Anatomy of the Vestibuloreticular Connections and Possible ‘Ascending' Vestibular Pathways from the Reticular Formation

Abstract

Few primary vestibular fibers end in the reticular formation (RF) in its most dorsolateral medullary part. Secondary vestibular fibers to the RF arise from all four main vestibular nuclei. Experimental studies of the distribution of degenerating fibers following lesions restricted to the particular nuclei show that each of the main nuclei has its particular pattern of distribution of fibers within the RF. The cerebellar projecting reticular nuclei are supplied by the superior and lateral vestibular nuclei only. These two reticular nuclei differ with regard to the source of their vestibular afferents. The superior, lateral and descending, and probably the medial, vestibular nucleus, project to the main RF in different patterns. The majority of the vestibular efferents end in the nucleus reticularis gigantocellularis in the medulla and the nucleus reticularis pontis caudalis. Both these reticular nuclei give rise to ascending fibers, which pass beyond the mesencephalon and to fibers to the spinal cord. Some data on the organization of these nuclei are discussed here. It is emphasized that their rostrally and caudally directed influence must be intimately linked. Little is known of the routes along which impulses ascending from the RF may reach the vestibular cortical area or influence stations in the optic pathways.