Direction-dependent excitatory and inhibitory ocular vestibular-evoked myogenic potentials (oVEMPs) produced by oppositely directed accelerations along the midsagittal axis of the head

Abstract

Oppositely directed displacements of the head need oppositely directed vestibulo-ocular reflexes (VOR), i.e. compensatory responses. Ocular vestibular-evoked myogenic potentials (oVEMPs) mainly reflect the synchronous extraocular muscle activity involved in the process of generating the VOR. The oVEMPs recorded beneath the eyes when looking up represent electro-myographic responses mainly of the inferior oblique muscle. We aimed: (1) to study the properties of these responses as they were produced by head acceleration impulses to the forehead and to the back of the head; (2) to investigate the relationships between these responses and the 3-D linear head accelerations that might reflect the true stimulus that acts on the vestibular hair cells. We produced backward- and forward-directed acceleration stimuli in four conditions (positive and negative head acceleration impulses to the hairline and to the inion) in 16 normal subjects. The oVEMPs produced by backward- and forward-directed accelerations of the head showed consistent differences. They were opposite in the phase. The responses produced by backward accelerations of the head began with an initial negativity, n11; conversely, those produced by accelerations directed forward showed initially a positive response, p11. There was a high inter-subject correlation of head accelerations along the head anteroposterior and transverse axes, but almost no correlation of accelerations along the vertical axis of the head. We concluded that backward-directed head accelerations produced an initial excitatory response, and forward-directed accelerations of the head were accompanied by an initial inhibitory response. These responses showed dependence on acceleration direction in the horizontal plane of the head. This could be consistent with activation of the utricle.

Influence of bone conduction transducer type and placement on ocular and cervical vestibular evoked myogenic potentials

“…The maximum output levels generated by the B81 were slightly lower than with the Mini-Shaker and most likely not feasible to elicit oVEMPs in most test subjects. It has been shown in a few studies that oVEMPs are very sensitive to direction of skull acceleration so that variation of stimulus site along the midline of the skull results in change of polarity and/or latency [24][25][26] .…”

Single motor unit activity in human extraocular muscles during the vestibulo‐ocular reflex

“…As extraocular muscle activity and eye movements are intrinsically linked, any change in evoked eye movement will result in a different pattern and timing of eye muscle activity. Latency shifts have been reported in oVEMP surface recordings following a simple reversal in the initial direction of skull vibration, with stimulus frequencies up to 500 Hz (Todd et al 2008 a ; Cai et al 2011; Jombik et al 2011). This suggests that the translational VOR is capable of encoding the net direction of such stimulation and produces meaningful responses in the appropriate extraocular muscles, even though vibration and sound are short‐duration, high frequency stimuli.…”

Vestibular evoked myogenic potentials in practice: Methods, pitfalls and clinical applications

“…Both cVEMPs and oVEMPs evoked by BC stimulation are sensitive to the direction of skull acceleration produced by the stimulus ( Brantberg and Tribukait, 2002 , Todd et al, 2008a , Rosengren et al, 2009 , Jombik et al, 2011 ). Responses can change polarity and/or latency with different sites of stimulation.…”