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

Inclusion Criteria: 1. Between 55 - 90 years of age, inclusive. 2. Immediate family history of Alzheimer's disease. 3. Mini-Mental State Exam (MMSE) score of 27 or greater at baseline or expected score range for cognitively normal adjusted for education level. 4. Clinical Dementia Rating Global Score of 0 at baseline. 5. Delayed Recall score on the Logical Memory IIa subtest of 8 to 15 at baseline or expected score range for cognitively normal adjusted for education level. 6. Low serum amyloid levels at baseline. 7. Elevated fibrillar amyloid using 11C PiB PET at baseline between 20 - 70 CL. 8. Willing and able to undergo MRI brain and PET brain scans. 9. Adequate visual and auditory acuity to allow for neuropsychological testing. 10. Able to comply with neuropsychological testing and other study procedures in opinion of site PI. 11. Willing and able to complete baseline assessments, and willing to participate in 13-month study protocol. 12. Willing to provide blood samples at specified timepoints. Willing to consider contributing CSF samples at specified timepoints, if asked. Exclusion Criteria: 1. MRI contraindications, such as presence of pacemakers, aneurysm clips, artificial heart valves, ear implants, metal fragments, or foreign objects in the eyes, skin, or body. 2. High myopia \< -7 diopters, or untreated cataracts that affect vision. 3. Any significant systemic illness or unstable medical condition which could lead to difficulty complying with the study protocol. 4. For subjects agreeing to undergo lumbar punctures, history of bleeding disorders or laboratory results indicating low platelet levels are exclusionary for the procedure. 5. Concomitant medications: 1. Treatment with NMDA antagonists. 2. For subjects undergoing lumbar puncture, current use of warfarin or similar anti-coagulants is exclusionary for the procedure. 6. Clinical conditions: 1. History of seizure or medical diagnosis of epilepsy. 2. Female subjects who are pregnant or currently breastfeeding. 3. History of severe allergic or anaphylactic reactions. 4. Longstanding premorbid history (i.e., longer than 10 years) of alcohol or substance abuse with continuous abuse up to and including the time that the symptoms leading to clinical presentation developed. 5. Neurodegenerative disorder associated with cognitive impairment. 6. Renal disease. 7. MR imaging findings such as stroke, tumor, leukoencephalopathy that could preclude meaningful analyses of clinical and imaging data in the opinion of the site PI, such as: 1. Severe leukoencephalopathy seen on MRI. 2. Relevant structural abnormality (i.e., normal pressure or obstructive hydrocephalus, hypoxic ischemic lesions, hemorrhages, tumors, malformations). 3. Cerebral amyloid angiopathy, evidenced by T2\* or other susceptibility weighted-MRI. 8. Laboratory findings, if known (study does not perform testing) suggestive of systemic illness such as renal disease. 9. Site investigator's discretion, if s/he feels the subject cannot complete sufficient key study procedures. Exceptions to these guidelines may be considered on a case-by-case basis at the discretion of the Project Director.