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Boothalingam S, Peterson A, Powell L, Easwar V. Auditory brainstem mechanisms likely compensate for self-imposed peripheral inhibition. Sci Rep 2023; 13:12693. [PMID: 37542191 PMCID: PMC10403563 DOI: 10.1038/s41598-023-39850-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 08/01/2023] [Indexed: 08/06/2023] Open
Abstract
Feedback networks in the brain regulate downstream auditory function as peripheral as the cochlea. However, the upstream neural consequences of this peripheral regulation are less understood. For instance, the medial olivocochlear reflex (MOCR) in the brainstem causes putative attenuation of responses generated in the cochlea and cortex, but those generated in the brainstem are perplexingly unaffected. Based on known neural circuitry, we hypothesized that the inhibition of peripheral input is compensated for by positive feedback in the brainstem over time. We predicted that the inhibition could be captured at the brainstem with shorter (1.5 s) than previously employed long duration (240 s) stimuli where this inhibition is likely compensated for. Results from 16 normal-hearing human listeners support our hypothesis in that when the MOCR is activated, there is a robust reduction of responses generated at the periphery, brainstem, and cortex for short-duration stimuli. Such inhibition at the brainstem, however, diminishes for long-duration stimuli suggesting some compensatory mechanisms at play. Our findings provide a novel non-invasive window into potential gain compensation mechanisms in the brainstem that may have implications for auditory disorders such as tinnitus. Our methodology will be useful in the evaluation of efferent function in individuals with hearing loss.
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Affiliation(s)
- Sriram Boothalingam
- Waisman Center and Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, 53705, USA.
- Macquarie University, Sydney, NSW, 2109, Australia.
- National Acoustic Laboratories, Sydney, NSW, 2109, Australia.
| | - Abigayle Peterson
- Waisman Center and Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, 53705, USA
- Macquarie University, Sydney, NSW, 2109, Australia
| | - Lindsey Powell
- Waisman Center and Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Vijayalakshmi Easwar
- Waisman Center and Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, 53705, USA
- Macquarie University, Sydney, NSW, 2109, Australia
- National Acoustic Laboratories, Sydney, NSW, 2109, Australia
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2
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Loh YM, Su MP, Ellis DA, Andrés M. The auditory efferent system in mosquitoes. Front Cell Dev Biol 2023; 11:1123738. [PMID: 36923250 PMCID: PMC10009176 DOI: 10.3389/fcell.2023.1123738] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Accepted: 02/17/2023] [Indexed: 03/02/2023] Open
Abstract
Whilst acoustic communication forms an integral component of the mating behavior of many insect species, it is particularly crucial for disease-transmitting mosquitoes; swarming males rely on hearing the faint sounds of flying females for courtship initiation. That males can hear females within the din of a swarm is testament to their fabulous auditory systems. Mosquito hearing is highly frequency-selective, remarkably sensitive and, most strikingly, supported by an elaborate system of auditory efferent neurons that modulate the auditory function - the only documented example amongst insects. Peripheral release of octopamine, serotonin and GABA appears to differentially modulate hearing across major disease-carrying mosquito species, with receptors from other neurotransmitter families also identified in their ears. Because mosquito mating relies on hearing the flight tones of mating partners, the auditory efferent system offers new potential targets for mosquito control. It also represents a unique insect model for studying auditory efferent networks. Here we review current knowledge of the mosquito auditory efferent system, briefly compare it with its counterparts in other species and highlight future research directions to unravel its contribution to mosquito auditory perception.
