Small effects of neck torsion on healthy human voluntary eye movements

Although several lines of research suggest that the head and eye movement systems interact, previous studies have reported that applying static neck torsion does not affect smooth pursuit eye movements in healthy controls. This might be due to several methodological issues. Here we systematically investigated the effect of static neck torsion on smooth pursuit and saccadic eye movement behavior in healthy subjects. In twenty healthy controls, we recorded eye movements with video-oculography while their trunk was in static rotation relative to the head (7 positions from 45A degrees to the left to 45A degrees to right). The subject looked at a moving dot on the screen. In two separate paradigms, we evoked saccadic and smooth pursuit eye movements, using both predictable and unpredictable target motions. Smooth pursuit gain and saccade peak velocity decreased slightly with increasing neck torsion. Smooth pursuit gains were higher for predictable target movements than for unpredictable target movements. Saccades to predictable targets had lower latencies, but reduced gains compared to saccades to unpredictable targets. No interactions between neck torsion and target predictability were observed. Applying static neck torsion has small effects on voluntary eye movements in healthy subjects. These effects are not modulated by target predictability.