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Hirvonen TP, Minor LB, Hullar TE, Carey JP. Effects of Intratympanic Gentamicin on Vestibular Afferents and Hair Cells in the Chinchilla. J Neurophysiol 2005; 93:643-55. [PMID: 15456806 DOI: 10.1152/jn.00160.2004] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Gentamicin is toxic to vestibular hair cells, but its effects on vestibular afferents have not been defined. We treated anesthetized chinchillas with one injection of gentamicin (26.7 mg/ml) into the middle ear and made extracellular recordings from afferents after 5–25 (early) or 90–115 days (late). The relative proportions of regular, intermediate, and irregular afferents did not change after treatment. The spontaneous firing rate of regular afferents was lower ( P < 0.001) on the treated side (early: 44.3 ± 16.3; late: 33.9 ± 13.2 spikes·s−1) than on the untreated side (54.9 ± 16.8 spikes·s−1). Spontaneous rates of irregular and intermediate afferents did not change. The majority of treated afferents did not measurably respond to tilt or rotation (82% in the early group, 76% in the late group). Those that did respond had abnormally low sensitivities ( P < 0.001). Treated canal units that responded to rotation had mean sensitivities only 5–7% of the values for untreated canal afferents. Treated otolith afferents had mean sensitivities 23–28% of the values for untreated otolith units. Sensitivity to externally applied galvanic currents was unaffected for all afferents. Intratympanic gentamicin treatment reduced the histological density of all hair cells by 57% ( P = 0.04). The density of hair cells with calyx endings was reduced by 99% ( P = 0.03), although some remaining hair cells had other features suggestive of type I morphology. Type II hair cell density was not significantly reduced. These findings suggest that a single intratympanic gentamicin injection causes partial damage and loss of vestibular hair cells, particularly type I hair cells or their calyceal afferent endings, does not damage the afferent spike initiation zones, and preserves enough hair cell synaptic activity to drive the spontaneous activity of vestibular afferents.
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Hullar TE, Della Santina CC, Hirvonen T, Lasker DM, Carey JP, Minor LB. Responses of irregularly discharging chinchilla semicircular canal vestibular-nerve afferents during high-frequency head rotations. J Neurophysiol 2004; 93:2777-86. [PMID: 15601735 DOI: 10.1152/jn.01002.2004] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mammalian vestibular-nerve afferents innervating the semicircular canals have been divided into groups according to their discharge regularity, gain at 2-Hz rotational stimulation, and morphology. Low-gain irregular afferents terminate in calyx endings in the central crista, high-gain irregular afferents synapse more peripherally in dimorphic (bouton and calyx) endings, and regular afferents terminate in the peripheral zone as bouton-only and dimorphic endings. The response dynamics of these three groups have been described only up to 4 Hz in previous studies. Reported here are responses of chinchilla semicircular canal vestibular-nerve afferents to rotational stimuli at frequencies up to 16 Hz. The sensitivity of all afferents increased with increasing frequency with the sensitivity of low-gain irregular afferents increasing the most and matching the high-gain irregular afferents at 16 Hz. All afferents increased their phase lead with respect to stimulus velocity at higher frequencies with the highest leads in low-gain irregular afferents and the lowest in regular afferents. No attenuation of sensitivity or shift in phase consistent with the presence of a high-frequency pole over the range tested was noted. Responses were best fit with a torsion-pendulum model combined with a lead operator (tau(HF1)s + 1)(tau(HF2)s + 1). The discharge regularity of individual afferents was correlated to the value of each afferent's lead operator time constants. These findings suggest that low-gain irregular afferents are well suited for encoding the onset of rapid head movements, a property that would be advantageous for initiation of reflexes with short latency such as the vestibulo-ocular reflex.
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Migliaccio AA, Schubert MC, Jiradejvong P, Lasker DM, Clendaniel RA, Minor LB. The three-dimensional vestibulo-ocular reflex evoked by high-acceleration rotations in the squirrel monkey. Exp Brain Res 2004; 159:433-46. [PMID: 15349709 DOI: 10.1007/s00221-004-1974-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2003] [Accepted: 05/04/2004] [Indexed: 10/26/2022]
Abstract
The aim of this study was to determine if the angular vestibulo-ocular reflex (VOR) in response to pitch, roll, left anterior-right posterior (LARP), and right anterior-left posterior (RALP) head rotations exhibited the same linear and nonlinear characteristics as those found in the horizontal VOR. Three-dimensional eye movements were recorded with the scleral search coil technique. The VOR in response to rotations in five planes (horizontal, vertical, torsional, LARP, and RALP) was studied in three squirrel monkeys. The latency of the VOR evoked by steps of acceleration in darkness (3,000 degrees /s(2) reaching a velocity of 150 degrees /s) was 5.8+/-1.7 ms and was the same in response to head rotations in all five planes of rotation. The gain of the reflex during the acceleration was 36.7+/-15.4% greater than that measured at the plateau of head velocity. Polynomial fits to the trajectory of the response show that eye velocity is proportional to the cube of head velocity in all five planes of rotation. For sinusoidal rotations of 0.5-15 Hz with a peak velocity of 20 degrees /s, the VOR gain did not change with frequency (0.74+/-0.06, 0.74+/-0.07, 0.37+/-0.05, 0.69+/-0.06, and 0.64+/-0.06, for yaw, pitch, roll, LARP, and RALP respectively). The VOR gain increased with head velocity for sinusoidal rotations at frequencies > or =4 Hz. For rotational frequencies > or =4 Hz, we show that the vertical, torsional, LARP, and RALP VORs have the same linear and nonlinear characteristics as the horizontal VOR. In addition, we show that the gain, phase and axis of eye rotation during LARP and RALP head rotations can be predicted once the pitch and roll responses are characterized.
