Electromagnetic mapping of the effects of deep brain stimulation and dopaminergic medication on movement-related cortical activity and corticomuscular coherence in Parkinson’s disease

Background Parkinson’s disease (PD) is a debilitating neurodegenerative disorder. PD can be treated with deep brain stimulation (DBS) when dopaminergic medication is no longer a viable option. Both treatments are effective in improving motor symptoms, however, their underlying mechanisms are not fully elucidated yet. Objectives To study the effects of DBS and dopaminergic medication treatments on cortical processing and corticomuscular drive during movements. Methods Magnetoencephalography (MEG) was recorded in 10 PD patients and 10 healthy controls, performing phasic hand contractions (hand gripping). Measurements were performed in DBS-treated, untreated and dopaminergic-medicated states; healthy controls received no treatment interventions. Participants performed phasic contractions with their right hand, recorded with electromyography (EMG). Our measures of interest were beta (13-30 Hz) corticomuscular coherence (CMC) and low-gamma (31-45 Hz) power. We used Bayesian statistics on summary values from sensor space data, and we localized the sources of the effects of treatments on beta-CMC and low-gamma power using beamforming. Results In PD patients, DBS led to reduced CMC values, whereas dopaminergic medication increased beta-CMC values (localized to contralateral M1) to even higher levels than the controls. DBS, on the other hand, increased low-gamma power (localized to M1) compared to controls and to other conditions. Yet both treatments had similar beneficial effects on the patients’ motor symptoms evaluated by UPDRS-III. Conclusion Despite comparable improvements from both treatments on motor symptoms, DBS and dopaminergic medication seem to have different effects on motor cortical function. This indicates that the treatments undertake different functional strategies to improve PD symptoms.