Effects of tDCS on motor learning and memory formation: A consensus and critical position paper

Abstract

Motor skills are required for activities of daily living. Transcranial direct current stimulation (tDCS) applied in association with motor skill learning has been investigated as a tool for enhancing training effects in health and disease. Here, we review the published literature investigating whether tDCS can facilitate the acquisition and retention of motor skills and adaptation. A majority of reports focused on the application of anodal tDCS over the primary motor cortex (M1) during motor skill acquisition, while some evaluated tDCS applied over the cerebellum during adaptation of existing motor skills. Work in multiple laboratories is under way to develop a mechanistic understanding of tDCS effects on different forms of learning, and to optimize stimulation protocols.Efforts are required to improve reproducibility and standardization. Overall, reproducibility remains to be fully tested, effect sizes with present techniques are moderate (up to d= 0.5) (Hashemirad, Zoghi, Fitzgerald, & Jaberzadeh, 2016) and the basis of inter-individual variability in tDCS effects is incompletely understood. It is recommended that future studies explicitly state in the Methods the exploratory (hypothesisgenerating) or hypothesis-driven (confirmatory) nature of the experimental designs. General research practices could be improved with prospective pre-registration of hypothesis-based investigations, more emphasis on detailed description of methods and use of post-publication open data repositories. A checklist is proposed for reporting tDCS investigations in a way that can improve efforts to assess reproducibility.

Effects of High-Definition Anodal Transcranial Direct Current Stimulation Applied Simultaneously to Both Primary Motor Cortices on Bimanual Sensorimotor Performance

“…There was still a significant and strong effect of the stimulation, which means that the significant interaction was not only attributable to baseline performance differences but also considerably to the stimulation itself. Generally, our results support previous studies reporting positive tDCS effects on unimanual motor behavior (for a review, see Buch et al, 2017) and extend these findings to bimanual motor performance (Gomes-Osman and Field-Fote, 2013; Pixa et al, 2017). …”

“…Such positive tDCS effects on motor skills have been reported for single-session applications, as well as for multiple applications over several days of training (Vines et al, 2008; Reis et al, 2009, 2015; Schambra et al, 2011; Saucedo Marquez et al, 2013; Waters-Metenier et al, 2014), with prolonged improvement of up to 3 months (Reis et al, 2009), suggesting an impact on neuroplasticity mediated by synaptic long-term potentiation (LTP) within the motor cortex (Liebetanz et al, 2002; Reis and Fritsch, 2011; Stagg and Nitsche, 2011). Unfortunately, most tDCS studies have focused almost exclusively on unimanual motor performance (for an overview, see Buch et al, 2017). …”

Remotely Supervised Transcranial Direct Current Stimulation Increases the Benefit of At-Home Cognitive Training in Multiple Sclerosis

“…It is theorized that pairing tDCS with rehabilitation strategies may lead to more meaningful and lasting benefit . A particularly promising application of tDCS is to improve the rate of learning and magnitude of benefit from cognitive training (CT) . While many questions remain, pairing tDCS with CT has been shown to increase learning and cognitive performance, particularly in tasks of information processing and working memory .…”

Effects of transcranial direct-current stimulation on laparoscopic surgical skill acquisition

“…Based on the ability of tDCS to enhance simple motor26 and complex tumour resection25 skill acquisition, it was hypothesized that anodal tDCS over the dominant primary motor cortex would enhance the acquisition of two FLS skills.…”