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Migliaccio AA, Minor LB, Carey JP. Vergence-mediated modulation of the human horizontal vestibulo-ocular reflex is eliminated by a partial peripheral gentamicin lesion. Exp Brain Res 2004; 159:92-8. [PMID: 15221168 DOI: 10.1007/s00221-004-1936-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2004] [Accepted: 04/07/2004] [Indexed: 11/29/2022]
Abstract
The angular vestibulo-ocular reflex normally has an increased response during vergence on a near target. Surgical unilateral vestibular deafferentation reduces the horizontal vestibulo-ocular reflex (VOR) in response to far target viewing and eliminates this vergence effect. Intratympanic gentamicin treatment reduces VOR gain during far viewing, but the reduction is less severe than that after unilateral vestibular deafferentation. We sought to determine how gentamicin would affect vergence-mediated modulation of the VOR. The VOR in response to passive head impulses in the horizontal plane while viewing a far (124 cm) or near (15 cm) target was evaluated in 11 subjects following intratympanic gentamicin treatment. Three of these subjects had also been tested immediately prior to receiving gentamicin. The impulses were low amplitude (approximately 20 degrees ), high velocity (approximately 150 degrees /s), high acceleration (approximately 3,000 degrees /s2) horizontal head rotations administered manually by the investigator. Binocular eye and head velocity were recorded using the scleral search coil technique. The VOR gain was defined as eye velocity divided by inverted head velocity. Prior to intratympanic gentamicin, the VOR gain during rotations to either side was symmetric and showed the same vergence-mediated increase. Following gentamicin, head impulses towards the untreated side yielded VOR gains of 0.91+/-0.12 while viewing a far target and 1.27+/-0.22 while viewing a near target, an increase of 33%. Head impulses towards the treated side produced a hypometric VOR with no increase between far and near viewing. The average latency of the VOR was 7.6+/-2.5 ms towards the untreated side for either near or far viewing and 20.7+/-13.1 ms towards the treated side for either near or far viewing. Our findings show that a peripheral lesion caused by gentamicin does not ablate the VOR but does eliminate a component of the vestibular signal that is necessary for vergence-mediated modulation of the VOR. Gentamicin has preferential toxicity for the hair cells in the central zone of the crista, where irregular afferents predominate. Our findings are consistent with the hypothesis that irregular afferents provide the necessary signal for vergence-mediated modulation of the VOR.
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Carey JP, Hirvonen TP, Hullar TE, Minor LB. Acoustic Responses of Vestibular Afferents in a Model of Superior Canal Dehiscence. Otol Neurotol 2004; 25:345-52. [PMID: 15129116 DOI: 10.1097/00129492-200405000-00024] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
HYPOTHESIS Afferents innervating the superior semicircular canal are rendered especially sensitive to acoustic stimulation when there is a dehiscence of the superior canal. Other vestibular end organs are also more sensitive to acoustic stimulation. BACKGROUND Dehiscence of the superior semicircular canal is associated with vertigo and nystagmus caused by loud sounds (Tullio phenomenon) or changes in middle ear or intracranial pressures. The mechanisms by which acoustic stimuli act on the vestibular end organs are unclear. The nystagmus caused by acoustic stimuli generally aligns with the affected superior canal. METHODS Responses to acoustic stimuli in the superior vestibular nerves of anesthetized chinchillas were recorded before and after fenestration of the superior canal. RESULTS Two acoustic response patterns were seen: rapid phase locking and slow tonic changes in firing rate. Phasic responses principally occurred in irregular afferents and tonic responses in regular afferents. Afferents from all of the vestibular end organs encountered could respond to acoustic stimuli, even before fenestration. However, fenestration lowered the thresholds for acoustic stimulation in superior canal afferents with phasic responses and increased the magnitude of tonic responses. CONCLUSIONS Superior canal dehiscence may render the irregular afferents innervating the superior canal particularly sensitive to loud sounds. Rapid phase-locking responses may explain the short latency of nystagmus seen in patients with superior canal dehiscence syndrome. The mechanisms by which acoustic stimuli activate the vestibular end organs may differ from the damped endolymph motion associated with head acceleration.
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Schubert MC, Minor LB. Vestibulo-ocular physiology underlying vestibular hypofunction. Phys Ther 2004; 84:373-85. [PMID: 15049730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
The vestibular system detects motion of the head and maintains stability of images on the fovea of the retina as well as postural control during head motion. Signals representing angular and translational motion of the head as well as the tilt of the head relative to gravity are transduced by the vestibular end organs in the inner ear. This sensory information is then used to control reflexes responsible for maintaining the stability of images on the fovea (the central area of the retina where visual acuity is best) during head movements. Information from the vestibular receptors also is important for posture and gait. When vestibular function is normal, these reflexes operate with exquisite accuracy and, in the case of eye movements, at very short latencies. Knowledge of vestibular anatomy and physiology is important for physical therapists to effectively diagnose and manage people with vestibular dysfunction. The purposes of this article are to review the anatomy and physiology of the vestibular system and to describe the neurophysiological mechanisms responsible for the vestibulo-ocular abnormalities in patients with vestibular hypofunction.
