Visuomotor Adaptation Deficits in Patients with Essential Tremor

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 evid