Fig 7 - uploaded by Wu Zhou
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Frequency tuning of sound sensitive (SS) vestibular afferents to tone bursts with different frequency and intensity. A, B, C, left panels, averaged CPEs of each condition. Right panels, percentages of SS afferents in each condition. AC, anterior canal units; HC, horizontal canal units; PC, posterior canal units; SO, otolith units in the superior branch; IO, otolith units in the inferior branch
Source publication
Vestibular evoked myogenic potentials (VEMPs) are routinely used to test otolith function, but which specific vestibular afferent neurons and central circuits are activated by auditory frequency VEMP stimuli remains unclear. To examine this question, we analyzed the sensitivity of individual vestibular afferents in adult Sprague-Dawley rats to tone...
Contexts in source publication
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... quantitatively assess how tone bursts activate canal and otolith afferents, we calculated averaged CPEs of the SS afferents for each end organ and plotted them against tone frequency at each of the three intensity levels (Fig. 7A, B, and C left panels, error bars are within the symbols). The percentages of SS afferents were also calculated in each condition (Fig. 7 right panels, error bars are within the symbols). The tuning curves were further calculated for the whole afferent population (SS and NSS afferents) from each end organ (Fig. 8A, B, and C, error bars ...
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... assess how tone bursts activate canal and otolith afferents, we calculated averaged CPEs of the SS afferents for each end organ and plotted them against tone frequency at each of the three intensity levels (Fig. 7A, B, and C left panels, error bars are within the symbols). The percentages of SS afferents were also calculated in each condition (Fig. 7 right panels, error bars are within the symbols). The tuning curves were further calculated for the whole afferent population (SS and NSS afferents) from each end organ (Fig. 8A, B, and C, error bars are within the symbols). These tuning curves were well defined for each end organ and exhibited the following three basic features. ...
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... the anatomical location defining the surface of each macula and across the cross section of each ampulla. Normalized velocities exciting each organ predicted by this model are plotted in Fig. 11B as a function of stimulus frequency. Averaging across organs, frequency dependence predicted by this simple model is remarkably similar to experiments (Figs. 7 and 8) showing a broadband tuning with a peak centered near 1500 ...
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... (Fig. 11B, red) receives the most mechanical excitation through stapes driven fluid motion. Excitation of the canals predicted by this model follows the same frequency dependence but is reduced in magnitude relative to the otolith organs. The fact that all organs are excited with similar frequency dependence is consistent with experimental data (Figs. 7 and 8), but excitation of the canals in the simulations is lower than that measured experimentally. This difference is most likely due to the fact that the model did not include the membranous labyrinth and therefore missed vibration transferred from the otolith organs to the canals along the vibrating membranous labyrinth. Wave propagation ...
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... syndrome ( Iversen et al. 2018;Iversen et al. 2017) and likely plays a role in the intact labyrinth as well. Precisely how local mechanics is related to afferent responses in otoliths vs. canals likely also contributes to the difference. Given simplifications in the model, the qualitative correspondence between the simulations (Fig. 11B) and data (Figs. 7 and 8) suggests sound excites vestibular organs by simple mechanical vibration of each end organ and associated displacement of sensory hair ...
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... of the vestibular end organs to model the VEMP tuning curves. The present FE model only includes 3D bony morphology, bulk fluid motion between the oval and round windows, and fluid compressibility and ignores wave propagation along the membranous labyrinth. But even with this simplification, results have qualitative correspondence to data (Figs. 7 and 8), indicating that frequency tuning arises primarily from the morphology of the labyrinth as a whole, and evanescent mechanical vibration of the fluids between the oval and round windows. This mode of excitation is consistent with the fact that all vestibular organs exhibited nearly the same frequency response, but different ...
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... that frequency tuning arises primarily from the morphology of the labyrinth as a whole, and evanescent mechanical vibration of the fluids between the oval and round windows. This mode of excitation is consistent with the fact that all vestibular organs exhibited nearly the same frequency response, but different sensitivities, at least < 70 dB SL (Fig. 7C). The FE model appears to underestimate activation of the HC, AC, and PC for stimuli > 70 dB SL, possibly because the model does not account wave propagation from the utricule and saccule along the compliant membranous labyrinth. Propagation of vibration along the membranous labyrinth has been shown previously to be important at ...
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... it is difficult to achieve selective activation of only otolith afferents with clicks in VEMP testing. One goal of the present study was to determine the parameters of tone bursts that allow us to achieve selective activation of the otolith afferents. Our approach was to compile tuning curves for different end organs at different intensities (Figs. 7 and 8). It is important to note that if tuning curves are scaled to give the same peak, the curves from all organs nearly overlap, indicating that all organs are activated by the same stimulus but to different extents. Thus, the only way to selectively excite the utricle and saccule would be to use a low strength stimulus, titrating the ...
