Procedures to be performed and visit schedule Screening Clinic Visit 1(Visit 1, week -2): At screen, participating subjects will sign informed consent. Subjects will undergo exam to determine whether they qualify for participation in the study. Examination will include a complete physical and neurological examination, vital signs, neuropsychological assessment, MMSE, and Berg Balance Test. Neuropsychological assessment will require about 2 hours of pen and paper testing. Participants must score within –1.0 SD of the mean performance of age- and education-matched peers on each neuropsychological test. Participants must also not present on the physical or neurological exam with any exclusionary criteria Participants that meet the screening criteria will be invited back for the baseline visit (week 0). Subjects will be asked to bring with them at the baseline visit their medical records from their primary care physician and signed releases for their medical records will be obtained.