China
Africa
Explore chapters and articles related to this topic
Vertigo
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Christopher C. Glisson, Jorge C. Kattah
To localize a central versus a peripheral AVS lesion, the horizontal HIT (h-HIT) remains the most sensitive test. If normal, the integrity of the horizontal VOR (h-VOR) is preserved, therefore, the lesion does not involve the primary vestibular afferents or the vestibular nerve. This is the expected finding in PICA strokes.1 Additionally, analysis of the spontaneous nystagmus direction (vertical, purely torsional, or horizontal direction changing with right and left gaze position) localizes the lesion to a central localization.16–18 In selective cases with involvement of the medial vestibular nucleus (MVN) and other brainstem structures that affect the VOR directly, an abnormal HIT may be present.19 Generally, involving the AICA distribution, which provides arterial supply to the labyrinth (Figure 7.2), AICA strokes could affect the lateral brainstem involving the vestibular root entry zone, the prepositus hypoglossi nucleus, and the cerebellar flocculus. To deal with this contingency, we proposed a triad (HINTS) analysis that include the h-HIT, the Nystagmus direction, and large amplitude (Test of Skew deviation). The combination of these signs is a strong predictor of central localization, and the acronym INFARCTS (Impulse Negative, Fast-phase Alternating, and Refixation during Cover Test) suggests central localization.17
Brain Motor Centers and Pathways
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The vestibulospinal tract has two components: (i) the lateral vestibulospinal tract, which originates in the lateral vestibular nucleus and descends, ipsilaterally, the length of the spinal cord; and (ii) the medial vestibulospinal tract, which originates in the medial vestibular nucleus and extends bilaterally through mid-thoracic levels of the spinal cord. The APs along the axons of the lateral vestibulospinal tract monosynaptically excite the motoneurons that activate the antigravity muscles, which are extensor muscles of the trunk and legs and flexor muscles of the arms, and they disynaptically inhibit motoneurons that activate the antagonists to the antigravity muscles. This pathway mediates balance, contributes to the maintenance of posture, and is involved in the vestibulospinal reflex (VSR) that stabilizes the body. When the head and trunk are tilted together to one side, for example, this reflexively activates the trunk and leg extensors on the side to which the head is tilted, so as to stabilize the body. The VSR, together with other reflexes, is also involved in the “righting” of the body to prevent a fall when slipping.
Torsional Eye Movements Evoked by Unilateral Labyrinthine Galvanic Polarizations in the Squirrel Monkey
Published in Michael Fetter, Thomas Haslwanter, Hubert Misslisch, Douglas Tweed, Three-Dimensional Kinematics of Eye, Head and Limb Movements, 2020
Lloyd B. Minor, David L. Tomko, Gary D. Paige
Interactions between torsional slow and fast phases are reminiscent of eye movements seen in the horizontal system when the velocity-to-position integrator has been made leaky. Such effects are noted after injections of neurotoxins (kainate or ibotenate) or muscimol into the region of the nucleus prepositus hypoglossi or central medial vestibular nucleus (Cannon and Robinson, 1987; Mittens et al., 1994). A reduction in time constant of the velocity-to-position integrator often occurs in association with imbalance in tonic activity between the two vestibular nerves. Its occurrence most likely accounts for Alexander’s Law, the phenomenon in which spontaneous nystagmus due to such an imbalance in vestibular activity is more intense when the subject looks in the fast-phase than in the slow-phase direction (Robinson et al., 1984).
Vestibular function in children with generalized epilepsy and treated with valproate
Published in Expert Review of Clinical Pharmacology, 2022
Sherifa Ahmed Hamed, Amira Mohamed Osiely
The vestibular system is divided into peripheral and central components. The peripheral component is composed of the semicircular canals, otolith (saccule and utricle) organs and the superior and inferior vestibular nerves. The central component begins from the point of entrance of vestibular nerves to the brainstem, the medial and lateral vestibular nuclei and the central inter-relations and connections to the thalamus and cerebral cortex. The semicircular canals sense horizontal angular head accelerations. Their afferents project to the medial vestibular nuclei via the vestibulo-ocular reflex (VOR). They provide reflexive ocular motor responses for maintenance of gaze stability. The otolith organs sense linear acceleration and static tilt in relation to gravity. Their afferents project to the lateral vestibular nucleus via the vestibulo-spinal reflex (VSR) for postural control and via connections to the cerebellar neurons, thalamus, and higher-cortical areas for balance, self-motion, and gravity direction [14].
Emerging evidence for noninvasive vagus nerve stimulation for the treatment of vestibular migraine
Published in Expert Review of Neurotherapeutics, 2020
Vagal afferents and efferents terminate in four medullary vagal nuclei: the nucleus tractus solitarius (NTS), nucleus ambiguus, trigeminal spinal nucleus, and dorsal motor vagus nucleus (DMX) [8]. The NTS is the first major relay station for vagal afferents, contains trigemino-vestibulo-vagal neurocircuitry, and plays an important role in motion sickness and migraine-related nausea [11–13]. It receives afferents from the ipsilateral medial vestibular nucleus (via the lateral pathway), the ipsilateral nucleus prepositus hypoglossi (via the medial pathway), and bilateral inferior vestibular nuclei [8]. The NTS receives vestibulo-cerebellar and vestibulo-hypothalamic afferents via the parabrachial and Kolliker-Fuse nuclei [14,15]. Indicating a role in migraine, neurons connecting the parabrachial nucleus and NTS express calcitonin gene-related peptide [16,17], and play a major role in conditioned taste aversion (the animal model for motion sickness) [18]. The DMX receives vestibular afferents [19,20], and projects to the cerebellar vermis, fastigial nucleus, and nucleus interpositus [21], structures that are important in ocular motor control [22]; these connections suggest a pathway by which nVNS modulates VM-associated vertigo and nystagmus. Other brainstem nuclei that host vestibulo-vagal connections, and thus provide a possible substrate for nVNS to act on VM episodes include the rostro-ventro-lateral medulla, reticular formation, locus coeruleus, and nucleus intercalatus [8,19,20].
Fixation stability as a biomarker for differentiating mild traumatic brain injury from age matched controls in pediatrics
Published in Brain Injury, 2021
Melissa Hunfalvay, Nicholas P. Murray, Frederick Robert Carrick
In clinical examination and clinical studies using questionnaires fixation stability is a standard part of the oculomotor exam (29). The gap between clinical practice and research reveals the need for examination of fixation stability in a quantifiable manner to determine if this construct helps further differentiate patients with TBI, especially mTBI which are the most difficult to diagnose, from those with no history of TBI and pediatrics. This study was conducted to add another element, specifically fixations, to the already important analysis of oculomotor behavior for examining mTBI. Introducing novel discriminatory measures relative to fixation assessments provides a less complicated measure of performance and thus represents a reliable and simple scheme of detection and analysis of oculomotor deficits associated with brain injury. Metrics for quantifying fixations include measurements of Bivariate Contour Ellipse Area (BCEA), Convergence Point, Depth, Disassociated Phoria, and Targeting Displacement (30). Due to the elliptical nature of fixation points, x and y coordinates are used to find an ellipse that fits the central set of x and y data points for left right and both eyes (31). Microsaccades and drifts of the human eye cause corrections of the eye back to a central point. These slight eye movements form an area of dispersion in the shape of an ellipse that is measured by the BCEA (32,33). A larger BCEA indicates a less stable fixation. Impaired fixation stability may indicate dysfunction in brainstem lesions affecting the Nucleus Prepositus Hypoglossi-Medial Vestibular Nucleus Region (NPH-MVN) which is essential for neural integration and vestibular imbalance (34,35).