The Flocculonodular Lobe (the Vestibulocerebellum)

The flocculonodular lobe is the oldest part of the cerebellum (i.e., the archicerebellum). It occupies the major portion of the primitive cerebellum (e.g., in the lamprey and urodele amphibia; Nieuwenhuys 1967), as indicated in Chapter 2. Further, it is with the flocculonodular (posterior) lobe of the cerebellum that the vestibular nuclei of the brain stem are most closely associated (Brodal and Jansen 1954). Correspondingly, among the afferent fibers to the flocculonodular lobe, the vestibular ones are the most significant. Primary or direct vestibular fibers (i.e., from the end-organ, the vestibular organ) reach the flocculus, nodulus, and the adjoining part of the uvula, as well as the fastigial nucleus and the lingula. Of these, the nodulus is a later phylogenetic development than the flocculus. It appears that, whereas primary vestibular fibers decrease in phylogenesis, secondary fibers undergo an increase.

In a study of the climbing fiber projection to the rat flocculus and adjacent ventral paraflocculus, Ruigrok, Osse, and Voogd (1992) found that two parts of the inferior olive (the dorsal cap of Kooy and the ventrolateral outgrowth) are both connected with a set of two alternating zones of floccular/ventral parafloccular Purkinje cells, suggesting that these zones reflect functionally distinct and discrete units related to specific aspects of visuomotor control.