Priming the primary motor cortex with transcranial direct current stimulation: Effect on learning the golf putt

Abstract

Background: Priming the primary motor cortex (M1) with transcranial direct current stimulation (tDCS) prior to motor practice modulates post-synaptic activity, thereby impacting learning of a motor skill. This effect has been shown for the acquisition of simple motor skills. It is not clear whether priming tDCS can impact the learning/retention of a more naturalistic motor task.

Objective/hypothesis: We investigated the effects of priming M1 with tDCS on the performance on a golf putting task. We hypothesized that participants who receive tDCS with the cathode over M1 (C-M1) would show better skill acquisition and retention performance, relative to participants who receive tDCS with the anode over M1 (A-M1) or sham tDCS.

Methods: Thirty-six participants were randomized into three groups: C-M1, A-M1, and sham tDCS. Participants received tDCS (1mA, 20 minutes) prior to practicing golf putting across two days. Performance (error) was measured for each putt. Participants returned on the third day for a retention test.

Results: After accounting for baseline performance, the C-M1 group performed significantly better compared to A-M1 [p = 0.02] and sham tDCS [p = 0.01] at the retention test. There was no difference in retention performance between A-M1 and sham tDCS.

Conclusion: Our findings partially support the Bienenstock-Cooper-Munro rule of metaplasticity. C-M1 tDCS priming enhanced motor learning, while A-M1 tDCS priming had no effect, relative to sham.

Fig 1. Study design.

On the first session, participants completed a pre-test, received transcranial direct current stimulation (tDCS), trained on the golf putting task, and completed a post-test. On the second session, participants completed a retention test (first retention), received tDCS, trained on the golf putting task, and completed another post-test. On the third session, participants completed a retention test (second retention) and two transfer tests on the golf putting task. Questionnaires were completed throughout the three sessions (see Section 2.5).

Fig 2. Golf putting green.

Figure is not to scale. The golf putting green has three targets. Target 1, Target 2, and Target 3 were 192 cm, 213 cm, and 234 cm from the home position, respectively. Targets were lit up using LEDs. Both transfer tests consisted of 12 trials to Target 2. To achieve this, the starting spot for the ball was moved 250 cm and 100 cm from Target 2 for the long and short transfer tests, respectively.

Fig 3. Data collection device.

An InfraRed Emitting Diode was connected to a device. Following each putt, the device was placed on top of the ball to collect ball end-point location using the Optotrak motion tracking system.

Fig 4. Baseline performance.

The x-axis displays the performance block at baseline (pre-test). The y-axis on the figure displays radial error (mm). Group mean radial error is plotted for each of the three groups (A-M1 (○), C-M1(▲), and sham (□)). Individual mean radial error is plotted for each participant (small circles). The error bars reflect standard deviation. A-M1 refers to tDCS with the anode over M1. C-M1 refers to tDCS with the cathode over M1.

Fig 5. Motor skill acquisition.

The x-axis displays performance blocks across day 1 (B1 – B5) and day 2 (B6 – B10) of acquisition. The y-axis displays radial error (mm). Group mean radial error is plotted for each of the three groups (A-M1 (○), C-M1 (▲), and sham (□)). Individual mean radial error is plotted for each participant (small circles). The error bars reflect standard deviation. A-M1 refers to tDCS with the anode over M1. C-M1 refers to tDCS with the cathode over M1.

Fig 6. Motor skill retention.

The x-axis in the figure displays performance blocks. The y-axis displays radial error (mm). Group mean radial error is plotted for each of the three groups (A-M1 (○), C-M1 (▲), and sham (□)). Individual mean radial error is plotted for each participant (small circles). The error bars reflect standard deviation. A-M1 refers to tDCS with the anode over M1. C-M1 refers to tDCS with the cathode over M1.

Fig 7. Motor skill transfer.

The x-axis displays the performance block. Transfer (long) refers to the long transfer test (250 cm) and Transfer (short) refers to the short transfer test (100 cm). The y axis displays error (mm). Group mean radial error is plotted for each of the three groups (A-M1 (○), C-M1 (▲), and sham (pone.0324983)). Individual mean radial error is plotted for each participant (small circles). The error bars reflect standard deviation. A-M1 refers to tDCS with the anode over M1. C-M1 refers to tDCS with the cathode over M1.