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Peng GCY, Zee DS, Minor LB. Phase-Plane Analysis of Gaze Stabilization to High Acceleration Head Thrusts: A Continuum Across Normal Subjects and Patients With Loss of Vestibular Function. J Neurophysiol 2004; 91:1763-81. [PMID: 14657187 DOI: 10.1152/jn.00611.2002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We investigated the vestibulo-ocular reflex (VOR) during high-acceleration, yaw-axis, head rotations in 12 normals and 15 patients with vestibular loss [7 unilateral vestibular deficient (UVD) and 8 bilateral vestibular deficient (BVD)]. We analyzed gaze stabilization within a 200-ms window after head rotation began, using phase planes, which allowed simultaneous analysis of gaze velocity and gaze position. These “gaze planes” revealed critical dynamic information not easily gleaned from traditional gain measurements. We found linear relationships between peak gaze-velocity and peak gaze-position error when normalized to peak head speed and position, respectively. Values fell on a continuum, increasing from normals, to normals tested with very high acceleration (VHA = 10,000–20,000°/s2), to UVD patients during rotations toward the intact side, to UVD patients during rotations toward the lesioned side, to BVD patients. We classified compensatory gaze corrections as gaze-position corrections (GPCs) or gaze-velocity error corrections (GVCs). We defined patients as better-compensated when the value of their end gaze position was low relative to peak gaze position. In the gaze plane this criterion corresponded to relatively stereotyped patterns over many rotations, and appearance of high velocity (100–400°/s) GPCs in the gaze plane ending quadrant (150–200 ms after head movement onset). In less-compensated patients, and normals at VHA, more GVCs were generated, and GPCs were generated only after gaze-velocity error was minimized. These findings suggest that challenges to compensatory vestibular function can be from vestibular deficiency or novel stimuli not previously experienced. Similar patterns of challenge and compensation were observed in both patients with vestibular loss and normal subjects.
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Abstract
PURPOSE OF REVIEW Ménière's disease is characterized by spontaneous attacks of vertigo, fluctuating sensorineural hearing loss, aural fullness, and tinnitus. The pathologic process involves distortion of the membranous labyrinth with the formation of endolymphatic hydrops. This review describes the pathogenesis and etiology as well as the diagnosis and treatment of Ménière's disease. RECENT FINDINGS Initial management of Ménière's disease can involve a low-salt diet and a diuretic. Treatment with intratympanic injection of gentamicin can be beneficial when vertigo persists despite optimal medical management. Recent studies have shown that gentamicin reduces vestibular function in the treated ear, although complete ablation of this vestibular function is not typically required in order to achieve control of vertigo. SUMMARY Vertigo is often the most debilitating symptom associated with Ménière's disease. Many treatment options exist for the management of vertigo. Intratympanic injection of gentamicin (low dose) can be used in patients for whom vertigo has not been controlled by medical measures. Ongoing research is providing a greater understanding of the effects of gentamicin on vestibular function and of the mechanisms through which gentamicin leads to control of vertigo.
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Abstract
PURPOSE OF REVIEW This article reviews literature on three manifestations of these pathologic mechanisms: leakage of perilymph from the inner ear into the middle ear, disruption of the bone of the labyrinth caused by cholesteatoma or other manifestations of chronic otitis media, and superior semicircular canal dehiscence syndrome. RECENT FINDINGS Labyrinthine fistulae are caused by abnormal communications between the inner ear and surrounding structures. Under normal circumstances, the fluid-filled spaces of the membranous labyrinth are encased in the dense bone of the otic capsule with only two places of increased compliance: the oval window and the round window. Disruption of the labyrinthine bone can lead to areas of increased compliance, with symptoms and signs that can be understood based upon abnormal pressure transmission in the system. Communication between the endolymphatic and perilymphatic spaces of the labyrinth or passage of perilymph from the labyrinth into the middle ear or mastoid can lead to hearing loss and/or vestibular disturbances. SUMMARY Findings on clinical examination as well as CT imaging of the temporal bone can be useful in making the diagnosis. Management is based upon the specific pathological factors and the impact of the symptoms and signs on the patient.
