Current approaches to studying human resting-state function in inflammatory bowel disease

Crohn's disease and ulcerative colitis are 2 subtypes of Inflammatory Bowel Disease (IBD). The chronic, alternating periods of relapsing, and remitting inflammation of the gastrointestinal tract that underlie these diseases trigger a range of gut-related symptoms, in addition to being related to burdensome psychological and cognitive comorbidities. With advancing knowledge of the brain-gut axis and its dysregulation in diseases such as IBD, understanding IBD-related brain changes is an important focus for current research in this area. "Resting state" function refers to the spontaneous fluctuations in neural activity when a person is awake and resting-not focussing attention on a task or stimulus. The recent surge in human resting-state functional magnetic resonance imaging (rs-fMRI) studies suggest that resting function is altered in IBD, representing a potential neural biomarker to target in the development of novel interventions. There are, however, multiple factors that contribute to the approach of these studies, including factors related to participant sample characteristics (IBD subtype and incorporation of disease activity in group definition and comparison), application of different resting-state metrics to assess resting brain activity (via regional homogeneity or amplitude of low-frequency fluctuations) or functional connectivity (via independent component analysis, region-of-interest, seed-to-voxel, or graph theory analyses) and incorporation of additional, multimodal variables of interest. The present review provides a summary of current approaches to studying resting-state brain function in IBD, the most commonly identified brain regions/networks to exhibit aberrant function, and avenues for advancement that forthcoming research in this field can strive to address. Inflammatory bowel disease (IBD) includes Crohn's disease and ulcerative colitis. IBD involves connections between the brain and the gut. Studying brain changes in IBD may help us to understand what causes IBD or how to treat IBD. One way to see brain changes is by using functional magnetic resonance imaging (fMRI). "Resting state" fMRI shows what the brain is doing when a person is awake but not focussed on a task or stimulus. The resting state can be studied in many ways. For example, researchers can test the link between resting brain function and disease-related factors. These factors can include the disease subtype, disease duration, active disease versus remission, and other disease symptoms. Different statistics are used to answer different questions about brain function. This review first explains the approaches that have been used to study resting-state brain function in IBD. Next, the review provides a detailed account of the approaches and statistics used in each study. A brief summary of the most common findings is discussed. The review ends with study limitations and future directions for research in this area.