Dynamic involvement of premotor and supplementary motor areas in bimanual pinch force control

Many bimanual activities of daily living require quick shifts between symmetric and asymmetric motor output generated by the right and left hand. Bimanual motor control has been mostly studied during continuous repetitive tasks, while little research has been carried out in experimental settings requiring dynamic changes in motor output generated by both hands. Here, we performed functional magnetic resonance imaging (MRI) while healthy volunteers performed a visually guided, bimanual pinch force task. This enabled us to map functional activity and connectivity of premotor and motor areas during bimanual pinch force control in different task contexts, requiring mirror-symmetric or inverse-asymmetric changes in discrete pinch force exerted with the right and left hand. The bilateral dorsal premotor cortex showed increased activity and effective coupling to the ipsilateral supplementary motor area (SMA) in the inverse-asymmetric context compared to the mirror-symmetric context of bimanual pitch force control. Compared to unilateral pinches, all bimanual pinch force conditions were characterized by an increased level of activation in the bilateral primary motor hand area (M1-HAND) and stronger coupling from SMA to the ipsilateral M1-HAND. Task-related activity of a cluster in the left caudal SMA scaled positively with the degree of synchronous initiation of bilateral pinch force adjustments, irrespectively of the task context. The results suggest that the dorsal premotor cortex mediates increasing complexity of bimanual coordination by increasing coupling to the SMA-M1 network.