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Comment on “The ocular vestibular-evoked myogenic potential to air-conducted sound: Probable superior vestibular nerve origin”
Clinical Neurophysiology 122 (2011) 1268–1273
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Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph
Letters to the Editor Comment on ‘‘The ocular vestibular-evoked myogenic potential to air-conducted sound: Probable superior vestibular nerve origin’’ I was pleased to read the article titled ‘‘The ocular vestibularevoked myogenic potential to air-conducted sound: Probable superior vestibular nerve origin’’ published in Clinical Neurophysiology. Curthoys et al. (2011) recorded the n10 component of the oVEMP to 500 Hz bone conducted vibration (BCV) and air-conducted sound (ACS) in 10 patients with superior vestibular neuritis (SVN), and drew a conclusion that 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. However, I would like to point out some shortcomings in the article. Firstly, Curthoys et al. did not investigate subjective visual vertical (SVV) values in these patients with ‘‘probable’’ SVN during eccentric rotation, the method used to assess utricular function during stimulation of one labyrinth (Hong et al., 2008, 2010; Clarke et al., 2003). Moreover, the cervical vestibular-evoked myogenic potentials (cVEMP) in response to BCV were not recorded in these patients. Since utricular function in these patients were not evaluated, we could not attribute reduced or absent oVEMP induced by ACS to the reduction or loss of utricular function. Secondly, in my opinion, there is probably another possibility that STB (short tone burst) sound-sensitive saccular afferents could also be classified into two categories. One kind of STB sound-sensitive saccular afferents are responsible for the descending vestibular pathway as an ipsilateral sacculocollic (cVEMP), and the other kind of STB sound-sensitive saccular afferents are responsible for the ascending vestibular pathway as a crossed vestibulo-ocular reflex (oVEMP). Therefore, oVEMP in response to air-conducted sound may also reflect the functions of saccular afferents which are different from those reflected by cVEMP. However, Curthoys et al. think that is unlikely just because of the demonstrably weak polysynaptic sacculo-ocular pathways in cats (Isu et al., 2000). Whereas Fluur and Mellström showed that electrical stimulation of different areas of the saccular evoked different patterns of eye movements (Fluur and Mellström, 1970). Moreover, Chan et al. found the crossed sacculo-ocular pathway in cats (Chan et al., 1977). Zhou et al. showed sound-evoked vestibulo-ocular reflexes (VOR) in trained monkeys and in their opinion the saccular and the utricular macula were also involved (Zhou et al., 2004). But it is worthwhile to note that the results from animal experiments cannot be completely extrapolated to humans. On the other hand, the superior division of the vestibular nerve innervates the lateral and superior semicircular canal ampullae, the utricle macula and a small portion of saccular macula as well (de Burlet, 1924). If
oVEMP in response to ACS originated from those saccular macula innervated by the superior vestibular nerve, a lack of correlation between AC-evoked oVEMPs and AC-evoked cVEMPs could be reasonable. Meanwhile, the apparent correlation between AC-evoked oVEMPs and BC-evoked oVEMPs, which was reported by Curthoys et al., might be explained. Although no direct evidence can support the hypothesis yet, Curthoys et al. could not exclude the abovementioned possibility. So the exact origin of oVEMP in response to ACS needs to be affirmed carefully. In addition, Curthoys et al. did not mention the intensity of BCV applied for the cVEMP test nor measured the level of the sternocleidomastoid muscles activation during the cVEMP test. Taking into account the above-mentioned shortcomings, the article of Curthoys et al. provides only limited evidence to back its claims. I am expecting more studies to ascertain the exact origin of oVEMP in response to ACS. References Chan YS, Hwang JC, Cheung YM. Crossed sacculo-ocular pathway via the Deiters’ nucleus in cats. Brain Res Bull 1977;2:1–6. Clarke AH, Schönfeld U, Helling K. Unilateral examination of utricle and saccule function. J Vestib Res 2003;13:215–25. Curthoys IS, Iwasaki S, Chihara Y, Ushio M, McGarvie LA, Burgess AM. The ocular vestibular-evoked myogenic potential to air-conducted sound: probable superior vestibular nerve origin. Clin Neurophysiol 2011;122(3):611–6. de Burlet HM. Zur Innervation der Macula sacculi bei Säugetieren. Anat Anzig 1924;58:26–32. Fluur E, Mellström A. Saccular stimulation and oculomotor reactions. Laryngoscope 1970;80:1713–21. Hong SM, Park MS, Cha CI, Park CH, Lee JH. Subjective visual vertical during eccentric rotation in patients with benign paroxysmal positional vertigo. Otol Neurotol 2008;29:1167–70. Hong SM, Yeo SG, Byun JY, Park MS, Park CH, Lee JH. Subjective visual vertical during eccentric rotation in patients with vestibular neuritis. Eur Arch Otorhinolaryngol 2010;267:357–61. Isu N, Graf W, Sato H, Kushiro K, Zakir M, Imagawa M, et al. Sacculo-ocular reflex connectivity in cats. Exp Brain Res 2000;131:262–8. Zhou W, Mustain W, Simpson I. Sound-evoked vestibulo-ocular reflexes (VOR) in trained monkeys. Exp Brain Res 2004;156:129–34.