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Migliaccio AA, Cremer PD, Aw ST, Halmagyi GM, Curthoys IS, Minor LB, Todd MJ. Vergence-mediated changes in the axis of eye rotation during the human vestibulo-ocular reflex can occur independent of eye position. Exp Brain Res 2003; 151:238-48. [PMID: 12783151 DOI: 10.1007/s00221-003-1447-z] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2002] [Accepted: 02/11/2003] [Indexed: 10/26/2022]
Abstract
The aim of this study was to determine whether vergence-mediated changes in the axis of eye rotation in the human vestibulo-ocular reflex (VOR) would obey Listing's Law (normally associated with saccadic eye movements) independent of the initial eye position. We devised a paradigm for disassociating the saccadic velocity axis from eye position by presenting near and far targets that were centered with respect to one eye. We measured binocular 3-dimensional eye movements using search coils in ten normal subjects and 3-dimensional linear head acceleration using Optotrak in seven normal subjects. The stimuli consisted of passive, unpredictable, pitch head rotations with peak acceleration of approximately 2000 degrees /s(2 )and amplitude of approximately 20 degrees. During the pitch head rotation, each subject fixated straight ahead with one eye, whereas the other eye was adducted 4 degrees during far viewing (94 cm) and 25 degrees during near viewing (15 cm). Our data showed expected compensatory pitch rotations in both eyes, and a vergence-mediated horizontal rotation only in the adducting eye. In addition, during near viewing we observed torsional eye rotations not only in the adducting eye but also in the eye looking straight ahead. In the straight-ahead eye, the change in torsional eye velocity between near and far viewing, which began approximately 40 ms after the start of head rotation, was 10+/-6 degrees /s (mean +/- SD). This change in torsional eye velocity resulted in a 2.4+/-1.5 degrees axis tilt toward Listing's plane in that eye. In the adducting eye, the change in torsional eye velocity between near and far viewing was 16+/-6 degrees /s (mean +/- SD) and resulted in a 4.1+/-1.4 degrees axis tilt. The torsional eye velocities were conjugate and both eyes partially obeyed Listing's Law. The axis of eye rotation tilted in the direction of the line of sight by approximately one-third of the angle between the line of sight and a line orthogonal to Listing's plane. This tilt was higher than predicted by the one-quarter rule. The translational acceleration component of the pitch head rotation measured 0.5 g and may have contributed to the increased torsional component observed during near viewing. Our data show that vergence-mediated eye movements obey a VOR/Listing's Law compromise strategy independent of the initial eye position.
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Cox KM, Lee DJ, Carey JP, Minor LB. Dehiscence of bone overlying the superior semicircular canal as a cause of an air-bone gap on audiometry: a case study. Am J Audiol 2003; 12:11-6. [PMID: 12894862 DOI: 10.1044/1059-0889(2003/004)] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Dehiscence of bone overlying the superior semicircular canal can result in a syndrome of vertigo and oscillopsia induced by loud noises or by maneuvers that change middle ear or intracranial pressure. Patients with this disorder can also experience a heightened sensitivity to bone-conducted sounds in the presence of normal middle ear function. High-resolution CT scans of the temporal bones demonstrate the dehiscence. The authors describe a patient with bilateral superior canal dehiscence who had bilateral low-frequency conductive hearing loss, normal middle ear function, intact acoustic reflexes, and intact vestibular-evoked myogenic potentials. These findings would not be expected on the basis of a middle ear cause of the conductive hearing loss. A high-resolution CT scan of the temporal bones in this patient revealed bilateral superior canal dehiscence. Normal acoustic immittance findings in the presence of conductive hearing loss should alert clinicians to the possibility of inner ear cause of an air-bone gap due to superior canal dehiscence.
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Hirvonen TP, Weg N, Zinreich SJ, Minor LB. High-resolution CT findings suggest a developmental abnormality underlying superior canal dehiscence syndrome. Acta Otolaryngol 2003; 123:477-81. [PMID: 12797581 DOI: 10.1080/0036554021000028099] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
OBJECTIVE Patients with superior canal dehiscence (SCD) syndrome experience vertigo and oscillopsia with loud sounds and/or stimuli that result in changes in middle ear or intracranial pressure. Findings on temporal bone CT were analyzed to determine if a developmental abnormality is associated with the syndrome. MATERIAL AND METHODS Temporal bone CT scans [0.5 mm collimation and projections into the superior semicircular canal (SC) plane] were used to compare the bone overlying the SC in patients with SCD syndrome (20 unilateral, 7 bilateral) and in 88 patients without SCD syndrome who had undergone temporal bone CT for evaluation of other otologic disorders (controls). RESULTS The thickness of bone overlying the SC in the controls measured 0.67 +/- 0.38 mm (mean +/- SD). For individual control subjects. the thickness of bone on one side was correlated with that on the other side (r = 0.43; p < 0.0001). The thickness of bone overlying the SC on the intact side in patients with unilateral dehiscence measured 0.31 +/- 0.23 mm, and was thinner than that noted in the controls (p < 0.0001). CONCLUSION These findings support the notion that there is a developmental abnormality underlying SCD syndrome. When dehiscence is found on one side, the contralateral side is likely to be thin.
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Wu IC, Minor LB. Long-term hearing outcome in patients receiving intratympanic gentamicin for Ménière's disease. Laryngoscope 2003; 113:815-20. [PMID: 12792316 DOI: 10.1097/00005537-200305000-00009] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
OBJECTIVE To determine the long-term hearing outcome in patients with intractable vertigo caused by unilateral Ménière's disease who were treated with intratympanic injection of gentamicin. STUDY DESIGN The study was a longitudinal analysis of hearing and control of vertigo in patients with unilateral Ménière's disease who received intratympanic gentamicin. METHODS Pure-tone thresholds and speech discrimination scores on audiometry were analyzed, along with the control of vertigo. Criteria described in 1995 by the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) were used. Patients treated with intratympanic gentamicin had "definite" Ménière's disease and had intractable vertigo despite optimal medical therapy, no symptoms suggestive of Ménière's disease in the contralateral ear, and serviceable hearing in the contralateral ear. The study analyzed the outcomes of 34 patients for whom follow-up data were available for periods greater than 24 months after intratympanic gentamicin. RESULTS Complete control of vertigo (AAOHNS Class A) was obtained in 90% of the patients. Profound sensorineural hearing loss occurred as a result of gentamicin injection in 1 of the 34 patients (3%). When data from all patients were grouped together, hearing was improved in 5 (15%), unchanged in 23 (68%), and worse in 6 (17%) patients. This distribution of hearing outcome is similar to that in patients whose symptoms of Ménière's disease were managed with medical measures. Recurrent vertigo developed in 10 patients (29%) at an interval of 4 to 15 months after initially complete control. Treatment with additional intratympanic injection(s) of gentamicin did not result in a change in hearing. CONCLUSION The risk of hearing loss in patients treated with infrequent intratympanic injection(s) of gentamicin is low.
