Audio‒Visual Gamma Stimulation for Alzheimer's Disease: Current Evidence and Future Directions.

Abstract

Introduction/objective: Alzheimer's Disease (AD) is characterized by progressive cognitive decline and disrupted neural oscillations. Recently, 40 Hz gamma stimulation has emerged as a potential non-invasive therapy. This review evaluates the safety, tolerability, and clinical outcomes of this intervention based on evidence from the past decade.

Methods: A literature search was conducted across PubMed, Web of Science, Google Scholar, and ClinicalTrials.gov for studies published during the last ten years. Registered and ongoing studies were also identified through ClinicalTrials.gov. Extracted data included stimulation modality, stimulation parameters, safety and tolerability outcomes, and reported effects on functional connectivity, brain atrophy, cognitive performance, and sleep-related measures.

Results: Thirty studies were identified, comprising eight sensory-based 40-Hz gamma stimulation approaches, 12 40-Hz transcranial Alternating Current Stimulation (tACS) protocols, and 10 ongoing clinical trials. Among the 20 completed studies, 40-Hz gamma stimulation was reported to be safe and well-tolerated. The synthesized evidence from these completed trials suggests potential beneficial effects on functional connectivity, brain atrophy progression, cognitive outcomes, and sleep-related measures.

Discussion: Gamma stimulation may represent a promising approach for modulating neural network activity and cognitive function in AD. Nevertheless, current evidence remains limited by small sample sizes, methodological heterogeneity, differences in stimulation protocols, and short follow-up periods. These factors limit the ability to draw definitive conclusions regarding therapeutic efficacy.

Conclusion: 40-Hz gamma stimulation is a feasible and generally well-tolerated non-invasive intervention with potential relevance for AD treatment. Further large-scale, randomized, and controlled studies are required to establish standardized stimulation protocols, determine long-term efficacy, and clarify its clinical utility.