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From the Institute of Medical Science (Drs. Diamant, Mikulis, and Davis, C.L. Kwan), Departments of Surgery (Dr. Davis), Medicine (Dr. Diamant), and Medical Imaging (Dr. Mikulis), University of Toronto, and Toronto Western Research Institute (Drs. Diamant, Mikulis, and Davis, C.L. Kwan, G. Pope, and K. Mikula), Toronto Western Hospital, University Health Network, Ontario, Canada.
Address correspondence and reprint requests to Dr Davis, Department of Surgery, University of Toronto, Toronto Western Research Institute, Toronto Western Hospital, Rm. MP14-306, 399 Bathurst St., Toronto, Ontario, Canada M5T 2S8; e-mail: kdavis{at}uhnres.utoronto.ca
Background: Abnormal cortical pain responses in patients with fibromyalgia and conversion disorder raise the possibility of a neurobiologic basis underlying so-called "functional" chronic pain.
Objective: To 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.
Methods: Eleven 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.
Results: In 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.
Conclusions: Percept-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.
Additional material related to this article can be found on the Neurology Web site. Go to www.neurology.org and scroll down the Table of Contents for the October 25 issue to find the title link for this article.
*These authors contributed equally as senior authors.
Supported by the Canadian Institutes of Health Research and the Canadian Research Chair Program. C.L.K. was supported by a Canadian Institutes of Health Research/Canadian Pain Society/Janssen–Ortho Doctoral Research Award.
Disclosure: The authors report no conflicts of interest.
Received March 1, 2005. Accepted in final form July 19, 2005.
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