Cognitive dysfunction is relatively common in Parkinson’s disease (PD), with approximately 50% of patients developing at least a mild cognitive impairment during the course of their disease. Cognitive dysfunction is heterogeneous and may include deficits in flexibility, planning, attention, concentration, working memory, problem solving, reinforcement learning and verbal fluency. Dementia is a common and disabling symptom, occurring in 30-40% of patients and increasing in severity as the disease progresses, so that up to 80-90% of patients with advanced PD may have dementia.