Dynamic synchronization between multiple cortical motor areas and muscle activity in phasic voluntary movements.

To study the functional role of synchronized neuronal activity in the human motor system, we simultaneously recorded cortical activity by high-resolution electroencephalography (EEG) and electromyographic (EMG) activity of the activated muscle during a phasic voluntary movement in seven healthy subjects. Here, we present evidence for dynamic beta-range (16-28 Hz) synchronization between cortical activity and muscle activity, starting after termination of the movement. In the same time range, increased tonic activity in the activated muscle was found. During the movement execution a low-frequency (2-14 Hz) synchronization was found. Using a novel analysis, phase-reference analysis, we were able to extract the EMG-coherent EEG maps for both, low- and high-frequency beta range synchronization. The electrical source reconstruction of the EMG-coherent EEG maps was performed with respect to the individual brain morphology from magnetic resonance imaging (MRI) using a distributed source model (cortical current density analysis) and a realistic head model. The generators of the beta-range synchronization were not only located in the primary motor area, but also in premotor areas. The generators of the low-frequency synchronization were also located in the primary motor and in premotor areas, but with additional participation of the medial premotor area. These findings suggest that the dynamic beta-range synchronization between multiple cortical areas and activated muscles reflects the transition of the collective motor network into a new equilibrium state, possibly related to higher demands on attention, while the low-frequency synchronization is related to the movement execution.