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. 2024 Sep 23:16:1454755.
doi: 10.3389/fnagi.2024.1454755. eCollection 2024.

A meta-analysis of the effects of transcranial direct current stimulation combined with cognitive training on working memory in healthy older adults

Yanxin Lv  1 , Shuo Wu  2 , Michael A Nitsche  3   4   5 , Tian Yue  1 , Volker R Zschorlich  6   7   8 , Fengxue Qi  1
Affiliations

A meta-analysis of the effects of transcranial direct current stimulation combined with cognitive training on working memory in healthy older adults

Yanxin Lv et al. Front Aging Neurosci. .

Abstract

Background: Working memory (WM) loss, which can lead to a loss of independence, and declines in the quality of life of older adults, is becoming an increasingly prominent issue affecting the ageing population. Transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, is emerging as a potential alternative to pharmacological treatments that shows promise for enhancing WM capacity and May enhance the effects of cognitive training (CT) interventions.

Objective: The purpose of this meta-analysis was to explore how different tDCS protocols in combination with CT enhanced WM in healthy older adults.

Methods: Randomized controlled trials (RCTs) exploring the effects of tDCS combined with CT on WM in healthy older adults were retrieved from the Web of Science, PubMed, Embase, Scopus and the Cochrane Library databases. The search time period ranged from database inception to January 15, 2024. Methodological quality of the trials was assessed using the risk-of-bias criteria for RCTs from the Cochrane Collaboration Network, and RevMan 5.3 (Cochrane, London, United Kingdom) was used for the meta-analysis of the final literature outcomes.

Results: Six RCTs with a total of 323 participants were ultimately included. The results of the meta-analysis show that tDCS combined with CT statistically significantly improves WM performance compared to the control sham stimulation group in healthy older adults [standard mean difference (SMD) = 0.35, 95% CI: 0.11-0.59, I 2 = 0%, Z = 2.86, p = 0.004]. The first subgroup analysis indicated that, when the stimulus intensity was 2 mA, a statistically significant improvement in WM performance in healthy older adults was achieved (SMD = 0.39, 95% CI: 0.08-0.70, I 2 = 6%, Z = 2.46, p = 0.01). The second subgroup analysis showed that long-term intervention (≥ 10 sessions) with tDCS combined with CT statistically significantly improved WM compared to the control group in healthy older adults (SMD = 0.72, 95% CI: 0.22-1.21, I 2 = 0%, Z = 2.85, p = 0.004).

Conclusion: tDCS combined with CT statistically significantly improves WM in healthy older adults. For the stimulus parameters, long-term interventions (≥ 10 sessions) with a stimulation intensity of 2 mA are the most effective.

Keywords: cognitive function; cognitive training; older adult; transcranial direct current stimulation; working memory.

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Conflict of interest statement

MAN was in the Scientific Advisory Boards of Neuroelectrics, and Precisis. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
PRISMA flow diagram of literature search strategies.
Figure 2
Figure 2
Summary of risk of bias by domain.
Figure 3
Figure 3
Forest plot depicting the effect of CT combined with actDCS vs. stDCS on working memory in healthy older adults. actDCS, active transcranial direct current stimulation; stDCS, sham transcranial direct current stimulation.
Figure 4
Figure 4
Forest plot of subgroup analysis by a different model of stimulus intensities (1 mA, 2 mA). tDCS, transcranial direct current stimulation.
Figure 5
Figure 5
Forest plot of subgroup analysis by a different model of number of interventions (< 10 times, > = 10 times). tDCS, transcranial direct current stimulation.
Figure 6
Figure 6
A funnel plot showing publication bias among included studies.
See this image and copyright information in PMC

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