Effect of Modulating Gamma Oscillations Using tACS

Inclusion Criteria: * Clinical Diagnosis of mild to moderate AD\* * Mini Mental State Examination (MMSE) \> 18 * Mild AD ≥ 21 * Moderate AD 18-20 * Demonstration or history of memory impairments. \* Confirmation of diagnosis will be made by the study MD based on a holistic consideration of the participant's cognitive evaluation and history. * Amyloid positive PET imaging * At least 45 years old * On a stable dose of medications for memory loss including cholinesterase inhibitors (e.g. donepezil, rivastigmine or memantine) as defined as 6 consecutive weeks of treatment at an unchanging dose * Minimum of completed 8th grade education * IQ\> 85 as determined by the WTAR and no history of intellectual disability Exclusion Criteria: * Current history of poorly controlled migraines including chronic medication for migraine prevention * Current or past history of any neurological disorder other than dementia, such as epilepsy, stroke, progressive neurologic disease (e.g. multiple sclerosis) or intracranial brain lesions; and history of previous neurosurgery or head trauma that resulted in residual neurologic impairment. * Past or current history of major depression, bipolar disorder or psychotic disorders, or any other major psychiatric condition. * Contraindication for undergoing MRI or receiving TMS or tACS, * \>50 mSv of radiation exposure for research within the past year (PET imaging exclusion) * Presence of the Thr/Thr polymorphism in the TSPO gene (rs6971) due to low af…