Increased aperiodic offset and heightened alpha power characterize resting-state EEG activity in Parkinson's disease

Parkinson's disease (PD) is characterized by widespread neurodegeneration across neuromodulatory systems, profoundly affecting cortico-basal ganglia-thalamic loops. The resulting cortical alterations can be detected with electroencephalography (EEG). Emerging evidence shows that non-oscillatory, aperiodic EEG activity provides meaningful information that complements the oscillatory, periodic features traditionally examined. Nonetheless, available information on periodic alpha and beta power as well as aperiodic features in PD patients during the OFF-medication state are inconclusive. Moreover, replicability of spectral EEG findings across different EEG systems has received little attention. Herein, we aimed at characterizing aperiodic and periodic EEG signatures in PD during OFF-medication resting-state and examining their relationships with age, disease duration, and levodopa-induced dyskinesias. Resting-state EEG was recorded from forty patients with PD OFF-medication and twenty-six age- and sex-matched healthy controls, and a subset of patients and controls returned for a second visit using a different EEG amplifier. Power spectra were parametrized to extract aperiodic parameters (exponent and offset, i.e. the slope and the intercept of the broadband signal, respectively) and power in the alpha and beta frequency bands, adjusted for the aperiodic component. Bayesian statistical tests were used to assess between-group differences and associations with clinical (MDS-UPRDS-III, LEDD, disease duration) and demographic (age) variables. We found that aperiodic offset and alpha power were higher in patients than controls across all channels (BF10=80.74; BF10=26.81) and when restricting analysis to pericentral channels (BF10=70.75; BF10=16.90). These differences were equally expressed in patients with and without a positive history of levodopa-induced dyskinesias and replicated at follow-up using a different EEG recording system. In patients, aperiodic offset and exponent, but not periodic alpha or beta power, scaled positively with age and disease duration (BF10=2.16-9.76). The successful replication of increased aperiodic offset and periodic alpha power highlights their potential as robust neurophysiological markers of PD, while aperiodic parameters may track disease duration.