Patients have 4 study visits. A psychiatric evaluation and a memory test are given at the first visit. During the second study visit, patients have a physical exam, an electrocardiogram (ECG), a neuropsychological assessment, an optional magnetic resonance imaging (MRI) brain scan, and other laboratory tests. On the third and fourth visits, patients are randomized to receive either their highest daily dose of lorazepam or placebo. Performance effects and postural sway are determined before drug administration and at 1, 2.5, and 5 hours after the drug is given. Blood samples for the determination of drug levels are also obtained.