Transcranial direct current stimulation leads to faster acquisition of motor skills, but effects are not maintained at retention

Abstract

Practice is required to improve one's shooting technique in basketball or to play a musical instrument well. Learning these motor skills may be further enhanced by transcranial direct current stimulation (tDCS). We aimed to investigate whether tDCS leads to faster attainment of a motor skill, and to confirm prior work showing it improves skill acquisition and retention performance. Fifty-two participants were tested; half received tDCS with the anode on primary motor cortex and cathode on the contralateral forehead while concurrently practicing a sequential visuomotor isometric pinch force task on Day 1, while the other half received sham tDCS during practice. On Day 2, retention of the skill was tested. Results from a Kaplan-Meier survival analysis showed that participants in the anodal group attained a pre-defined target level of skill faster than participants in the sham group (χ2 = 9.117, p = 0.003). Results from a nonparametric rank-based regression analysis showed that the rate of improvement was greater in the anodal versus sham group during skill acquisition (F(1,249) = 5.90, p = 0.016), but there was no main effect of group or time. There was no main effect of group or time, or group by time interaction when comparing performance at the end of acquisition to retention. These findings suggest anodal tDCS improves performance more quickly during skill acquisition but does not have additional benefits on motor learning after a period of rest.

Fig 1. Study design.

Study protocol for participants in the anodal and sham tDCS groups. Participants in the anodal tDCS group (Anodal Group) participated over 2 days, and participants in the sham tDCS group (Sham Group) participated over 5 days. In each day, participants performed the sequential visuomotor isometric pinch force task (SVIPT) with and without tDCS. Each black bar represents one block of practice that comprised 30 trials of practice on the SVIPT, with tDCS (anodal or sham) applied concurrently. Each hatched bar represents one block of practice that comprised 40 trials where no tDCS is applied.

Fig 2. Sequential visuomotor isometric pinch force task.

Participants navigate the on-screen cursor between the Home target (black square on the left of the screen) and four other targets, in a sequential order, ending at Target 5.

Fig 3. Performance across days of practice.

Mean skill performance (y-axis) for each block of practice across days (x-axis). Bars represent standard error. Red circles represent data associated with performance of the anodal tDCS group (Anodal Group), and black squares represent data associated with performance of the sham tDCS group (Sham Group). On day 1 block 1, there is no significant difference (NS) in performance between the Anodal and Sham Groups (t = 0.234, p = 0.816). On day 1 across both groups, there is a significant improvement in performance across blocks of practice (F(1,249) = 49.21, p<0.001). The Anodal Group also had a significantly greater increase in performance across blocks of practice as compared to the Sham Group (F(1,249) = 5.90, p = 0.015), indicated by the star (*).

Fig 4. Learning probability.

The y-axis corresponds to the percentage of participants who were unable to complete the event. The x-axis corresponds to the number of blocks of practice. At the start of the study, 100% of participants did not reach the event (i.e. y-axis “Event free probability” = 100%); this percentage drops as the study progresses over time. Fifty percent (i.e. y-axis “Event free probability” = 50%) of the anodal group (red line) completed the event by 4 blocks (i.e. x-axis “Blocks” = 4), whereas for the sham group (black line), 50% of participants completed the event by 8 blocks. These two curves are significantly different from each other (χ2 = 9.117, p = 0.003).