This is a multi-centre study to be conducted in Sweden and Finland. Up to 24 male and/or female patients of non-childbearing potential aged 45 to 75 years (inclusive), with a clinical diagnosis Parkinson's Disease will be randomised in the study to allow for 20 patients to complete this study.The study will evaluate the effect of 8 weeks treatment with AZD3241 on microglia activation as measured via PET examinations.