Alzheimer's Disease (AD) is characterized by amyloid-β (Aβ) plaque buildup and phosphorylated tau (p-tau) in the brain, as well as widespread neurodegeneration. The evidence suggests that both amyloid and tau play a critical role in AD and interventions that reliably and safely decrease the intracerebral burden of amyloid or tau could potentially be of marked clinical importance. Currently, therapeutic options are very limited and while there are pharmacologic interventions that transiently improve cognitive function, there are no treatments that alter disease progression. The current study seeks to use a novel therapeutic intervention that uses noninvasive brain stimulation to target amyloid in the brain. The investigators anticipate this will decrease the amyloid levels in the brain, as evidence by Positron Emission Tomography (PET) imaging.

Alzheimer's Disease (AD) is characterized by amyloid-β (Aβ) plaque buildup and phosphorylated tau (p-tau) in the brain, as well as widespread neurodegeneration. There is no current treatments that alter disease progression.

Investigators will recruit 20 individuals with AD with evidence of amyloid placques in the brain through Positron Emission Tomography (PET) imaging. Investigators will use a novel approach, transcranial alternating current stimulation (tACS), to target the region of maximum amyloid burden in the brain. All participants will receive tACS. Each individual's participation in the study will consist of approximately 16 visits: 3 days for screening/baseline procedures as described below, 10 tACS study visits, and 3 days for follow-up assessments. Subjects will undergo baseline cognitive assessment, structural and functional MRI characterization, and resting-state EEG measurement. Additionally, patients will undergo a tACS-EEG recording session to assess brain plasticity levels and identify markers of response to stimulation. All subjects will then undergo 10 1-hour sessions of gamma-frequency (40 Hz) tACS, targeted to the region of maximal tracer uptake on the amyloid PET study. Subjects will take a standardized adverse effect questionnaire before and after each session and complete a short cognitive test after each session to demonstrate safety and tolerability. At the end of the 10 sessions, subjects will then repeat the baseline assessments, followed by repeat amyloid PET imaging to assess for changes in amyloid burden.

Investigators anticipate that targeting the region of amyloid burden in the brain with tACS will reduce the amyloid burden as evidence by the follow up PET imaging and show improvement on electrophysiological measures of brain function and on cognitive testing. If our prediction is correct, this will will provide a critical first step in the development of a novel intervention to prevent and treat AD.

Inclusion Criteria:

• Clinical Diagnosis of mild AD defined by: Clinical Dementia Rating (CDR) = 0.5-1, Mini Mental State Examination (MMSE) >/= 20, Demonstration or history of memory impairments
• 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
• Intelligence Quotient (IQ) > 85 as determined by the Wechsler Test of Adult Reading (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 Transcranial Magnetic Stimulation (TMS) or tACS,

  • History of fainting spells of unknown or undetermined etiology that might constitute seizures.

• History of seizures, diagnosis of epilepsy, history of abnormal (epileptiform) EEG or immediate (1st degree relative) family history of epilepsy; with the exception of a single seizure of benign etiology (e.g. febrile seizure) in the judgment of the investigator.

• Chronic (particularly) uncontrolled medical conditions that may cause a medical emergency in case of a provoked seizure (cardiac malformation, cardiac dysrhythmia, asthma, etc.).

• Metal implants (excluding dental fillings) or devices such as pacemaker, medication pump, nerve stimulator, Transcutaneous Electrical Nerve Stimulator (TENS) unit, ventriculo-peritoneal shunt, cochlear implant, unless cleared by the study MD.

• Substance abuse or dependence within the past six months.

• Medications will be reviewed by the responsible MD and a decision about inclusion will be made based on the following: The patient's past medical history, drug dose, history of recent medication changes or duration of treatment, and combination of Central Nervous System (CNS) active drugs.

• All female participants that are pre-menopausal will be required to have a pregnancy test; any participant who is pregnant will not be enrolled in the study.

• BMI > 40 kg/m2. We will limit the BMI to <40 kg/m2 because of weight limits of the scanner bed and width limits of the MRI.

• Subjects who, in the investigator's opinion, might not be suitable for the study

• A hair style or head dress that prevents electrode contact with the scalp or would interfere with the stimulation (for example: thick braids, hair weave, afro, wig)

5 months