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Affiliation(s)
- YuMin M. Loh
- Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan
| | - Matthew P. Su
- Graduate School of Science, Nagoya University, Nagoya, Aichi, Japan
- Institute for Advanced Research, Nagoya University, Nagoya, Aichi, Japan
| | - David A. Ellis
- UCL Ear Institute, University College London, London, United Kingdom
- The Francis Crick Institute, London, United Kingdom
| | - Marta Andrés
- UCL Ear Institute, University College London, London, United Kingdom
- The Francis Crick Institute, London, United Kingdom
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3
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Boothalingam S, Goodman SS, MacCrae H, Dhar S. A Time-Course-Based Estimation of the Human Medial Olivocochlear Reflex Function Using Clicks. Front Neurosci 2021; 15:746821. [PMID: 34776849 PMCID: PMC8581223 DOI: 10.3389/fnins.2021.746821] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2021] [Accepted: 09/28/2021] [Indexed: 11/22/2022] Open
Abstract
The auditory efferent system, especially the medial olivocochlear reflex (MOCR), is implicated in both typical auditory processing and in auditory disorders in animal models. Despite the significant strides in both basic and translational research on the MOCR, its clinical applicability remains under-utilized in humans due to the lack of a recommended clinical method. Conventional tests employ broadband noise in one ear while monitoring change in otoacoustic emissions (OAEs) in the other ear to index efferent activity. These methods, (1) can only assay the contralateral MOCR pathway and (2) are unable to extract the kinetics of the reflexes. We have developed a method that re-purposes the same OAE-evoking click-train to also concurrently elicit bilateral MOCR activity. Data from click-train presentations at 80 dB peSPL at 62.5 Hz in 13 young normal-hearing adults demonstrate the feasibility of our method. Mean MOCR magnitude (1.7 dB) and activation time-constant (0.2 s) are consistent with prior MOCR reports. The data also suggest several advantages of this method including, (1) the ability to monitor MEMR, (2) obtain both magnitude and kinetics (time constants) of the MOCR, (3) visual and statistical confirmation of MOCR activation.
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Affiliation(s)
- Sriram Boothalingam
- Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, United States.,Waisman Center, University of Wisconsin-Madison, Madison, WI, United States
| | - Shawn S Goodman
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, United States
| | - Hilary MacCrae
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, United States
| | - Sumitrajit Dhar
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, United States.,Knowles Center, Northwestern University, Evanston, IL, United States
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4
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Hernández-Pérez H, Mikiel-Hunter J, McAlpine D, Dhar S, Boothalingam S, Monaghan JJM, McMahon CM. Understanding degraded speech leads to perceptual gating of a brainstem reflex in human listeners. PLoS Biol 2021; 19:e3001439. [PMID: 34669696 PMCID: PMC8559948 DOI: 10.1371/journal.pbio.3001439] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 11/01/2021] [Accepted: 10/07/2021] [Indexed: 11/19/2022] Open
Abstract
The ability to navigate "cocktail party" situations by focusing on sounds of interest over irrelevant, background sounds is often considered in terms of cortical mechanisms. However, subcortical circuits such as the pathway underlying the medial olivocochlear (MOC) reflex modulate the activity of the inner ear itself, supporting the extraction of salient features from auditory scene prior to any cortical processing. To understand the contribution of auditory subcortical nuclei and the cochlea in complex listening tasks, we made physiological recordings along the auditory pathway while listeners engaged in detecting non(sense) words in lists of words. Both naturally spoken and intrinsically noisy, vocoded speech-filtering that mimics processing by a cochlear implant (CI)-significantly activated the MOC reflex, but this was not the case for speech in background noise, which more engaged midbrain and cortical resources. A model of the initial stages of auditory processing reproduced specific effects of each form of speech degradation, providing a rationale for goal-directed gating of the MOC reflex based on enhancing the representation of the energy envelope of the acoustic waveform. Our data reveal the coexistence of 2 strategies in the auditory system that may facilitate speech understanding in situations where the signal is either intrinsically degraded or masked by extrinsic acoustic energy. Whereas intrinsically degraded streams recruit the MOC reflex to improve representation of speech cues peripherally, extrinsically masked streams rely more on higher auditory centres to denoise signals.
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Affiliation(s)
- Heivet Hernández-Pérez
- Department of Linguistics, The Australian Hearing Hub, Macquarie University, Sydney, Australia
| | - Jason Mikiel-Hunter
- Department of Linguistics, The Australian Hearing Hub, Macquarie University, Sydney, Australia
| | - David McAlpine
- Department of Linguistics, The Australian Hearing Hub, Macquarie University, Sydney, Australia
| | - Sumitrajit Dhar
- Department of Communication Sciences and Disorders, Northwestern University, Evanston, Illinois, United States of America
| | - Sriram Boothalingam
- University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Jessica J. M. Monaghan
- Department of Linguistics, The Australian Hearing Hub, Macquarie University, Sydney, Australia
- National Acoustic Laboratories, Sydney, Australia
| | - Catherine M. McMahon
- Department of Linguistics, The Australian Hearing Hub, Macquarie University, Sydney, Australia
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5
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Skoe E, Krizman J, Spitzer ER, Kraus N. Auditory Cortical Changes Precede Brainstem Changes During Rapid Implicit Learning: Evidence From Human EEG. Front Neurosci 2021; 15:718230. [PMID: 34483831 PMCID: PMC8415395 DOI: 10.3389/fnins.2021.718230] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Accepted: 07/20/2021] [Indexed: 11/28/2022] Open
Abstract
The auditory system is sensitive to stimulus regularities such as frequently occurring sounds and sound combinations. Evidence of regularity detection can be seen in how neurons across the auditory network, from brainstem to cortex, respond to the statistical properties of the soundscape, and in the rapid learning of recurring patterns in their environment by children and adults. Although rapid auditory learning is presumed to involve functional changes to the auditory network, the chronology and directionality of changes are not well understood. To study the mechanisms by which this learning occurs, auditory brainstem and cortical activity was simultaneously recorded via electroencephalogram (EEG) while young adults listened to novel sound streams containing recurring patterns. Neurophysiological responses were compared between easier and harder learning conditions. Collectively, the behavioral and neurophysiological findings suggest that cortical and subcortical structures each provide distinct contributions to auditory pattern learning, but that cortical sensitivity to stimulus patterns likely precedes subcortical sensitivity.
