Defining Central Circuits of Pain

The purpose of the study is to use functional Magnetic Resonance Imaging (MRI) to help us understand what parts of the subject's brain are involved when he experiences visceral pain, or pain in the gut. To stimulate the brain, he will be infused with a liquid meal (Ensure) into his stomach until he is maximally full. Magnetic resonance imaging (MRI) is a technique for making images (pictures) of the brain; it uses magnetic fields and radio waves and is not harmful. This study uses a new investigational technique called functional MRI (fMRI), which is a very fast MRI technique that will allow the investigators to evaluate changes in how blood flows to parts of his brain.