Methods.

Right-handed healthy control subjects (n= 11, 7 women, 4 men; 24 to 50 years old) and patients with IBS (n= 9, 6 women, 3 men; 30 to 58 years old) provided written consent to procedures approved by the University Health Network Research Ethics Board. Control subjects were excluded if they had a history of bowel disorders, chronic pain, fibromyalgia, diabetes, or psychiatric illness. Patients were recruited from the Toronto Western Hospital Gastrointestinal Unit, met Rome III criteria 2 for diagnosis of IBS, and had mild to moderate symptoms and pain for more than 2 years. Exclusion criteria were a history of other organic diseases, including diabetes, Crohn disease, bowel resection, or psychiatric illness. Participants underwent structural and functional MR 1 with a 1.5 T GE MRI. A T1-weighted three-dimensional IR-SPGR anatomic scan (echo time= 5 msec, repetition time= 25 msec, 45 flip) acquired 124 1.5-mm-thick sagittal images (field of view= 24, matrix= 256× 256).