L-dopa treatment increases oscillatory power in the motor cortex of Parkinson's disease patients

Parkinson's disease (PD) is a movement disorder caused by dopaminergic neurodegeneration. Levodopa (L-dopa) is an effective medication for alleviating motor symptoms in PD that has been shown previously to reduce subcortical beta (13–30 Hz) oscillations. How L-dopa influences oscillations in the motor cortex is unclear. In this study, 21 PD patients were recorded with magnetoencephalography (MEG) in L-dopa ON and OFF states. Oscillatory components of resting-state power spectra were compared between the two states and the significant effect was localized using beamforming. Unified Parkinson's Disease Rating Scale (UPDRS) III akinesia and rigidity sub-scores for the most affected hemibody were correlated with source power values for the contralateral hemisphere. An L-dopa-induced power increase was found over the central sensors significant in the 18–30 Hz range (F((1,20)) > 14.8, P(FWE corr) < 0.05, cluster size inference with P = 0.001 cluster-forming threshold). Beamforming localization of this effect revealed distinct peaks at the bilateral sensorimotor cortex. A significant correlation between the magnitude of L-dopa induced 18–30 Hz oscillatory motor-cortical power increase and the degree of improvement in contralateral akinesia and rigidity was found (F((2, 19)) = 4.9, p(one-tailed) = 0.02, R(2) = 0.2). Power in the same range was also inversely correlated with combined akinesia and rigidity scores in the L-dopa OFF state (F((2, 19)) = 9.2, p(two-tailed) = 0.007, R(2) = 0.33) but not in the L-dopa ON state (F((2, 19)) = 0.27, p(two-tailed) = 0.6, R(2) = 0.01). These results suggest that the role of motor cortical beta oscillations in PD is distinct from that of subcortical beta.