Vestibular-evoked myogenic potentials as a test of otolith function

Parameters of Off-Vertical Axis Rotation in Unilateral and Bilateral Vestibulopathy and Their Correlation with Vestibular Evoked Myogenic Potentials

Off-vertical axis rotation (OVAR) is a laboratory test to assess the otolith function. This study aimed to analyze the parameters of OVAR in patients with unilateral vestibular hypofunction (UVH) and bilateral vestibulopathy (BVP), and to correlate the parameters of OVAR with those of VEMPs. Ten healthy volunteers, 41 UVH, and 13 BVP patients performed OVAR. Bias component (BIC) and modulation component (MOC) of UVH and BVP patients were compared with those of healthy controls. BIC and MOC were correlated with amplitude and interaural difference (IAD) of cervical VEMP (cVEMP) and ocular VEMP (oVEMP). In UVH patients, the direction of BICs to affected side rotation were reversed and the absolute value of BICs were decreased when they were compared to healthy controls. In BVP patients, BICs were markedly attenuated. MOCs were not changed in UVH and BVP patients. There was no statistically significant correlation between VEMPs and OVAR.

The Vestibulo-Collic Reflex is Abnormal in Migraine

Interictal evoked central nervous system responses are characterized in migraineurs by a deficit of habituation, at both cortical and subcortical levels. The click-evoked vestibulo-collic reflex (VCR) allows the assessment of otolith function and an oligosynaptic pathway linking receptors in the saccular macula to motoneurons of neck muscles. Three blocks of 75 averaged responses to monaural 95-dB normal hearing level 3-Hz clicks were recorded over the contracted ipsilateral sternocleidomastoid muscle in 25 migraineurs between attacks and 20 healthy subjects, without vestibular symptoms. Amplitudes, raw and corrected for baseline electromyography, were significantly smaller in migraine patients. Whereas in healthy volunteers the VCR habituated during stimulus repetition (-4.96% ± 14.3), potentiation was found in migraineurs (4.34% ± 15.3; P = 0.04). The combination with a reduced mean amplitude does not favour vestibular hyperexcitability as an explanation for the habituation deficit in migraine, but rather an abnormal processing of repeated stimuli in the reflex circuit.

Properties of binaural vestibular evoked myogenic potentials elicited with air-conducted and bone-conducted tone bursts

The purpose of this investigation was to compare the effects of monaural and binaural stimulation on unilaterally-measured vestibular evoked myogenic potential (VEMP) magnitude and latency. The subjects were eighteen normal-hearing adults with no history of vestibular disease. Monaural VEMPs were acquired with air-conducted (AC) and bone-conducted (BC) 500 Hz tone bursts presented at 95 dB nHL and 70 dB nHL, respectively. These stimuli were simultaneously paired with 95 dB nHL contralateral tone bursts at 250, 500, 750, or 1000 Hz during acquisition of binaural VEMPs. Results indicated that AC-VEMP relative magnitudes decreased in each of the binaural conditions compared to the monaural condition. However, no changes in relative magnitude between conditions occurred for BC-VEMPs. Similar latencies were observed for monaural and binaural VEMPs. Differences in bilateral interaction seen between the AC-VEMP and BC-VEMP conditions are consistent with modification of sound transmission through the ear during presentations of binaural sound.

Morphometry of otoliths in chicken macula lagena

The macula lagena located at the apical end of the cochlea in birds is characterized by the presence of numerous otoliths with unclear sensory functions. These otoliths are reported to be similar to those in the vestibular system but their detailed features in morphology are unknown. In the present study, we examined the number, size and shape of otoliths from the macula lagena in Chinese domestic chickens (Gallus Ling Nan) with a scanning electron microscope for morphometry. For chickens aged 10-15 post-hatch days, the otoliths in each macula lagena were counted to be 16,055 +/- 4038 (mean +/- S.D., n = 4). The average length and width were 12.98 +/- 3.70 microm and 5.10 +/- 1.48 microm (n = 526 otoliths), respectively. The ratio of length to width for the otolith was 2.58 +/- 0.39 (n = 526 otoliths) and remained relatively constant despite their variations in physical size. Almost all the otoliths were in regular shape and appeared like isolated cylinders with smooth facets at each end, but a few of them (0.025% of 64,221 otoliths screened) were found to be in odd shapes, such as T-shape and cross-shape. The results suggest that otoliths in the macula lagena and those in the vestibular system of bird's inner ear have similar physical properties and may play a similar role in sensing gravitational and acceleration signals.