Different features of the cortical sensorimotor rhythms are uniquely linked to the severity of specific symptoms in Parkinson's disease

Parkinson's disease (PD) is associated with functional changes in the neural activity within the brain's sensorimotor network, which in turn are related to the characteristic motor symptoms in PD. The functional changes in PD are particularly prominent in terms of oscillatory neuronal activity in the characteristic sensorimotor alpha and beta rhythms. However, summaries in terms of alpha or beta power do not capture the full range of the complex dynamic nature of the signals from the somatosensory cortex. This raises the question of how to quantify and summarise the functional changes in such oscillatory features in a manner that captures the relevant disease- and symptom-related neural activity. We investigated the role of spontaneous cortical somatosensory activity in the electrophysiological alpha and beta bands among a cohort of early- to mid-stage PD patients (N=78) and age- and gender-matched healthy controls (N=60) using source reconstructed resting-state magnetoencephalography (MEG) recordings. We quantified the oscillatory features of the neural time series by its oscillatory alpha power, beta power, and 1/f broadband characteristics using power spectral density, and additionally by characterising "burst" properties in the signals. We examined the relationship between the signal features and disease state, age, sex, and cortical thickness. Using multiple regression, we examined the relative contribution of the oscillatory features on the clinical manifestation of motor symptoms in the PD group. Our results show that PD patients differ from healthy controls on several of the oscillatory features, showing higher beta-band power, higher burst amplitude, and steeper 1/f broadband characteristics compared to healthy controls, as well as a steeper age-related decrease in the bursts rate. While there was a high degree of correlation between some of the oscillatory features, several features also appeared functionally separated, showing independent feature-to-symptom relationships. For instance, oscillatory beta power increased with the severity of midline function symptoms, while burst rate decreased with the severity of bradykinesia. Our study shows that quantification of distinct features within the oscillatory sensorimotor neural time series in PD captures different underlying mechanisms related to disease progression and symptom severity, which in turn has a potential for a more individualised and precision-based approach to assessing functional neural changes in PD.