Exploring properties of the human vestibular evoked myogenic potential

Abstract

Vestibular evoked myogenic potentials (VEMPs) are widely used to assess otolith organ function, yet the precise mechanisms underlying their generation remain under debate. This thesis investigates how stimulus parameters, particularly frequency, duration, and transducer type, affect VEMP responses, with the aim of refining the physiological interpretation of ocular (o)VEMPs and cervical (c) VEMPs and improving their diagnostic accuracy.
Three experimental studies were conducted. The first compared the effects of frequency, stimulus polarity, and eye position on bone-conducted and vibration-elicited VEMPs to explore their underlying mechanisms. The B71 and mini-shaker have different output frequency ranges and VEMPs elicited by them have different properties, in that 125 Hz mini-shaker responses appear highly sensitive to changes in stimulus polarity, whereas 500 Hz B71 responses are not. These differences may reflect differences in underlying response mechanisms.
The second study explored how stimulus duration affects cVEMP and oVEMP responses at 125 Hz and 500 Hz using various transducers (AC, B81, BEST, Mini shaker). 500 Hz stimulation elicited a reflex response (the well documented VEMP waveform) that is not sensitive to stimulus duration. Previous literature has suggested that the 500 Hz VEMP is saccular. In contrast, 125 Hz Mini-shaker oVEMPs showed prolonged, polarity-sensitive responses that increased with stimulus duration, which could be consistent with a linear vestibular ocular reflex.
The third study introduced a new stimulus, a 1-second linear chirp stimulus (50–600 Hz), to elicit low-frequency oVEMP responses and explored effects of transducer type, stimulus polarity, and gaze direction. Chirp-evoked responses were phase-locked in the low-frequency range (100–200 Hz) and were reliably elicited with the Mini-shaker and BEST transducers, but not with B81 or AC devices. Gaze modulation confirmed the likely physiological origin of these responses.
Together, these findings provide strong evidence that low-frequency oVEMP responses have different properties than onset-driven 500 Hz responses, suggesting a different generation mechanism. The results also highlight the critical role of transducer choice and calibration in obtaining reliable vestibular responses. Results appear consistent with frequency-specific VEMP generation mechanisms and support the development of frequency-targeted diagnostic protocols, particularly for clinical use in disorders such as Meniere's disease. It is possible that the novel chirp stimulation approach may allow assessment of VEMP function over a wider frequency range than existing approaches, potentially rapidly assessing the frequency response of the utricle, although this needs further study.

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Identifiers

ORCID for Busra Kocak Erdem: orcid.org/0000-0003-3017-0361

ORCID for Ying Ye: orcid.org/0000-0002-7721-5451

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