Differential modulation of STN-cortical and cortico-muscular coherence by movement and levodopa in Parkinson's disease.

Previous research suggests that oscillatory coupling between cortex, basal ganglia and muscles plays an important role in motor behavior. Furthermore, there is evidence that oscillatory coupling is altered in patients with movement disorders such as Parkinson's disease (PD). In this study, we performed simultaneous magnetoencephalography (MEG), local field potential (LFP) and electromyogram (EMG) recordings in PD patients selected for therapeutic subthalamic nucleus (STN) stimulation. Patients were recorded (i) after withdrawal of anti-parkinsonian medication (OFF) and (ii) after levodopa administration (ON). We analyzed STN-cortical and cortico-muscular coherence during static forearm contraction and repetitive hand movement in order to evaluate modulations of coherence by movement and medication. Based on previous results from studies investigating resting state coherence in PD patients, we selected primary motor cortex (M1) and superior temporal gyrus (STG) as regions of interest. We found beta coherence between M1 and STN to be suppressed by administration of levodopa. M1-muscular coherence was strongly reduced in the alpha and beta band during repetitive movement compared to static contraction, but was unaffected by administration of levodopa. Strong STG-STN but not STG-muscular coherence could be observed in the alpha band. Coherence with STG was modulated neither by movement nor by medication. Finally, we found both M1-STN and M1-muscular beta coherence to be negatively correlated with UPDRS akinesia and rigidity sub-scores in the OFF state. The present study provides new insights into the functional roles of STN-cortical and cortico-muscular coherence and their relationship to PD symptoms. The results indicate that STN-cortical and cortico-muscular coupling are correlated, but can be modulated independently. Moreover, they show differences in their frequency-specific topography. We conclude that they represent partly independent sub-loops within the motor system. Given their negative correlation with akinesia, neither can be considered "antikinetic".

Distinct oscillatory STN-cortical loops revealed by simultaneous MEG and local field potential recordings in patients with Parkinson's disease.

Neuronal oscillations are assumed to play a pivotal role in the pathophysiology of Parkinson's disease (PD). Neurons in the subthalamic nucleus (STN) generate oscillations which are coupled to rhythmic population activity both in other basal ganglia nuclei and cortical areas. In order to localize these cortical areas, we recorded local field potentials (LFPs) and magnetoencephalography (MEG) simultaneously in PD patients undergoing surgery for deep brain stimulation (DBS). Patients were withdrawn from antiparkinsonian medication and recorded at rest. We scanned the entire brain for oscillations coherent with LFPs recorded from the STN with a frequency domain beamformer. Coherent activity in the low (12-20 Hz) and high (20-35 Hz) beta range was found in the ipsilateral sensorimotor and the premotor cortex. Coherence in the alpha range (7-12 Hz) was observed at various locations in the ipsilateral temporal lobe. In a subset of subjects, the superior temporal gyrus consistently showed coherent alpha oscillations. Our findings provide new insights into patterns of frequency-specific functional connectivity between basal ganglia and cortex and suggest that simultaneous inter-regional interactions may be segregated in the frequency domain. Furthermore, they demonstrate that simultaneous MEG-LFP recordings are a powerful tool to study interactions between brain areas in PD patients undergoing surgery for DBS.