On the Effects of Transcranial Direct Current Stimulation on Hand Movement in Parkinson's Disease: A Primary Study

Parkinson's disease (PD) is a neurodegenerative disorder that mainly affects the motor areas of patients, although cognitive disorders are common among them, too. Various invasive and non-invasive neuromodulations have been proposed for treatment of the symptoms of PD, in which tDCS is one of the emerging methods. In this study, six right-handed patients with PD in drug-off condition were stimulated with 2mA tDCS in left primary motor cortex (Ml) for 20 minutes. Two new tasks were performed by the participants thrice pre and post stimulation to limit the effects of learning or anxiety. The trajectory signals of their hand movements were recorded using a graphical tablet. To investigate the effects of tDCS on the performance of hand movement in the participants, various features were extracted from the signals. Wilcoxon signed-rank test was applied to statistically evaluate them. The results showed that the time, velocity, acceleration and Approximate Entropy (ApE n) of participants improved significantly (p <; 0.05) in spiral drawing task. PCA was also performed on difference of velocity signals. Ratio of power in 0.1-5 Hz to 5-10 Hz, peak of frequency, and Lyapunov exponent of first principle component showed meaningful changes (p <; 0.05). However, tDCS had no significant effects on the performance of writing a Farsi sentence. The features extracted from the standardized motor tasks provided in this study indicated that tDCS could be capable of improving hand movement in PD.