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Lustig LR, Yeagle J, Niparko JK, Minor LB. Cochlear implantation in patients with bilateral Ménière's syndrome. Otol Neurotol 2003; 24:397-403. [PMID: 12806291 DOI: 10.1097/00129492-200305000-00009] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE To evaluate the indications and clinical outcomes (audiologic and vestibular) in patients with Ménière's syndrome who have undergone cochlear implantation. STUDY DESIGN This is a retrospective review of patients at a large tertiary academic medical center. PATIENTS Nine patients were included in the study with AAO-HNS criteria for diagnosis of Ménière's syndrome as well as bilateral severe to profound sensorineural hearing loss as an indication for undergoing cochlear implantation. Audiologic criteria for implantation were considered in the context of speech recognition performance with well-fit, powerful hearing aids noting large fluctuations in performance levels in some patients. In all cases, the poorer hearing ear was implanted. Seven subjects had bilateral disease and had progressed to profound sensorineural hearing loss. The average age of the patients was 61 years. Six patients had undergone previous surgery to control vertigo, including endolymphatic shunt surgery and vestibular nerve section. No patient had received previous treatment with intra-tympanic gentamicin. Symptoms of Ménière's syndrome had been present in all patients for at least 10 years before implantation. INTERVENTION Cochlear Implantation. MAIN OUTCOME MEASURES Pre- and Postoperative audiometric scores (monosyllable words/phonemes, Central Institute for the Deaf (CID) sentences, Hearing in Noise Test (HINT) in quite/noise (+10 db)), pre- and postoperative vestibular symptoms (number of vestibular attacks, aural fullness, tinnitus). RESULTS Follow-up after implantation ranged from 1 to 5 years. Average 6 month postimplantation scores were: monosyllable words/phonemes = 52%/65%, CID sentences = 82%, HINT in quiet/noise = 70%/50%. Average 1-year postimplant scores were: monosyllable words/phonemes = 60%/76%, CID sentences = 97%, HINT in quiet/noise = 89%/78%. Postoperative speech recognition scores were, on average, substantially greater than preoperative scores. While there were few complications associated with implantation, some patients experienced alterations in their implant performance in association with fluctuations in vestibular symptoms. CONCLUSIONS Patients with advanced binaural involvement with Ménière's Disease may present a challenge to conventional criteria for cochlear implant candidacy because of fluctuating symptoms. We observed significant benefit over baseline in a consecutive series of patients with Ménière's syndrome who progressed to bilateral, severe-to-profound sensorineural hearing loss and underwent cochlear implantation. Further, previous vestibular surgery, including labyrinthectomy, does not contraindicate cochlear implantation.
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Minor LB, Carey JP, Cremer PD, Lustig LR, Streubel SO, Ruckenstein MJ. Dehiscence of bone overlying the superior canal as a cause of apparent conductive hearing loss. Otol Neurotol 2003; 24:270-8. [PMID: 12621343 DOI: 10.1097/00129492-200303000-00023] [Citation(s) in RCA: 197] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE To identify patients with superior semicircular canal dehiscence and apparent conductive hearing loss and to define the cause of the air-bone gap. STUDY DESIGN Prospective study of patients with superior canal dehiscence. SETTING Tertiary referral center. PATIENTS Vestibular and/or auditory findings indicative of canal dehiscence and demonstration of superior canal dehiscence on computed tomography of the temporal bone. INTERVENTION Vestibular-evoked myogenic potentials, three-dimensional eye movement recordings, and surgical resurfacing of the superior canal. OUTCOME MEASURE Association of superior canal dehiscence with an air-bone gap on audiometry. RESULTS Four patients with dehiscence of bone overlying the superior canal were found to have air-bone gaps in the affected ears that were greatest at lower frequencies and averaged 24 +/- 7 dB over the frequency range of 250 to 4,000 Hz. Three of these patients had undergone stapedectomy before the identification of superior canal dehiscence. The air-bone gap was unchanged postoperatively. Each patient had an intact vestibular-evoked myogenic potential (VEMP) response from the affected ear, a finding that would not have been expected based on a middle ear cause of conductive hearing loss. One patient underwent resurfacing of the superior canal through a middle fossa approach. Postoperatively, his vestibular symptoms were relieved, and his air conduction thresholds were improved by 20 dB. CONCLUSIONS Superior canal dehiscence can result in apparent conductive hearing loss. The third mobile window created by the dehiscent superior canal results in dissipation of acoustic energy and is a cause of inner ear conductive hearing loss.
