The role of the vestibular commissure in the gaze holding of the cat.

Recent theoretical studies have proposed that the vestibular commissure is a major component of the horizontal gaze-holding system. In order to test this hypothesis, we disrupted the vestibular commissure of the cat by a parasagittal cut running between an abducens nucleus and the adjacent medial vestibular nucleus. Successfully lesioned cats suffered of a characteristic syndrome. In the light, gaze holding was impaired when the animal was looking toward the side of the lesion, but normal when looking toward the opposite side. We conclude (1) that the vestibular commissure is a component of the gaze-holding system, (2) that the vestibular commissure is less essential for gaze holding than other structures as the nucleus prepositus hypoglossi, and (3) that the horizontal gaze-holding system consists of two halves, each being more active in ipsilateral than in contralateral gaze.