This trial is testing a non-invasive brain stimulation technique called rTMS on healthy people and those with IBS or FD. The goal is to see if it can help regulate automatic body functions like digestion and heart rate by changing brain activity. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation technique that has been used to treat various neurological and psychiatric conditions, including major depression, migraine-associated headaches, and obsessive-compulsive disorder.