Cerebral Cortical Influences on Autonomic Function

Inclusion Criteria: * Adults between age 21 and 60 * Participants without gastrointestinal symptoms (Healthy Subjects) * Participants with gastrointestinal symptoms compatible with functional dyspepsia (FD) and or irritable bowel syndrome (IBS) Exclusion Criteria: * history of myocardial infarction, supplemental oxygen requirement, or diabetes * history of chronic gastrointestinal symptoms (for healthy subjects only) * history of gastric surgery * psychosis or altered cognitive status * history of head injury, metal in the skull, stroke, or a history of seizures * implantable devices, such as a pacemaker or nerve stimulator * current use of the following medications or use of substances which are known to lower the seizure threshold: amitriptyline (Elavil), nortriptyline (Pamelor), imipramine (Tofranil), doxepin (Sinequan), clozapine (Clozaril), chlorpromazine (Thorazine), amphetamines or methamphetamine, Ecstasy, Ketamine, Angel Dust/phencyclidine (PCP), cocaine, or 3 or more alcoholic drinks per day * pregnancy * Body-Mass-Index (BMI) \> 35