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Idealized finite element model of the rat fluid filled labyrinth. A Pure tones applied to the rat bony labyrinth at the oval window (OW) predict that fluid displacement is mostly localized between the oval and round window (RW). AC, anterior canal; HC, horizontal canal; PC, posterior canal; Sacc, saccule; Utr, utricle. B Frequency tuning with a peak near 1500 Hz similar to experimen-
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...
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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.
