Descending control of the vestibular nuclei: physiology.
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Although the use of vestibular exercises for patients with persistent vertigo and dysequilibrium has received some attention for many years, organized vestibular rehabilitation therapy programs have only recently been introduced. The benefits of such programs are becoming widely accepted. They typically involve a three-pronged approach: habituation exercises designed to facilitate central nervous system compensation by extinguishing pathologic responses to head motion, postural control exercises, and general conditioning activities. This article will describe the programmatic approach to vestibular rehabilitation, emphasizing selection criteria and reviewing results that may be anticipated when this treatment modality is used in a variety of patient populations.
This study attempts to characterize the residual vestibular function remaining after incomplete supralabyrinthine vestibular neurectomy performed for disabling vertigo. Patients with bilateral vestibular neurectomy had preserved horizontal vestibulo-ocular reflexes in response to high angular accelerations with gain enhancement over time. A torsional down-beating spontaneous nystagmus and an important tilt of the subjective vertical were observed when the remaining eighth nerve was sectioned after homolateral incomplete supralabyrinthine vestibular neurectomy. These findings suggest that a reorganization of vestibular reflexes may occur after incomplete supralabyrinthine vestibular neurectomy if afferents of the inferior vestibular branch are partially spared. The vestibular function after incomplete supralabyrinthine vestibular neurectomy does not affect the postoperative control of vertiginous attacks and may have positive effects in case of deterioration of the contralateral inner ear.
Quantitative analysis of electro-oculographic recordings of eye movement in response to precise visual and vestibular stimuli makes possible the differentiation of three categories of vestibular syndromes due to pathological changes in three different parts of the visual vestibulo-ocular reflex arc: (1) decreased vestibulo-ocular reflex gain (e.g., decrease in slow component velocity), but normal fast components and visual-vestibular interaction (labyrinth and eighth nerve); (2) normal slow component velocity but abnormal fast components to all stimuli (pontine or medullar reticular formation); and (3) normal slow component velocity to vestibulo-ocular stimulaton but abnormal visual-vestibular interaction as well as normal fast components (visual-motor pathways or cerebellum).
The aim of the present study was to determine whether a tap on the forehead evokes a vestibulospinal reflex in sternocleidomastoid muscles in normal human subjects and patients with central or vestibular lesions. While first positive-negative short-latency EMG potentials with a mean positive potential peak of about 12 ms and a mean negative potential peak of about 17 ms were found in the bilateral sternocleidomastoid muscles in normal subjects, they disappeared or were attenuated in patients with central or peripheral vestibular lesions.
AIM: To evaluate vestibular evoked myogenic potentials in patients with multiple sclerosis as method of diagnostic support. STUDY DESIGN: Case-control. MATERIAL AND METHOD: We studied a group of normal individuals (n=15) and a Studied group (n=15) that comprised patients with diagnosis of multiple sclerosis. Both groups were submitted to vestibular evoked myogenic potential exam. In each ear it was applied 200 stimuli by clicks and repeated for 2 consecutive cycles with the purpose of evaluating reproducibility. The active electrode of surface was put on the superior S++ of sternocleidomastoid muscle and the reference electrode on the anterior border of the clavicle. The individuals were instructed to rotate theirs head to the opposite side to the stimulated ear. RESULTS: Vestibular evoked myogenic potential responses were prompt, reproducible and biphasic. The latency of wave P1 and N2 and P1-N2 amplitude showed a higher value in the studied group when compared with the normal group. There was no significant difference when the ears were compared in P1 and N2 amplitude. We noticed that individuals with multiple sclerosis showed no response in 30% of the cases. In evaluating the individuals of the Studied group with otoneurology symptoms and compared with individuals without symptoms, it was observed that P1 and N2 latencies and P1-N2 amplitude were higher in symptomatic cases. CONCLUSION: Vestibular evoked myogenic potential was considered a good method of diagnostic support of vestibulospinal tract in cases of multiple sclerosis.
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A survey of the literature concerning reversible hearing loss in tumours of the cerebello-pontine angle is presented together with two additional cases. After removal of one meningioma and one epidermoid tumour, respectively, the abolished acoustico-vestibular function returned in both cases. The pre-requisites for the restoration of hearing are discussed.
It has been reported that the galvanic body sway test does not correlate with the caloric test. We evaluated the galvanic body sway test in patients with vestibular schwannomas using three parameters: the angle of deviation response onset, the maximum value of the deviation response, and the area of deviation. These parameters reflect velocity, position, and locus of the centre of pressure, respectively. Among these parameters, only the angle of deviation response onset showed unilateral weakness of the response correlating with the canal paresis value, which indicates that velocity is responsible for conduction in the vestibular nerve. However, the galvanic body sway test is apt to be preferred to the caloric test. This might be attributed to the decreased sensitivity of this test.
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BACKGROUND: Vestibuloocular and vestibulospinal reactions following the bilateral loss of vestibular function are designated as Bechterew's phenomenon. In vestibular physiology, under experimental conditions, this phenomenon has played an important role for understanding the mechanisms underlying vestibular compensation. However, clinical reports about this phenomenon in humans are extremely rare. PATIENTS AND METHODS: Bechterew's phenomen was observed throughout every stage of its development in a patient with consecutive bilateral loss of vestibular function. The disorder was documented by electronystagmography and posturography. DISCUSSION AND CONCLUSIONS: Bechterew's phenomenon depends on different states of vestibular function developing in a certain succession, whereby the varying relations between failure and compensation are decisive. The phenomen very impressively demonstrates the resilience of the central nervous system in adapting to varying peripheral functional states. From a clinical standpoint, knowledge of these relationships is important for understanding vestibular compensation.
BACKGROUND: Positioning nystagmus of the peripheral benign type (BPPV) has long been considered to be due to cupulolithiasis-i.e. attachment of inorganic material to the cupula-of the posterior vertical semicircular canal. Meanwhile it has generally been recognized that not all characteristics of this type of nystagmus/vertigo can be explained by assuming a gravity-dependent reaction of the posterior canal. Canalolithiasis-i.e. floating material within the canal, heavier than endolymphe-of the posterior semicircular canal is now widely regarded as the cause of BPPV. Again, however, this is a concept far too simple to explain most of the properties of BPPV. METHODS: Clearly defined, carefully performed positioning and positional maneuvers were carried out on 79 patients suffering from typical BPPV in order to reveal those positioning movements and positions necessary to elicit BPPV. RESULTS: Detailed analysis of those positioning maneuvers necessary to elicit BPPV clearly reveals that canalolithiasis cannot be the cause of BBPV. CONCLUSIONS: BPPV is a combination of positioning, and positional-dependent reactions in which the otolithic organs, and particularly the sacculus, seem to be involved.