Plasma levels of catalase (CAT), total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), total glutathione (T-GSH) and malondialdehyde (MDA) were measured by ELISA . 
ELISA
Cognition function of all the patients with PD and the controls were measured by using Montreal Cognitive Assessment (MoCA) scale. 
Montreal Cognitive Assessment (MoCA)