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Affiliation(s)
- Erika Skoe
- Department of Speech, Language and Hearing Sciences, Connecticut Institute for Brain and Cognitive Sciences, University of Connecticut, Storrs, CT, United States
| | - Jennifer Krizman
- Auditory Neuroscience Laboratory, Department of Communication Sciences, Northwestern University, Evanston, IL, United States
| | - Emily R Spitzer
- Department of Otolaryngology, Head and Neck Surgery, New York University Grossman School of Medicine, New York, NY, United States
| | - Nina Kraus
- Auditory Neuroscience Laboratory, Department of Communication Sciences, Northwestern University, Evanston, IL, United States.,Department of Neurobiology and Physiology, Northwestern University, Evanston, IL, United States.,Department of Otolaryngology, Northwestern University, Evanston, IL, United States.,Institute for Neuroscience, Northwestern University, Evanston, IL, United States
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6
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Goodman SS, Boothalingam S, Lichtenhan JT. Medial olivocochlear reflex effects on amplitude growth functions of long- and short-latency components of click-evoked otoacoustic emissions in humans. J Neurophysiol 2021; 125:1938-1953. [PMID: 33625926 DOI: 10.1152/jn.00410.2020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Functional outcomes of medial olivocochlear reflex (MOCR) activation, such as improved hearing in background noise and protection from noise damage, involve moderate to high sound levels. Previous noninvasive measurements of MOCR in humans focused primarily on otoacoustic emissions (OAEs) evoked at low sound levels. Interpreting MOCR effects on OAEs at higher levels is complicated by the possibility of the middle-ear muscle reflex and by components of OAEs arising from different locations along the length of the cochlear spiral. We overcame these issues by presenting click stimuli at a very slow rate and by time-frequency windowing the resulting click-evoked (CE)OAEs into short-latency (SL) and long-latency (LL) components. We characterized the effects of MOCR on CEOAE components using multiple measures to more comprehensively assess these effects throughout much of the dynamic range of hearing. These measures included CEOAE amplitude attenuation, equivalent input attenuation, phase, and slope of growth functions. Results show that MOCR effects are smaller on SL components than LL components, consistent with SL components being generated slightly basal of the characteristic frequency region. Amplitude attenuation measures showed the largest effects at the lowest stimulus levels, but slope change and equivalent input attenuation measures did not decrease at higher stimulus levels. These latter measures are less commonly reported and may provide insight into the variability in listening performance and noise susceptibility seen across individuals.NEW & NOTEWORTHY The auditory efferent system, operating at moderate to high sound levels, may improve hearing in background noise and provide protection from noise damage. We used otoacoustic emissions to measure these efferent effects across a wide range of sound levels and identified level-dependent and independent effects. Previous reports have focused on level-dependent measures. The level-independent effects identified here may provide new insights into the functional relevance of auditory efferent activity in humans.
