EP 58. Corticomuscular coherence during isotonic contractions with DBS and medication in PD patients

Abstract

Introduction Deep brain stimulation (DBS) effectively alleviates the motor symptoms in Parkinson’s disease (PD) although its effect mechanism is still unclear. Corticomuscular coherence (CMC) is a marker of the functional connectivity between the pyramidal system and the periphery ( Hari and Salenius, 1999 ). CMC has been shown to be reduced in PD patients but restorable with medication ( Salenius et al., 2002 ). DBS, on the other hand, has been shown to variably affect CMC in advanced PD patients ( Airaksinen et al., 2015 ). Objectives We investigated movement related cortical oscillations with primary focus on beta CMC (13–30 Hz). The objective was to discern whether both medication and DBS affect CMC in similar manners in unison with their comparable effects on PD patients’ motor symptoms as measured by the Unified Parkinson’s Disease Rating Scale (UPDRS-III). Patients and methods We recorded magnetoencephalography (MEG) from three PD patients performing hand gripping during DBS ON and medicated (MED ON) conditions and from three age-matched healthy control. For the MED ON condition, patients were administered 200 mg of levodopa with MEG measurements one hour later. Participants performed isotonic contractions with their right hand (hand gripping), and electromyography (EMG) was recorded from the extensor digitorum communis muscle in a belly-tendon montage. We calculated the mean-squared coherence between MEG and the rectified EMG signals. Confidence intervals were set at 99% of the time-shifted MEG-EMG coherence (3 s delay of EMG signal) ( [Halliday et al., 1995] , [Airaksinen et al., 2015] ). For each group and condition, we selected the maximum CMC value in the beta range (13–30 Hz) within the average of an a priori selection of nine left sensorimotor gradiometer pairs in the grand averaged data for each group and condition. Results The grand averaged CMC results are shown in Fig. 1. Medication (MED ON) seemed to normalize beta CMC values in PD patients to comparable levels of the controls whereas DBS led to reduced beta CMC values while both treatments had similar effects on the patients’ motor symptoms (UPDRS-III). Conclusion Although both medication and DBS ameliorate clinical motor performance to similar extents, they seem to have differentiated effects on CMC which may point to differences in the effects mechanisms of the two treatments.