Objective: To assess the integrity of forward model-driven predictions in a visuomotor task in adults with Tourette syndrome (TS).

Background: Tics, such as those encountered in TS, are movements or sounds that resemble voluntary actions but appear inopportune and repetitive. Although tics are typically experienced as unwilled behaviors, patients report difficulties in classifying them as either voluntary or involuntary. This distinction critically relies on the precision of internal predictions of motor output and its sensory consequences by forward models [1]. Here, we hypothesize that impaired forward model-driven predictions in TS may lead to misclassification of actions and ultimately the occurrence of tic behaviors. We explore this hypothesis by using an established oculomotor task, probing the accuracy and precision of internal predictions in the visuomotor domain.

Method: 18 patients (age 32±14.8 years) and 19 age-matched (27.8±3.9 years) healthy controls completed the study protocol. Neuropsychiatric comorbidities, such as attention-deficit hyperactivity disorder, obsessive-compulsive disorder, depression and anxiety were assessed by means of standardized scales, as previously reported [2]. In the oculomotor task, subjects performed a saccadic eye movement and reported the apparent direction of an intra-saccadic target displacement. Correct decisions in this task require accurate and precise internal predictions of eye movement metrics and its perceptual consequences [3,4]. Furthermore, we asked subjects to report the subjective uncertainty associated with this visuomotor decision.

Results: Basic oculomotor performance (saccadic reaction time and targeting error) did not differ between patients and healthy control groups. Likewise, no significant between-group differences emerged for accuracy and precision of associated visuomotor decisions, as assessed by the bias and slope of psychometric functions fitted to individual data. For the additional ratings of decisional confidence, preliminary results indicate stronger deviations of subjective confidence from a simple statistical model of optimal confidence computation [5] in a subgroup of patients.

Conclusion: Basic oculomotor performance and associated internal monitoring of action consequences may be intact in TS, arguing against a global deficit in forward-model driven internal predictions of sensorimotor contingencies.

References: 1. Wolpert DM, Miall RC (1996) Forward Models for Physiological Motor Control. Neural Netw 9:1265–1279. 2. Ganos C, Asmuss L, Bongert J, Brandt V, Münchau A, Haggard P (2015) Volitional action as perceptual detection: Predictors of conscious intention in adolescents with tic disorders. Cortex 64:47–54. 3. Ostendorf F, Liebermann D, Ploner CJ (2010) Human thalamus contributes to perceptual stability across eye movements. Proc Natl Acad Sci U S A 107:1229–1234. 4. Cavanaugh J, Berman RA, Joiner WM, Wurtz RH (2016) Saccadic Corollary Discharge Underlies Stable Visual Perception. J Neurosci 36:31–42. 5. Sanders JI, Hangya B, Kepecs A (2016) Signatures of a Statistical Computation in the Human Sense of Confidence. Neuron 90:499–506.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/intact-visuomotor-forward-models-in-adults-with-tourette-syndrome/