Effect of Modulating Gamma Oscillations Using tACS

Study Overview
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Brief Summary
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This study aims to implement an intervention based on multiple, individualized multifocal tACS stimulation sessions based on individual PET and MRI information in patients with amyloid-positive PET with the hope that this leads to microglia activation and decrease in cerebral amyloid and tau depositions in human patients with AD.

Detailed Description
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This study will leverage all this accumulated knowledge by implementing an intervention based on multiple, individualized multifocal tACS stimulation sessions based on individual PET and MRI information in patients with amyloid-positive PET with the hope that this leads to microglia activation and decrease in cerebral amyloid and tau depositions in human patients with AD.This would have immense translational impact, as gamma tACS is an intervention that is portable, does not require expensive hardware, can be widely applied to large numbers of patients with AD, as well as, given its favorable side effect profile, even to patients at earlier stages of the disease who have cerebral amyloid/tau without clinical symptoms. The investigators aim to enroll 10 individuals with AD with evidence of increased cerebral amyloid burden on amyloid PET imaging. This would allow for a final sample size of 5-6 fully evaluable subjects. Each subject's participation in this study will consist of approximately 31-35 visits: 1 day for consent and screening procedures, 5-7 days of baseline procedures (this includes the PET scans), 20 tACS study visits, and 5-7 days of follow-up assessments. Subjects will undergo baseline cognitive assessment, structural and functional MRI characterization, PET imaging to assess amyloid burden, tau deposition and level of microglia activation, and resting-state EEG measurement. Additionally, subjects will undergo a TMS-EEG and a tACS-EEG recording session to assess brain plasticity levels and identify markers of response to stimulation. All subjects will subsequently undergo 20 sessions of gamma-frequency (40 Hz) tACS. At the end of the 20 sessions, subjects will then repeat the baseline assessments over 5-7 visits, including repeat PET imaging to assess for changes in amyloid burden, tau deposition, and microglia activation.

Official Title
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Effect of Modulating Gamma Oscillations by Transcranial Alternating Current Stimulation on Brain Structure and Function in Humans

Conditions
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Alzheimer Disease

Intervention / Treatment
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* Device: Transcranial Alternating Current Stimulation (tACS)


Participation Criteria
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Eligibility Criteria
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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)

Ages Eligible for Study
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Minimum Age: 45 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: tACS<br>Transcranial alternating current stimulation (tACS) tuned at the frequency of 40Hz (gamma frequency) will be applied for 1 hour in 20 sessions on consecutive weekdays. The tACS intervention (20 sessions) will be preceded and followed by amyloid, microglia and tau PET imaging as well as a clinical/cognitive evaluation. The assessment of the effect of stimulation on microglia activation, amyloid deposition and tau deposition will constitute a primary outcome measure. Assessment of adverse effects will be also evaluated as a secondary outcome. The effect of brain stimulation on brain connectivity will be assessed by EEG and MRI and cognitive function. | Device: Transcranial Alternating Current Stimulation (tACS)<br>* tACS will be applied at a frequency of 40Hz and targeting the area of maximal tracer uptake on amyloid PET imaging using an individualized multielectrode design to maximize the induced electrical current to the target region.<br>* Other names: Non-invasive Brain Stimulation;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| PET Amyloid Burden | Changes in the amyloid load observed via PET imaging will be evaluated by comparing PET data acquired before and after the 20 tACS sessions. The metric used is standardized uptake value ratio (SUVR), a measure of the amount of proteins in the brain identified at the PET exam. We will calculate the difference between pre and post tACS SUVR for the entire brain and report the average value (and standard deviation) for the entire group of patients. A negative value express a decrease in the amount of proteins in the brain post tACS intervention. | baseline and up to 12 weeks | 
| PET Tau Deposition | Changes in the tau deposition observed via PET imaging will be evaluated by comparing PET data acquired before and after the 20 tACS sessions. The metric used is SUVR, a measure of the amount of proteins in the brain identified at the PET exam. We will calculate the difference between pre and post tACS SUVR (dSUVR) for the entire brain and report the average value (and standard deviation) for the entire group of patients. A negative value express a decrease in the amount of proteins in the brain post tACS intervention. | up to 12 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| PET Microglia Activation | Changes in the microglia activation observed via PET imaging will be evaluated by comparing PET data acquired before and after the 20 tACS sessions. The metric used is SUVR, a measure of the amount of proteins in the brain identified at the PET exam. We will calculate the difference between pre and post tACS SUVR (dSUVR) for the entire brain and report the average value (and standard deviation) for the entire group of patients. A negative value express a decrease in the amount of proteins in the brain post tACS intervention. | up to 12 weeks | 
| Changes in Brain Perfusion as Measured by Arterial Spin Labeling | Patients underwent a comprehensive MRI exam before and after the tACS intervention, including measures of brain perfusion via Arterial Spin Labeling (ASL) sequences. The outcome measure represent the average change in perfusion (i.e. blood flow) recorded in regions targeted by tACS. Since Alzheimer's Disease is also characterized by a decrease of brain metabolism, an increased of blood flow after treatment would constitute a very promising sign of tACS efficacy in reducing Alzheimer's pathology in the brain. We will report the change in blood flow (mean, standard deviation) after tACS treatment. | 6 weeks (pre-post tACS intervention) | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Alzheimer Disease