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

We investigated whether functional coupling between different cortical area s is impaired in Parkinson's disease, using corticocortical coherence as a surrogate measure of coupling. We recorded scalp EEG from different sites i n seven parkinsonian patients while they tracked a visual target using thei r wrist, or copied the same movement from memory. Differences in EEG-EEG co herence between the tracking and copying tasks and their respective control s, visual tracking alone and fixation of a stationary target, were determin ed on and off levodopa. After levodopa we found extensive task-specific and broad band cortico-cortical coherence. Off levodopa cortico-cortical coher ence was much reduced. Ascending dopaminergic projections from the ventral mesencephalon may therefore be important in determining the pattern and ext ent of corticocortical coupling during executive tasks. NeuroReport 12:703- 707 (C) 2001 Lippincott Williams & Wilkins.