Affective modulation of nociception at spinal and supraspinal levels.

This study was designed to examine the effect of emotion on the nociceptive flexion reflex and pain ratings. To do so, 28 participants viewed pictures varying in emotional valence (unpleasant, neutral, pleasant) and electric stimulations were delivered during and in between pictures. Biceps femoris EMG resulting from the stimulations was used to quantify the nociceptive flexion reflex (spinal nociception), and pain ratings to the stimulations were used as an evaluative measure of supraspinal nociception. Manipulation checks suggested that pictures effectively manipulated emotion. Moreover, nociceptive flexion reflex magnitudes and pain ratings were modulated in a parallel manner. Specifically, viewing unpleasant pictures enhanced the nociceptive flexion reflex and pain, whereas viewing pleasant pictures inhibited the reflex and pain. Analyses suggested that emotional valence, but not arousal, mediated the effects of pictures.