PROJECT TITLE :
Impaired Inhibitory Force Feedback in Fixed Dystonia
Advanced regional pain syndrome (CRPS) could be a multifactorial disorder related to an aberrant host response to tissue injury. About 25percent of CRPS patients suffer poorly understood involuntary sustained muscle contractions related to dysfunctional reflexes that end in abnormal postures (mounted dystonia). A recent modeling study simulated mounted dystonia (FD) caused by aberrant force feedback. The present study aims to validate this hypothesis by experimentally recording the modulation of reflexive force feedback in patients with FD. CRPS patients with and while not FD, patients with FD but while not CRPS, also healthy controls participated in the experiment. 3 task instructions and 3 perturbation characteristics were used to evoke a wide selection of responses to force perturbations. During position tasks (“maintain posture”), healthy subjects along with patients resisted the perturbations, becoming more stiff than when being relaxed (i.e., the relax task). Healthy subjects and CRPS patients without FD were each more compliant throughout force tasks (“maintain force”) than throughout relax tasks, that means they actively gave method to the imposed forces. Remarkably, the patients with FD failed to do so. A neuromuscular model was fitted to the experimental data to separate the distinct contributions of position, velocity and force feedback, plus co-contraction to the motor behavior. The neuromuscular modeling indicated that inhibitory force feedback is deregulated in patients with FD, for each CRPS and non-CRPS patients. From previously printed simulation results and the current experimental study, it is concluded that aberrant force feedback plays a role in mounted dystonia.
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