Abstract
Electrocochleography (EcochG), incorporating the Cochlear Microphonic (CM), the Summating Potential (SP), and the cochlear Compound Action Potential (CAP), has been used to study cochlear function in humans and experimental animals since the 1930s, providing a simple objective tool to assess both hair cell (HC) and nerve sensitivity. The vestibular equivalent of ECochG, termed here Electrovestibulography (EVestG), incorporates responses of the vestibular HCs and nerve. Few research groups have utilized EVestG to study vestibular function. Arguably, this is because stimulating the cochlea in isolation with sound is a trivial matter, whereas stimulating the vestibular system in isolation requires significantly more technical effort. That is, the vestibular system is sensitive to both high-level sound and bone-conducted vibrations, but so is the cochlea, and gross electrical responses of the inner ear to such stimuli can be difficult to interpret. Fortunately, several simple techniques can be employed to isolate vestibular electrical responses. Here, we review the literature underpinning gross vestibular nerve and HC responses, and we discuss the nomenclature used in this field. We also discuss techniques for recording EVestG in experimental animals and humans and highlight how EVestG is furthering our understanding of the vestibular system.
Highlights
Reviewed by: Larry Hoffman, University of California, Los Angeles, United States John Carey, Johns Hopkins University, United States
The greatest obstacle with performing EVestG measures and using them as a faithful measure of peripheral vestibular function is that both air conducted sound (ACS) and bone conducted vibration (BCV) stimuli can evoke cochlear field potentials (i.e., Cochlear Microphonic (CM) and Compound Action Potential (CAP)), which are an order of magnitude larger than vestibular responses, and will summate with the Vestibular Evoked Potential (VsEP) or Vestibular Microphonic’’ (VM)
When recorded from the inner ear fluids, the VM is a ‘‘global’’ response from all vestibular hair cell (HC) types, because all vestibular HCs respond to low-frequency stimulation, and the extracellular potentials will summate in the fluids
Summary
The history of Electrocochleography (ECochG) as a technique for recording cochlear field potentials is well established (Eggermont, 2017), beginning with Wever and Bray’s (1930) recordings of the Cochlear Microphonic (CM) in response to air conducted sound (ACS) stimuli in cats, and the 8th nerve compound action potential (CAP) response shortly after by Fromm et al (1935). The authors use a signal analysis process to localize any stochastically occurring field potentials that have characteristics resembling the VsEP, occurring within the raw electrical recording from the ear canal. They average these asynchronous field potentials, somewhat similar to the methods involving spike-triggered averaging (Kiang et al, 1976). Researchers have demonstrated much simpler techniques for objectively measuring peripheral vestibular function, via the VM and VsEP. Most of these studies have been performed in experimental animals, with a limited number of human studies
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