Abstract
Dystonia has historically been considered a disorder of the basal ganglia, mainly affecting planning and execution of voluntary movements. This notion comes from the observation that most lesions responsible for secondary dystonia involve the basal ganglia. However, what emerges from recent research is that dystonia is linked to the dysfunction of a complex neural network that comprises basal ganglia–thalamic–frontal cortex, but also the inferior parietal cortex and the cerebellum. While dystonia is clearly a motor problem, it turned out that sensory aspects are also fundamental, especially those related to proprioception. We outline experimental evidence for proprioceptive dysfunction in focal dystonia from intrinsic sensory abnormalities to impaired sensorimotor integration, which is the process by which sensory information is used to plan and execute volitional movements. Particularly, we will focus on proprioceptive aspects of dystonia, including: (i) processing of vibratory input, (ii) temporal discrimination of two passive movements, (iii) multimodal integration of visual-tactile and proprioceptive inputs, and (iv) motor control in the absence of visual feedback. We suggest that these investigations contribute not only to a better understanding of dystonia pathophysiology, but also to develop rehabilitation strategies aimed at facilitating the processing of proprioceptive input.
Highlights
Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both (Fahn, 1988)
The common idea is that a dysfunction of the basal ganglia and/or their connections to motor cortex plays a major role in the pathogenesis of dystonia, by influencing the final organization and execution of movement (Berardelli et al, 1998)
The contribution of the somatosensory system to the mechanism of the dystonia is supported by the following clinical aspects: (1) alleviation of dystonia with “sensory tricks” (Wissel et al, 1999; Müller et al, 2001); (2) photosensitivity and other ocular discomforts in patients with blepharospasm (Stamelou et al, 2012); (3) neck pain that often precedes cervical dystonia (Ghika et al, 1993; Stamelou et al, 2012); (4) improvement of dystonic movements after administration of local anesthetic (Kaji et al, 1995)
Summary
Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both (Fahn, 1988). Proprioceptive function in dystonia was studied with different approaches: muscle vibration of the arm and neck, temporal discrimination of two passive movements, reaching movements in absence of visual input, and the rubber hand illusion (RHI). The selective impairment of the proprioceptive drift in focal hand dystonia could suggest a failure in integrating the synchronous visual-tactile input with the proprioceptive location sense, because of an underlying kinesthetic deficit (Fiorio et al, 2011).
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