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Belden CJ, Weg N, Minor LB, Zinreich SJ. CT evaluation of bone dehiscence of the superior semicircular canal as a cause of sound- and/or pressure-induced vertigo. Radiology 2003; 226:337-43. [PMID: 12563123 DOI: 10.1148/radiol.2262010897] [Citation(s) in RCA: 171] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To describe the computed tomographic (CT) findings at different collimation widths associated with superior semicircular canal (SSC) dehiscence syndrome and to determine the frequency of these findings in a control population. MATERIALS AND METHODS Temporal bone CT scans with 1.0-mm and/or 0.5-mm collimation were obtained in 50 patients with sound- and/or pressure-induced vestibular symptoms. The control population consisted of 50 patients undergoing CT at 1.0-mm collimation and 57 patients undergoing CT at 0.5-mm collimation for other reasons. RESULTS SSC dehiscence was documented on CT scans in all 36 patients with the clinical syndrome, with bilateral findings in six patients. Six other patients without specific clinical signs appeared to have dehiscence on 1.0-mm-collimated scans. Intact bone overlaying the SSC was subsequently identified with 0.5-mm-collimated CT in each case. On the 1.0-mm-collimated scans in 50 control patients, an area judged as possible or definite dehiscence was identified in 18 of 100 ears. The bone overlaying the SSC was intact in each of the 114 control ears evaluated with 0.5-mm-collimated CT. CT findings from the patients with vestibular symptoms combined with those in the control population indicated that the positive predictive value of an apparent dehiscence in the diagnosis of SSC dehiscence syndrome improved from 50% with 1.0-mm-collimated CT with transverse and coronal images to 93% with 0.5-mm-collimated CT with reformation in the plane of the SSC. CONCLUSION The positive predictive value of CT in identification of SSC dehiscence syndrome improves with 0.5-mm-collimated helical CT and reformation in the SSC plane.
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Carey JP, Minor LB, Peng GCY, Della Santina CC, Cremer PD, Haslwanter T. Changes in the three-dimensional angular vestibulo-ocular reflex following intratympanic gentamicin for Ménière's disease. J Assoc Res Otolaryngol 2002; 3:430-43. [PMID: 12486598 PMCID: PMC3202443 DOI: 10.1007/s101620010053] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2000] [Accepted: 01/21/2002] [Indexed: 11/24/2022] Open
Abstract
The 3-dimensional angular vestibulo-ocular reflexes (AVOR) elicited by rapid rotary head thrusts were studied in 17 subjects with unilateral Ménière's disease before and 2-10 weeks after treatment with intratympanic gentamicin and in 13 subjects after surgical unilateral vestibular destruction (SUVD). Each head thrust was in the horizontal plane or in either diagonal plane of the vertical semicircular canals, so that each head thrust effectively stimulated only one pair of canals. The AVOR gains (eye velocity/head velocity during the 30 ms before peak head velocity) for the head thrusts exciting each individual canal were averaged and taken as a measure of the function of that canal. Prior to intratympanic gentamicin, gains for head thrusts that excited canals on the affected side were 0.91 +/- 0.20 (horizontal canal, HC), 0.78 +/- 0.20 (anterior canal, AC), and 0.83 +/- 0.10 (posterior canal, PC). The asymmetries between these gain values and those for head thrusts that excited the contralateral canals were <2%. In contrast, caloric asymmetries averaged 40% +/- 32%. Intratympanic gentamicin resulted in decreased gains attributable to each canal on the treated side: 0.40 +/- 0.12 (HC), 0.35 +/- 0.14 (AC), 0.31 +/- 0.14 (PC) (p <0.01). However, the gains attributable to contralateral canals dropped only slightly, resulting in marked asymmetries between gains for excitation of ipsilateral canals versus their contralateral mates: HC: 34% +/- 12%, AC: 24% +/- 25%, and PC: 42% +/- 13%. There was no difference in the AVOR gain for excitation of the ipsilateral HC after gentamicin in patients who received a single intratympanic injection (0.39 +/- 0.11, n = 12) in comparison to those who received 2-3 injections (0.42 +/- 0.15, n = 5, p = 0.7). Gain decreases attributed to the gentamicin-treated HC and AC were not as severe as those observed after SUVD. This finding suggests that intratympanic gentamicin causes a partial vestibular lesion that may involve preservation of spontaneous discharge and/or rotational sensitivity of afferents.
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Clendaniel RA, Lasker DM, Minor LB. Differential adaptation of the linear and nonlinear components of the horizontal vestibuloocular reflex in squirrel monkeys. J Neurophysiol 2002; 88:3534-40. [PMID: 12466466 DOI: 10.1152/jn.00404.2002] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previous work in squirrel monkeys has demonstrated the presence of linear and nonlinear components to the horizontal vestibuloocular reflex (VOR) evoked by high-acceleration rotations. The nonlinear component is seen as a rise in gain with increasing velocity of rotation at frequencies more than 2 Hz (a velocity-dependent gain enhancement). We have shown that there are greater changes in the nonlinear than linear component of the response after spectacle-induced adaptation. The present study was conducted to determine if the two components of the response share a common adaptive process. The gain of the VOR, in the dark, to sinusoidal stimuli at 4 Hz (peak velocities: 20-150 degrees /s) and 10 Hz (peak velocities: 20 and 100 degrees /s) was measured pre- and postadaptation. Adaptation was induced over 4 h with x0.45 minimizing spectacles. Sum-of-sines stimuli were used to induce adaptation, and the parameters of the stimuli were adjusted to invoke only the linear or both linear and nonlinear components of the response. Preadaptation, there was a velocity-dependent gain enhancement at 4 and 10 Hz. In postadaptation with the paradigms that only recruited the linear component, there was a decrease in gain and a persistent velocity-dependent gain enhancement (indicating adaptation of only the linear component). After adaptation with the paradigm designed to recruit both the linear and nonlinear components, there was a decrease in gain and no velocity-dependent gain enhancement (indicating adaptation of both components). There were comparable changes in the response to steps of acceleration. We interpret these results to indicate that separate processes drive the adaptation of the linear and nonlinear components of the response.
