Ann M. Burgess

Head taps evoke a crossed vestibulo-ocular reflex

Taps to the forehead on the midline, at the hairline (Fz), with a reflex hammer or powerful bone conduction vibrator caused short-latency surface potentials from beneath both eyes in all healthy subjects. The earliest negative responses were invariably absent from the eye contralateral to the side of a previous vestibular nerve section but were preserved despite sensorineural hearing loss. These responses probably reflect vestibular function via crossed otolith–ocular pathways.

Ocular vestibular evoked myogenic potentials to bone conducted vibration of the midline forehead at Fz in healthy subjects

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 8.47microV+/-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.

The role of the superior vestibular nerve in generating ocular vestibular-evoked myogenic potentials to bone conducted vibration at Fz

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.

The ocular vestibular-evoked myogenic potential to air-conducted sound; probable superior vestibular nerve origin

OBJECTIVE Intense air-conducted sound (ACS) elicits an ocular vestibular-evoked myogenic potential (oVEMP), and it has been suggested that it does so by stimulating saccular receptors and afferents in the inferior vestibular nerve and so activating a crossed sacculo-ocular pathway. Bone conducted vibration (BCV) also elicits an oVEMP probably by activating utricular receptors and a crossed utriculo-ocular pathway. Are there two separate pathways mediating oVEMPs for ACS and BCV? If saccular receptors and afferents are primarily responsible for the oVEMP to ACS, then the oVEMP to ACS should be normal in patients with reduced or absent utricular function--unilateral superior vestibular neuritis (SVN). If utricular receptors and afferents are primarily responsible for oVEMP n10, then oVEMP to ACS should be reduced or absent in SVN patients, and in these patients there should be a close relationship between the size of the oVEMP n10 to BCV and to ACS. METHODS The n10 component of the oVEMP to 500 Hz BCV and to 500 Hz ACS was recorded in 10 patients with unilateral SVN but who had saccular and inferior vestibular nerve function preserved, as shown by their normal cVEMP responses to ACS. RESULTS In SVN patients with normal saccular and inferior vestibular nerve function, the oVEMP n10 in response to ACS was reduced or absent. Across SVN patients there was a very close correspondence between the size of oVEMP n10 for ACS and for BCV. CONCLUSIONS The n10 component of the oVEMP to ACS is probably mediated predominantly by the superior vestibular nerve and so most likely by utricular receptors and afferents. SIGNIFICANCE The n10 component of the oVEMP to either ACS or BCV probably indicates mainly superior vestibular nerve function.

Ocular Vestibular Evoked Myogenic Potentials in Response to Bone-Conducted Vibration of the Midline Forehead at Fz

If a patient, who is lying supine and looking upward, is given bone-conducted vibration (BCV) of the forehead at the hairline in the midline (Fz) with a clinical reflex hammer or a powerful bone conduction vibrator, short-latency surface potentials called ocular vestibular evoked myogenic potentials (oVEMP) can be recorded from just beneath the eyes. The early negative (excitatory) component (n10) is approximately equal in amplitude for both eyes in healthy subjects, but in patients with unilateral vestibular loss, the n10 component is significantly asymmetrical under the 2 eyes – the n10 component is small or absent under the eye on the side contralateral to the prior unilateral vestibular nerve removal, but of normal amplitude under the eye on the side contralateral to the healthy ear. The n10 component of the oVEMP response to BCV at Fz stimuli reflects vestibular and probably mainly otolithic function via crossed otolithic-ocular pathways, and so n10 asymmetry is a new way of identifying the affected side in patients with unilateral otolithic loss.

