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A systematic review and meta-analysis of transcranial direct-current stimulation effects on cognitive function in patients with Alzheimer’s disease

Molecular Psychiatry volume 27, pages 2000–2009 (2022)Cite this article

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Abstract

Transcranial direct-current stimulation (tDCS) appears to enhance cognitive function in Alzheimer’s disease (AD). Accordingly, over the last two decades, the number of studies using tDCS for AD has grown. This study aimed to provide a quantitative assessment of the efficacy of tDCS in improving cognitive function in patients with AD. We systematically searched the literature until May 2021 to identify relevant publications for inclusion in our systematic review and meta-analysis. Eligible studies were sham-controlled trials assessing the impacts of anodal or cathodal tDCS on cognitive function in patients with AD. The outcome measure of this study was the effects of tDCS on distinct cognitive domains including memory, attention, and global cognitive function. The initial search yielded a total of 323 records. Five other articles were found using manual search of the databases. Of these, 13 publications (14 different studies) with a total of 211 patients of various degrees of AD severity underwent meta-analysis. Meta-analysis revealed the non-significant effects of tDCS on attention (0.425 SMD, 95% CI, −0.254 to 1.104, p = 0.220), and significant positive impacts on the amelioration of general cognitive measures (1.640 SMD, 95% CI, 0.782 to 2.498, p < 0.000), and memory (1.031 SMD, 95% CI, 0.688 to 1.373, p < 0.000) dysfunction in patients with AD. However, the heterogeneity of the studies were high in all subdomains of cognition (ϰ2 = 22.810, T2 = 0.552, d.f. = 5, I2 = 78.80%, p < 0.000 for attention, ϰ2 = 96.29, T2 = 1.727, d.f. = 10, I2 = 89.61%, p < 0.000 for general cognition, and ϰ2 = 7.253, T2 = 0.085, d.f. = 5, I2 = 31.06%, p = 0.203 for memory). Improved memory and general cognitive function in patients with AD was shown in this meta-analysis. However, due to the small number of studies and the high heterogeneity of the data, more high-quality studies using standardized parameters and measures are needed before tDCS can be considered as a treatment for AD.

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Fig. 1: PRISMA flow diagram.
Fig. 2: Forest plot of standardized mean difference (SMD) for attention after transcranial direct-current stimulation in patients with Alzheimer’s disease.
Fig. 3: Forest plot of standardized mean difference (SMD) for general cognitive measures after transcranial direct-current stimulation in patients with Alzheimer’s disease.
Fig. 4: Forest plot of standardized mean difference (SMD) for memory after transcranial direct-current stimulation in patients with Alzheimer’s disease.
Fig. 5: Percentage of different levels of risk of bias for each item in included studies.

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Authors and Affiliations

  1. Exp ORL, Department of Neuroscience, Leuven Brain Institute, KU Leuven, Leuven, Belgium

    Alireza Majdi, Luuk van Boekholdt & Myles Mc Laughlin

  2. Neurosciences Research Center, Tabriz University of Medical Sciences, Tabriz, Iran

    Saeed Sadigh-Eteghad

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Study conception and design: AM and MML. Data extraction and analyses: AM and SSE. Additional input and interpretation: AM, LvB, and MML. Paper drafted by AM with input from LvB and MML. All authors reviewed and approved the submitted paper.

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Correspondence to Myles Mc Laughlin.

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Majdi, A., van Boekholdt, L., Sadigh-Eteghad, S. et al. A systematic review and meta-analysis of transcranial direct-current stimulation effects on cognitive function in patients with Alzheimer’s disease. Mol Psychiatry 27, 2000–2009 (2022). https://doi.org/10.1038/s41380-022-01444-7

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