Changes in subthalamic activity during movement observation in Parkinson's disease: Is the mirror system mirrored in the basal ganglia?

Objective: The observation of a voluntary movement executed by another person is associated with an alpha and beta EEG desynchronization over the motor cortex, thought to reflect activity from the human "mirror neuron" system. The aim of our work was to study the changes in local field potentials (LFP) recorded from the subthalamic nucleus (STN) and their relationship with cortical activity, during movement observation. Methods: Bilateral EEG and STN LFP recordings were acquired in 18 patients with Parkinson's disease, through surgically implanted electrodes for deep brain stimulation. Oscillatory changes during movement execution and movement observation were compared with two different control conditions (simple stimulus and rotating stimulus observation), in "off" and "on" motor states. Time-frequency transforms and event-related coherence were used for the analysis. Results: Movement observation was accompanied by bilateral beta reduction in subthalamic power and cortico-STN coherence, which was smaller than the decrease observed during movement execution, but significant when compared with the two control conditions. Conclusions: Movement observation is accompanied by changes in the beta oscillatory activity of the STN, similar to those observed in the EEG. Significance: These changes suggest that the basal ganglia might be engaged by the activity of the human mirror system. (C) 2009 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.