Imaging visceral pain.

The application of functional imaging to study visceral sensation has generated considerable interest regarding insight into the function of the brain-gut axis. Brain activation in normal control subjects during visceral sensation includes the perigenual cingulate cortex, which is involved in affective processing and has direct connections to autonomic centers. In contrast, somatic pain rarely activates the perigenual cingulate. This difference in brain activation is highly interpretable because visceral stimuli are experienced as more unpleasant than somatic stimuli. Clinical studies are suggestive of functional changes that may be a consequence or cause of conditions such as irritable bowel syndrome, but the findings are not consistent and are not as obviously interpretable as the differences observed when contrasting visceral and somatic stimulation. Although this is partly because brain imaging is still a relatively new technique, it also reflects weaknesses inherent to the understanding of chronic visceral pain as a biopsychosocial phenomenon. The biopsychosocial concept is very broad and rarely provides for precise predictions or mechanisms that can be directly tested using brain imaging. Future use of brain imaging to examine chronic visceral pain and other pain disorders will be more likely to succeed by describing clear theoretical and clinical endpoints.