Abstract
BACKGROUND: Alzheimer's disease (AD) is a progressive neurodegenerative disorder associated with cognitive decline and significant global health burden. Current treatments offer limited benefits, highlighting the need for novel therapies. Gamma-frequency auditory and visual stimulation (GFAVS), utilizing 40 Hz neuromodulation, has gained attention as a non-invasive treatment for cognitive deficits and underlying pathophysiology in AD. OBJECTIVE: This systematic review and meta-analysis aimed to assess the safety and efficacy of GFAVS in treating Alzheimer's disease (AD) and mild cognitive impairment (MCI). METHODS: A comprehensive literature search across multiple databases (PubMed, Cochrane Library, MEDLINE, Web of Science, and Embase) was performed up to November 2025. Controlled trials involving adults (≥50 years) with AD or MCI, using GFAVS, were included. Meta-analyses assessed adverse events, cognitive function, and brain changes. RESULTS: Eleven studies (341 participants) were included. GFAVS was safe, with no significant increase in overall adverse events (RR = 0.99, P = 0.93; RD = -0.01, P = 0.93). However, GFAVS significantly increased the risk of tinnitus (RR = 6.46, P = 0.08; RD = 0.16, P = 0.01). GFAVS significantly improved structural brain changes (SMD = 1.74, P = 0.02), especially in mixed AD and MCI populations (SMD = 3.05, P < 0.00001). Nevertheless, no significant improvements were observed in cognitive function (SMD = 0.16, 95% CI [-0.36 to 0.68], P = 0.55) or activities of daily living (SMD = 0.53, 95% CI [-1.26 to 2.33], P = 0.56), despite the observed structural brain changes. High heterogeneity was observed. CONCLUSION: GFAVS appears to be well tolerated and may induce structural brain alterations in individuals with Alzheimer's disease or mild cognitive impairment; however, its impact on cognition or daily functioning remains to be established. Large-scale, rigorously designed trials are required to clarify optimal protocols and address the observed heterogeneity.