title: Thicker posterior insula is associated with disease duration in women with irritable bowel syndrome (IBS) whereas thicker orbitofrontal cortex predicts reduced pain inhibition in both IBS patients and controls.
abstract: Patients with irritable bowel syndrome (IBS) are affected by chronic abdominal pain and show decreased pain inhibition. Moreover, they exhibit differences in brain morphology compared with healthy volunteers. The aim of this study was to examine whether decreased pain inhibition is associated with altered brain morphology in IBS patients. Structural magnetic resonance imaging scans were acquired in 14 female patients with diarrhea-predominant IBS and 14 controls. Pain and anxiety modulation were characterized using electrical stimulation of the sural nerve and heterotopic noxious counterstimulation. IBS patients reported decreased pain inhibition (P = .02) as well as increased shock anxiety, pain catastrophizing, depressive symptoms, and trait anxiety (P's ≤ .05). IBS patients also showed a thicker right posterior insula (pINS), associated with longer IBS duration (r = .67, P = .02). In addition, thicker right lateral orbitofrontal cortex was strongly associated with less pain inhibition in both IBS patients (r = .70, P = .02) and controls (r = .68, P = .01). Results are consistent with the role of the insula in interoception and pain and suggest that IBS may induce thickening of the pINS. Reduced pain inhibition may further involve a modification of the regulatory influence of the orbitofrontal cortex on pain-related processes.
  
  
  CONCLUSIONS
  This study investigated the brain morphology of IBS patients. IBS patients showed thicker right pINS, associated with longer disease duration but not with psychological symptoms. This suggests that IBS induces thickening of pINS, which may contribute to its pathophysiology, consistent with the role of the pINS in interoception and pain.
authors.affiliation: Department of Chiropractic, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada; Centre de Recherche en Neuropsychologie et Cognition (CERNEC), Montréal, Québec, Canada; Centre de Recherche de l'Institut Universitaire de Gériatrie de Montréal (CRIUGM), Montréal, Québec, Canada. Electronic address: Mathieu.piche@uqtr.ca.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Piché
authors.forename: Jen-I
authors.initials: JI
authors.lastname: Chen
authors.forename: Mathieu
authors.initials: M
authors.lastname: Roy
authors.forename: Pierre
authors.initials: P
authors.lastname: Poitras
authors.forename: Mickael
authors.initials: M
authors.lastname: Bouin
authors.forename: Pierre
authors.initials: P
authors.lastname: Rainville
mesh_terms: D015746:Abdominal Pain / Q000209:etiology / Q000523:psychology; D000328:Adult; D001007:Anxiety / Q000523:psychology; D058443:Catastrophization / Q000523:psychology; D002540:Cerebral Cortex / Q000473:pathology*; D003863:Depression / Q000523:psychology; D004558:Electric Stimulation; D004597:Electroshock; D005260:Female; D006801:Humans; D043183:Irritable Bowel Syndrome / Q000473:pathology* / Q000523:psychology*; D008279:Magnetic Resonance Imaging; D010146:Pain / Q000473:pathology* / Q000523:psychology*; D058748:Pain Perception; D017288:Pain Threshold / Q000523:psychology; D017397:Prefrontal Cortex / Q000473:pathology*; D012372:ROC Curve; D013003:Somatosensory Cortex / Q000473:pathology
keywords: Cortical thickness; conditioned pain modulation; diffuse noxious inhibitory controls; heterotopic noxious counterstimulation; orbitofrontal cortex; pain modulation