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Affiliation(s)
- Shawn S Goodman
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa
| | - Sriram Boothalingam
- Department of Communication Sciences and Disorders, Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin
| | - Jeffery T Lichtenhan
- Department of Otolaryngology, Washington University School of Medicine in St. Louis, St. Louis, Missouri
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Boothalingam S, Allan C, Allen P, Purcell DW. The Medial Olivocochlear Reflex Is Unlikely to Play a Role in Listening Difficulties in Children. Trends Hear 2020; 23:2331216519870942. [PMID: 31558110 PMCID: PMC6767729 DOI: 10.1177/2331216519870942] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The medial olivocochlear reflex (MOCR) has been implicated in several auditory processes. The putative role of the MOCR in improving speech perception in noise is particularly relevant for children who complain of listening difficulties (LiD). The hypothesis that the MOCR may be impaired in individuals with LiD or auditory processing disorder has led to several investigations but without consensus. In two related studies, we compared the MOCR functioning of children with LiD and typically developing (TD) children in the same age range (7-17 years). In Study 1, we investigated ipsilateral, contralateral, and bilateral MOCR using forward-masked click-evoked otoacoustic emissions (CEOAEs; n = 17 TD, 17 LiD). In Study 2, we employed three OAE types: CEOAEs (n = 16 TD, 21 LiD), stimulus frequency OAEs (n = 21 TD, 30 LiD), and distortion product OAEs (n = 17 TD, 22 LiD) in a contralateral noise paradigm. Results from both studies suggest that the MOCR functioning is not significantly different between the two groups. Some likely reasons for differences in findings among published studies could stem from the lack of strict data quality measures (e.g., high signal-to-noise ratio, control for the middle ear muscle reflex) that were enforced in the present study. The inherent variability of the MOCR, the subpar reliability of current MOCR methods, and the heterogeneity in auditory processing deficits that underlie auditory processing disorder make detecting clinically relevant differences in MOCR function impractical using current methods.
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Affiliation(s)
- Sriram Boothalingam
- Department of Communication Sciences and Disorders, University of Wisconsin, Madison, WI, USA.,Waisman Center, University of Wisconsin, Madison, WI, USA
| | - Chris Allan
- School of Communication Sciences and Disorders, Western University, London, ON, Canada.,National Centre for Audiology, Western University, London, ON, Canada
| | - Prudence Allen
- School of Communication Sciences and Disorders, Western University, London, ON, Canada.,National Centre for Audiology, Western University, London, ON, Canada
| | - David W Purcell
- School of Communication Sciences and Disorders, Western University, London, ON, Canada.,National Centre for Audiology, Western University, London, ON, Canada
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8
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Marian V, Lam TQ, Hayakawa S, Dhar S. Spontaneous Otoacoustic Emissions Reveal an Efficient Auditory Efferent Network. JOURNAL OF SPEECH, LANGUAGE, AND HEARING RESEARCH : JSLHR 2018; 61:2827-2832. [PMID: 30458524 PMCID: PMC6693566 DOI: 10.1044/2018_jslhr-h-18-0025] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Revised: 04/30/2018] [Accepted: 06/05/2018] [Indexed: 06/09/2023]
Abstract
PURPOSE Understanding speech often involves processing input from multiple modalities. The availability of visual information may make auditory input less critical for comprehension. This study examines whether the auditory system is sensitive to the presence of complementary sources of input when exerting top-down control over the amplification of speech stimuli. METHOD Auditory gain in the cochlea was assessed by monitoring spontaneous otoacoustic emissions (SOAEs), which are by-products of the amplification process. SOAEs were recorded while 32 participants (23 women, nine men; Mage = 21.13) identified speech sounds such as "ba" and "ga." The speech sounds were presented either alone or with complementary visual input, as well as in quiet or with 6-talker babble. RESULTS Analyses revealed that there was a greater reduction in the amplification of noisy auditory stimuli compared with quiet. This reduced amplification may aid in the perception of speech by improving the signal-to-noise ratio. Critically, there was a greater reduction in amplification when speech sounds were presented bimodally with visual information relative to when they were presented unimodally. This effect was evidenced by greater changes in SOAE levels from baseline to stimuli presentation in audiovisual trials relative to audio-only trials. CONCLUSIONS The results suggest that even the earliest stages of speech comprehension are modulated by top-down influences, resulting in changes to SOAEs depending on the presence of bimodal or unimodal input. Neural processes responsible for changes in cochlear function are sensitive to redundancy across auditory and visual input channels and coordinate activity to maximize efficiency in the auditory periphery.
