Effects of affective pictures on pain sensitivity and cortical responses induced by laser stimuli in healthy subjects and migraine patients

Visually induced analgesia has been correlated with the affective content of pleasant, neutral or unpleasant pictures. The aim of the present study was to assess the effect of affective images vision on laser evoked potentials and pain perception, in a cohort of healthy subjects and migraine patients. Twenty-two healthy subjects and 24 migraine without aura patients (recorded during the inter-critical phase) participated in the study. Eighty-four colour slides, arranged in two blocks, each consisting of 14 pleasant, 14 unpleasant and 14 neutral images, in random presentation, were chosen from the International Affective Picture System. The CO2 laser stimuli were delivered on the dorsum of the right hand and supra-orbital zone at 7.5-watt intensity and 25-ms duration, in basal condition and during the viewing of affective pictures. Migraine patients expressed higher scores of valence and arousal for pleasant and unpleasant pictures, compared to controls. In both groups, a late positive potential in the 400–700 ms time range was clear for pleasant and unpleasant pictures, but its amplitude was significantly reduced in migraine patients. The pain rating and the N2 component were reduced in both groups during the visual task compared to basal condition. In migraineurs and controls the P2 wave was reduced during the vision of pleasant pictures, compared to basal condition. This indicates that stimulation by images with different affective content reduces subjective pain for a cognitive mechanism of attentive engagement, while a special inhibition of later LEPs is produced by a positive emotional impact. In migraine, affective images are able to modulate pain perception and LEPs, differently from other modalities of distraction, suggesting a possible emotive elaboration of painful stimuli.