Transcranial Photobiomodulation for Alzheimer's Disease (TRAP-AD)

This multi-site study will be the first to evaluate the dose-dependent effects of t-PBM in amnestic Mild Cognitive Impairment (aMCI) and early Alzheimer's Disease (AD) (CDR of 0.5-1, FAST 1-4; age 65-85) in a randomized clinical trial of 8 weeks of t-PBM vs. sham. At baseline, all subjects will complete initial neuropsychological testing. To elucidate mechanisms of action of t-PBM, prior to treatment, subjects will undergo neuroimaging related to critical features of AD: tau 18F MK-6240 load (PET), measures of brain bioenergetics (31P-MRS), and functional connectivity (rs-fMRI). After undergoing target engagement testing (t-PBM session performed during fMRI to detect BOLD changes with active t-PBM), subjects will then be randomized to t-PBM/sham and complete 24 t-PBM/sham treatments, \~11 min per day, 3 days per week, for 8 weeks. t-PBM will be administered via continuous, 808 nm wavelength laser delivery to the forehead bilaterally (at standard EEG electrode positions F4, F3).

Inclusion Criteria: 1. Able to give written informed consent and follow study procedures. 2. Age \> or = 65 years and \< or = 85 years. 3. Meets the Petersen MCI criteria for Amnestic MCI (single and multiple domain) with a Clinical Dementia Rating (CDR) between 0.5-1.0, and a Functional Assessment Staging (FAST) of 1-4. 4. Be willing to identify an informed relative, family member, spouse, or friend for study staff to interview to confirm subject reports as per UDS 3.0 guidelines; however the lack of a study informant is not exclusionary. 5. Have at least a high school diploma/12 years of education. 6. Participants with current mild MDD may be allowed to participate, given that mild MDD does not affect cognition and does not pose increased risk to the participant, as determined by site PI on a case-by-case basis. Exclusion Criteria: 1. Unwilling/unable to comply with study procedures. 2. Other diagnosis of dementia (i.e. not Alzheimer's type), history of brain tumor, MRI evidence of brain damage or brain disease including significant trauma, hydrocephalus, seizures, intellectual disability, or other serious neurological disorder (e.g. Parkinson's disease or other movement disorders). 3. History of significant cerebrovascular pathology (e.g., significant stroke). Subjects with a history of cardiovascular disease (e.g., myocardial infarction) will be allowed to participate at site PI's discretion, on a case-by-case basis, given that the cardiovascular disease is stable and does not reflect the presence of significant cerebrovascular pathology. 4. Clinically unstable systemic medical disorders. 5. Current DSM-5 diagnosis of alcohol or drug use disorder or other major psychiatric illness (e.g., schizophrenia, bipolar, PTSD, depression). Participants with current mild MDD may be allowed to participate, given that mild MDD does not affect cognition and does not pose increased risk to the participant, as determined by site PI on a case-by-case basis. Participants with current moderate/severe MDD will be excluded. 6. Clinical or laboratory evidence of hypothyroidism. 7. Clinically significant abnormal findings of laboratory parameters or at physical examination. 8. Medications affecting cognition (e.g., narcotic analgesics; chronic use of medications with anticholinergic activity, anti-Parkinsonian medications, antipsychotic meds, etc.). Stable use (i.e., = 6 months) of memantine or acetylcholinesterase inhibitors will be allowed. 9. Family history of early onset (\