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Affiliation(s)
- Viorica Marian
- Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL
| | - Tuan Q. Lam
- Department of Psychological Sciences, Loyola University, New Orleans, LA
| | - Sayuri Hayakawa
- Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL
| | - Sumitrajit Dhar
- Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL
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9
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Marian V, Lam TQ, Hayakawa S, Dhar S. Top-Down Cognitive and Linguistic Influences on the Suppression of Spontaneous Otoacoustic Emissions. Front Neurosci 2018; 12:378. [PMID: 29937708 PMCID: PMC6002685 DOI: 10.3389/fnins.2018.00378] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Accepted: 05/17/2018] [Indexed: 11/13/2022] Open
Abstract
Auditory sensation is often thought of as a bottom-up process, yet the brain exerts top-down control to affect how and what we hear. We report the discovery that the magnitude of top-down influence varies across individuals as a result of differences in linguistic background and executive function. Participants were 32 normal-hearing individuals (23 female) varying in language background (11 English monolinguals, 10 Korean-English late bilinguals, and 11 Korean-English early bilinguals), as well as cognitive abilities (working memory, cognitive control). To assess efferent control over inner ear function, participants were presented with speech-sounds (e.g., /ba/, /pa/) in one ear while spontaneous otoacoustic emissions (SOAEs) were measured in the contralateral ear. SOAEs are associated with the amplification of sound in the cochlea, and can be used as an index of top-down efferent activity. Individuals with bilingual experience and those with better cognitive control experienced larger reductions in the amplitude of SOAEs in response to speech stimuli, likely as a result of greater efferent suppression of amplification in the cochlea. This suppression may aid in the critical task of speech perception by minimizing the disruptive effects of noise. In contrast, individuals with better working memory exert less control over the cochlea, possibly due to a greater capacity to process complex stimuli at later stages. These findings demonstrate that even peripheral mechanics of auditory perception are shaped by top-down cognitive and linguistic influences.
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Affiliation(s)
- Viorica Marian
- Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, United States
| | - Tuan Q Lam
- Department of Psychological Sciences, Loyola University, New Orleans, LA, United States
| | - Sayuri Hayakawa
- Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, United States
| | - Sumitrajit Dhar
- Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, United States
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10
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Lopez-Poveda EA. Olivocochlear Efferents in Animals and Humans: From Anatomy to Clinical Relevance. Front Neurol 2018; 9:197. [PMID: 29632514 PMCID: PMC5879449 DOI: 10.3389/fneur.2018.00197] [Citation(s) in RCA: 81] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Accepted: 03/13/2018] [Indexed: 11/13/2022] Open
Abstract
Olivocochlear efferents allow the central auditory system to adjust the functioning of the inner ear during active and passive listening. While many aspects of efferent anatomy, physiology and function are well established, others remain controversial. This article reviews the current knowledge on olivocochlear efferents, with emphasis on human medial efferents. The review covers (1) the anatomy and physiology of olivocochlear efferents in animals; (2) the methods used for investigating this auditory feedback system in humans, their limitations and best practices; (3) the characteristics of medial-olivocochlear efferents in humans, with a critical analysis of some discrepancies across human studies and between animal and human studies; (4) the possible roles of olivocochlear efferents in hearing, discussing the evidence in favor and against their role in facilitating the detection of signals in noise and in protecting the auditory system from excessive acoustic stimulation; and (5) the emerging association between abnormal olivocochlear efferent function and several health conditions. Finally, we summarize some open issues and introduce promising approaches for investigating the roles of efferents in human hearing using cochlear implants.
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Affiliation(s)
- Enrique A Lopez-Poveda
- Instituto de Neurociencias de Castilla y León, Universidad de Salamanca, Salamanca, Spain.,Departamento de Cirugía, Facultad de Medicina, Universidad de Salamanca, Salamanca, Spain.,Instituto de Investigación Biomédica de Salamanca, Universidad de Salamanca, Salamanca, Spain
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11
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Olivocochlear efferents: Their action, effects, measurement and uses, and the impact of the new conception of cochlear mechanical responses. Hear Res 2017; 362:38-47. [PMID: 29291948 DOI: 10.1016/j.heares.2017.12.012] [Citation(s) in RCA: 101] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2017] [Revised: 11/08/2017] [Accepted: 12/12/2017] [Indexed: 12/27/2022]
Abstract
The anatomy and physiology of olivocochlear (OC) efferents are reviewed. To help interpret these, recent advances in cochlear mechanics are also reviewed. Lateral OC (LOC) efferents innervate primary auditory-nerve (AN) fiber dendrites. The most important LOC function may be to reduce auditory neuropathy. Medial OC (MOC) efferents innervate the outer hair cells (OHCs) and act to turn down the gain of cochlear amplification. Cochlear amplification had been thought to act only through basilar membrane (BM) motion, but recent reports show that motion near the reticular lamina (RL) is amplified more than BM motion, and that RL-motion amplification extends to several octaves below the local characteristic frequency. Data on efferent effects on AN-fiber responses, otoacoustic emissions (OAEs) and human psychophysics are reviewed and reinterpreted in the light of the new cochlear-mechanical data. The possible origin of OAEs in RL motion is considered. MOC-effect measuring methods and MOC-induced changes in human responses are also reviewed, including that ipsilateral and contralateral sound can produce MOC effects with different patterns across frequency. MOC efferents help to reduce damage due to acoustic trauma. Many, but not all, reports show that subjects with stronger contralaterally-evoked MOC effects have better ability to detect signals (e.g. speech) in noise, and that MOC effects can be modulated by attention.
