Neural substrate for facilitation of pain processing during sadness.

It is well known that emotion can modify the experience of pain. However, it is unclear how an emotional state and its concomitant neural activity affects activity in brain regions responsive to pain, thus altering the experience of pain itself. In this study, we examined the effect of sad mood on perception of painful stimuli and used functional MRI (fMRI) to identify neural activity changes in 15 participants who, in separate trials, (a) received painful electric shocks; (b) experienced a sad mood; and (c) received electric shocks as they were experiencing a sad mood. Sad mood was induced using a previously validated paradigm using sad pictures. As predicted, participants rated pain as more intense when they were experiencing a sad mood (viewing sad pictures) than when they were viewing neutral pictures, even though the intensity of the painful stimulation was identical under both conditions. Analysis of fMRI data showed that when pain was delivered while participants were feeling sad, neural activation was significantly greater in some areas known to process pain information as well as some that are believed to primarily process emotion. The 'pain-processing' areas included the secondary somatosensory cortex and the adjacent posterior insula (pIn/SII) as well as periaqueductal gray. The 'emotional-processing' regions included the subgenual cingulate cortex and the amygdala. On the basis of these results, we suggest that increased activation in the pIn/SII is part of a top-down system of pain facilitation that includes the anterior cingulate cortex, amygdala, and periaqueductal gray.