Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by recurrent abdominal pain or discomfort accompanied by disturbed bowel habits. It is among the most frequently... Show moreIrritable bowel syndrome (IBS) is a functional bowel disorder characterized by recurrent abdominal pain or discomfort accompanied by disturbed bowel habits. It is among the most frequently occurring functional bowel syndromes, but the pathophysiology is poorly understood. A variety of mechanisms have been proposed in symptom generation, including enhanced visceral sensitivity, disturbed intestinal motility, autonomic dysfunction, mucosal inflammation, altered immune activity, altered processing of afferent sensory information, and psychological disturbances. These alterations probably reflect dysfunction at different levels of the brain-gut axis. The concept of the brain-gut axis as a model to improve our understanding of the pathophysiology of IBS has been the basis of research in IBS over the last decades and the framework for this thesis. In IBS patients, we demonstrate altered autonomic function by decreased baroreflex sensitivity, changes in proximal and distal gut hormone secretion, impaired postprandial rectocolonic reflex, and increased frequency of a high-producer TNF-alpha gene Single Nucleotide Polymorphism (SNP), compared to healthy individuals. Furthermore, results from a randomized controlled trial favour relaxation training over standard medical care for the treatment of IBS. Finally, we test the validity of a previously published comprehensive working model of IBS, based on the brain-gut axis. Show less