Method and apparatus for disrupting a gastric vagal nerve in the gastroesophageal region and testing the function and disruption of the vagal nerve. In one example embodiment, a treatment device applies ultrasound at a high energy level, such as high intensity focused ultrasound, to a vagal nerve to disrupt it and then ultrasound at a lower energy level to another portion of the vagal nerve, preferably further from the stomach, so as to stimulate the vagal nerve. Alternative ways to test the function or disruption of the vagal nerve involve using PCP-GABA, a pancreatic polypeptide, pressure changes inside the stomach, the gastric mucusol pH, a dye agent in the stomach, and other tests.