Significant differences were found in the cortical pain responses of patients with irritable bowel syndrome, compared with healthy controls, in a small study by Canadian researchers.
C.L. Kwan of the Institute of Medical Science, University of Toronto, and associates used functional MRI to evaluate the responses of 9 IBS patients and 11 controls during rectal distensions that elicited either pain or a moderate urge to defecate. They noted specific differences between the two groups' responses in the insular cortex, where visceral and somatosensory input are known to be integrated. Regardless of distension level, the dorsal pole of the right anterior insula was activated in controls but not in IBS patients, suggesting a “ceiling” effect from the chronic pain state in IBS (Neurology 2005;65:1268–77).
This contrasted with findings of urge-related responses in the primary sensory cortex and pain-related responses in the medial thalamus and hippocampus in the IBS patients that were absent in the controls. The authors noted that interpreting brain activation during rectal distension combined both conscious responses and unconscious processing, through which the IBS patients were found to be abnormally conscious of the brain-gut relationship.