Post-labyrinthectomy balance compensation influenced by pre-placement of descending medial longitudinal fasciculus lesion.

To characterize the functional role of the descending medial longitudinal fasciculus (d-MLF) in vestibular compensation, vestibulo-ocular and vestibulo-spinal balance functions were studied comparatively in the squirrel monkey. When a unilateral lesion was made on the d-MLF, the animals showed a slight head deviation to the intact side, slight locomotor ataxia and irregular spontaneous nystagmus. About 2 months later, the ipsilateral labyrinthectomy was placed, and the compensatory process was compared between 3 experimentals and 3 controls (labyrinthectomy without pre-lesion). During the acute stage of the vestibular compensation, locomotor deviation was clearly greater in experimentals than those in controls. However, no significant difference existed in the final attainment and maintenance of the balance. The same result was found in the spontaneous nystagmus, although the difference in the two groups was less remarkable.