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Reti IM, Minor LB, Baraban JM. Prominent expression of Narp in central vestibular pathways: selective effect of labyrinth ablation. Eur J Neurosci 2002; 16:1949-58. [PMID: 12453059 DOI: 10.1046/j.1460-9568.2002.02284.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Recent in vitro studies demonstrated that Narp, a secreted immediate early gene (IEG) product, induces AMPA receptor clustering. Accordingly, Narp has been implicated in mediating activity-dependent changes in synaptic efficacy. To help define the role of Narp in vivo, we conducted immunohistochemical studies of Narp in rat brain. Unexpectedly, we found robust Narp expression in several discrete areas linked to the vestibular system: the anterodorsal nucleus (ADN) of the thalamus, which relays head orientation information to the cortex, the lateral vestibulospinal (Deiters') nucleus and Purkinje cells in the flocculonodular lobe of the cerebellum. Although strong Narp expression in Deiters' nucleus and the cerebellum was present consistently, Narp expression in the ADN displayed a high degree of variability among animals. To check if this variability in ADN Narp expression reflects its dependence on fluctuating levels of vestibular input, we monitored Narp immunostaining following bilateral labyrinth ablation. This procedure significantly suppressed Narp immunostaining in the ADN, indicating that it is stimulated by naturally occurring vestibular input. In contrast, labyrinth ablation did not affect Narp staining in Deiters' nucleus or the flocculonodular lobe of the cerebellum, presumably because these areas are driven by inputs from multiple systems. As previous studies implicate Narp in synaptic plasticity, these findings suggest that this IEG may mediate ongoing adjustments in synaptic strength or connectivity in several pathways linked to the vestibular system.
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Della Santina CC, Cremer PD, Carey JP, Minor LB. Comparison of head thrust test with head autorotation test reveals that the vestibulo-ocular reflex is enhanced during voluntary head movements. ARCHIVES OF OTOLARYNGOLOGY--HEAD & NECK SURGERY 2002; 128:1044-54. [PMID: 12220209 DOI: 10.1001/archotol.128.9.1044] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
OBJECTIVES To compare 2 clinical tests of vestibular function, the head autorotation test (HART) and the head thrust test (HTT), and to determine why they give disparate results in patients with known unilateral vestibular deficiency (UVD) due to labyrinthectomy. METHODS We used scleral coils to measure the horizontal (yaw) vestibulo-ocular reflex (VOR) in 5 healthy human subjects and in 11 patients who underwent labyrinthectomy. We used 2 paradigms. Using HART, subjects visually fixated a target during self-generated, swept-frequency, sinusoidal, horizontal head rotations. Using HTT, patients fixated the target during horizontal head thrusts delivered randomly in direction and time. RESULTS In subjects without UVD, eye movements were almost perfectly compensatory for both paradigms. In subjects with UVD, VOR gain for ipsilesional head thrusts was low for both paradigms, but significantly (P<.001) higher (less abnormal) for HART (0.60 +/- 0.13) than for HTT (0.14 +/- 0.13). Contralesional gain was reduced for both, to 0.64 +/- 0.20 for HART and to 0.57 +/- 0.17 for HTT. Because ipsilesional and contralesional gains were not statistically different for HART (P =.69), comparison of VOR gains for half-cycle responses to the HART stimulus could not reliably identify the side of the known lesion. In contrast, HTT consistently identified the side of the lesion for all subjects with UVD. To investigate whether preprogramming contributes to the boost in VOR as measured by HART, we compared the gain and response delay of eye movements during actively self-generated and passively received head thrusts. For subjects without UVD, response delays were shorter for active (6 +/- 1 milliseconds) than for passive (12 +/- 1 milliseconds) HTT. For ipsilesional rotations of subjects with UVD, active HTT yielded a significantly higher gain (0.44 +/- 0.20) (P<.001) and a shorter delay (15 +/- 6 milliseconds) (P<.001) than did passive HTT (0.14 +/- 0.13 and 37 +/- 15 milliseconds, respectively). Contralesional test results revealed a similar performance boost for active head movements. Data are given as mean +/- SD. CONCLUSION When comparison of half-cycle gains is used to identify the lesion side, self-generated predictable head movement paradigms, such as HART and active HTT, are less accurate than passive HTT in the characterization of UVD, in part because preprogramming can augment the VOR during voluntary head movements.
