Contributions of visual and motor signals in cervical dystonia.

Sir, We read with great interest the article by Shaikh et al. (2016) presenting a pathophysiological explanation of cervical dystonia. Cervical dystonia is a neurological disorder characterized by involuntary twisting and turning of the head in any of the three dimensions. The authors proposed that the abnormalities of head movements seen in the disease stem from a malfunctioning head neural integrator caused by either an intrinsic dysfunction or as a result of impaired cerebellar, basal ganglia, or peripheral feedback. Several studies hypothesized that the head neural integrator relies on feedback using visual information, neck proprioception, and input from the cerebellum (Chan-Palay, 1977; Noda et al. , 1990; Fukushima and Fukushima, 1992). Starting from the hypothesis that visual feedback may play a crucial role in the functionality of the head neural integrator and, subsequently, in the pathophysiology of dystonia, we decided to analyse the straight-ahead preference in healthy human subjects and patients with cervical dystonia. Several studies had previously demonstrated a dysfunction of …