Objective: To examine motor variability in DYT1 dystonia and its interaction with subtypes of motor learning.

Background: In healthy subjects it is now known that some aspects of motor variability are a central component of motor learning. Motor variability, which was commonly attributed to unwanted noise, may in fact represent exploration in motor command space, with greater variability predicting faster learning. The precise motor deficit in humans with DYT1 dystonia is poorly defined and little is known about the interaction of variability metrics and motor learning indices.

Methods: We examined 10 patients with DYT1 dystonia and an equal number of aged matched controls. All were tested in their clinically affected right arm with a purpose built robot. During a baseline block variability metrics for position, velocity and force were calculated. In addition we examined adaptation (feedforward) learning and online (feedback) learning rates in response to visuomotor perturbation onset and subsequent removal.

Results: Patients had significantly greater motor variability which was most marked in parameters defining positional qualities of movement (in comparison to velocity or force). A median split of dystonic subjects by variability revealed that those with high variability had lower rates of adaptation learning which was almost entirely compensated by online learning mechanisms. This was the converse to healthy controls in which the rate of adaptation positively correlated to the magnitude of motor variability.

Conclusions: Preliminary analysis suggests that subjects with DYT1 dystonia have increased variability in motor performance. In contrast to healthy subjects this variability did not predict higher rates of learning but correlated with poor cerebellar adaptation learning. It is to be established whether the increased variability in dyt1 dystonia is a reflection of increased noise within the dystonia network to the detriment of motor learning or whether a subset of patients have a primary cerebellar deficit which is at the root of problematic movement variability.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/motor-variability-and-learning-indices-in-dyt1-dystonia/