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

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 CO2 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.