The influence of dorsal neck proprioceptive inputs on vestibular compensation--by three-dimensional analysis of neck-induced nystagmus

The influence of dorsal neck proprioceptive inputs on vestibular compensation was investigated in 21 patients with unilateral vestibular dysfunction. Subjects neither had history of spontaneous nystagmus nor of disequilibrium, indicating that they were in a good compensated stage. However, marked nystagmus was induced by applying vibratory stimulation to the dorsal neck of the patients, using a vibrator with a frequency of 110 Hz. The nystagmus was three-dimensional as analyzed by applying computerized eye movement analysis system. Twelve of 21 patients (57%) demonstrated three components of eye movement. All subjects showed a horizontal component directed towards the contralateral side of the vestibular lesion. Vertical and torsional components of the nystagmus were exhibited by 18 and 14 subjects, respectively. The average percentages of slow phase velocity of the horizontal, vertical and torsional components were 57%, 23% and 20%, respectively. No tendency towards any of the three components was observed. Furthermore, in order to investigate the relation between dorsal neck proprioceptive inputs and vestibular outputs, especially semicircular canal outputs, the author compared the direction of the nystagmus with the orientation of the semicircular canals. Normalized average velocity vectors of the nystagmus were calculated. In most subjects, the velocity vectors of the nystagmus were related to the horizontal semicircular canal. These results suggest that by controlling the neck proprioceptive inputs, neck vibration can cause discompensation in vestibularly well-compensated subjects with unilateral dysfunction secondary to vestibular lesion, and that neck proprioceptive inputs have a great influence on the horizontal vestibulo-ocular reflex pathways. However, in a few subjects the average vectors of the nystagmus were related to the vertical semicircular canals. This suggests that the proprioceptive inputs may also be related to the vertical vestibulo-ocular reflex pathways.