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12
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Bhatt I. Increased medial olivocochlear reflex strength in normal-hearing, noise-exposed humans. PLoS One 2017; 12:e0184036. [PMID: 28886123 PMCID: PMC5590870 DOI: 10.1371/journal.pone.0184036] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Accepted: 08/16/2017] [Indexed: 11/23/2022] Open
Abstract
Research suggests that college-aged adults are vulnerable to tinnitus and hearing loss due to exposure to traumatic levels of noise on a regular basis. Recent human studies have associated exposure to high noise exposure background (NEB, i.e., routine noise exposure) with the reduced cochlear output and impaired speech processing ability in subjects with clinically normal hearing sensitivity. While the relationship between NEB and the functions of the auditory afferent neurons are studied in the literature, little is known about the effects of NEB on functioning of the auditory efferent system. The objective of the present study was to investigate the relationship between medial olivocochlear reflex (MOCR) strength and NEB in subjects with clinically normal hearing sensitivity. It was hypothesized that subjects with high NEB would exhibit reduced afferent input to the MOCR circuit which would subsequently lead to reduced strength of the MOCR. In normal-hearing listeners, the study examined (1) the association between NEB and baseline click-evoked otoacoustic emissions (CEOAEs) and (2) the association between NEB and MOCR strength. The MOCR was measured using CEOAEs evoked by 60 dB pSPL linear clicks in a contralateral acoustic stimulation (CAS)-off and CAS-on (a broadband noise at 60 dB SPL) condition. Participants with at least 6 dB signal-to-noise ratio (SNR) in the CAS-off and CAS-on conditions were included for analysis. A normalized CEOAE inhibition index was calculated to express MOCR strength in a percentage value. NEB was estimated using a validated questionnaire. The results showed that NEB was not associated with the baseline CEOAE amplitude (r = -0.112, p = 0.586). Contrary to the hypothesis, MOCR strength was positively correlated with NEB (r = 0.557, p = 0.003). NEB remained a significant predictor of MOCR strength (β = 2.98, t(19) = 3.474, p = 0.003) after the unstandardized coefficient was adjusted to control for effects of smoking, sound level tolerance (SLT) and tinnitus. These data provide evidence that MOCR strength is associated with NEB. The functional significance of increased MOCR strength is discussed.
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Affiliation(s)
- Ishan Bhatt
- Department of Communication Sciences & Disorders, Northern Arizona University, Flagstaff, AZ, United States of America
- * E-mail:
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13
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Marks KL, Siegel JH. Differentiating Middle Ear and Medial Olivocochlear Effects on Transient-Evoked Otoacoustic Emissions. J Assoc Res Otolaryngol 2017; 18:529-542. [PMID: 28432471 DOI: 10.1007/s10162-017-0621-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2016] [Accepted: 03/22/2017] [Indexed: 10/19/2022] Open
Abstract
The response of the inner ear is modulated by the middle ear muscle (MEM) and olivocochlear (OC) efferent systems. Both systems can be activated reflexively by acoustic stimuli delivered to one or both ears. The acoustic middle ear muscle reflex (MEMR) controls the transmission of acoustic signals through the middle ear, while reflex activation of the medial component of the olivocochlear system (the MOCR) modulates cochlear mechanics. The relative prominence of the two efferent systems varies widely between species. Measuring the effect of either of these systems can be confounded by simultaneously activating the other. We describe a simple, sensitive online method that can identify the effects both systems have on otoacoustic emissions (OAEs) evoked by transient stimuli such as clicks or tone pips (TEOAEs). The method detects directly in the time domain the changes in the stimulus and/or emission pressures caused by contralateral noise. Measurements in human participants are consistent with other reports that the threshold for MOCR activation is consistently lower than for MEMR. The method appears to control for drift and subject-generated noise well enough to avoid the need for post hoc processing, making it promising for application in animal experiments (even if awake) and in the hearing clinic.
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Affiliation(s)
- Kendra L Marks
- Department of Communication Sciences and Disorders, School of Communication, Northwestern University, 2240 Campus Drive, Evanston, IL, 60208-2952, USA
| | - Jonathan H Siegel
- Department of Communication Sciences and Disorders, School of Communication, Northwestern University, 2240 Campus Drive, Evanston, IL, 60208-2952, USA.
