Task-related EEG-EEG coherence depends on dopaminergic activity in Parkinson's disease.

We investigated whether functional coupling between different cortical areas is impaired in Parkinson's disease, using corticocortical coherence as a surrogate measure of coupling. We recorded scalp EEG from different sites in seven parkinsonian patients while they tracked a visual target using their wrist, or copied the same movement from memory. Differences in EEG-EEG coherence between the tracking and copying tasks and their respective controls, visual tracking alone and fixation of a stationary target, were determined on and off levodopa. After levodopa we found extensive task-specific and broad band cortico-cortical coherence. Off levodopa cortico-cortical coherence was much reduced. Ascending dopaminergic projections from the ventral mesencephalon may therefore be important in determining the pattern and extent of corticocortical coupling during executive tasks.