Effects of acoustic stimulus duration on cervical vestibular evoked myogenic potentials: A neurophysiological and modeling study.

Abstract

To analyze and model the effects of acoustic stimulus duration on cervical vestibular evoked myogenic potentials (cVEMPs). Subjects with normal hearing and no vestibular or cervical disorders were tested using 1 kHz tone bursts (TBs) of different durations to evoke cVEMPs from the ipsilateral sternocleidomastoid muscle. VEMP modeling was performed in Labview. The increase in TB duration initially resulted in a non-linear increase in cVEMP amplitude, followed by more complex cVEMP modifications that were mainly related to the appearance of a new wave (nX) that interfered with n23. With long TBs there were two distinct negative peaks with an identical threshold, suggesting a common vestibular nature. A two-level inhibition model qualitatively accounted for the two distinct negative peaks. However, good fitting of the cVEMP waveform required a multi-level model that included an excitatory phase after the inhibitory period. The two negative components (n23 and nX) observed in cVEMPs elicited by long TBs may result from the involvement of two different pathways with different dynamics or a single pathway with quick adaptation in the activity along the vestibulo-collic arc. Excitatory activity following the period of inhibition may represent rebound activity at the motor unit level.