It has been proposed that food cues, especially from foods high in fat and calories, may trigger overeating in obese individuals. The neural basis of this effect is thought to be exaggerated activity within a distributed circuit referred to as the reward system, which includes such brain regions as the amygdala and orbitofrontal cortex. The proposed studies will use functional magnetic resonance imaging (fMRI) to compare reward-system activation elicited by pictures of high and low calorie foods in obese participants in a 12-week weight loss program vs. normal-weight controls. In the first study, fMRI scans will be performed prior to the program to test the predictions (1) that food images, especially of the high calorie foods, elicit greater reward-system activation in the obese men and women than in controls and (2) that degree of activation will predict subsequent weight loss, such that obese individuals with the greatest activation will lose the least weight. For the second study, scans will be performed after completion of the program. This study will test the prediction that those obese individuals whose elicited activity has been most normalized over the course of the treatment, will be those who show the greatest weight loss, both by the end of the program and at one-year follow-up. Both studies will also investigate the relationship of psychological variables -- appetite stimulated by food images, ratings of the emotional valence of the food images, reward sensitivity, and dietary restraint -- to brain activation patterns and to weight loss. Because obesity is one of the most serious health problems in the United States, there is a pressing need to understand underlying factors and to develop effective long-term treatments. It is hoped that this project will contribute to the development of weight-management techniques which are effective by reducing reactivity to food cues in obese individuals. An important factor underlying obesity may be hypersensitivity to food cues, such as the sight of appetizing foods. This study will use functional brain imaging to investigate brain activation patterns by obese participants in a weight loss program in response to viewing pictures of appetizing foods. We wish to determine whether long-term weight-loss is related to the amount of activation elicited by these images prior to the program and to the degree to which activation is normalized in a scan after completion of the program. [unreadable] [unreadable] [unreadable] [unreadable]