Irritable bowel syndrome is responsible for chronic abdominal pain, diarrhea and/or constipation. It is a very frequent problem. However, the exact cause of irritable bowel syndrome remains unknown. The purpose of this study is to look for a different cerebral response by magnetic resonance imaging after rectal stimulation in patients with irritable bowel syndrome compared to healthy subjects and to patients with digestive organic disease. Our hypothesis is that irritable bowel syndrome could be a problem of cerebral integration of visceral stimulation.