AUTHOR=Pastras Christopher J. , Gholami Nastaran , Jennings Skyler , Zhu Hong , Zhou Wu , Brown Daniel J. , Curthoys Ian S. , Rabbitt Richard D. 

TITLE=A mathematical model for mechanical activation and compound action potential generation by the utricle in response to sound and vibration

JOURNAL=Frontiers in Neurology

VOLUME=Volume 14 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2023.1109506

DOI=10.3389/fneur.2023.1109506

ISSN=1664-2295

ABSTRACT=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 a empirical integrate-and-fire 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 for transient stimuli show short-latency vCAPs scale in magnitude and timing with hair bundle mechanical shear rate for both ACS and BCV.  For pulse BCV stimuli with durations <0.8ms, the vCAP magnitude increased in proportion to temporal bone acceleration, but for pulse durations >0.9ms the magnitude increased in proportion to temporal bone jerk.  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.  Once validated, the model was applied to predict blast-induced hair bundle shear, with results predicting acute mechanical damage to bundles immediately upon exposure.