Cerebral Cortical Influences on Autonomic Function

The overall goal of this study is to determine the impact of non-invasive brain stimulation on autonomic function in human subjects without functional gastrointestinal disorders and in subjects with Irritable Bowel Syndrome (IBS) or Functional Dyspepsia (FD). Aim 1: Determine whether repetitive transcranial magnetic stimulation (rTMS) of specific cortical areas alters physiologic measures of gastrointestinal and cardiac function. The investigators will use rTMS to transiently induce changes in neural excitability within specific cortical regions identified as being linked to autonomic regulation. Based on preliminary neuroanatomical data, one of the leading candidate cortical areas associated with sympathetic regulation lies within the trunk representation of the primary motor cortex. Thus, the investigators first plan on targeting this region of the primary motor cortex with rTMS and assess the effect of various parameters of rTMS on gastrointestinal and cardiac function in healthy human subjects. The investigators will then perform additional experiments using rTMS targeted to other specific cortical sites, such as the dorsal premotor area and rostral cingulate cortex that have also been linked to autonomic control. Each of these identified cortical regions may make unique contributions to autonomic reactivity. Aim 2: Determine whether patients with functional gastrointestinal disorders demonstrate altered physiological reactivity to targeted rTMS. The investigators will use the optimal parameters of rTMS and regions of interest determined in Aim 1 to assess the gastrointestinal and cardiac reactivity in participants with functional dyspepsia (FD) and/or irritable bowel syndrome (IBS). These physiological responses will be correlated with assessments of disease severity, mood, and quality of life. --This study description has been revised since its original posting. Because all study procedures are performed in all subjects, regardless of being a healthy subject or one with FD and/or IBS, rather than a three arm trial, this trial should be regarded as having a single arm study design.