Affiliations: [a]
Service of Otorynolaryngology, S. Giuseppe Hospital, IRCCS-Istituto Auxologico Italiano, Piancavallo, Oggebbio (VB), Italy
| [b]
Division of Neurology and Neurorehabilitation, S. Giuseppe Hospital, IRCCS-Istituto Auxologico Italiano, Piancavallo, Oggebbio (VB), Italy
| [c]
Department of Neuroscience, University of Turin, Italy
Correspondence:
[*]
Corresponding author: Alberto Ciardo, Service of Otorynolaryngology, S. Giuseppe Hospital, IRCCS-Istituto Auxologico Italiano, Piancavallo, Oggebbio (28824-VB), Italy. Tel.: +39 0323 514234; Fax: +39 0323 514364; E-mail: alciardo@libero.it.
Abstract: OBJECTIVE: To analyze and model the effects of acoustic stimulus duration on cervical vestibular evoked myogenic potentials (cVEMPs). DESIGN: 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. RESULTS: 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. CONCLUSIONS: 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.
