Objective: This study was conceptualized to asses if patients with cervical dystonia (CD) exhibit deficits in cerebellar function tested by motor adaptation and motor sequence learning.

Background: Despite many years of research the neurophysiological changes leading to dystonia remain elusive. In recent years the concept of dystonia as a network disorder involving the basal ganglia, the motor cortex and secondary cortical motor areas gained increasing attention. The cerebellum exerts an excitatory tone via the detato-thalamo-cortical pathway on the motor cortex. Animal studies and human imaging studies point to an important role of the cerebellum on the development of dystonia. Motor sequence learning was shown to be modulated by M1-cerebellar connectivity, while motor adaptation is mainly mediated by cerebellar function.

Methods: Patients with idiopathic CD and age-matched healthy controls (HC) underwent an implicit motor-sequence-learning task (MSL). Four squares were presented on a computer screen, each position corresponds to a button on the keyboard. Participants were instructed to respond as quick as possible when one of the squares changed its color to blue. The order of the color change followed a 12-items sequence in a repetitive manner, alternating with presentation in random order. Improvement in reaction time over repetition of the sequence and differences in reaction times between sequence and random blocks were analyzed. The same set of patients participated in an implicit motor-adaptation (MA) task. They performed a straight movement on a digitizing tablet from a starting point to one of eight radially arrayed targets. The movement was presented on a computer screen, the view on the hand was prevented by special glasses. Unbeknown to the participant the direction of the cursor movement shown on the screen was rotated counterclockwise in a step-wise manner to a maximum of 30°. Performance was measured as angular error.

Results: HC showed typical implicit MSL effects reflected by a fastening of reaction times over sequence blocks and decreased reaction times in sequence blocks compared to random blocks. Patients with CD showed no sequence learning. The MA protocol revealed no differences between CD patients to the age matched HC.

Conclusions: Both tasks are known to critically involve cerebellar functioning and are impaired in patients with cerebellar lesions or ataxia. Normal performance of CD patients in motor adaptation and abnormal motor sequence learning argues against a primary cerebellar dysfunction in CD and favors the hypothesis of a network disease including the cerebellum.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/abnormal-cerebellar-learning-in-cervical-dystonia/