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Abstract: The aim of this study was to establish an animal model of acoustically evoked vestibulo-collic reflex using guinea pigs. A special clamp was applied to restrain the head and body of the guinea pigs, but leaving its four legs free. Each animal underwent vestibular evoked myogenic potential (VEMP) and caloric tests using clip electrode method without general anesthesia or decerebrate surgery. The response rates for the myogenic potentials on the neck of guinea pigs using 100, 90, 80 and 70dB monaural acoustic stimulation with unilateral recording were 100%, 62%, 50% and 0%, respectively. The mean latencies of the positive and negative peaks for the myogenic potentials were 7.24±0.49 and 9.15±0.47ms, 7.09±0.43 and 9.28±0.42ms, as well as 7.03±0.59 and 9.14±0.56ms, when elicited by 100, 90 and 80dB acoustic stimulation, respectively. The median (minimum–maximum) peak-to-peak amplitudes were 11.93 (6.14–16.86), 10.99 (5.28–19.40), and 11.17 (5.02–20.72)μV, when elicited by 100, 90 and 80dB acoustic stimulation, respectively. We found no significant relationship between the stimulus intensity and the mean latencies or peak-to-peak amplitude of the myogenic potentials in guinea pigs. For those treated with gentamicin unilaterally, all guinea pigs showed absent caloric responses on the lesion side, and absent myogenic potentials on the neck when using ipsi-lesional acoustic stimulation, while the hearing was preserved. Hence, the use of gentamicin-treated animals, along with normal controls and auditory brainstem responses, results in convincing results that the recorded myogenic potentials are in fact of vestibular origin. [Copyright &y& Elsevier]

Abstract: The aim of this study was to investigate the side-difference of vestibular evoked myogenic potentials (VEMPs) in relation to the provocation rates, latencies and amplitudes using binaural acoustic stimulation with bilateral recording. Fourteen healthy volunteers underwent a serial VEMP testings elicited binaurally by a sequence of alternating stimulus intensities, that is, 95–95 (right–left), 85–95, 95–85, and 85–85 dBHL tone burst, respectively. The provocation rates as well as the mean latencies of p13 and n23 for the VEMPs demonstrated no significant side-difference despite using 95–95, 85–95, 95–85 and 85–85 dBHL binaural acoustic stimulation. In contrast, nine (64%) of the 14 subjects showed side-difference of absolute p13–n23 amplitude, including right side dominant in five subjects, and left side dominant in four subjects. However, there was no significant side-difference in terms of relative amplitude despite using 95–95, 85–95, 95–85 and 85–85 dBHL binaural acoustic stimulation. Furthermore, the relative amplitude or interaural amplitude difference (IAD) ratios between those with and without side-difference of p13–n23 amplitude did not differ significantly. Hence, this study provides a potentially important method for adjusting the side difference of p13–n23 amplitudes by using a relative amplitude or IAD ratio adjustment. It also adds confidence to the successful use of binaural stimulation and recording of VEMPs under conditions of bilateral SCM muscular contractions. [Copyright &y& Elsevier]

The aim of this study was to further investigate the response rates, thresholds, latencies and amplitudes of the earlier and later components of tone burst evoked myogenic potentials (TEMPs) in conditions of binaural and monaural stimulation and recordings in a group of normal subjects in response to a 500-Hz tone burst. Each subject underwent simultaneous binaural acoustic stimulation with bilateral recording (B-TEMP) initially, then monaural acoustic stimulation with ipsilateral recording (M-TEMP) on another day. The results showed 100%, 100%, 54%, and 23% response rates for the earlier components of B-TEMPs, when using 105, 95, 85, and 75 dB acoustic stimulation, respectively. It exhibited a significant decrease in the response rate when the stimulus intensity was attenuated from 95 to 75 dB. In addition, no significant difference in the response rate of the earlier components existed between B-TEMPs and M-TEMPs. For the later components of B-TEMPs obtained from 105, 95, 85, and 75 dB acoustic stimulation, the response rates were 85%, 85%, 62%, and 42%, respectively, higher than those of M-TEMPs significantly. Nevertheless, there were no statistical differences in the mean latencies of each peak (p13, n23, n34, and p44) between B-TEMPs and M-TEMPs under similar stimulus intensity. Meanwhile, no significant relationship existed between the stimulus intensity and the latency, regardless of B-TEMPs or M-TEMPs. Comparing the relative amplitudes between B-TEMPs and M-TEMPs, the former displayed significant smaller p13-n23 amplitude, but larger n34-p44 amplitude. However, the mean thresholds for the earlier and later components between B-TEMPs and M-TEMPs did not differ significantly. In conclusion, monaural acoustic stimulation with ipsilateral recording may elicit larger amplitude of the earlier components, whereas binaural acoustic stimulation with bilateral recording evokes higher response rate and larger amplitude of the later components. Although the nerve pathways for both components are different, the thresholds for these potentials do not differ significantly, indicating that both components may, at least in part, share a common origin, but different pathways. [Copyright &y& Elsevier]

The aim of this study is to investigate the feasibility of recording vestibular evoked myogenic potential (VEMP) using simultaneous binaural acoustic stimulation (B-VEMP), and compare it with that using monaural acoustic stimulation (M-VEMP). Seven healthy volunteers were evoked by initial B-VEMP test and subsequent M-VEMP test, whereas vice versa in another 7 volunteers. All 14 subjects demonstrated both B-VEMPs and M-VEMPs, without significant difference in the latencies of p13 and n23. When using interaural amplitude difference (IAD) ratio for interpreting amplitude, B-VEMPs did not differ significantly from that of M-VEMPs. Hence, B-VEMPs can produce information equivalent to M-VEMPs in terms of response rate, latencies, and IAD ratio in healthy subjects. Likewise, similar results were also shown in the patients with unilateral Meniere’s disease. In conclusion, B-VEMPs provide neither different information nor less variability, as compared with M-VEMPs. In addition, B-VEMPs can offer information on unilateral inner ear (saccular) pathology similar to that by M-VEMPs. Furthermore, recording from binaural stimulation can be used as a possibly more convenient mode compared with two monaural recordings, especially when testing young or old or disabled patients, since a continuous muscular effort is required during recording. [Copyright &y& Elsevier]