AIM: To investigate whether SV2A loss spreads from brainstem to cerebral cortex with progression of Parkinson's disease (PD) and to determine whether longitudinal cortical SV2A loss correlates with cognitive decline in PD. STUDY DESIGN: The investigators will re-invite participants (both patients with PD and healthy controls) of a previous longitudinal study (NCT04243304, S61477) to undergo evaluation approximately 7 years after the initial baseline study visit (i.e. on average 10 years since the first motor symptoms). All participants will undergo clinical assessment of motor and non-motor symptoms (including cognitive testing), as well as 11C-UCB-J PET-CT (targeting synaptic density marker SV2A), 18F-FE-PE2I PET-CT (targeting DAT) and brain MRI.