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 affinity binding for the PBR 28 (microlgia) PET scan
• 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, 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 CNS active drugs.
• All female participants that are pre-menopausal will be required to have a pregnancy test; any participant who is pregnant or breastfeeding will not be enrolled in the study.
• 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)