Sujiang Xie Vestibular Laboratory, Institute of Aviation Medicine, Air Force, No. 28 Fucheng Road, Beijing 100142, PR China Tel.: +86 1066927122; fax: +86 1066927120 E-mail address: [email protected] Available online 30 November 2010 1388-2457/$36.00 Ó 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2010.09.027
Contents lists available at ScienceDirect
Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph
Letters to the Editor Comment on ‘‘The ocular vestibular-evoked myogenic potential to air-conducted sound: Probable superior vestibular nerve origin’’ I was pleased to read the article titled ‘‘The ocular vestibularevoked myogenic potential to air-conducted sound: Probable superior vestibular nerve origin’’ published in Clinical Neurophysiology. Curthoys et al. (2011) recorded the n10 component of the oVEMP to 500 Hz bone conducted vibration (BCV) and air-conducted sound (ACS) in 10 patients with superior vestibular neuritis (SVN), and drew a conclusion that 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. However, I would like to point out some shortcomings in the article. Firstly, Curthoys et al. did not investigate subjective visual vertical (SVV) values in these patients with ‘‘probable’’ SVN during eccentric rotation, the method used to assess utricular function during stimulation of one labyrinth (Hong et al., 2008, 2010; Clarke et al., 2003). Moreover, the cervical vestibular-evoked myogenic potentials (cVEMP) in response to BCV were not recorded in these patients. Since utricular function in these patients were not evaluated, we could not attribute reduced or absent oVEMP induced by ACS to the reduction or loss of utricular function. Secondly, in my opinion, there is probably another possibility that STB (short tone burst) sound-sensitive saccular afferents could also be classified into two categories. One kind of STB sound-sensitive saccular afferents are responsible for the descending vestibular pathway as an ipsilateral sacculocollic (cVEMP), and the other kind of STB sound-sensitive saccular afferents are responsible for the ascending vestibular pathway as a crossed vestibulo-ocular reflex (oVEMP). Therefore, oVEMP in response to air-conducted sound may also reflect the functions of saccular afferents which are different from those reflected by cVEMP. However, Curthoys et al. think that is unlikely just because of the demonstrably weak polysynaptic sacculo-ocular pathways in cats (Isu et al., 2000). Whereas Fluur and Mellström showed that electrical stimulation of different areas of the saccular evoked different patterns of eye movements (Fluur and Mellström, 1970). Moreover, Chan et al. found the crossed sacculo-ocular pathway in cats (Chan et al., 1977). Zhou et al. showed sound-evoked vestibulo-ocular reflexes (VOR) in trained monkeys and in their opinion the saccular and the utricular macula were also involved (Zhou et al., 2004). But it is worthwhile to note that the results from animal experiments cannot be completely extrapolated to humans. On the other hand, the superior division of the vestibular nerve innervates the lateral and superior semicircular canal ampullae, the utricle macula and a small portion of saccular macula as well (de Burlet, 1924). If
oVEMP in response to ACS originated from those saccular macula innervated by the superior vestibular nerve, a lack of correlation between AC-evoked oVEMPs and AC-evoked cVEMPs could be reasonable. Meanwhile, the apparent correlation between AC-evoked oVEMPs and BC-evoked oVEMPs, which was reported by Curthoys et al., might be explained. Although no direct evidence can support the hypothesis yet, Curthoys et al. could not exclude the abovementioned possibility. So the exact origin of oVEMP in response to ACS needs to be affirmed carefully. In addition, Curthoys et al. did not mention the intensity of BCV applied for the cVEMP test nor measured the level of the sternocleidomastoid muscles activation during the cVEMP test. Taking into account the above-mentioned shortcomings, the article of Curthoys et al. provides only limited evidence to back its claims. I am expecting more studies to ascertain the exact origin of oVEMP in response to ACS. References Chan YS, Hwang JC, Cheung YM. Crossed sacculo-ocular pathway via the Deiters’ nucleus in cats. Brain Res Bull 1977;2:1–6. Clarke AH, Schönfeld U, Helling K. Unilateral examination of utricle and saccule function. J Vestib Res 2003;13:215–25. Curthoys IS, Iwasaki S, Chihara Y, Ushio M, McGarvie LA, Burgess AM. The ocular vestibular-evoked myogenic potential to air-conducted sound: probable superior vestibular nerve origin. Clin Neurophysiol 2011;122(3):611–6. de Burlet HM. Zur Innervation der Macula sacculi bei Säugetieren. Anat Anzig 1924;58:26–32. Fluur E, Mellström A. Saccular stimulation and oculomotor reactions. Laryngoscope 1970;80:1713–21. Hong SM, Park MS, Cha CI, Park CH, Lee JH. Subjective visual vertical during eccentric rotation in patients with benign paroxysmal positional vertigo. Otol Neurotol 2008;29:1167–70. Hong SM, Yeo SG, Byun JY, Park MS, Park CH, Lee JH. Subjective visual vertical during eccentric rotation in patients with vestibular neuritis. Eur Arch Otorhinolaryngol 2010;267:357–61. Isu N, Graf W, Sato H, Kushiro K, Zakir M, Imagawa M, et al. Sacculo-ocular reflex connectivity in cats. Exp Brain Res 2000;131:262–8. Zhou W, Mustain W, Simpson I. Sound-evoked vestibulo-ocular reflexes (VOR) in trained monkeys. Exp Brain Res 2004;156:129–34.
Sujiang Xie Vestibular Laboratory, Institute of Aviation Medicine, Air Force, No. 28 Fucheng Road, Beijing 100142, PR China Tel.: +86 1066927122; fax: +86 1066927120 E-mail address: [email protected] Available online 30 November 2010 1388-2457/$36.00 Ó 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2010.09.027