Anodal Transcranial Direct Current Stimulation Enhances Retention of Visuomotor Stepping Skills in Healthy Adults

Abstract

Transcranial direct current stimulation (tDCS) paired with exercise training can enhance learning and retention of hand tasks; however, there have been few investigations of the effects of tDCS on leg skill improvements. The purpose of this study was to investigate whether tDCS paired with visuomotor step training can promote skill learning and retention. We hypothesized that pairing step training with anodal tDCS would improve skill learning and retention, evidenced by decreased step reaction times (RTs), both immediately (online skill gains) and 30 min after training (offline skill gains). Twenty healthy adults were randomly assigned to one of two groups, in which 20-min anodal or sham tDCS was applied to the lower limb motor cortex and paired with visuomotor step training. Step RTs were determined across three time points: (1) before brain stimulation (baseline); (2) immediately after brain stimulation (P0); and (3) 30 min after brain stimulation (P3). A continuous decline in RT was observed in the anodal tDCS group at both P0 and P3, with a significant decrease in RT at P3; whereas there were no improvements in RT at P0 and P3 in the sham group. These findings do not support our hypothesis that anodal tDCS enhances online learning, as RT was not decreased significantly immediately after stimulation. Nevertheless, the results indicate that anodal tDCS enhances offline learning, as RT was significantly decreased 30 min after stimulation, likely because of tDCS-induced neural modulation of cortical and subcortical excitability, synaptic efficacy, and spinal neuronal activity.

Effects of Transcranial Direct Current Stimulation Combined With Physical Training on the Excitability of the Motor Cortex, Physical Performance, and Motor Learning: A Systematic Review

“…Fifteen studies implemented a double-blinded design (Vines et al, 2008;Reis et al, 2009Reis et al, , 2013Williams et al, 2010;Kang and Paik, 2011;Thirugnanasambandam et al, 2011;Goodwill et al, 2013;Hendy and Kidgell, 2013;Kim and Ko, 2013;Fujimoto et al, 2014;Steiner et al, 2016;Rumpf et al, 2017;Baltar et al, 2018;Yosephi et al, 2018;Jafarzadeh et al, 2019), in which both the study personnel and participants were not aware of the types of intervention. Five studies used a single-blinded design (Stagg et al, 2011;Naros et al, 2016;Zandvliet et al, 2018;Bruce et al, 2020;Tseng et al, 2020), and the blinding was not reported in other four studies (Karok and Witney, 2013;Looi et al, 2016;Washabaugh et al, 2016;Chen et al, 2020).…”

“…The total number of recruited participants was 784 (462 males and 322 females, age range: 18-80 years). For the design of tDCS, 19 studies used tDCS to target the M1 (Vines et al, 2008;Reis et al, 2009Reis et al, , 2013Williams et al, 2010;Kang and Paik, 2011;Stagg et al, 2011;Thirugnanasambandam et al, 2011;Goodwill et al, 2013;Hendy and Kidgell, 2013;Karok and Witney, 2013;Kim and Ko, 2013;Naros et al, 2016;Washabaugh et al, 2016;Rumpf et al, 2017;Baltar et al, 2018;Jafarzadeh et al, 2019;Bruce et al, 2020;Chen et al, 2020;Tseng et al, 2020), two studies targeted the cerebellum (Steiner et al, 2016;Zandvliet et al, 2018), one study targeted both the M1 and the cerebellum (Yosephi et al, 2018), one study targeted the primary somatosensory cortex (Fujimoto et al, 2014), and one study targeted the dorsolateral prefrontal cortex (Looi et al, 2016). The current intensities of tDCS were between 1.5 and 2 mA, and the duration of each stimulation session was between 15 to 20 min.…”

“…The size of the electrodes was between 35 and 40 cm 2 . Most studies used sham protocol as the control, in which the current was delivered only during the initial period of each session (i.e., the first 15 to 30 s) and then turned off (Vines et al, 2008;Reis et al, 2009Reis et al, , 2013Williams et al, 2010;Kang and Paik, 2011;Stagg et al, 2011;Thirugnanasambandam et al, 2011;Goodwill et al, 2013;Hendy and Kidgell, 2013;Karok and Witney, 2013;Kim and Ko, 2013;Fujimoto et al, 2014;Looi et al, 2016;Naros et al, 2016;Steiner et al, 2016;Washabaugh et al, 2016;Rumpf et al, 2017;Baltar et al, 2018;Yosephi et al, 2018;Zandvliet et al, 2018;Jafarzadeh et al, 2019;Chen et al, 2020;Tseng et al, 2020); One study used the sham protocol that delivered current during the initial 120 s (Bruce et al, 2020). Different timing of applying tDCS was used.…”

“…Different timing of applying tDCS was used. Two studies applied tDCS before physical training (Thirugnanasambandam et al, 2011;Baltar et al, 2018), and two studies conducted tDCS after physical training (Rumpf et al, 2017;Chen et al, 2020); The other 20 studies applied tDCS during the physical training (Vines et al, 2008;Reis et al, 2009Reis et al, , 2013Williams et al, 2010;Kang and Paik, 2011;Stagg et al, 2011;Goodwill et al, 2013;Hendy and Kidgell, 2013;Karok and Witney, 2013;Kim and Ko, 2013;Fujimoto et al, 2014;Looi et al, 2016;Naros et al, 2016;Steiner et al, 2016;Washabaugh et al, 2016;Yosephi et al, 2018;Zandvliet et al, 2018;Jafarzadeh et al, 2019;Bruce et al, 2020;Tseng et al, 2020).…”

“…Two types of tDCS are commonly used, that is, anodal tDCS (a-tDCS) aiming to increase the excitability of the targeting cortical regions by depolarizing the resting membrane potentials of neurons, and cathodal tDCS (c-tDCS) that often induces inhibitory effects of neural excitability in the targeted brain regions Paulus, 2000, 2001;Bastani and Jaberzadeh, 2012). Recent studies in the field of sports sciences have shown that using tDCS can significantly enhance physical performance, such as the toe abduction strength (Tanaka et al, 2009) and reaction time (Tseng et al, 2020) in healthy people and the knee extensor force in patients with hemiparetic stroke. Several previous systematic reviews have also confirmed that using tDCS can induce benefits to important functionalities, such as motor control, in different populations (e.g., people with Parkinson's disease (PD) (Broeder et al, 2015) and healthy cohorts (Machado et al, 2019).…”