Parkinson's disease is characterized by a large number of non motor, especially neuropsychiatric, signs. Their pathophysiology is complex but the role of dopaminergic and serotoninergic systems dysfunction is suggested by several studies. In addition, the serotoninergic system is involved in the pathophysiology of dyskinesias. Very few studies have analyzed the abnormalities of these two neurotransmission systems at disease onset, in de novo PD patients. Furthermore, the parallel evolution of the degeneration of the dopaminergic and serotoninergic systems with disease progression remains unknown. Thus the present study aims at determining, by using PET and 11C-PE2I and 11C-DASB the respective role of the serotoninergic and dopaminergic systems dysfunction in motor and non motor manifestations in PD, at different evolution stages.