Gamma Light and Sound Stimulation to Prevent Dementia in Cognitively Normal People at Risk for Alzheimer's Disease

The investigators are recruiting participants aged 55+ with normal memory who have or had a close family member with Alzheimer's disease. 200 participants will undergo a blood test and a subset will undergo an amyloid PET scan and only 50 participants who have cerebral amyloid deposits will continue in the study. Neither the participant nor the investigators will know whether the participant is receiving sham or active stimulation. Participants will use the device for 12 months at home, for 60 minutes each day when they are awake. Participants will come to the Massachusetts General Hospital in Boston for 4-6 visits: before starting the stimulation, at 6 months, and after 12 months of usage. The participants will undergo PET scans, MRI, EEG, blood tests and memory tests and questionnaires at each visit to monitor progress. In addition, people may elect to allow for us to study their cerebral spinal fluid. Participants will also wear a "fitbit" like watch to monitor sleep and activity throughout the study. The goal of this study is to evaluate whether stimulation with our device at 40Hz will reduce AD pathology in the brain.