Tremor-correlated cortical activity detected by electroencephalography

Objective: In this study we investigated whether cortical activity related to Parkinsonian resting tremor can be detected by electroencephalography (EEG). Methods: Seven patients with idiopathic Parkinsonʹs disease suffering from unilateral tremor participated in the study. Electromyography (EMG) signals arising from the wrist extensor and flexor muscles as well as a high resolution EEG were recorded simultaneously. Coherencies between EEG and EMG were calculated. Results: In all patients, we found highly significant coherencies at the tremor frequency or its first harmonic between the tremor EMG and contralateral EEG channels. There were no significant coherencies between the tremor EMG and ipsilateral EEG channels. Isocoherency maps illustrating the topography of the coherencies over the scalp showed that the maximum coherencies were situated over the cortical motor areas. In one case, a high coherency was also found over the parietal cortex. Conclusions: The results show for the first time that tremor-correlated cortical activity can be detected by electroencephalography. The findings underline that motor areas of the cerebral cortex are involved in the neuronal network generating resting tremor in Parkinsonʹs disease.