Excitability of the supplementary motor area in Parkinson's disease depends on subcortical damage

Cortical dysfunctioning significantly contributes to the pathogenesis of motor symptoms in Parkinson's disease (PD). We aimed at testing whether an acute levodopa administration has measurable and specific cortical effects possibly related to striatal dopaminergic deficit. In thirteen PD patients, we measured the electroencephalographic responses to transcranial magnetic stimulation (TMS/EEG) of the supplementary motor area and superior parietal lobule (n = 8) before and after an acute intake of levodopa. We also performed a single-photon emission computed tomography and [123I]N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane to identify the more affected and the less affected brain side in each patient, according to the dopaminergic innervation loss of the putamen. Cortical excitability changes before and after an acute intake of levodopa were computed and compared between the more and the less affected brain side at the single-patient as well as at the group level. We found that levodopa intake induces a significant increase (P