Function of the dorsal neck muscles and tbeir afferent in put in Lateral gaze

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To examine the role of the ventral neck muscles in lateral geze shift, the eye and head movements towards a visual target were analyzed in subjects with unilateral neck dissection and normal subjects. The eye position was derived by an electro-oculographic technique and the head position with a potentiometer on the helmet.When a peripheral target was lit, the eye made an initial saccade towards it and the head then began to turn towards it. The patients made a gaze shift to the target accurately as the normal subjects. However, decrease in the amplitude and increase in the duration of the head displacement from the values of the normal subject were observed in the patient. Accordingly, the trajectory of eye movement between two groups was different, especially when the target was presented out of the ouclomotor range (over 50 deg). In the patient, time for the gaze to reach the target was significantly longer, and the vestibulo-ocular reflex was almost suppressed during head movements. Moreover, when the subjects were ordered to continue to maintain their gaze direction towards the imaginary target after the target lamp was off, the patient showed a tendency that their gaze gradually deviated to the nasal direction due solely to unsteadiness of the eye position, probably reflecting a loss of appropriate afferent signals form the neck muscles to the oculomotor center.