Neurophysiology of the nodulofloccular system

The nodulofloccular lobe is the phylogenetically oldest part of the cerebellum. The nodulus is divided into 6 zones and the flocculus into 7 zones, each of which receives ascending fiber projections from a small region of the inferior olive and which projects Purkinje cell axons to a small group of cerebellar or vestibular nuclear neurons. This zonal structure is a basis of crucial importance for understanding the complex functional involvement of the nodulofloccular system. The best studied is the H zone of the flocculus which receives horizontal retinal slip signals through climbing fibers and which projects to relay cells of the horizontal vestibulocular reflex (VOR). The flocculus hypothesis of VOR control proposes that the H zone adaptively controls the gain of the horizontal vestibuloocular reflex by referring to retinal errors, and has been supported by lesion experiments and recording from Purkinje cells and also by theoretical modeling of the flocculo-oculomotor system.