Neuroimaging and biomarkers in functional gastrointestinal disorders: What the scientists and clinicians need to know about basic neuroimaging, biomarkers, microbiome, gut and brain interactions

The gut-brain axis is a bidirectional communication system involving the autonomic nervous system, immune system, and hypothalamic-pituitary-adrenal axis. Visceral afferent signals from the gut are modulated by cognitive and affective circuits at the brain level and through the descending modulatory pathways a communication loop is created that is capable of changing and regulating gut function and symptoms. In this chapter we review common functional, structural and molecular brain imaging techniques that are used to investigate central nervous system alterations in irritable bowel syndrome, the most common disorder of gut- brain interactions. We review specific alterations associated with symptom presentations and examine their molecular basis both in health and irritable bowel syndrome. We also describe sex-related differences and the emerging link between the brain, the gut and the microbiome as well as the current status of neuroimaging and gastrointestinal disorders.