The safety and effectiveness of 40 Hz γ-tACS in Alzheimer's disease: A meta-analysis

Abstract

Background: The efficacy and safety of 40 Hz gamma transcranial alternating current stimulation (γ-tACS) in Alzheimer's disease (AD) are still uncertain.

Objective: This meta-analysis was conducted to investigate the therapeutic potential and safety of 40 Hz γ-tACS for AD.

Methods: The meta-analysis was conducted by systematically searching four databases from their start to 28 December 2023. Subgroup analyses were performed to identify the intervention effects of γ-tACS.

Results: Of the 7 included studies, γ-tACS has a notable impact on improving overall cognition [standardized mean difference (SMD): 0.49, 95% CI: 0.09 to 0.89], memory (SMD: 0.79, 95% CI: 0.18 to 1.41), and cholinergic transmission (weighted mean difference: -0.40, 95% CI: -0.43 to -0.37). Furthermore, subgroup analysis revealed that γ-tACS treatment had a substantial impact on enhancing memory targeting the left angular gyrus in both home (SMD: 3.12, 95% CI: 1.54 to 4.70) and non-home settings (SMD: 0.53, 95% CI: 0.24 to 0.82). However, γ-tACS had a positive effect on overall cognition in non-home settings (SMD: 0.55, 95% CI 0.11 to 0.98), but not in home settings (SMD: 0.22, 95% CI -0.76 to 1.20). Additionally, targeting temporo-frontal or bitemporal γ-tACS treatment resulted in improvement in overall cognition (SMD: 0.61, 95% CI: 0.06 to 1.16), but not targeting the left angular gyrus (SMD: 0.22, 95% CI: -0.76 to 1.20).

Conclusions: γ-tACS could be beneficial in enhancing cognition, memory and restoring cholinergic dysfunction in AD. The different selection of stimulation sites plays distinct roles. Meanwhile, AD patients are recommended to receive γ-tACS treatment at home.

Keywords: Alzheimer's disease; cognitive functions; meta-analysis; neuromodulation; transcranial alternating current stimulation.