Contralateral suppression of distortion-product otoacoustic emissions: A potential diagnostic tool to evaluate the vestibular nerve
Introduction
Distortion-product otoacoustic emission (DPOAE) is a test that records low-intensity acoustic signals arising from the functional cochlea in response to two-tone stimulations at frequencies f1 and f2 (where f1 < f2) [1], [2]. The amplitude of DPOAEs can be suppressed by sound stimulation in the contralateral ear, and this phenomenon is called contralateral suppression of DPOAE [3], [4], [5], [6], [7], [8]. Contralateral suppression of DPOAE has been suggested to be a reflex phenomenon via auditory efferent neurons in the olivocochlear bundle. The efferent innervation from the superior olivary complex (SOC) to the auditory hair cells comprises the lateral olivocochlear bundle (LOCB) and the medial olivocochlear bundle (MOCB). The MOCB innervates the outer hair cells of the cochlea mainly via the inferior vestibular nerve and is suggested to generate DPOAE contralateral suppression [3], [4], [9]. For example, afferent auditory input from the left ear is projected to the left cochlear nucleus and then to the right SOC. The right MOCB from the SOC directly innervates the outer hair cells of the right cochlea via right inferior vestibular nerve.
Because this efferent innervation is mediated by the inferior vestibular nerve, the level of contralateral suppression of DPOAE would be altered by any lesion in the vestibular nerve running with the MOCB. To test this hypothesis, we recorded and compared the amount of DPOAE suppression in healthy subjects and patients with vestibular neuritis when noise was presented to the contralateral ear. The results of this study may provide a new diagnostic test with the potential to evaluate the functional integrity of the vestibular nerve by simple audiometry.
Section snippets
The hypothesis
Contralateral suppression of DPOAE is a reflex phenomenon mediated by the auditory efferent system. The efferent innervation of the outer hair cells of the cochlea is mediated by the MOCB originating from the SOC, and the nerve fibers run through the inferior vestibular nerve in the internal auditory canal. Thus, we hypothesize that a lesion in the vestibular nerve will interfere with the MOC reflex and alter the level of contralateral suppression of DPOAE.
Evaluation of the hypothesis
Because the response of DPOAE is affected by the subject’s hearing, patients with a definite vestibulopathy, but without hearing loss, would be good candidates to test our hypothesis. Vestibular neuritis is a disorder of acute unilateral peripheral vestibular loss contributing to whirling-type vertigo, nausea, and vomiting without hearing loss, and its pathogenic mechanism is considered to be viral or to involve a vascular insult to the vestibular nerve territory [10]. We compared the amount of
Empirical data
Of the 40 healthy ears evaluated, three showed an S/N ratio <6 dB. These three ears were excluded from the analysis, and data from the remaining 37 ears were analyzed. The f2 frequencies at which the DPOAE amplitude was significantly suppressed in the presence of contralateral NBN compared with the absence of contralateral NBN were determined. The DPOAE amplitude was significantly suppressed at f2s of 1257, 1587, and 2002 Hz (P = 0.004, P < 0.001, P < 0.001, respectively) (Fig. 1). The DPOAE
Consequences of the hypothesis and discussion
DPOAE contralateral suppression is a well-known reflex, and several methods have been developed to maximize its effects. In this study, 70 dB HL NBN with a center frequency of 2 kHz was used as contralateral noise. There has been controversy regarding the suppressive effects depending on the type of noise. One earlier study suggested greater suppressive effects of broad-band noise (BBN) than NBN or two-tone complexes [11]. However, another study showed a comparatively small difference in the
Funding
None.
Conflicts of interest
None.
Ethical approval
The study was approved by the Institutional Review Boards at the Seoul National University Bundang Hospital (IRB No. B-0910-085-010).
References (20)
Cochlear mechanics: implications of electrophysiological and acoustical observations
Hear Res
(1980)- et al.
Effect of contralateral sound stimulation on the distortion product 2f1–f2 in humans: evidence of a frequency specificity
Hear Res
(1993) - et al.
Changes in spontaneous otoacoustic emissions produced by acoustic stimulation of the contralateral ear
Hear Res
(1989) - et al.
Vestibular neuritis
Otolaryngol Clin North Am
(2011) - et al.
Contralateral noise has possible asymmetric frequency-sensitive effect on the 2f1–f2 otoacoustic emission in humans
Neurosci Lett
(2008) - et al.
Effects of the crossed acoustic reflex on distortion-product otoacoustic emissions in awake rabbits
Hear Res
(1991) - et al.
Contralateral suppression of non-linear click evoked otoacoustic emissions
Hear Res
(1993) - et al.
Voluntary contraction of middle ear muscles: effects on input impedance, energy reflectance and spontaneous otoacoustic emissions
Hear Res
(1993) The contralateral acoustic-reflex threshold
- et al.
Contralateral auditory stimulation alters acoustic distortion products in humans
Hear Res
(1993)
Cited by (2)
Association of Central Auditory Processing Dysfunction With Preclinical Alzheimer's Disease
2023, Otolaryngology - Head and Neck Surgery (United States)