Vestibulocerebellar connections

Abstract

The vestibular system projects onto the cerebellum via three major pathways that are composed of primary and secondary vestibular mossy fiber afferents and tertiary vestibular climbing fibers. Vestibular primary afferent mossy fibers project to the ipsilateral uvula-nodulus (folia 9d and 10). Secondary vestibular mossy fibers originate from three of the five vestibular nuclei: medial, descending, and superior (MVN, DVN, and SVN). These mossy fibers terminate in the uvula-nodulus and flocculus. The MVN, DVN, and SVN receive convergent vestibular, optokinetic, and neck proprioceptive information. Vestibular tertiary afferents originate from two subnuclei of the inferior olive, the β-nucleus and dorsomedial cell column (DMCC), and send climbing fibers to the contralateral uvula-nodulus. The β-nucleus and DMCC receive direct projections from the parasolitary nucleus (Psol). The Psol, β-nucleus, and DMCC convey information to the cerebellum from the vertical semicircular canals and otoliths, but not from the horizontal semicircular canals. Climbing fiber projections are arrayed in sagittal zones, establishing a mediolateral map on the uvula-nodulus of the 180° of possible head angles during roll-tilt. Signals conveyed from climbing fibers are preeminent in modulating the discharge of both complex and simple spikes (CSs and SSs) in cerebellar Purkinje cells. This discharge is fed back onto a fraction of neurons in the dorsal aspect of the descending and medial vestibular nuclei as well as the prepositus hypoglossal nucleus. The vestibulocerebellum imposes a climbing fiber-constructed coordinate system on postural responses and permits adaptive guidance of movement.