Vestibular disorders in roll plane from brainstem to cortex

Abstract

The aim is to review current knowledge of the perception of verticality, its normal function and disorders. This is based on an integrative graviceptive input from the vertical semicircular canals and the otolith organs. The focus is particularly on human psychophysics, neurophysiological and imaging data on vestibular disorders in the roll plane. The signs and symptoms are head tilt, vertical divergence of the eyes (skew deviation), ocular torsion, and tilts of subjective visual vertical (SVV) adjustments, all of which represent the so-called ocular tilt reaction (OTR). Furthermore, these signs will be related to mathematical modeling of specific vestibular cell functions for orientation in space in rodents and in patients. Pathological tilts of the SVV in the roll plane are most sensitive and frequent clinical vestibular signs of unilateral lesions extending from the labyrinths via the brainstem and thalamus to the parieto-insular vestibular cortex [[1]Brandt T. Dieterich M. The dizzy patient: Don’t forget disorders of the central vestibular system.Nat. Rev. Neurol. 2017 Jun; 13: 352-362https://doi.org/10.1038/nrneurol.2017.58Google Scholar]. Due to crossings of ascending graviceptive fibers, peripheral vestibular and pontomedullary lesions cause ipsilateral tilts of the SVV; ponto-mesencephalic lesions cause contralateral tilts. In contrast, SVV tilts, which are measured in unilateral vestibular lesions at thalamic and cortical levels, have two different characteristic features: (i) they may be ipsi- or contralateral, and (ii) they are smaller than those found in lower brainstem or peripheral lesions. Motor signs such as head tilt and body lateropulsion, i.e. components of OTR, are typical for vestibular lesions of the peripheral vestibular organ and the pontomedullary brainstem (vestibular nucleus). They are less frequent in midbrain lesions (interstitial nucleus of Cajal) and rare in cortical lesions. Vestibular function in the roll plane and its disorders can be mathematically modeled by an attractor model of the function of angular head velocity cells and head direction cells [[2]Glasauer S. Dieterich M. Brandt T. Neuronal network-based mathematical modelling of perceived verticality in acute unilateral vestibular lesions: from nerve to thalamus and cortex.J. Neurol. 2018 May 29; https://doi.org/10.1007/s00415-018-8909-5Google Scholar]. Conclusion: Clinical determinations of the SVV are easy and reliable. They indicate acute unilateral vestibular dysfunctions, the causative lesion of which extends from labyrinth to cortex. Together with additional ocular motor or brainstem signs they allow precise topographical diagnosis of side and level.