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Bone-conducted vibration of the forehead, in the midline at the hairline (Fz) causes linear acceleration stimulation of both mastoids and results in an ocular vestibular-evoked myogenic potential (oVEMP), recorded by surface electromyogram (EMG) electrodes just beneath the eyes. The early n10 component of the oVEMP is symmetrical in healthy subjects, absent in patients with bilateral vestibular loss, and in patients after unilateral vestibular loss (uVL) n10 is small or absent on the side contralateral to the uVL, but of normal amplitude on the side contralateral to the healthy ear. The n10 component probably reflects mainly otolithic function, since in the guinea pig, primary otolith irregular neurons are selectively activated by bone-conducted vibration (BCV) at low intensities (0.1 g), whereas semicircular canal primary afferents are not activated even at high intensities (10 g). [ABSTRACT FROM AUTHOR]

Abstract: Objective: Bone-conducted vibration (BCV) in the midline at the hairline (Fz), results in short latency potentials recorded by surface electrodes beneath the eyes – the ocular vestibular-evoked myogenic potential (oVEMP). The early negative component of the oVEMP, n10, is due to vestibular stimulation, however it is similar to the early R1 component of the blink reflex. Here we seek to dissociate n10 from R1. Methods: Surface potentials were recorded from the infraorbital electromyogram of 10 healthy subjects, 6 patients with bilateral vestibular loss, 2 with unilateral vestibular loss, 4 with facial palsy and 3 with facial and vestibular nerve lesions on the same side. BCV was delivered at Fz, the inion, the glabella or the supraorbital ridge using a tendon hammer or a bone-conduction vibrator. Results: Onset latencies of the n10 evoked by taps at Fz or inion were significantly shorter than the R1 components of blink responses to supraorbital and glabellar stimuli. Upward gaze increased the amplitude of n10 but not R1. The n10 was absent bilaterally in patients with bilateral vestibular loss and beneath the contralesional eye in patients with unilateral vestibular loss, but in both these groups of patients R1 was preserved. In severe facial palsy the R1 component was absent or delayed and attenuated ipsilesionally, but n10 was preserved bilaterally. In subjects with unilateral facial and vestibular nerve lesions (Herpes Zoster of the facial and vestibulocochlear nerves) the dissociation was complete – the ipsilesional R1 was absent or attenuated whereas the ipsilesional n10 was preserved. Conclusions: n10 is distinguished from R1 by its earlier onset, laterality, modulation by gaze position and dissociation in patient groups. Significance: The n10 component evoked by BCV at Fz is not the R1 component of the blink reflex. [Copyright &y& Elsevier]

Abstract: Objective: The n10 component (n10) of the ocular vestibular evoked myogenic potential (oVEMP) to brief bone conducted vibration (BCV) of the forehead at Fz is probably caused by the vibration selectively activating vestibular otolithic receptors. If the n10 is due primarily to utricular activation then diseases which affect only the superior division of the vestibular nerve (SVN) should reduce or eliminate n10. Methods: The n10 component of the oVEMP was measured in 13 patients with unilateral SVN but with inferior vestibular nerve function preserved. Results: We compared the n10 to BCV of these 13 SVN patients to previously published data for healthy subjects and patients after complete unilateral vestibular loss. We found that in 12 out of the 13 patients with SVN, n10 was markedly reduced or absent under the contralesional eye. Conclusion: Since all utricular afferents course in the superior vestibular nerve and in 12/13 of these patients the n10 was reduced we conclude that the n10 component of the oVEMP to BCV is probably mediated by the superior vestibular nerve and probably due to activation of mainly utricular receptors. Significance: The n10 appears to be a simple new test of superior vestibular nerve and probably mainly utricular function. [Copyright &y& Elsevier]

Abstract: Objective: To provide the empirical basis for using ocular vestibular evoked myogenic potentials (oVEMPS) in response to Fz bone conducted vibration (BCV) stimulation to indicate vestibular function in human subjects. To show the generality of the response by testing a large number of unselected healthy subjects across a wide age range and the repeatability of the response within subjects. To provide evidence that the response depends on otolithic function. Methods: The early negative component (n10) of the oVEMP to brief BCV of the forehead, in the midline at the hairline (Fz) is recorded by surface EMG electrodes just beneath the eyes. We used a Bruel and Kjaer 4810 Mini-Shaker or a light tap with a tendon hammer to provide adequate BCV stimuli to test a large number (67) of unselected healthy people to quantify the individual differences in n10 magnitude, latency and symmetry to Fz BCV. A Radioear B-71 bone oscillator at Fz is not adequate to elicit a reliable n10 response. Results: The n10 oVEMP response showed substantial differences in amplitude between subjects, but is repeatable within subjects. n10 is of equal magnitude in both eyes with an average asymmetry around 11%. The average n10 amplitude for Mini Tone Burst BCV is 8.47μV±4.02 (sd), the average latency is 10.35ms±0.63 (sd). The amplitude of n10 decreases and its latency increases with age. Conclusions: oVEMPs are a new reliable, repeatable test to indicate vestibular and probably otolithic function. Significance: This study shows the optimum conditions for recording oVEMPs and provides baseline values for individual differences and asymmetry. oVEMPs can be measured in senior subjects without difficulty. [Copyright &y& Elsevier]