Reduced Frequency of Ipsilateral Express Saccades in Cervical Dystonia: Probing the Nigro‐Tectal Pathway

BACKGROUND: Cervical dystonia is a hyperkinetic movement disorder of unknown cause. Symptoms of cervical dystonia have been induced in animals in which the integrity of the nigro‐tectal pathway is disrupted, resulting in reduced inhibition of the deep layers of the superior colliculus. This same pathway is believed to play a critical role in saccade generation, particularly visually guided, express saccades. It was hypothesized that individuals with cervical dystonia would present with a higher frequency of express saccades and more directional errors. METHODS: Eight individuals with cervical dystonia and 11 age‐ and sex‐matched control participants performed three saccadic paradigms: pro‐saccade, gap, and anti‐saccade (120 trials per task). Eye movements were recorded using electro‐oculography. RESULTS: Mean saccadic reaction times were slower in the cervical dystonia group (only statistically significant in the anti‐saccade task, F(1, 35) = 4.76, p = 0.036); participants with cervical dystonia produced fewer directional errors (mean 14% vs. 22%) in the anti‐saccade task; and had similar frequencies of express saccades in the gap task relative to our control population (chi‐square = 1.13, p = 0.287). All cervical dystonia participants had lower frequencies of express saccades ipsilateral to their dystonic side (the side to which their head turns), (chi‐square = 3.57, p = 0.059). DISCUSSION: The finding of slower saccadic reaction times in cervical dystonia does not support the concept of reduced inhibition in the nigro‐tectal pathway. Further research is required to confirm the observed relationship between the lateralization of lower frequencies of express saccades and direction of head rotation in cervical dystonia.