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Abstract
The perceptual insensitivity to low frequency (LF) sound in humans has led to an underestimation of the physiological impact of LF exposure on the inner ear. It is known, however, that intense, LF sound causes cyclic changes of indicators of inner ear function after LF stimulus offset, for which the term "Bounce" phenomenon has been coined.Here, we show that the mechanical amplification of hair cells (OHCs) is significantly affected after the presentation of LF sound. First, we show the Bounce phenomenon in slow level changes of quadratic, but not cubic, distortion product otoacoustic emissions (DPOAEs). Second, Bouncing in response to LF sound is seen in slow, oscillating frequency and correlated level changes of spontaneous otoacoustic emissions (SOAEs). Surprisingly, LF sound can induce new SOAEs which can persist for tens of seconds. Further, we show that the Bounce persists under free-field conditions, i.e. without an in-ear probe occluding the auditory meatus. Finally, we show that the Bounce is affected by contralateral acoustic stimulation synchronised to the ipsilateral LF sound. These findings clearly demonstrate that the origin of the Bounce lies in the modulation of cochlear amplifier gain. We conclude that activity changes of OHCs are the source of the Bounce, most likely caused by a temporary disturbance of OHC calcium homeostasis. In the light of these findings, the effects of long-duration, anthropogenic LF sound on the human inner ear require further research.
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15
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Ubiali T, Sanfins MD, Borges LR, Colella-Santos MF. Contralateral Noise Stimulation Delays P300 Latency in School-Aged Children. PLoS One 2016; 11:e0148360. [PMID: 26849224 PMCID: PMC4744065 DOI: 10.1371/journal.pone.0148360] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2015] [Accepted: 01/19/2016] [Indexed: 11/18/2022] Open
Abstract
Background and Objective The auditory cortex modulates auditory afferents through the olivocochlear system, which innervates the outer hair cells and the afferent neurons under the inner hair cells in the cochlea. Most of the studies that investigated the efferent activity in humans focused on evaluating the suppression of the otoacoustic emissions by stimulating the contralateral ear with noise, which assesses the activation of the medial olivocochlear bundle. The neurophysiology and the mechanisms involving efferent activity on higher regions of the auditory pathway, however, are still unknown. Also, the lack of studies investigating the effects of noise on human auditory cortex, especially in peadiatric population, points to the need for recording the late auditory potentials in noise conditions. Assessing the auditory efferents in schoolaged children is highly important due to some of its attributed functions such as selective attention and signal detection in noise, which are important abilities related to the development of language and academic skills. For this reason, the aim of the present study was to evaluate the effects of noise on P300 responses of children with normal hearing. Methods P300 was recorded in 27 children aged from 8 to 14 years with normal hearing in two conditions: with and whitout contralateral white noise stimulation. Results P300 latencies were significantly longer at the presence of contralateral noise. No significant changes were observed for the amplitude values. Conclusion Contralateral white noise stimulation delayed P300 latency in a group of school-aged children with normal hearing. These results suggest a possible influence of the medial olivocochlear activation on P300 responses under noise condition.
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Affiliation(s)
- Thalita Ubiali
- Faculty of Medical Sciences, State University of Campinas, Campinas, São Paulo, Brazil
- * E-mail:
| | | | - Leticia Reis Borges
- Faculty of Medical Sciences, State University of Campinas, Campinas, São Paulo, Brazil
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Zhao W, Dewey JB, Boothalingam S, Dhar S. Efferent Modulation of Stimulus Frequency Otoacoustic Emission Fine Structure. Front Syst Neurosci 2015; 9:168. [PMID: 26696843 PMCID: PMC4674573 DOI: 10.3389/fnsys.2015.00168] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Accepted: 11/19/2015] [Indexed: 11/26/2022] Open
Abstract
Otoacoustic emissions, sounds generated in the inner ear, have become a convenient non-invasive tool to examine the efferent modulation of cochlear mechanics. Activation of the medial olivocochlear (MOC) efferents has been shown to alter the magnitude of these emissions. When the effects of efferent activation on the detailed spectral structures of these emissions have been examined, a shift of the spectral patterns toward higher frequencies has been reported for distortion product and spontaneous otoacoustic emissions. Stimulus frequency otoacoustic emissions (SFOAEs) have been proposed as the preferred emission type in the study of efferent modulation due to the simplicity of their production leading to the possibility of clearer interpretation of results. The effects of efferent activation on the complex spectral patterns of SFOAEs have not been examined to the best of our knowledge. We have examined the effects of activating the MOC efferents using broadband noise in normal-hearing humans. The detailed spectral structure of SFOAEs, known as fine structure, was recorded with and without contralateral acoustic stimulation. Results indicate that SFOAEs are reduced in magnitude and their fine structure pushed to higher frequencies by contralateral acoustic stimulation. These changes are similar to those observed in distortion product or spontaneous otoacoustic emissions and behavioral hearing thresholds. Taken together with observations made about magnitude and phase changes in otoacoustic emissions and hearing thresholds upon contralateral acoustic stimulation, all changes in otoacoustic emission and hearing threshold fine structure appear to be driven by a common set of mechanisms. Specifically, frequency shifts in fine structure patterns appear to be linked to changes in SFOAE phase due to contralateral acoustic stimulation.
