Disrupted functional connectivity density in irritable bowel syndrome patients

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder resulting from a dysregulation of the brain-gut axis. However, its exact neural substrate still remains unclear. This study investigated the changes of intrinsic whole brain functional connectivity pattern in IBS using functional connectivity density (FCD). We acquired resting-state functional magnetic resonance imaging (rs-fMRI) data from thirty-two IBS patients and thirty-two healthy controls. Functional connectivity density, a data-driven algorithm, was used to compute the long-range and short-range FCD values for each voxel in the brain of each subject, implying the amount of distant and local functional connections of cortical hubs. The FCD maps were compared between IBS patients and healthy controls. Pearson correlations analysis was also performed between abnormal FCD values and clinical/psychometric scores in patients. Compared to healthy controls, IBS patients showed concurrently decreased long- and short-range FCD in bilateral anterior midcingulate cortices (aMCC) and inferior parietal lobules (IPL), and decreased long-range FCD in right anterior insula, and decreased short-range FCD in bilateral prefrontal cortices, subgenual anterior cingulate cortices and caudates. IBS patients also had concurrently increased long- and short-range FCD mainly in primary sensorimotor cortices, as well as increased long-range FCD in right supplementary motor area and increased short-range FCD in occipital lobe. In addition, some regions with altered FCD showed abnormal functional connectivity in brain regions involved in pain matrix of IBS patients. Furthermore, the abnormal FCD values in right anterior insula and left caudate showed significant correlation with severity of symptoms and disease duration of IBS patients respectively. In conclusion, patients with IBS have widely disrupted FCD, which decreased in brain regions involved in homeostatic afferent network, emotional arouse, and cognitive regulation, while increased in regions associated with sensorimotor modulation. And the observed functional connectivity alterations unveiled complicated working patterns of pain matrix in IBS patients. This study may provide us with new insight into the underlying brain network topology of IBS.