Cortical EEG network analysis reveals stage-specific rich-club reorganization across the patients with iRBD and PD.

Idiopathic rapid eye movement sleep behavior disorder (iRBD) has been recognized as a prodromal stage of Parkinson's disease (PD) - a well-known neurodegenerative brain disorder that is characterized by dysconnectivity. Elucidating how brain network topology evolves across the healthy controls (HCs)-iRBD-PD cohorts is crucial for clarifying disease-stage-related neurophysiological alterations. Using EEG source-space connectivity, we aimed to reveal the stage-specific spatio-spectral alterations of rich-club organization (the network's backbone architecture) across these three cohorts. Resting-state high-density EEG data was recorded from 104 participants (HCs/iRBD/PD = 32/33/39). Functional brain networks were estimated via source reconstructed and quantitatively compared across groups. A robust rich-club architecture was identified in all groups, with hubs primarily residing in parietal and temporal areas and exhibiting leftward dominance in the δ, θ, and β bands. Statistical comparisons revealed a significant graded enhancement of rich-club metrics (specifically local connection strength, global efficiency within feeder subnetwork, rich-club-feeder and feeder-local internetworks), predominantly in the θ band, across the three groups. This graded hyperconnectivity likely underscores a disease-stage-dependent reorganization, manifesting as a complex interplay between early compensatory responses and maladaptive pathological synchronization. These findings highlight EEG-based rich-club metrics as potential non-invasive biomarkers for characterizing the PD continuum and provide nascent insights into the neurophysiological mechanisms underlying PD-related disorders.