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The aims of this study were to investigate otolith dysfunction, especially isolated otolith dysfunction (with preserved semicircular canal function) in persistent postural-perceptual dizziness (PPPD) patients. Twenty-one patients who had been diagnosed with PPPD were enrolled in this study. The subjects filled out questionnaires [the Dizziness Hand...
Citations
... Auditory frequency ACS and BCV are commonly used to activate vestibular otolith organs in the inner ear for basic science applications and as part of the neuro-otology clinical test battery. Utricular and saccular afferent neurons with irregularly spaced inter-spike intervals are the most sensitive to sound and vibration (1)(2)(3), and for sinusoidal stimuli fire action potentials at a precise phase in the stimulus cycle. Transient pulse or click stimuli evoke synchronized action potential firing in these sensitive neurons, resulting in detectable whole-nerve vestibular compound action potentials (vCAPs), similar to extracellular field potentials first observed in peripheral nerves a century ago (4). ...
Introduction
Calyx bearing vestibular afferent neurons innervating type I hair cells in the striolar region of the utricle are exquisitely sensitive to auditory-frequency air conducted sound (ACS) and bone conducted vibration (BCV). Here, we present experimental data and a mathematical model of utricular mechanics and vestibular compound action potential generation (vCAP) in response to clinically relevant levels of ACS and BCV. Vibration of the otoconial layer relative to the sensory epithelium was simulated using a Newtonian two-degree-of-freedom spring-mass-damper system, action potential timing was simulated using an empirical model, and vCAPs were simulated by convolving responses of the population of sensitive neurons with an empirical extracellular voltage kernel. The model was validated by comparison to macular vibration and vCAPs recorded in the guinea pig, in vivo.
Results
Transient stimuli evoked short-latency vCAPs that scaled in magnitude and timing with hair bundle mechanical shear rate for both ACS and BCV. For pulse BCV stimuli with durations <0.8 ms, the vCAP magnitude increased in proportion to temporal bone acceleration, but for pulse durations >0.9 ms the magnitude increased in proportion to temporal bone jerk. Once validated using ACS and BCV data, the model was applied to predict blast-induced hair bundle shear, with results predicting acute mechanical damage to bundles immediately upon exposure.
Discussion
Results demonstrate the switch from linear acceleration to linear jerk as the adequate stimulus arises entirely from mechanical factors controlling the dynamics of sensory hair bundle deflection. The model describes the switch in terms of the mechanical natural frequencies of vibration, which vary between species based on morphology and mechanical factors.
... Here, we show that utricular afferent fibers exhibit robust responses to passive and active movements yet maintain sensitivity to conspecific boatwhistle vocalization playbacks. Across vertebrates, the inner ear otolithic end organs are thought to primarily serve a vestibular function as they detect translational movements and maintain static balance; however, they also detect vibrations at auditory frequencies [e.g., fish (5), frogs (60,61), rats (62)(63)(64), and guinea pigs (65)(66)(67)]. In teleost fishes, the utricle acts as an inertial accelerometer and responds to direct displacement by acoustic particle motion and linear accelerations primarily in the horizontal plane (5,7,68). ...
The inner ear of teleost fishes is composed of three paired multimodal otolithic end organs (saccule, utricle, and lagena), which encode auditory and vestibular inputs via the deflection of hair cells contained within the sensory epithelia of each organ. However, it remains unclear how the multimodal otolithic end organs of the teleost inner ear simultaneously integrate vestibular and auditory inputs. Therefore, microwire electrodes were chronically implanted using a 3D printed micromanipulator into the utricular nerve of oyster toadfish (Opsanus tau) to determine how utricular afferents respond to conspecific mate vocalizations termed boatwhistles (180 Hz fundamental frequency) during movement. Utricular afferents were recorded while fish were passively moved using a sled system along an underwater track at variable speeds (velocity: 4.0 - 12.5 cm/s; acceleration: 0.2 - 2.6 cm/s ² ) and while fish freely swam (velocity: 3.5 - 18.6 cm/s; acceleration: 0.8 - 29.8 cm/s ² ). Afferent fiber activities (spikes/s) increased in response to the onset of passive and active movements; however, afferent fibers differentially adapted to sustained movements. Additionally, utricular afferent fibers remained sensitive to playbacks of conspecific male boatwhistle vocalizations during both passive and active movements. Here, we demonstrate in alert toadfish that utricular afferents exhibit enhanced activity levels (spikes/s) in response to behaviorally-relevant acoustic stimuli during swimming.
