Motor-cortical oscillations in early stages of Parkinson's disease

Key points Parkinson's disease (PD) is a common movement disorder due to dopaminergic denervation of the basal ganglia. It is characterized by exaggerated oscillatory activity within central motor-control loops, while cerebro-muscular coherence is reduced at frequencies below 30 Hz. So far, studies investigating the neurophysiological alterations of PD have focused on patients with advanced PD. It remains open to what extent changes of oscillatory activity might occur at early disease stages, representing a characteristic feature of the disease. Using magnetoencephalography we show that cerebro-muscular coherence is unaffected in early PD while beta band oscillations of bilateral primary sensori-motor cortices are already increased at the earliest stages of PD and, as the disease progresses, evolve a hemispheric imbalance associated with movement execution. Abstract Pathophysiological changes in basal ganglia-thalamo-cortical circuits are well established in idiopathic Parkinson's disease (PD). However, it remains open whether such alterations already occur at early stages representing a characteristic neurophysiological marker of PD. Therefore, the present study aims at elucidating changes of synchronised oscillatory activity in early PD patients. In this study, we performed whole-head magnetoencephalography (MEG) in a resting condition and during steady state contraction of the more severely affected forearm in 10 drugnaive, de novo patients, in 10 early-stage patients with chronic medication and in 10 age-matched control subjects. While cortico-muscular coherence (CMC) did not differ between groups, patients showed increased sensori-motor cortical power at beta frequency (1330 Hz) during rest as well as during isometric contraction compared to controls. In healthy control subjects the power of the contralateral hemisphere was significantly suppressed during isometric contraction. By contrast, both hemispheres were activated equally strongly in de novo patients. In medicated patients, the pattern was found to be reversed. Contralateral beta power was significantly correlated with motor impairment during isometric contraction but not during rest. The present results suggest that the reduced ability of the primary motor cortex to disengage from increased beta band oscillations during the execution of movements is an early marker of PD.