Task-dependent oscillations during unimanual and bimanual movements in the human primary motor cortex and SMA studied with magnetoencephalography.

The neural mechanisms subserving uni- and bimanual control of movements are not well understood. Nevertheless, recent studies indicate a functional role of oscillatory activity in movement control and point towards a hemispheric asymmetry in motor control. This study specifically addresses the issues of (i) task-relatedness, (ii) hemispheric symmetry, and (iii) frequency specificity of the measures power, cerebro-muscular coherence, and cerebro-cerebral coherence in bilateral primary motor cortex and supplementary motor area (SMA). We have studied 10 right-handed subjects with simultaneous recordings of magnetoencephalography and surface electromyography during different unimanual and bimanual tasks. Using the analysis technique Dynamic Imaging of Coherent Sources (DICS), left and right primary motor cortex and SMA were functionally localized. Power, cerebro-musclar coherence, and cerebro-cerebral coherence between these areas were computed for four frequency bands in each condition and subjected to ANOVA. Results show a task-specific modulation of power and coherence, and further indicate a hemispheric asymmetry in the control of unimanual and bimanual movements. In addition, different frequency bands showed different task-dependent variations. The gamma band (26-40 Hz) showed strongest modulation for cerebro-muscular coherence and was strongest for the isometric contraction conditions. In contrast, the beta band (13-24 Hz) showed the strongest variations between static and dynamic conditions, and seems to play a particular role in movement control. In summary, our results indicate a differential functional role of oscillatory activity and coupling in the motor system.