• C L Kwan, N E Diamant, G Pope, K Mikula, D J Mikulis, and K D Davis.
• Institute of Medical Science, University of Toronto, Ontario, Canada.
• Neurology. 2005 Oct 25; 65 (8): 1268-77.

BackgroundAbnormal cortical pain responses in patients with fibromyalgia and conversion disorder raise the possibility of a neurobiologic basis underlying so-called "functional" chronic pain.ObjectiveTo use percept-related fMRI to test the hypothesis that patients with a painful functional bowel disorder do not process visceral input or sensations normally or effectively at the cortical level.MethodsEleven healthy subjects and nine patients with irritable bowel syndrome (IBS) underwent fMRI during rectal distensions that elicited either a moderate level of urge to defecate or pain. Subjects continuously rated their rectal stimulus-evoked urge or pain sensations during fMRI acquisition. fMRI data were interrogated for activity related to stimulus presence and to specific sensations.ResultsIn IBS, abnormal responses associated with rectal-evoked sensations were identified in five brain regions. In primary sensory cortex, there were urge-related responses in the IBS but not control group. In the medial thalamus and hippocampus, there were pain-related responses in the IBS but not control group. However, pronounced urge- and pain-related activations were present in the right anterior insula and the right anterior cingulate cortex in the control group but not the IBS group.ConclusionsPercept-related fMRI revealed abnormal urge- and pain-related forebrain activity during rectal distension in patients with irritable bowel syndrome (IBS). As visceral stimulation evokes pain and triggers unconscious processes related to homeostasis and reflexes, abnormal brain responses in IBS may reflect the sensory symptoms of rectal pain and hypersensitivity, visceromotor dysfunction, and abnormal interoceptive processing.

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