Home-Based Gamma Transcranial Alternating Current Stimulation in Patients With Alzheimer Disease

Importance: Alzheimer disease (AD) is characterized by dysregulated gamma brain oscillations. Transcranial alternating current stimulation (tACS) is a novel, noninvasive brain stimulation technique capable of entraining cerebral oscillations at targeted frequencies. Objective: To assess the safety, feasibility, and efficacy of home-based gamma tACS applied over the precuneus in patients with prodromal and mild AD. Design, Setting, and Participants: This double-blind, randomized, sham-controlled clinical trial with an open-label extension phase was conducted at a tertiary AD research clinic in Italy from December 10, 2022, to October 15, 2024. Patients with a diagnosis of AD were eligible to participate. Intervention: Participants were randomized to receive either home-based gamma tACS (5 sessions/wk, 60 minutes each) or sham stimulation for 8 weeks (double-blind phase). All participants subsequently received gamma tACS for an additional 8 weeks (open-label phase) and an 8-week follow-up. Main Outcomes and Measures: The primary end points were safety, feasibility, and clinical efficacy. Secondary end points included measures of biological efficacy, including gamma band power via electroencephalography, cholinergic neurotransmission, AD plasma biomarker levels, and brain connectivity as assessed via magnetic resonance imaging. Results: Sixty consecutive patients with prodromal or mild AD were screened; 50 were randomized to gamma or sham tACS (mean [SD] age, 67.3 [7.8] years; 25 [50.0%] female and 25 [50.0%] male). Home-based gamma tACS was safe and well-tolerated. A significant enhancement in global cognitive functions, activities of daily living, and associative memory performances was observed. Marginal mean differences between the sham vs gamma tACS groups were significant for the Clinical Dementia Rating sum of boxes (0.35; 95% CI, 0.10-0.61; P = .007), Alzheimer Disease Assessment Scale-cognitive subscale (0.93; 95% CI, 0.50-1.36; P = .001), Alzheimer Disease Cooperative Study-Activities of Daily Living (-0.55; 95% CI, -0.89 to -0.21; P = .02), and Face-Name Association Test (-1.14; 95% CI, -1.66 to -0.61; P ≤ .001). During the open-label phase, a significant marginal mean difference was observed for Alzheimer Disease Assessment Scale-cognitive subscale (-0.59; 95% CI, -1.02 to -0.16; P = .007), Alzheimer Disease Cooperative Study-Activities of Daily Living (0.41; 95% CI, 0.04-0.08; P = .02), and Face-Name Association Test (1.04; 95% CI, 0.50-1.57; P = .003). Neurophysiological measures showed an increase in cholinergic transmission, coinciding with an increase in gamma power following gamma tACS, effects not seen with sham stimulation. No changes of plasma biomarkers were observed. No add-on effect was observed after 2 repeated treatments with gamma tACS, suggesting that 8 rather than 16 weeks of treatment represents the ideal duration. Conclusions and Relevance: In this randomized clinical trial, home-based gamma tACS was feasible and improved clinical outcomes in AD, with neurophysiological evidence of brain engagement. These findings support further investigation of gamma tACS as a potential therapeutic intervention for AD. Trial Registration: ClinicalTrials.gov Identifier: NCT05643326.