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. 2020 Jun 5;11:505. doi: 10.3389/fneur.2020.00505

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Copyright © 2020 Rastoldo, Marouane, El Mahmoudi, Péricat, Bourdet, Timon-David, Dumas, Chabbert and Tighilet.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Overview of vestibulospinal reflexes to support the head tilt and hypotonia observed after unilateral vestibular neurectomy. The medial vestibulo-spinal tract (purple) is primarily composed of axons from the medial vestibular nucleus (MVN) and mainly projects contralaterally to the cervical spinal cord to mediate the vestibulocollic reflex. The lateral vestibulospinal tracts (blue) is primarily composed of axons from the lateral vestibular nucleus (LVN) and projects ipsilaterally to the entire length of the spinal cord to influence the extensor musculature of the body involved in balance. Both tracts exert excitatory effects on extensor motoneurons with some inhibitory effects on flexor motoneurons in normal condition. Left unilateral vestibular neurectomy (UVN) induces a electrophysiological imbalance between homologous vestibular nuclei. Loss of activity in the ipsilateral vestibular nucleus induces hypotonia of the lumbar extensor muscles via the lateral vestibulospinal tract. In contrast, the increase in activity in the contralateral lateral vestibular nucleus induces hypertonia of the extensor muscles opposite to the lesion as observed on the picture. Left UVN induces a head tilted (rolled) to the left side (see picture). Extensor activity is induced on the side to which the head is inclined, and flexor activity is induced on the opposite side via the medial vestibulospinal tract (11). Ex, Extensor muscle; Fl, Flexor muscle; LVN, Lateral vestibular nucleus; MVN, Medial vestibular nucleus.