Curthoys Ian S, Fröhlich Laura, McGarvie Leigh, Manzari Leonardo, Iwasaki Shinichi, Dlugaiczyk Julia, Halmagyi G Michael
Vestibular Research Laboratory, School of Psychology, The University of Sydney, Sydney, NSW, Australia.
Department of Otorhinolaryngology, Head and Neck Surgery, University Medical Center Bonn, Bonn, Germany.
Front Neurol. 2025 Aug 6;16:1644120. doi: 10.3389/fneur.2025.1644120. eCollection 2025.
Vestibular evoked myogenic potentials (VEMPs) are widely used clinical vestibular tests and their interpretation is derived from the original proposal by Colebatch that the cVEMP is due to saccular activation by air conducted sound (ACS). This was based on previous extensive evidence that sounds selectively activate saccular afferent neurons and not semicircular canal neurons at clinical testing conditions. We revisit that earlier data and the results since. Despite that evidence, a recent partial review of the neural basis of cVEMPs has raised the possibility that canal afferents may be activated at clinical test frequencies and intensities and contribute to VEMPs, which would weaken their clinical specificity. This possibility is largely based on evidence that ACS clicks activate canal afferents in the rat - but not in the guinea pig. We show that result from the rat study is due to the very high sound pressure levels used - intensities which were far higher than those in the guinea pig study. When ACS stimuli of comparable intensity are used for both species at comparable clinically effective frequencies and intensities (~110 dB SPL), otolithic neurons are activated in both species but canal activation by ACS clicks is negligible (and so most probably in humans also). Furthermore, the evidence from lesion and electrical stimulation studies and human clinical data complements the neural evidence and confirms the cVEMP to ACS is a specific test of saccular function. Audibility curves show rats have very high thresholds for frequencies most commonly used for human VEMP testing (500-1000 Hz). That result questions the applicability of results of sound evoked vestibular responses from rat for understanding human vestibular function. There is a range of stimulus intensities and frequencies appropriate for measuring VEMPs. Using stimulus values within this range, neural evidence from rats and guinea pigs shows minimal contribution of canal afferents, meaning that VEMPs are specific tests of otolith function and that any contribution from semicircular canals to human cVEMPs (tones at 500 Hz, clicks at 100 dB nHL) is negligible. Using stimulus values outside that range will stimulate semicircular canal afferents as well as otolith afferents, thus compromising the otolithic specificity of VEMPs.
前庭诱发肌源性电位（VEMPs）是广泛应用的临床前庭测试，其解读源于科尔巴奇最初的提议，即颈肌前庭诱发肌源性电位（cVEMP）是由气导声音（ACS）激活球囊所致。这是基于此前大量证据，即在临床测试条件下，声音选择性激活球囊传入神经元而非半规管神经元。我们重新审视了早期数据及此后的结果。尽管有这些证据，但最近对cVEMPs神经基础的部分综述提出，在临床测试频率和强度下，半规管传入神经可能被激活并对VEMPs有贡献，这会削弱其临床特异性。这种可能性很大程度上基于ACS短声在大鼠中激活半规管传入神经的证据——但在豚鼠中并非如此。我们表明，大鼠研究的结果是由于所使用的极高声压水平——其强度远高于豚鼠研究中的强度。当在可比的临床有效频率和强度（约110 dB SPL）下对两个物种使用强度相当的ACS刺激时，两个物种的耳石神经元均被激活，但ACS短声对半规管的激活可忽略不计（因此在人类中很可能也是如此）。此外，来自损伤和电刺激研究以及人类临床数据的证据补充了神经学证据，并证实cVEMP对ACS的反应是球囊功能的特异性测试。听力曲线显示，大鼠对人类VEMP测试最常用频率（500 - 1000 Hz）的阈值非常高。这一结果质疑了大鼠声音诱发前庭反应结果对于理解人类前庭功能的适用性。存在一系列适合测量VEMPs的刺激强度和频率。在该范围内使用刺激值时，来自大鼠和豚鼠的神经学证据表明半规管传入神经的贡献极小，这意味着VEMPs是耳石功能的特异性测试，并且半规管对人类cVEMPs（500 Hz纯音、100 dB nHL短声）的任何贡献都可忽略不计。在该范围之外使用刺激值将同时刺激半规管传入神经和耳石传入神经，从而损害VEMPs的耳石特异性。