The video head impulse test (vHIT) of semicircular canal function – age dependent normative values of VOR gain in healthy subjects

Background/hypothesis The video Head Impulse Test (vHIT) is now widely used to test the function of each of the six semicircular canals individually by measuring the eye rotation response to an abrupt head rotation in the plane of the canal. The main measure of canal adequacy is the ratio of the eye movement response to the head movement stimulus, i.e., the gain of the vestibulo-ocular reflex (VOR). However, there is a need for normative data about how VOR gain is affected by age and also by head velocity, to allow the response of any particular patient to be compared to the responses of healthy subjects in their age range. In this study, we determined for all six semicircular canals, normative values of VOR gain, for each canal across a range of head velocities, for healthy subjects in each decade of life. Study design The VOR gain was measured for all canals across a range of head velocities for at least 10 healthy subjects in decade age bands: 10–19, 20–29, 30–39, 40–49, 50–59, 60–69, 70–79, 80–89. Methods The compensatory eye movement response to a small, unpredictable, abrupt head rotation (head impulse) was measured by the ICS impulse prototype system. The same operator delivered every impulse to every subject. Results Vestibulo-ocular reflex gain decreased at high head velocities, but was largely unaffected by age into the 80- to 89-year age group. There were some small but systematic differences between the two directions of head rotation, which appear to be largely due to the fact that in this study only the right eye was measured. The results are considered in relation to recent evidence about the effect of age on VOR performance. Conclusion These normative values allow the results of any particular patient to be compared to the values of healthy people in their age range and so allow, for example, detection of whether a patient has a bilateral vestibular loss. VOR gain, as measured directly by the eye movement response to head rotation, seems largely unaffected by aging.

Ocular vestibular-evoked myogenic potentials to bone-conducted vibration in superior vestibular neuritis show utricular function:

OBJECTIVE: To determine whether the first negative component (n10) of the ocular vestibular-evoked myogenic potential (oVEMP) to bone-conducted vibration (BCV) is due primarily to activation of the utricular macula. STUDY DESIGN: The n10 was recorded in response to brief BCV at the midline of the forehead at the hairline (Fz). If the n10 is due primarily to utricular activation, then diseases that affect only the superior division of the vestibular nerve in which all utricular afferents course (i.e., superior vestibular neuritis [SVN]) should reduce or eliminate n10 beneath the contralesional eye, whereas the n10 beneath the ipsilesional eye and the sacculo-collic cervical vestibular-evoked myogenic potential (cVEMP) on the ipsilesional side should be preserved. SETTING: A prospective study at a tertiary neurotological referral center. SUBJECTS AND METHODS: The n10 component of the oVEMP was measured in 133 patients with unilateral SVN but with inferior vestibular nerve function preserved, as shown by ipsilesional cVEMPs. RESULTS: The n10 to Fz BCV of 133 SVN patients was reduced beneath the contralesional eye relative to the ipsilesional eye so that there was an n10 asymmetry that was significantly greater than the n10 asymmetry in the 50 healthy subjects. In terms of predicting the affected side (shown by canal paresis), using an n10 asymmetry ratio (asymmetry ratio for the relative size of the n10 of the oVEMPs for the two eyes [AR]) of 46.5 percent, the n10 AR has a diagnostic accuracy of 94 percent. CONCLUSION: The n10 component of the oVEMP to BCV is probably mediated by the superior vestibular nerve and so mainly by the utricular receptors. The n10 AR is almost as good as canal paresis in identifying the affected side in patients.

Ocular and cervical vestibular-evoked myogenic potentials to bone conducted vibration in Ménière’s disease during quiescence vs during acute attacks

