Objective: To assess by functional magnetic resonance imaging, the response of the superior colliculi to a looming stimulus in cervical dystonia patients and their unaffected relatives with and without abnormal temporal discrimination.

Background: Cervical dystonia is the most frequent phenotype of adult-onset idiopathic isolated focal dystonia.  The underlying pathogenesis of this common movement disorder remains poorly understood. A heritable marker that is more penetrant, an endophenotype, may reveal pathomechanisms not obvious from the phenotype. Abnormal temporal discrimination threshold is an endophenotype for cervical dystonia, however, the networks involved in temporal discrimination are incompletely understood. We hypothesise that both abnormal temporal discrimination and cervical dystonia are due to disordered covert attentional orienting involving the superior colliculi. Looming stimuli (as opposed to random stimuli) indicate potential threat and activate both superior colliculi. 

Methods: We examined by functional magnetic resonance imaging the responses at whole brain level and within the superior colliculi (region of interest analysis) to looming, receding and random stimuli in 32 participants with abnormal temporal discrimination (cervical dystonia patients and their unaffected first degree relatives) and 32 participants with normal temporal discrimination (unaffected first degree relatives and healthy controls). A correlation analysis was then performed to explore the relationship between temporal discrimination and peak activations at superior collicular level.

Results: Compared to the 32 participants with normal temporal discrimination, the 32 participants with abnormal temporal discrimination demonstrated (i) disrupted superior collicular activation to looming stimuli; (ii) significantly reduced superior collicular activation for whole brain and region of interest analysis to looming stimuli; (iii) a statistically significant negative correlation between TDT z-score and superior collicular peak values during the loom condition.

Conclusions: Our results suggest that an abnormal temporal discrimination threshold is associated with disrupted superior collicular processing.  The findings from our study shed new light on potential pathomechanisms in cervical dystonia.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/disrupted-superior-collicular-activity-may-reveal-cervical-dystonia-disease-pathomechanisms/