Motor Learning and Multi-session tDCS in Parkinson's Disease

The Effect of Multi-session Transcranial Direct Current Stimulation Applied Over the Primary Motor Cortex on Motor Sequence Learning in Parkinson's Disease

The present study seeks to examine the efficacy of multi-session transcranial direct current stimulation applied over the primary motor cortex in people with Parkinson's disease on sequential motor learning performance.

Parkinson's disease is characterised by deficits of motor control triggered by impaired basal ganglia function, such as bradykinesia and tremor. Beyond the visibly recognisable motor symptoms of Parkinson's disease, the ability to learn a sequence of movements is also compromised and poses a significant barrier to effective rehabilitation. In healthy individuals, transcranial direct current stimulation applied over the primary motor cortex during motor task practice has been shown to significantly improve motor learning compared to placebo conditions. The present study seeks to examine the effect of multi-session transcranial direct current stimulation applied over the primary motor cortex in people with Parkinson's disease on sequential motor learning performance. Participants will be required to attend eight laboratory sessions, comprising five intervention and three assessment sessions and will be tested on their ability to learn a 16-digit finger tapping sequence with their right hand. Sessions one to five will form the intervention and will be performed at the same time on consecutive days (i.e. mon-fri). In addition, session one will double as a baseline assessment and intervention session. Assessments sessions will be performed once before the intervention (session one), and three times following the intervention on day three, one week, and four weeks post intervention.

Anodal electrode (35 cm2 sponge electrode) placed over C3. Cathodal electrode (35 cm2 sponge electrode) placed over the right supraorbital area. 20 minutes of stimulation at 2 mA with a 30-second phase-in and phase-out period.

Cathodal electrode (35 cm2 sponge electrode) placed over C3. Anodal electrode (35 cm2 sponge electrode) placed over the right supraorbital area. 20 minutes of stimulation at 2 mA with a 30-second phase-in and phase-out period.

Anodal electrode (35 cm2 sponge electrode) placed over C3. Cathodal electrode (35 cm2 sponge electrode) placed over the right supraorbital area. Stimulation was phased in for 30 seconds up to 2 mA and then switched off. Stimulation was again phased in for 30 seconds following 20 minutes of no stimulation.

Transcranial electrical stimulation device. A weak direct electrical current, up to 2 mA, is passed between two electrodes placed on the scalp. Electrodes are housed in 35 cm2 sponges saturated with 4 ml of saline solution (0.9 % NaCl) per side, per pad. Stimulation is phased in with a 30-second ramp up of the electrical current to the specified stimulation parameters. Following the specified stimulation period, the current is phased-out with a ramp down of the current. For sham stimulation, the ramp-up and ramp-down periods are retained, but stimulation is switched off during the specified stimulation period.

A skill index reflecting the accuracy and speed that participants perform a specified finger tapping sequence.

Four assessments: Baseline (pre-intervention), 3 days, 1 week, and 4 weeks post intervention. Performance is also assessed during the intervention period on each day the intervention is applied. Once immediately before and after intervention is applied.

The percentage of shape counting error during dual task assessments. Sequential finger tapping + visual shape counting task.

Four assessments: Baseline (pre-intervention), 3 days, 1 week, and 4 weeks post intervention. Performance is also assessed during the intervention period on each day the intervention is applied. Once immediately before and after intervention is applied.

Task related changes of oxygenated haemoglobin as measured using functional near-infrared spectroscopy.

Four assessments: Baseline / pre-intervention, three-days post intervention, 1 week post intervention, and 4 weeks post intervention

Change from baseline: Movement Disorders Society Unified Parkinson's Disease Rating Scale Motor Section (Part 3)

Participants physical function is assessed according to the criteria of the Movement Disorders Society Unified Parkinson's Disease Rating Scale Motor Section (Part 3). Minimum value = 0, maximum value = 132. Lower scores indicate a better outcome.

Four assessments: Baseline / pre-intervention, three-days post intervention, 1 week post intervention, and 4 weeks post intervention

Timed sequential movement of the arm and hand. The participant sits upright on a chair that has no arm support with their arms relaxed by their side. The time taken to perform the following sequence 10 times is recorded: 1. Close and open hand, 2) flex elbow, 3) close and open hand, 4) extend elbow. Right and left arms are assessed separately.

Four assessments: Baseline / pre-intervention, three-days post intervention, 1 week post intervention, and 4 weeks post intervention

Participants are required to pick up a metal peg and place the peg in a specified row of holes. Pegs must be placed one at a time. The maximum number of pegs placed within 30 seconds is recorded. The assessment is repeated three times for each hand. Each hand is assessed separately.

Four assessments: Baseline / pre-intervention, three-days post intervention, 1 week post intervention, and 4 weeks post intervention

Inclusion Criteria: Right-handed (Edinburgh Handedness Inventory; ≥50) Cognitively capable (Montreal Cognitive Assessment (MoCA); ≥23) Mild to moderate Parkinson's disease severity (Hoehn and Yar disease stage 2-3) On stable dopaminergic medication Exclusion Criteria: History of stroke Comorbidity Cephalic implants