Anorexia nervosa (AN) is a disordered eating disease characterized by a persistent pursuit of thinness, intense fear of weight gain, distorted body image, and obsessive eating habits. People with AN are at high risk for certain health problems, such as depression, osteoporosis, substance abuse, and cardiovascular and neurological complications. Current treatments for AN include different forms of psychotherapy and medications, but the success of these treatments is highly variable among people with AN. A better pathophysiologic understanding of AN is needed in order to develop novel therapeutic strategies for preventing and treating the disorder. Current research is targeting dopamine (DA), a neurotransmitter that is released in response to pleasurable stimuli, such as food and drugs. Animal studies have found that chronic food restriction may alter functioning of the DA system by reducing DA response to food and drug stimuli. A better understanding of the effects of disordered eating on the DA systems of people with AN may provide insight into the development of new and improved treatments for people with AN. This study will use positron emission tomography (PET) imaging to investigate changes in DA systems in people with AN before and after both weight restoration and administration of methylphenidate, a psychostimulant medication. The study will also use PET imaging to compare DA systems of people with AN with DA systems of people who are healthy.