Effects of Transcranial Direct Current Stimulation on Episodic Memory in Older Adults: A Meta-analysis

Abstract

Objectives In the last two decades, the number of intervention studies using transcranial direct current stimulation (tDCS) has grown enormously. Though some studies have shown positive influences on episodic memory among older adults, disagreement exists in the literature. Therefore, the current meta-analysis aimed to provide a quantitative assessment of the efficacy of tDCS in modulating episodic memory functions in older adults. Method Eligible studies were sham-controlled trials examining the effects of anodal tDCS on episodic memory in older adults. Twenty-four articles comprising 566 participants aged over 60 qualified for inclusion. Results Compared to the sham tDCS group, the active tDCS group showed significant memory improvements at both immediate poststimulation (Hedges’ g = 0.625, p = .001) and long-term follow-up (Hedges’ g = 0.404, p = .002). There were no differences in effect sizes between cognitively healthy and impaired older adults. Moderator analyses suggested that tDCS having a duration of 20 min or less, bilateral stimulation, or a larger stimulation area would produce greater benefits for episodic memory performance in older adults. Discussion These findings suggest that tDCS holds great promise to ameliorate memory decline in older individuals. In the future, well-designed randomized controlled trials are expected to verify the optimal stimulation protocols and determine the factors impacting the long-term effects of tDCS in enhancing episodic memory.

Effects of transcranial direct current stimulation combined with listening to preferred music on memory in older adults

“…However, some studies find no change in working memory for older adults following tDCS with n-back tasks 30 , 58 , which are in accordance with the present study’s findings in the tDCS-only condition. Inconsistent findings are also present when examining tDCS effects in other cognitive domains, which may be attributed to differences in stimulation parameters, such as current intensity, duration of stimulation, and stimulation site 59 .…”

“…However, several studies have also found null effects after stimulation over the DLPFC 71 or temporoparietal cortex 72 , and even impaired associative memory after stimulation of the left inferior frontal gyrus 73 . Nonetheless, a meta-analysis showed that tDCS strengthened episodic memory for older adults with moderate effect sizes 59 . The null accuracy and RT effects on the auditory WRT add to this mixed pattern of findings, and may reflect some limitations in our experimental design.…”

tDCS-Induced Memory Reconsolidation Effects and Its Associations With Structural and Functional MRI Substrates in Subjective Cognitive Decline

“…Recently, Sandrini et al (2020) reviewed the effects of tDCS on episodic memory in aging and concluded that one of the main limitations in this field is the lack of reliability. Thus, despite the growing body of work suggesting that brain stimulation techniques might be used to induce episodic memory improvements in aging ( Huo et al, 2019 ), many of the reported cognitive effects still need to be independently replicated and mechanistically elucidated ( Sandrini et al, 2020 ). One of the major factors underlying this lack of reliability is the observed individual variability in response to the various non-invasive brain stimulation (NIBS) protocols (i.e., López-Alonso et al, 2014 ; Wiethoff et al, 2014 ).…”

Transcranial Direct Current Stimulation Enhances Episodic Memory in Healthy Older Adults by Modulating Retrieval-Specific Activation

“…Fortunately, a growing body of literature has described the role of atDCS in improving episodic memory, including both item and associative memory, in older adults [ 18 – 21 ]. According to the latest meta-analysis, older adults receiving atDCS showed memory improvements, with a significant and modest effect size (Hedges′ g = 0.625, [ 22 ]). Beneficial effects of atDCS on episodic memory may result from modify learning-related synaptic connections and then modulating brain functions.…”