Studies show that inducing a positive mood or diverting attention from pain decreases pain perception. Nevertheless, induction manipulations, such as viewing interesting movies or performing mathematical tasks, often influence both emotional and attentional state. Imaging studies have examined the neural basis of psychological pain modulation, but none has explicitly separated the effects of emotion and attention. Using odors to modulate mood and shift attention from pain, we previously showed that the perceptual consequences of changing mood differed from those of altering attention, with mood primarily altering pain unpleasantness and attention preferentially altering pain intensity. These findings suggest that brain circuits involved in pain modulation provoked by mood or attention are partially separable. Here we used functional MRI to directly compare the neuro-circuitry involved in mood- and attention-related pain modulation. We manipulated independently mood state and attention direction, using tasks involving heat pain and pleasant and unpleasant odors. Pleasant odors, independent of attentional focus, induced positive mood changes and decreased pain unpleasantness and pain-related activity within the anterior cingulate (ACC), medial thalamus (medialTH), and primary and secondary somatosensory cortices. The effects of attentional state were less robust, with only the activity in anterior insular cortex (aIC) showing possible attentional modulation. Lateral inferior frontal cortex (LinfF-BA45/47) activity correlated with mood-related modulation while superior posterior parietal (SPP-BA7) and entorhinal activity correlated with attention-related modulation. ACC activity covaried with LinfF and PAG activity, whereas aIC activity covaried with SPP activity. These findings suggest that separate neuro-modulatory circuits underlie emotional and attentional modulation of pain.
Keywords: pain, fMRI, attention, emotion, odor, heat