Levodopa Reduces the Phase lag Index of Parkinson's Disease Patients: A Magnetoencephalographic Study

Objectives. As a method of measuring the phase difference between 2 signals, the phase lag index (PLI) of the alpha and beta bands in patients with Parkinson's disease (PD) was investigated by using magnetoencephalography (MEG). Methods. Eighteen PD patients were measured by MEG in the state of overnight withdrawal of levodopa and after levodopa treatment; meanwhile, Unified Parkinson's Disease Rating Scale (UPDRS) III scale was evaluated. Results. Compared with healthy controls, alpha (8-13 Hz) PLI in the frontal and parietal areas elevated in PD patients, while the elevation was reversed by the levodopa treatment. The alterations of the UPDRS III total scale (r_s = 0.552, P = .013, n = 16) and the changes of akinesia scale (r_s = 0.622, P = .005, n = 16) were correlated to the change of beta (13-30 Hz) PLI in the left parietal area. The change of the UPDRS total scale was negatively correlated to duration of disease (r_s = 0.432, P = .047, n = 16). There was a negative correlation between the age of PD patients and the change of alpha PLI in the left frontal area (r_s = 0.519, P = .020, n = 16). Conclusions. PD patients showed a higher mu PLI in the sensorimotor area relative to the healthy controls. The improvement of motor symptoms of PD patients by levodopa was correlated to the inhibition of beta PLI in the sensorimotor area.