UCLA

Irritable Bowel Syndrome (IBS) is the most common chronic visceral pain syndrome characterized by chronic abdominal pain/discomfort associated with altered bowel habits. Cognitive, affective and psychosocial factors such as hypervigilance, hypersensitivity and selective attention of visceral pain are commonly seen in IBS patients. Many studies have demonstrated IBS-related biological alterations in the immune system, gut microbiota, gene polymorphisms and hypothalamic-pituitary-adrenal system. However, these findings are not able to explain the subjective pain experience of IBS patients. By applying different brain imaging technology (e.g. Magnetic Resonance Imaging [MRI]) in pain research, multiple brain regions involved in emotional arousal, reward, attentional and cognitive processes have been identified during the past decade. Based on the extensive epidemiological, psychophysiological and neurobiological information about pain mechanisms, there is a growing consensus that the central nervous system plays an important role in the pathophysiology of IBS symptoms, in addition to multiple other peripheral factors.

This dissertation aims to identify IBS-related structural and functional brain signatures, and to integrate these signatures and clinical characteristics into a comprehensive disease model, which takes sex-related differences into account. The following analysis approaches were used to accomplish these aims: 1. Fractional amplitude of low frequency fluctuation was applied to measure the power spectrum intensity of spontaneous brain oscillations during task-free resting-state functional MRI. 2. Functional connectivity analysis was performed to examine how different parts of the brain work together and to identify dysfunction of the communication in the disease group. 3. Task-based functional MRI study approach was used to study how brain responses to certain stimuli differ between individuals with IBS and healthy controls. In addition, to determine the disease specificity of observed brain networks, brain structural changes were compared between IBS patients and patients with inflammatory bowel diseases. Altogether, with different aspects of research approaches to investigate IBS, progress has been made to better understand the pathophysiology of the disorder.