OBJECTIVE Two indicators of otolithic function were used to measure dynamic otolith function in the same patients both during an acute attack of Ménières disease (MD) and in the quiescent period between attacks. METHODS The early negative component (n10) of the ocular vestibular-evoked myogenic potential (the oVEMP) to brief 500 Hz bone conducted vibration (BCV) stimulation of the forehead, in the midline at the hairline (Fz) was recorded by surface EMG electrodes just beneath both eyes while the patient looked up. It has been proposed that the n10 component of the oVEMP to 500 Hz Fz BCV indicates utricular function. It has been proposed that the early positive component (p13) of the cervical vestibular-evoked myogenic potential (the cVEMP) recorded by surface electrodes on both tensed SCM neck muscles to 500 Hz Fz BCV indicates saccular function. RESULTS Sixteen healthy control subjects tested on two occasions showed no detectable change in the symmetry of oVEMPs or cVEMPs to 500 Hz Fz BCV. In response to 500 Hz Fz BCV 15 early MD patients tested at both attack and quiescent phases showed a dissociation: there was a significant increase in contralesional of n10 of the oVEMP during the attack compared to quiescence but a significant decrease in the ipsilesional p13 of the cVEMP during the attack compared to quiescence. CONCLUSIONS During an MD attack, dynamic utricular function in the affected ear as measured by the n10 of the oVEMP to 500 Hz Fz BCV is enhanced, whereas dynamic saccular function in the affected ear as measured by the p13 of the cVEMP to 500 Hz Fz BCV is not similarly affected. SIGNIFICANCE The MD attack appears to affect different otolithic regions differentially.

High acceleration impulsive rotations reveal severe long-term deficits of the horizontal vestibulo-ocular reflex in the guinea pig

Abstract While there is agreement that unilateral vestibular deafferentation (UVD) invariably produces an immediate severe horizontal vestibulo-ocular reflex (HVOR) deficit, there is disagreement about whether or not this deficit recovers and, if so, whether it recovers fully or only partly. We suspected that this disagreement might mainly be due to experimental factors, such as the species studied, the means chosen to carry out the UVD, or the nature of the test stimulus used. Our aim was to sort out some of these factors. To do this, we studied the HVOR of alert guinea pigs in response to low and high acceleration sinusoidal and high acceleration impulses after UVD by either labyrinthectomy or by vestibular neurectomy. The HVOR in response to high acceleration impulsive yaw rotations was measured before, and at various times after, either unilateral labyrinthectomy or superior vestibular neurectomy. Following UVD, there was a severe impairment of the HVOR for ipsilesional rotations and a slight impairment for contralesional rotations, after either operation. This asymmetrical HVOR deficit in the guinea pig parallels the deficit observed in humans. Between the first measurement, which was made 1 week after UVD, and the last, which was made 3 months after UVD, there was no change in the HVOR. This lack of recovery was the same after labyrinthectomy as after vestibular neurectomy. The HVOR to low and high acceleration sinusoidal yaw rotations were measured after UVD, and the results were compared with those in response to impulsive rotations. For low acceleration sinusoidal rotations (250°/s2), the gain was symmetrical, although reduced bilaterally. As the peak head acceleration increased, the HVOR became increasingly asymmetric. The HVOR asymmetry for sinusoidal rotations was significantly less than for impulsive rotations that had the same high peak head acceleration (2500°/s2). Our results show that the HVOR deficit after UVD is the same in guinea pigs as in humans; that it is the same after vestibular neurectomy as after labyrinthectomy; that it is lasting and severe in response to high acceleration rotations; and, that it is more obvious in response to impulses than to sinusoids.

The basis for using bone-conducted vibration or air-conducted sound to test otolithic function.

Extracellular single neuron recordings of primary vestibular neurons in Scarpas ganglion in guinea pigs show that low‐intensity 500 Hz bone‐conducted vibration (BCV) or 500 Hz air‐conducted sound (ACS) activate a high proportion of otolith irregular neurons from the utricular and saccular maculae but few semicircular canal neurons. In alert guinea pigs, and humans, 500 Hz BCV elicits otolith‐evoked eye movements. In humans, it also elicits a myogenic potential on tensed sternocleidomastoid muscles. Although BCV and ACS activate both utricular and saccular maculae, it is possible to probe the functional status of these two sense organs separately because of their differential neural projections. Saccular neurons have a strong projection to neck muscles and a weak projection to the oculomotor system. Utricular afferents have a strong projection to eye muscles. So measuring oculomotor responses to ACS and BCV predominantly probes utricular function, while measuring neck muscle responses to these stimuli predominantly probes saccular function.