Patients in the study must have a caregiver and designated representative. Candidates will be given a medical history and physical examination that includes a complete neurologic and neuropsychologic evaluation, blood tests, and an electrocardiogram. A chest X ray and magnetic resonance imaging (MRI) test will be done on patients who have not had these tests within the previous two years. During the 20-week study, each patient will take three pills twice a day for twenty weeks of either Nefiracetame or placebo (sugar pill). Neither the patients nor the doctors will know which patients are getting the drug and which are getting the placebo. Blood and urine tests will be done frequently throughout the study. Patients will be asked to have a spinal tap (on a voluntary basis) to measure the levels of drug in the spinal fluid, and a PET scan (a brain imaging test).