involved in the localisation of pain. The topography of N300-T7 is consistent with a source in contralateral secondary somatosensory cortex/insula and maybe primary somatosensory cortex. Significance : This study confirms a role of the lateral pain system in the localisation of pain, and distinguishes it from stimulus novelty or attention.