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We studied click-evoked potentials in the anterior horn of the spinal cord in 17 cats. A concentric needle electrode was inserted into the anterior horn of the spinal cord at levels C3-C6. Potentials evoked with 105 dB SPL clicks were recorded with a peak latency of 4.89-5.10 ms only at the C3 level. These responses were observed 45-60 dB SPL above the auditory brainstem response (ABR) threshold, and no potentials were evoked by stimulation of the contralateral ear. Average was performed 100 times with changes in stimulation frequency of 1-20 Hz. The amplitude of the potentials decreased with increasing stimulus frequency, but there were no changes in ABRs. The responses disappeared after destruction of the medial vestibulospinal tract at the obex level, but ABRs were still recorded. The spinal nucleus of the accessory nerves was located in the anterior horn of the spinal cord at levels C1-C6, and the sternocleidomastoid muscle motoneurons were found at levels C1-C3. The click-evoked potentials recorded in this study reflect responses of the spinal nucleus of accessory nerves through the vestibulospinal tract to click stimulation. The responses have the same characteristics as vestibular-evoked myogenic potentials that can be recorded using surface electrodes over the sternocleidomastoid muscles of humans. [ABSTRACT FROM AUTHOR]

The detection of intense sound-induced vestibular-evoked myogenic potentials (VEMPs) on the sternocleidomastoid muscle comprises the basis of the saccular function test. In order to evaluate the endolymphatic hydrops (EH) of the saccule of the inner ear, a glycerol VEMP (GVEMP) test was performed in 15 patients with unilateral typical Meniere's disease (UMD) and 7 with delayed endolymphatic hydrops (DEH). Using the GVEMP test, 8 of the 15 patients (53%) with UMD were evaluated as being abnormal. In addition, a greater number of patients (67%) were judged to be abnormal when the results of the GVEMP test were combined with those from a glycerol dehydration test, trans-tympanic electrocochleography (ECochG) or furosemide vestibulo-ocular reflex test (FVOR). Four of the 7 patients with DEH (57%) showed abnormal results in the GVEMP test. In particular, in patients with the ipsilateral type of DEH, only the GVEMP test was able to detect the affected side. These findings suggest that the GVEMP test is a new and useful test for EH, and that a test battery comprising the GVEMP test together with one of the other three tests is useful for diagnosing EH of the inner ear. [ABSTRACT FROM AUTHOR]

A total of 13 patients, who were diagnosed with localized brainstem lesions using MRI, were investigated. The diagnoses were multiple sclerosis in five patients, brainstem hemorrhage in three patients, pontomedullary infarction in one patient and Wallenberg's syndrome in four patients. In addition, 42 ears of 21 normal adult volunteers were also examined. In a patient with upper brainstem lesions mainly affecting the midbrain, the auditory brainstem response (ABR) was abnormal but the vestibular-evoked myogenic potential (VEMP) was normal. In four patients with middle brainstem lesions which mainly affected the pons, both ABR and VEMP were abnormal. In five patients with lower brainstem lesions which mainly affected the medulla, the ABR was normal but the VEMP was abnormal. In those patients with middle-to-lower brainstem lesions, a disappearance of VEMP reactions, delay of the positive-negative (PN) wave, increase in PN interpeak latency and decrease in PN amplitude on the affected side were confirmed. In conclusion, the VEMP test comprises a useful new diagnostic method for identifying lower brainstem lesions. [ABSTRACT FROM AUTHOR]

In this study, short latency vestibular evoked potentials (VsEPs) were recorded in five guinea pigs in response to alternating linear acceleration pulses with and without acoustic masking. A steel bolt was implanted in the skull and coupled to a shaker. Linear acceleration pulses (n=400) in upward, downward or alternating directions were given, with a peak acceleration of 4g after 0.5 msec. Tests were repeated with acoustic masking, after modiolus destruction and after application of KCl in the vestibule. Stimuli of the vestibular nerve were recorded with a platinum electrode in the bony facial nerve canal in the bulla. Unilateral linear acceleration showed a shallow plateau at 0.5 msec, which disappeared with alternating acceleration impulses and after modiolus destruction. Therefore all further tests were done with alternating impulses. After a latency time of 0.8 msec a multiwave response was seen, with a first positive peak P1 at 1.16 ms. These were followed by other positive and negative peaks (N1, P2, N2, P3, N3). With the elimination of cochlear influences by using acoustic masking, P1 remained stable, while subsequent peaks were altered or eliminated. After modiolus destruction, the P1 peak remained, although with a smaller amplitude due to vestibular damage. After application of a saturated KCl solution in the vestibule all responses, including P1, disappeared, thus confirming the vestibular origin of these responses. We conclude that the onset latency of the VsEP and the peak latency and level of the first positive peak P1 in response to alternating linear acceleration pulses without acoustic masking, measured in the facial canal, are good and stable parameters of vestibular function in guinea pigs. [ABSTRACT FROM AUTHOR]

Recently Minor and co-workers described patients with sound- and pressure-induced vertigo due to dehiscence of the superior semicircular canal. Identifying patients with this 'new' vestibular entity is important, not only because the symptoms are sometimes very incapacitating, but also because they can be treated. We present symptoms and findings in eight such patients, all of whom reported pressure-induced vertigo that increased during periods of upper respiratory infections. Pulse-synchronous tinnitus and gaze instability during head movements were also common complaints. All patients lateralized Weber's test to the symptomatic ear. In some of the patients the audiogram also revealed a small conductive hearing loss. However, the stapedius reflexes were always normal. A vertical/torsional eye movement related to the superior semicircular canal was seen in most of the patients in response to pressure changes and/or sound stimulation. One patient also had superior canal-related positioning nystagmus. Testing vestibular evoked myogenic potentials revealed in all patients a vestibular hypersensitivity to sounds. In the coronal high-resolution 1-mm section CT scans the dehiscence was visible on 1 to 4 sections. Moreover, the skull base was rather thin in this area and cortical bone separating the middle ear and the antrum from the middle cranial fossa was absent in many of the patients. Two of the patients have undergone plugging of the superior semicircular canal using a transmastoid approach and both patients were relieved of the pressure-induced symptoms. [ABSTRACT FROM AUTHOR]