Children With and Without Dystonia Share Common Muscle Synergies While Performing Writing Tasks

Abstract

Childhood dystonia is a movement disorder characterized by muscle overflow and variability. This is the first study that investigates upper limb muscle synergies in childhood dystonia with the twofold aim of deepening the understanding of neuromotor dysfunctions and paving the way to possible synergy-based myocontrol interfaces suitable for this neurological population. Nonnegative matrix factorization was applied to the activity of upper-limb muscles recorded during the execution of writing tasks in children with dystonia and age-matched controls. Despite children with dystonia presented compromised kinematics of the writing outcome, a strikingly similarity emerged in the number and structure of the synergy vectors extracted from children in the two groups. The analysis also revealed that the timing of activation of the synergy coefficients did not significantly differ, while the amplitude of the peaks presented a slight reduction. These results suggest that the synergy analysis has the ability of capturing the uncorrupted part of the electromyographic signal in dystonia. Such an ability supports a possible future use of muscle synergies in the design of myocontrol interfaces for children with dystonia.

High motor variability in DYT1 dystonia is associated with impaired visuomotor adaptation

“…Interestingly such variability appeared random in its nature with no directional preponderance shown in any of the reach conditions. This finding fits with work in children which suggests that the patterns of muscle groups or muscle synergies recruited to tasks are surprisingly intact in a disorder in which the balance between different muscle groups appears so impaired 22 , 23 .…”

Motor primitives are determined in early development and are then robustly conserved into adulthood

“…The construction of bipedal motor behaviors in humans might conceivably cause synergies expressed in walking and running in ablebodied adults to depart still further from the early default synergies or show more pervasive individual variations and suppressions than in the rats (36)(37)(38)50). Our work here suggests that a core set of synergies in common in all individuals may nonetheless underlie aspects of these variations (27,37,44,49). However, although there are well-established and significant evolutionary parallels (4) in overall pattern generation and modularity, the details of synergy adjustments across different species remain to be better understood.…”

“…Second, some synergies were not altered in weights but instead, ceased to be used strongly in patterns. Both of these types of changes are likely significant in motor drive infrastructure, pattern generation, and the pathologies and injury effects where synergies may have impact (27,(33)(34)(35)(36)(37)(38)(39)(40)(44)(45)(46)(47)(48)(49). Synergies normally weakly activated in intact CNS that become active in disease would interfere with normal function and be pathological.…”

Comparison of Initialization Techniques for the Accurate Extraction of Muscle Synergies from Myoelectric Signals via Nonnegative Matrix Factorization

“…Modular motor control strategies have been investigated in a variety of motor acts [ 4 – 11 ], and evidence has been provided that a set of muscle synergies is able to represent the control strategies underlying the movement, with motor modules that can be either typical for a particular task or shared among different tasks. These studies also revealed how the analysis of motor modules in conjunction with mechanical measurements can provide a neuromechanical description of human movement [ 12 ] and that it can be proposed as a means for quantifying motor impairment and planning neurorehabilitation [ 13 , 14 ].…”