BACKGROUND: Rapid eye movement (REM) sleep behavior disorder (RBD) may precede motor symptoms in Parkinson's disease (PD) by years. According to a recent hypothesis, premotor RBD (pRBD) is a marker of the PD body-first subtype, where synucleinopathy originates from the peripheral autonomic nervous system. Conversely, in the brain-first subtype, pathology would arise in the brain. Functional connectivity (FC) could provide additional insight into the neurodegenerative process of these putative PD subtypes. OBJECTIVES: We aim to analyze the possible FC differences between early-stage PD patients with (PD METHODS: We enrolled 28 PD RESULTS: We found a significant trend of decreased α-FC across PD CONCLUSIONS: Compared to PD