Brain Responses to Visceral Stimuli Reflect Visceral Sensitivity Thresholds in Patients With Irritable Bowel Syndrome

Abstract

Background & aims Only a fraction of IBS patients show increased perceptual sensitivity to rectal distension, suggesting possible differences in processing and/or modulation of visceral afferent signals within this group. The aim was to identify brain mechanisms which may underlie these perceptual differences. Methods 44 women with IBS and 20 female healthy control subjects (HCs) were included. Symptom severity in IBS was determined by Severity Scoring System (IBS-SSS). Anxiety and depression symptoms were assessed using the Hospital anxiety & depression score (HAD). Blood oxygen level dependent (BOLD) signals were measured by functional Magnetic Resonance Imaging (fMRI) during expectation and delivery of high (45mmHg) and low (15mmHg) intensity rectal distensions. Perception thresholds to rectal distension were determined in the scanner. Brain imaging data from 18 normosensitive, 15 hypersensitive IBS patients and 18 HCs were compared. Results were reported significant if peak p-value ≤ 0.05 with family wise error correction in regions of interest. Results The two IBS subgroups were similar in age, symptom duration, psychological symptoms and IBS symptom severity. While brain responses to distension were similar in normosensitive patients and HCs, hypersensitive IBS demonstrated greater activation of insula and reduced deactivation in pregenual anterior cingulate cortex during noxious rectal distensions, compared to both HCs and normosensitive IBS. During expectation of rectal distension, normosensitive IBS had more activation in right hippocampus than HCs. Conclusions Despite similarities in symptoms, hyper- and normosensitive IBS patients differed substantially in cerebral response to standardized rectal distensions and their expectation, consistent with differences in ascending visceral afferent input.