tDCS of the Primary Motor Cortex to Improve Implicit Motor Sequence Learning in Parkinson's Disease

Implicit motor sequence learning (IMSL) is a form of cognitive function that is known to be directly associated with impaired motor function in Parkinson's disease (PD). Research in healthy young participants shows the potential for transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, over the primary motor cortex (M1) to enhance IMSL. tDCS has direct effects on the underlying cortex, but also induces distant (basal ganglia) network effects - hence its potential value in PD, a prime model of basal ganglia dysfunction. To date, however, only null-effects have been reported in persons with PD. In the present study, the investigators will investigate the potential of tDCS delivered over M1 to enhance IMSL, as measured by the Serial Reaction Time task, in persons with PD. The investigators will determine immediate effects that may occur concurrently with the application of tDCS but also short-term (five minutes post-tDCS) and long-term (one week post-tDCS) consolidation effects, as previous studies suggest that tDCS exerts its beneficial effects on IMSL in a consolidation phase rather than in an acquisition phase. Establishing possible consolidation effects is of a particular interest, as long-term effects are vital for the successful functional rehabilitation of persons with PD.

Inclusion Criteria: * diagnosed with the idiopathic form of PD by a neurologist (PD subjects only) * Dutch or French speaking * sufficient upper limb motor skills to perform the SRT-task (determined by means of a practice version of the SRT-task consisting of one block of 50 random trials) * able to signal pain or discomfort * able to give informed consent Exclusion Criteria: * additional neurological disorders * any of the following tDCS contra-indications: deep brain stimulator; pacemaker; head wound; skin condition of the scalp; a history of epilepsy