Objective: 1) To test whether PD reduces the ability to improve motor acuity (speed-accuracy trade-off performance) in goal-directed movements; 2) To examine the effect of PD on exploration during practice of these skilled movements.

Background: The striatum is thought to make specific and crucial contributions to certain types of motor skill learning, possibly due to dopamine’s role in synaptic plasticity at corticostriatal synapses. Studies of motor skill learning in patients with Parkinson’s disease (PD), a condition that reduces striatal dopamine, however, have yielded mixed results that depend on the motor task learned. Because of striatal dopamine’s presumed role in driving exploration in reinforcement learning, we hypothesized that a specific type of motor learning that might be affected by PD should be motor skill learning that requires improvement in the speed-accuracy trade-off. This type of motor learning allows exploration of the balance between practicing faster and less accurately, vs. practicing slowly and more accurately.

Methods: Participants with PD in the operational off-medication state (PD group) and participants without neurologic or musculoskeletal disorders (CLT group) made wrist movements that guided a screen cursor through a semicircular arc channel (PMID 22514286) and obtained points for moving faster while keeping the cursor in the channel. Motor acuity was tested before and after practice in testing blocks that imposed matched speeds. Practice occurred in a separate block that allowed self-directed exploration of various speeds.

Results: PD subjects had the same accuracy as CTL in baseline testing, and practiced at similar speeds as CTL, but exhibited reduced motor skill learning, i.e. they achieved smaller gains of motor acuity after practice. They also exhibited less trial-to-trial variation of trajectories during practice.

Conclusions: PD disrupts motor skill learning that requires improvement in the speed-accuracy trade-off, independently of its effects on movement execution speed or accuracy. This disruption may be due to reduced trial-to-trial variation of movements during practice. Such a mechanisms would be consistent with a possible role of striatal dopamine in guiding exploration of movement parameters in the search for increased reward, analogously to dopamine’s better-established role in reinforcement learning of simple behavioral choices.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/parkinsons-disease-disrupts-motor-skill-learning-that-requires-improvement-of-a-speed-accuracy-trade-off/