This study investigates the effects of the glucocorticoid hormone cortisol on brain structure and function. Patients with Cushing's disease are studied before and after treatment. Brain imaging and neuropsychologic tests are used to study changes in the hippocampus and thinking and learning functions as well as mood during the period of elevated cortisol. At several intervals after treatment, these are reexamined to study the degree of reversibility of the abnormalities. The contribution of cortisol as well as testosterone and estrogen to dysfunction and recovery is studied. Since elevated cortisol and dysregulation of its secretory system occurs in a significant proportion of the aged and in Alzheimers Disease and Major Depressive Disorder, these studies will help advance knowledge of the role of cortisol in these conditions.