Effect of vestibular nerve section on torsion and on evoked rotatory movements

Abstract

The effect of acute and chronic section of the vestibular nerves, unilateral and bilateral, was measured on spontaneous torsion and on rotation elicited by electrical stimulation of the region of the zona incerta. In cats prepared as encéphales isolés, acute section of the vestibular nerve was followed by persistent spontaneous clockwise torsion of both eyes. This torsion was partially corrected for the right eye, and over-corrected for the left eye, following acute section of the right vestibular nerve. Rotational movements of both eyes could be elicited upon stimulation of left or right zona incerta or interstitial nucleus before and after unilateral and bilateral vestibular damage. Head rotation was elicited by stimulation of left and right zona incerta through electrodes implanted chronically in eight cats. Following unilateral section of the vestibular nerve, an enduring head tilt toward the side of the lesion was observed. In spite of this spontaneous tilt, stimulation of either incertal site still elicited head rotation comparable in extent to that seen upon control stimulation. Section of the other vestibular nerve in five of the cats resulted in correction or over-correction of the spontaneous head tilt. Stimulation of either incertal site was still capable of evoking head rotation, though this was less coordinated and more variable in threshold and extent than that seen before or after unilateral vestibular damage. Thus although vestibular nerves contribute to maintenance of posture and provide muscle tone, rotatory movements can be performed even after chronic bilateral vestibular nerve section.