Motor Learning and tDCS in Parkinson's Disease

The Effect of Single Session Transcranial Direct Current Stimulation on Sequential Motor Learning in Parkinson's Disease

The present study sought to examine the efficacy of single 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 sought to examine the effect of a single session of transcranial direct current stimulation applied over the primary motor cortex in people with Parkinson's disease on sequential motor learning performance. Participants learnt two finger tapping sequences, with task difficulty indexed by sequence length, and task consolidation further examined using a dual-task paradigm. Task related cortical haemodynamic activity was recorded using functional near-infrared spectroscopy.

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 period prior to the specified stimulation period and phased-out with a ramp down of the current following the specified stimulation period. For sham stimulation, the ramp-up and ramp-down periods are retained, but stimulation is switched off for during the specified stimulation period.

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

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

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

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) Exclusion Criteria: History of stroke Comorbidity Cephalic implants