Abstract
Irritable bowel syndrome (IBS) is a functional disorder of brain-gut interactions. Differential brain responses to rectal distention between IBS and healthy controls (HCs) have been demonstrated, particularly in the pain matrix and the default mode network. This study aims to compare resting-state functional properties of these networks between IBS patients and HCs using graph analysis in two independent cohorts. We used a weighted graph analysis of the adjacency matrix based on partial correlations between time series in the different regions in each subject to determine subject specific graph measures. These graph measures were normalized by values obtained in equivalent random networks. We did not find any significant differences between IBS patients and controls in global normalized graph measures, hubs, or modularity structure of the pain matrix and the DMN in any of our two independent cohorts. Furthermore, we did not find consistent associations between these global network measures and IBS symptom severity or GI-specific anxiety but we found a significant difference in the relationship between measures of psychological distress (anxiety and/or depressive symptoms) and normalized characteristic path length. The responses of these networks to visceral stimulation rather than their organisation at rest may be primarily disturbed in IBS.
Highlights
Irritable bowel syndrome (IBS) is a functional disorder of brain-gut interactions
IBS patients scored significantly higher than healthy controls (HCs) on IBS symptom severity and GI-specific anxiety, but not on trait anxiety or depressive symptoms (Table 1)
We found no significant differences in graph measures nor in their association with psychological scores between HC and IBS groups (Supplementary Material Tables S2–S7)
Summary
Irritable bowel syndrome (IBS) is a functional disorder of brain-gut interactions. Differential brain responses to rectal distention between IBS and healthy controls (HCs) have been demonstrated, in the pain matrix and the default mode network. The regions of the pain matrix can be subdivided into: (1) sensorimotor areas (e.g. thalamus, posterior insula, and basal ganglia), (2) salience areas (e.g. anterior midcingulate cortex (aMCC), anterior insula, and amygadala), (3) emotional arousal areas (e.g. amygdala, hippocampus, pregenual and subgenual anterior cingulate cortex [pgACC, sgACC], medial prefrontal cortex [mPFC], (4) descending pain modulation and central autonomic network (e.g. hypothalamus, periaqueductal gray [PAG], Locus coeruleus complex [LCC], amygdala, anterior insula, aMCC, and mPFC) (5) central executive network (e.g. dorsolateral prefrontal cortex [dlPFC] and posterior parietal cortex [PCC])[9,10,11,12,13] These pain-responsive networks dynamically interact with the default-mode network (DMN), which is active when attention is not directed to a specific exteroceptive or interoceptive stimulus. This approach has only rarely been used to analyse rs-fMRI data in IBS19,23
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