Abstract
Background: Transcranial direct current stimulation (tDCS) has previously been reported to improve facets of upper limb motor performance such as accuracy and strength. However, the magnitude of motor performance improvement has not been reviewed by contemporaneous systematic review or meta-analysis of sham vs. active tDCS.Objective: To systematically review and meta-analyse the existing evidence regarding the benefits of tDCS on upper limb motor performance in healthy adults.Methods: A systematic search was conducted to obtain relevant articles from three databases (MEDLINE, EMBASE, and PsycINFO) yielding 3,200 abstracts. Following independent assessment by two reviewers, a total of 86 articles were included for review, of which 37 were deemed suitable for meta-analysis.Results: Meta-analyses were performed for four outcome measures, namely: reaction time (RT), execution time (ET), time to task failure (TTF), and force. Further qualitative review was performed for accuracy and error. Statistically significant improvements in RT (effect size −0.01; 95% CI −0.02 to 0.001, p = 0.03) and ET (effect size −0.03; 95% CI −0.05 to −0.01, p = 0.017) were demonstrated compared to sham. In exercise tasks, increased force (effect size 0.10; 95% CI 0.08 to 0.13, p < 0.001) and a trend towards improved TTF was also observed.Conclusions: This meta-analysis provides evidence attesting to the impact of tDCS on upper limb motor performance in healthy adults. Improved performance is demonstrable in reaction time, task completion time, elbow flexion tasks and accuracy. Considerable heterogeneity exists amongst the literature, further confirming the need for a standardised approach to reporting tDCS studies.
Highlights
Transcranial Direct Current Stimulation is a noninvasive method of brain stimulation proposed to have beneficial effects in both cognitive and motor domains
Randomization was utilized in 78% of studies but only 14% were deemed to sufficiently explain methods used for random sequence generation
Considerable heterogeneity exists amongst the literature, further confirming the need for a standardised approach to reporting Transcranial Direct Current Stimulation (tDCS) studies
Summary
Transcranial Direct Current Stimulation (tDCS) is a noninvasive method of brain stimulation proposed to have beneficial effects in both cognitive and motor domains. Benefits have been demonstrated in patients with chronic pain syndromes (Fregni et al, 2006; Fenton et al, 2009; Fagerlund et al, 2015) and neuropsychiatric conditions (Baker et al, 2010; Loo et al, 2012; Palm et al, 2012; Kaski et al, 2014; Bandeira et al, 2016; Breitling et al, 2016), whilst in the healthy population, there is increasing scientific interest in the motor enhancing properties of the technology Aligning with this trend, an increasing number of commercial companies (Edwards et al, 2017) promote the augmentation of motor abilities with tDCS including greater muscular power output (Okano et al, 2015; Huang et al, 2019), longer athletic endurance (Vitor-Costa et al, 2015; Park et al, 2019) and improved posture and balance (Kaminski et al, 2016; Saruco et al, 2017). The magnitude of motor performance improvement has not been reviewed by contemporaneous systematic review or meta-analysis of sham vs. active tDCS
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