Effects of noninvasive brain stimulation on cognitive function in healthy aging and Alzheimer's disease: a systematic review and meta-analysis

Abstract

The study aimed to evaluate the effects of noninvasive brain stimulation on cognitive function in healthy older adults and patients with Alzheimer's disease. A comprehensive literature search was performed on noninvasive stimulation studies published from January 1990 to November 2014 in Pubmed and Web of Science. Fourteen articles with a total of 331 participants were identified as studies with healthy older adults, and the mean effect size and 95% confidence interval were estimated. A significant effect size of 0.42 was found for the cognitive outcome. Further subgroup analyses demonstrated more prominent effects for studies delivering the stimulation before the execution of the task and studies applying multiple sessions of stimulation. To assess the effects of stimulation on Alzheimer's disease patients, 11 studies with a total of 200 patients were included in the analysis. A significant effect size of 1.35 was found for the cognitive outcomes. Subgroup analyses indicated more pronounced effects for studies applying the stimulation during the execution of the task compared with studies delivering the stimulation before the execution of the task. Noninvasive brain stimulation has a positive effect on cognitive function in physiological and pathological aging.

Keywords: Aging; Alzheimer's disease (AD); Cognitive function; Meta-analysis; Neuronal plasticity; Repetitive transcranial magnetic stimulation (rTMS); Transcranial direct current stimulation (tDCS).

Copyright © 2015 Elsevier Inc. All rights reserved.

Figures

Figure 1

Statistical summary and forest plot of effect sizes for cognitive outcome measures in healthy older adults. Five articles contributed more than one effect size. CI, confidence interval; L, left; R, right; ATL, anterior temporal lobe; DLPFC, dorsolateral prefrontal cortex; PARC, parietal cortex.

Figure 2

Statistical summary and forest plot of effect sizes for cognitive outcome measures in patients with Alzheimer’s disease. Five articles contributed more than one effect size. CI, confidence interval; L, left; R, right; DLPFC, dorsolateral prefrontal cortex; atDCS, anodal transcranial direct current stimulation; ctDCS, cathodal transcranial direct current stimulation.

Figure 3

(A) Funnel plot of standard errors and effect sizes of the studies with healthy older adults included in the meta-analysis. (B) Funnel plot for studies with Alzheimer’s disease included in the meta-analysis. Red circles represent the imputed missing studies. Red rhombus shows the adjusted mean effect size.