Bilateral tDCS on Primary Motor Cortex: Effects on Fast Arm Reaching Tasks

Abstract

BackgroundThe effects produced by transcranial direct current stimulation (tDCS) applied to the motor system have been widely studied in the past, chiefly focused on primary motor cortex (M1) excitability. However, the effects on functional tasks are less well documented.ObjectiveThis study aims to evaluate the effect of tDCS-M1 on goal-oriented actions (i.e., arm-reaching movements; ARM), in a reaction-time protocol.Methods13 healthy subjects executed dominant ARM as fast as possible to one of two targets in front of them while surface EMG was recorded. Participants performed three different sessions. In each session they first executed ARM (Pre), then received tDCS, and finally executed Post, similar to Pre. Subjects received three different types of tDCS, one per session: In one session the anode was on right-M1 (AR), and the cathode on the left-M1 (CL), thus termed AR-CL; AL-CR reversed the montage; and Sham session was applied likewise. Real stimulation was 1mA-10min while subjects at rest. Three different variables and their coefficients of variation (CV) were analyzed: Premotor times (PMT), reaction-times (RT) and movement-times (MT).Resultstriceps-PMT were significantly increased at Post-Sham, suggesting fatigue. Results obtained with real tDCS were not different depending on the montage used, in both cases PMT were significantly reduced in all recorded muscles. RT and MT did not change for real or sham stimulation. RT-CV and PMT-CV were reduced after all stimulation protocols.ConclusiontDCS reduces premotor time and fatigability during the execution of fast motor tasks. Possible underlying mechanisms are discussed.

The Impact of Transcranial Direct Current Stimulation on Upper-Limb Motor Performance in Healthy Adults: A Systematic Review and Meta-Analysis

“…This was commonly observed in unilateral (Nitsche et al, 2003b; Kantak et al, 2012; Karok and Witney, 2013; Heise et al, 2014; Dumel et al, 2016, 2018; Ehsani et al, 2016) and dual (Karok and Witney, 2013; Waters-Metenier et al, 2014) anodal motor stimulation or anodal cerebellar stimulation (Ferrucci et al, 2013; Ehsani et al, 2016; Samaei et al, 2017) with benefits consistent at 24 h retention tests as well (Shimizu et al, 2017). However, improvements were not universal throughout the literature with similar stimulation protocols (Nitsche et al, 2003b; Galea et al, 2011; Stagg et al, 2011; Lindenberg et al, 2013, 2016; Heise et al, 2014; Ambrus et al, 2016; Arias et al, 2016; Horvath et al, 2016; Focke et al, 2017; Apšvalka et al, 2018). Interestingly, RT worsened with cathodal stimulation regardless of site (Leite et al, 2011; Stagg et al, 2011; Carlsen et al, 2015; Shimizu et al, 2017), potentially due to reduced motor cortex excitability with cathodal tDCS (Nitsche et al, 2003a).…”

Ergogenic Effects of Bihemispheric Transcranial Direct Current Stimulation on Fitness: a Randomized Cross-over Trial

“…In fact, young bodybuilders improved their knee extension tests (i. e. onerepetition maximum; short-term muscular endurance index) when they were excited over the M1 leg area and left temporal area [40]. In this regard, bilateral tDCS of M1 has been demonstrated to improve motor tasks, such as fast arm reaching tasks [41]. M1 is the elective brain area to modulate both bimanual tests [42] or unimanual tasks [43].…”

Stimulating the Healthy Brain to Investigate Neural Correlates of Motor Preparation: A Systematic Review

“…Patterned rTMS was also used in 6 studies using cTBS [ 31 , 58 – 61 ] or both cTBS and iTBS [ 62 ]. Finally, 7 studies used tDCS [ 63 – 69 ].…”

“…For rTMS studies, sham condition was applied on a control site not involved in the motor preparation [ 48 , 51 , 52 , 59 ] or at the same experimental stimulation position with the coil angled at approximately 45° from the scalp [ 44 , 45 , 50 , 54 , 55 ], to mimic sensation and noise artifacts of TMS without depolarizing cortical neurons [ 70 ]. For tDCS studies, five studies used a single-blind or double-blind sham condition consisting in applying 1 mA current (<30 s ramp-up time) then shutting off the current for the rest of the stimulation period, to generate similar scalp sensations than during the first seconds of stimulation without modulating neural activity [ 63 – 66 ].…”

“…Two high-quality studies applying anodal tDCS over the M1 reported no significant effect [ 65 , 69 ]. Four others studies using either high-frequency rTMS or anodal tDCS applied over the M1 also failed to reveal any effect on RT [ 44 , 55 , 56 , 63 ]. Only one recent study using anodal tDCS over the right and left M1 showed a decreased in a precued choice RT paradigm [ 66 ].…”