Descending Control of the Vestibular Nuclei: Physiology

Abstract

The vestibular system and the vestibulo-ocular reflex arc are influenced by a number of higher functions and centers. The phenomenon of “alertness” has a cortical aspect; and it clearly facilitates vestibular activity. The role of the cortex in other behavioral states such as “habituation” or sleep is less clear. Childhood schizophrenia, a severe thought and behavioral disorder, is accompanied by hypoactive and variable responses to caloric and post-rotatory nystagmus. The latter is strongly influenced by vision. Ablation of the occipital and frontal cortex tends to release vestibulo-ocular activity while stimulation studies of the same areas are not amenable to such generalizations. The ablation evidence, however, suggests that the cortex has a generally inhibitory effect in vestibular activity. Both the caudate nucleus and an area medial to the lateral geniculate body act to augment, while the nucleus of Darkschewitsch inhibits vestibular nystagmus. The mechanisms of these actions are not clear. The interstitial nucleus of Cajal, a center for head rotation and eye rotation and vertical movement, when stimulated, inhibits type-I vestibular neurons of the horizontal canal. The inhibitory action on type-I neurons of the anterior vertical canal is infrequent and weaker. This function may enhance rotatory head and eye movements; or may serve as a means by which cortical or subcortical stations could modulate vestibular-induced horizontal eye movement.