Slowed luminance reaction times in cervical dystonia: disordered superior colliculus processing

Background: Abnormal temporal discrimination in cervical dystonia is hypothesised to be due to disrupted processing in the superior colliculus. The fast, luminance-based, retino-tectal pathway, projects to the superior colliculus; chromatic stimuli responses, via the retino-geniculo-calcarine pathway, are up to 30ms longer. Methods: In 20 cervical dystonia and 20 age-matched control participants, we compared reaction times to two flashing visual stimuli: (i) a chromatic annulus and (ii) a luminant, non-coloured annulus. Participants pressed a joystick control when they perceived the annulus flashing. Results: Reaction times in control participants were 20ms significantly faster in the luminant condition than the chromatic (p= 0.017). Patients with cervical dystonia had no reaction time advantage in response to the luminant stimulus. Conclusion: Cervical dystonia patients (compared to control participants) demonstrated no reduction in their reaction time to luminant stimuli, processed through the retino-tectal pathway. This finding is consistent with superior colliculus dysfunction in cervical dystonia.