# Evaluation of Visceral Sensation in IBS Patients Using Subliminal Stimulation



## eric (Jul 8, 1999)

"From Medscape GastroenterologyLiterature Review -- Select Topics in IBS and Chronic ConstipationLatest From the Literature in IBS and Chronic Constipation: September 2006Posted 09/07/2006Brian E. Lacy, MD, PhD IntroductionIn this second installment in our quarterly literature review series on topical issues in irritable bowel syndrome (IBS) and chronic constipation, 3 original research studies are reviewed. These reports describe new information regarding the pathophysiology of IBS, the role of alternative therapies in the treatment of IBS, and the treatment of constipation.""Lawal A, Kern M, Sidhu H, Hofmann C, Shaker R. Novel evidence for hypersensitivity of visceral sensory neural circuitry in irritable bowel syndrome patients. Gastroenterology. 2006;130:26-33.The pathophysiology of IBS involves multiple underlying factors, including abnormalities in visceral sensation, disturbances in gut motility, and differences in the central nervous system (CNS) processing of visceral pain.[1] Many investigators now believe that visceral hypersensitivity is the most important pathophysiologic abnormality in IBS patients. The mechanism that leads to visceral hypersensitivity in patients with IBS is unknown, although current theories postulate the presence of abnormal sensory receptors and sensory afferents, deficient descending modulating factors, and a hypervigilant CNS. This latter component has been demonstrated in studies using functional magnetic resonance imaging (fMRI) and positron emission tomography scans.[2,3] The end result is that IBS patients sense abdominal discomfort at lower levels than normal individuals and often misinterpret normal sensations as painful (allodynia).[4] This has been demonstrated in a number of studies that typically involve distending the lumen of the gastrointestinal tract with a balloon.[5] One concern is that these studies may be influenced by cognitive processes associated with perceived sensory stimulation. Stated another way, anticipation of a possibly unpleasant sensation (balloon distention of the rectum) may alter cortical activity and thus change fMRI findings. Lawal and colleagues[6] addressed this potentially confounding factor by evaluating visceral sensation in IBS patients using subliminal stimulation."The investigators used fMRI to quantitate cerebral cortical activity after rectal balloon distention. In contrast to other balloon distention studies, however, these investigators used subliminal balloon distention. Patients with IBS meeting Rome II criteria (age range, 19-38 years; all female) and age- and sex-matched volunteers were first evaluated to determine the perception threshold for balloon distention in each patient. Confirming findings from prior studies,[4,5] these authors again demonstrated that patients with IBS are more sensitive to balloon distention of the gastrointestinal tract than normal volunteers. Patients and volunteers then underwent balloon distention with subliminal pressures (10-20 mm Hg) while fMRI measurements were taken. Two scans were performed at each distention level. Cortical fMRI activity (quantitated by measuring cortical volume) was significantly greater in patients with IBS at all 3 levels of distention compared with volunteers. In volunteers, there was a direct relationship between stimulus intensity and cortical activity volume, with higher levels of subliminal intensity associated with increased cortical activity. However, this relationship was not present in IBS patients; high levels of cortical activity were identified at even the lowest level (10 mm Hg) of rectal distention.This well-designed, novel study is the first to show that very low levels of distention in the gastrointestinal tract, without any related cognitive processes typically associated with perceived distention, lead to increased CNS activity in IBS patients compared with healthy volunteers. In addition, patients with IBS demonstrated a maximum response to subliminal distention, as compared with the graded response seen in healthy volunteers. These findings are important for a number of reasons. *One, it confirms the now widely accepted view that the brain-gut axis is a critical component in IBS. Two, it emphasizes that hypersensitivity is a key underlying pathophysiologic mechanism in the generation of symptoms in IBS patients. And finally, although not evaluated in this study, these findings point out that therapeutic options for patients with IBS should focus on treating both the hypersensitive gut and the hypersensitive CNS."*http://www.medscape.com/viewarticle/544018_2


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## Guest (Sep 14, 2006)

great find eric...very positive article


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