Reinforcement Signaling Can Be Used to Reduce Elements of Cerebellar Reaching Ataxia
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ORIGINAL ARTICLE
Reinforcement Signaling Can Be Used to Reduce Elements of Cerebellar Reaching Ataxia Amanda S. Therrien 1
&
Matthew A. Statton 2 & Amy J. Bastian 2,3
# Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Damage to the cerebellum causes a disabling movement disorder called ataxia, which is characterized by poorly coordinated movement. Arm ataxia causes dysmetria (over- or under-shooting of targets) with many corrective movements. As a result, people with cerebellar damage exhibit reaching movements with highly irregular and prolonged movement paths. Cerebellar patients are also impaired in error-based motor learning, which may impede rehabilitation interventions. However, we have recently shown that cerebellar patients can learn a simple reaching task using a binary reinforcement paradigm, in which feedback is based on participants’ mean performance. Here, we present a pilot study that examined whether patients with cerebellar damage can use this reinforcement training to learn a more complex motor task—to decrease the path length of their reaches. We compared binary reinforcement training to a control condition of massed practice without reinforcement feedback. In both conditions, participants made target-directed reaches in 3-dimensional space while vision of their movement was occluded. In the reinforcement training condition, reaches with a path length below participants’ mean were reinforced with an auditory stimulus at reach endpoint. We found that patients were able to use reinforcement signaling to significantly reduce their reach paths. Massed practice produced no systematic change in patients’ reach performance. Overall, our results suggest that binary reinforcement training can improve reaching movements in patients with cerebellar damage and the benefit cannot be attributed solely to repetition or reduced visual control. Keywords Cerebellum . Ataxia . Reinforcement . Motor learning . Reaching
Introduction Damage to the cerebellum impairs motor coordination, causing a disabling movement disorder called ataxia. During reaching, ataxia is characterized by dysmetria (over- and undershooting of target locations) and multiple feedback-driven corrections causing irregular and prolonged hand trajectory paths [1, 2]. As a result, people with cerebellar damage can experience significant difficulty with many activities of daily life, such as reaching for a glass of water, eating, and dressing.
* Amanda S. Therrien [email protected] 1
Moss Rehabilitation Research Institute, 50 Township Line Rd., Elkins Park, PA 19027, USA
2
Kennedy Krieger Institute, Baltimore, MD, USA
3
Department of Neuroscience, Johns Hopkins School of Medicine, Baltimore, MD, USA
Reaching ataxia is thought to stem from impaired sensorimotor prediction [3–5], which involves computing the expected sensory outcome of motor commands based on an internal model of limb dynamics. Prediction signals keep movement well calibrated in the face of time-delayed peripheral feedback, and adaptive motor
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