Essential tremor (ET) is the most common movement disorder worldwide and is characterized by an isolated tremor of the upper limb that worsens over the course of time. Evidence has accumulated to support the theory that the cerebellum is primary involved in the development of ET disease, although the contribution of cerebellar pathology to ET’s aetiology remains poorly understood. Beside motor deficits, numerous studies report the presence of cognitive impairment in ET patients.
The cerebellum is crucial for motor as well as cognitive functions as it integrates sensorimotor information to create an internal model of movement using prediction errors. In this study, I tested the performance of 34 ET patients and 34 age-matched healthy controls in a visuomotor adaptation (VMA) task whose proper execution critically depends on the cerebellum. Participants performed the
VMA while sitting in front of a computer screen. At the beginning of each trial, eight grey circles in one of eight possible positions arrayed around a central cross appeared on the screen. Next, one of the eight circles was marked as a blue target, and participants had to move from the central cross towards the target using a digital pen moved on a digital tablet. The movement on the tablet was represented
as a cursor on the screen. Visual feedback from the moving hand was prevented. Over the course of the experiment, a 30° clockwise visuomotor perturbation of the cursor movement on the screen was
introduced abruptly. To this end, subjects implicitly modified the reach direction such that they are able to hit the target again. The extent to which a subject adapts to the visuomotor perturbation can be measured by the angular error between a straight line connecting the center cross and the target, and a line connecting the center cross and the position of the cursor at peak velocity. Reaction times and movement times were analyzed to assess motor performance. In accordance with my hypothesis, I found evidence for impaired visuomotor adaptation in ET that could not be explained
by altered general motor performance due to tremor. This deficit was also specific to both early and late adaptation phases. There were no group differences during a baseline phase, in which no visual perturbation was present, as well as at a de-adaptation phase, when the visual perturbation was suddenly removed. This deficit seems to also not relate to clinical features, i.e., disease state
(measured by TETRAS/SARA), disease duration, current medication, and patients’ cognitive state (evaluated by MoCA). Thus, these findings support the hypothesis that a functional disturbance of the cerebellum is present in mildly to moderately affected ET patients without marked cerebellar signs and is detectable using a behavioral task that targets cerebellar functionality.
What could be further mechanisms that negatively affect visuomotor adaptation in patients with ET and are not associated with basic motor functions? Unlike a pure motor task, the visuomotor adaptation task entails a cognitive component with implicit and/or explicit learning processes. Thus, it could be that cognitive deficits in ET, frequently reported among studies may have driven performance deficits in this task. Note however that I did not find any association between cognitive abilities as measured by MoCA and visuomotor adaptation impairment in the ET cohort. As no
extensive neurocognitive testing was performed in our cohort and MoCA was shown to be not very sensitive for cerebellar cognitive symptoms, it is impossible to rule out the effect of cognitive decline in ET on visuomotor adaptation.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:91997 |
| Date | 11 June 2024 |
| Creators | Bindel, Laura |
| Contributors | Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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