Gait impairments in PD are often resistant to treatment, particularly as the disease progresses. Therefore, insight in the pathophysiology of gait disturbances is essential for improving treatment options and quality of life for PD patients. This study will answer the question of whether cerebellar hyperactivity alleviates or worsens gait deficits in PD patients. If cerebellar hyperactivity in PD is compensatory, anodal (i.e. excitatory) tDCS should improve gait in PD patients, whereas cathodal (i.e. inhibitory) tDCS will make matters worse. In contrast, if cerebellar hyperactivity is pathological, cathodal tDCS will improve gait and anodal tDCS will worsen it. Hence, this study will improve the fundamental understanding of gait pathophysiology in PD patients. The investigators will focus on the aspects of gait that are particularly affected in PD and associated with fall risk, such as stride length and gait speed (Paul et al. 2013). In this way, this study may identify the cerebellum as a potential new target for treatment, opening up new possibilities improving gait and balance disturbances in PD.