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-resolut ion electroencephalography (EEG) and electromyographic (EMG) activity of th e activated muscle during a phasic voluntary movement in seven healthy subj ects. Here, we present evidence for dynamic beta-range (16-28 Hz) synchroni zation between cortical activity and muscle activity, starting after termin ation of the movement. In the same time range, increased tonic activity in the activated muscle was found. During the movement execution a low-frequen cy (2-14 Hz) synchronization was found. Using a novel analysis, phase-refer ence analysis, we were able to extract the EMG-coherent EEG maps for both, low- and high-frequency beta range synchronization. The electrical source r econstruction of the EMG-coherent EEG maps was performed with respect to th e individual brain morphology from magnetic resonance imaging (MRI) using a distributed source model (cortical current density analysis) and a realist ic head model. The generators of the beta-range synchronization were not on ly located in the primary motor area, but also in premotor areas. The gener ators of the low- frequency synchronization were also located in the primar y motor and in premotor areas, but with additional participation of the med ial premotor area. These findings suggest that the dynamic beta-range synch ronization between multiple cortical areas and activated muscles reflects t he 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.