Slow Oscillation Dynamics During NREM Sleep in Parkinson’s Disease: A Continuous Spectral Framework for Power, Coupling, and Neurophysiological Profiling

Sleep plays a critical role in synaptic regulation, memory consolidation, and neural recovery. According to the Synaptic Homeostasis Hypothesis (SHY), delta-band activity (typ- ically 1–4 Hz) during non-REM (NREM) sleep reflects a homeostatic process of synaptic downscaling, characterized by a progressive decline across the night. While previous studies have focused on delta power as an index of sleep pressure, the present work targeted a slower spectral component—slow oscillations (SO, <1.5 Hz)—to investigate their topographic modulation and potential sensitivity to neurodegeneration in Parkinson’s disease (PD), where sleep regulation may be disrupted. Sleep-related cortical dynamics were analyzed in four groups by exploiting high-density EEG recordings: healthy controls (CTL), drug-naive patients (DNV), advanced patients without dyskinesias (ADV), and patients with levodopa-induced dyskinesias (DYS). This stratification was designed to capture the heterogeneity of disease progression and treatment effects. Global analysis involved extracting SO power (0.3–1.5 Hz) from NREM sleep and modeling changes using linear mixed-effects models with spatial correction. A significant frontal cluster of SO power reduction from mid to late NREM was observed in the CTL group, consistent with typical downscaling. In contrast, no significant change emerged in the DYS group, suggesting impaired homeostatic regulation. The ADV group showed an abnormally strong downscaling pattern, while the DNV group exhibited a lateralized reduction of SO power only over the right hemisphere, possibly reflecting early asymmetric pathology. Local analysis with the PyDYNAMO toolbox - a data-driven package identifying EEG time-frequency peaks - identified transient oscillatory events. Contrary to expectations, no significant reduction in sigma power was found in PD groups, despite known spindle alterations. This may be due to the inclusion of diverse oscillatory phenomena within the sigma band beyond canonical spindles. However, a significant reduction in frontal theta peak density was detected in DYS patients. Other trends included increased alpha low peak density in DYS and enhanced fast