Objective: We postulate that cephalomotor responses (onset of head turning and speed of head turning) to the appearance of a novel peripheral visual stimulus will be impaired in patients with cervical dystonia and their unaffected first-degree relatives with abnormal temporal discrimination (TD) (reflecting abnormal sensory processing in the superior colliculus) compared to unaffected relatives with normal TD and healthy controls.

Background: Abnormal TD reflects disordered sensory processing within the superior colliculus and, as a mediational endophenotype, indicates a pathomechanism for the generation of cervical dystonia via disinhibited motor output from the superior colliculus to brain stem and cervical cord motor pathways. By examining head turning, in response to the appearance of a novel visual stimulus we aimed to demonstrate that unaffected first-degree relatives with abnormal TD have abnormalities in the initiation of, and speed of head turning compared to unaffected relatives with normal TD and healthy control participants. This will confirm the relevance of abnormal sensory processing in the superior colliculus in this disorder. 

Methods: A lightweight head mounted display (Oculus Rift DK2) was employed for simultaneous data collection and task presentation. All participants completed a modified Posner task in which head movements towards validly- and invalidly-cued eccentric targets were employed as the response. Patients, relatives and control participants were balanced by gender and age.

Results: A delay in onset of head movement was observed during invalid trials (compared to valid trials) in patients and healthy controls. Head turns were earlier during valid trials. This novel representation of the behavioural impact of orientation of attention (Posner effect) was clearly visible in both cohorts but more than doubled in the patient group. We will demonstrate that unaffected relatives with abnormal TD will show abnormalities in head turning initiation and velocity.

Conclusions: We hypothesise that abnormal TD represents delayed sensory processing within the superficial layers of the superior colliculus, manifested in a subclinical disordered motor output from the deeper layers of the superior colliculus. 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/head-turning-onset-and-velocity-in-response-to-a-peripheral-visual-stimulus-in-cervical-dystonia-patients-their-unaffected-relatives-with-and-without-abnormal-temporal-discrimination-and-healthy-cont/