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Lasker DM, Ramat S, Carey JP, Minor LB. Vergence-mediated modulation of the human horizontal angular VOR provides evidence of pathway-specific changes in VOR dynamics. Ann N Y Acad Sci 2002; 956:324-37. [PMID: 11960816 DOI: 10.1111/j.1749-6632.2002.tb02831.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The horizontal vestibulo-ocular reflex (VOR) evoked by passive, high-acceleration, head-on-body rotations (head thrusts) while viewing a far (124-cm) or near (15-cm) target was recorded (scleral search coil) in four subjects with normal vestibular function and in one subject with unilateral vestibular hypofunction. For responses in the subjects with normal vestibular function, the latency of responses relative to the onset of head movement was 7.5 +/- 1.5 ms for the VOR and 21.6 +/- 1.2 ms for the vergence-mediated increase in VOR gain. The gain of the VOR at the peak of the velocity response while viewing a far target was 1.01 +/- 0.06; while viewing a near target, it was 1.25 +/- 0.08 (p <0.003). The responses were modeled with two pathways based on the different latencies. The "far-viewing" pathway was represented by a constant gain term. The "near-viewing" pathway was represented by a first-order lead term, a gain that was dependent on viewing distance, and a delay. Analysis of the responses revealed that the lead term was greater for the adducting than the abducting eye. In the subject with unilateral vestibular hypofunction, ipsilesional responses showed no change in VOR gain with respect to viewing distance. Contralesional responses retained the vergence-dependent increase in gain. A bilateral model was developed based on the data from the subjects with normal vestibular function. Simulations of this model when inputs were eliminated from one side predict the changes observed in the subject with unilateral vestibular hypofunction. The response asymmetries arise because the near-viewing pathway is more susceptible to inhibitory cutoff than is the far-viewing pathway.
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Carey JP, Hirvonen T, Peng GCY, Della Santina CC, Cremer PD, Haslwanter T, Minor LB. Changes in the angular vestibulo-ocular reflex after a single dose of intratympanic gentamicin for Ménière's disease. Ann N Y Acad Sci 2002; 956:581-4. [PMID: 11960873 DOI: 10.1111/j.1749-6632.2002.tb02888.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Streubel SO, Cremer PD, Carey JP, Weg N, Minor LB. Vestibular-evoked myogenic potentials in the diagnosis of superior canal dehiscence syndrome. ACTA OTO-LARYNGOLOGICA. SUPPLEMENTUM 2002; 545:41-9. [PMID: 11677740 DOI: 10.1080/000164801750388090] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Patients with superior canal dehiscence (SCD) syndrome have vertigo and oscillopsia induced by loud noises and by stimuli that result in changes in middle ear or intracranial pressure. We recorded vestibular-evoked myogenic potentials (VEMP responses) in 10 patients with SCD syndrome. The diagnosis had been confirmed in each case by evoked eye movements and by high-resolution CT scans of the temporal bones that showed a dehiscence overlying the affected superior canal. For the 8 patients without prior middle ear disease, the VEMP threshold from the dehiscent ears measured 72 +/- 8 dB NHL (normal hearing level) whereas the threshold from normal control subjects was 96 +/- 5 dB NHL (p < 0.0001). The VEMP threshold measured from the contralateral ear in patients with unilateral dehiscence was 98 +/- 4 dB NHL (p > 0.9 with respect to normal controls). Two patients with apparent conductive hearing loss from middle ear disease, and SCD, had VEMP responses from the affected ears. In the absence of dehiscence, VEMP responses would not have been expected in the setting of conductive hearing loss. These findings confirm earlier studies demonstrating that patients with SCD syndrome have lowered VEMP thresholds. Conditions other than SCD syndrome may also lead to lowered VEMP thresholds. Rather than being based upon a single test, the diagnosis of SCD syndrome is best established when the characteristic symptoms, signs, VEMP response, and CT imaging all indicate SCD.
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Limb CJ, Mabrie DC, Carey JP, Minor LB. Hemangioma of the external auditory canal. Otolaryngol Head Neck Surg 2002; 126:74-5. [PMID: 11821770 DOI: 10.1067/mhn.2002.120697] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Hirvonen TP, Carey JP, Liang CJ, Minor LB. Superior canal dehiscence: mechanisms of pressure sensitivity in a chinchilla model. ARCHIVES OF OTOLARYNGOLOGY--HEAD & NECK SURGERY 2001; 127:1331-6. [PMID: 11701069 DOI: 10.1001/archotol.127.11.1331] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
BACKGROUND Patients with superior canal dehiscence syndrome may experience vertigo and nystagmus when pressure changes occur in the external auditory canal, the middle ear, or the intracranial space. The cause is a defect in the bone of the superior canal. OBJECTIVE To study the mechanisms of pressure sensitivity of the labyrinth in superior canal dehiscence syndrome and its surgical repair in a chinchilla model. METHODS We investigated the changes in firing rates of vestibular nerve afferents in the chinchilla in response to changes in external auditory canal pressure before and after fenestration of the superior canal, and after repair of the fenestra. RESULTS Before superior canal fenestration, external auditory canal pressure changes caused no responses in horizontal canal or otolith afferents, and only 1 of 9 superior canal afferents responded to pressure. After fenestration, all superior canal afferents were excited by positive pressure and inhibited by negative pressure. Half of 18 otolith and most (21 of 33) horizontal canal afferents were unaffected by pressure. The superior canal afferents had higher pressure gain than the horizontal canal afferents (P =.03). Pressure responses could be abolished only by applying a rigid seal to the fenestra. CONCLUSIONS Fenestration of the superior canal rendered all superior canal afferents sensitive to pressure, whereas less than half of the other afferents became pressure sensitive. The direction of the superior canal afferent responses agreed with the predictions of our model of endolymph flow within the superior canal. A rigid seal applied to the fenestra abolished pressure sensitivity while maintaining physiologic rotational sensitivity.
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