Changes in Synergy Formation and Modulation During Cyclic Force Production Tasks in Dystonic Cerebral Palsy in Female Adults

This study investigated alterations in coordinative actions observed in female adults diagnosed with dystonic cerebral palsy (DCP), focusing on finger forces and forearm muscle activity. Bothe the DCP and control groups performed a series of maximal and submaximal repetitive force production tasks that required the exertion of flexion and extension forces in an isometric manner. Electromyography (EMG) was measured in sets of flexors and extensors. These two levels of finger forces and muscles were analyzed within the framework of the uncontrolled manifold hypothesis to quantify indices of multi-element synergies. The results showed that the DCP group had lower maximal forces, less independent force production of individual fingers, lower performance consistency, and lower indices of multi-element synergies. Specifically, the magnitude of synergy, i.e., synergy formation, of the four finger forces in the DCP group was found to nearly zero, indicating an impaired ability to modulate synergy during cyclic force production. These results could be associated with higher levels of flexor and extensor co-contraction, as demonstrated in the DCP group. The DCP group’s impaired abilities, along with their low maximal force and higher finger interdependency, were qualitatively similar to those reported in patients with Parkinson’s disease or cerebellar atrophy, both of which involve malfunctioning subcortical circuit. These findings align with the hypotheses concerning the role of the subcortical circuit in formatting and modulating motor synergies. This suggests that the synergy index measured in artificial, constrained laboratory tasks may predict more general changes in motor behavior.