Deposition and spreading of misfolded proteins have been linked to cognitive dysfunction in Parkinson’s disease (PD). The glymphatic system responsible for removing brain wastes thus may play a role in cognitive impairment in PD. This hypothesis is however difficult to test in clinical populations due to the lack of non-invasive measurements of glymphatic function. Low-frequency (< 0.1 Hz) resting-state fMRI (rsfMRI) signal was recently linked to glymphatic function primarily based on its sleep-dependent coupling with CSF flows. This study found early evidence that the coupling of global rsfMRI and CSF signals is indeed related to cognitive decline in PD.