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Affiliation(s)
- Wei Zhao
- L.E.K. Consulting, Boston MA, USA
| | - James B Dewey
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston IL, USA
| | - Sriram Boothalingam
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston IL, USA
| | - Sumitrajit Dhar
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston IL, USA ; Knowles Hearing Center, Northwestern University, Evanston IL, USA
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17
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Kugler K, Wiegrebe L, Gürkov R, Krause E, Drexl M. Concurrent Acoustic Activation of the Medial Olivocochlear System Modifies the After-Effects of Intense Low-Frequency Sound on the Human Inner Ear. J Assoc Res Otolaryngol 2015; 16:713-25. [PMID: 26264256 DOI: 10.1007/s10162-015-0538-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Accepted: 07/22/2015] [Indexed: 12/31/2022] Open
Abstract
>Human hearing is rather insensitive for very low frequencies (i.e. below 100 Hz). Despite this insensitivity, low-frequency sound can cause oscillating changes of cochlear gain in inner ear regions processing even much higher frequencies. These alterations outlast the duration of the low-frequency stimulation by several minutes, for which the term 'bounce phenomenon' has been coined. Previously, we have shown that the bounce can be traced by monitoring frequency and level changes of spontaneous otoacoustic emissions (SOAEs) over time. It has been suggested elsewhere that large receptor potentials elicited by low-frequency stimulation produce a net Ca(2+) influx and associated gain decrease in outer hair cells. The bounce presumably reflects an underdamped, homeostatic readjustment of increased Ca(2+) concentrations and related gain changes after low-frequency sound offset. Here, we test this hypothesis by activating the medial olivocochlear efferent system during presentation of the bounce-evoking low-frequency (LF) sound. The efferent system is known to modulate outer hair cell Ca(2+) concentrations and receptor potentials, and therefore, it should modulate the characteristics of the bounce phenomenon. We show that simultaneous presentation of contralateral broadband noise (100 Hz-8 kHz, 65 and 70 dB SPL, 90 s, activating the efferent system) and ipsilateral low-frequency sound (30 Hz, 120 dB SPL, 90 s, inducing the bounce) affects the characteristics of bouncing SOAEs recorded after low-frequency sound offset. Specifically, the decay time constant of the SOAE level changes is shorter, and the transient SOAE suppression is less pronounced. Moreover, the number of new, transient SOAEs as they are seen during the bounce, are reduced. Taken together, activation of the medial olivocochlear system during induction of the bounce phenomenon with low-frequency sound results in changed characteristics of the bounce phenomenon. Thus, our data provide experimental support for the hypothesis that outer hair cell calcium homeostasis is the source of the bounce phenomenon.
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Affiliation(s)
- Kathrin Kugler
- German Center for Vertigo and Balance Disorders (IFB), Grosshadern Medical Centre, University of Munich, 81377, Munich, Germany.,Department of Otorhinolaryngology, Head and Neck Surgery, Grosshadern Medical Centre, University of Munich, 81377, Munich, Germany.,Division of Neurobiology, Department Biology II, University of Munich, 82152, Martinsried, Germany
| | - Lutz Wiegrebe
- German Center for Vertigo and Balance Disorders (IFB), Grosshadern Medical Centre, University of Munich, 81377, Munich, Germany.,Division of Neurobiology, Department Biology II, University of Munich, 82152, Martinsried, Germany
| | - Robert Gürkov
- German Center for Vertigo and Balance Disorders (IFB), Grosshadern Medical Centre, University of Munich, 81377, Munich, Germany.,Department of Otorhinolaryngology, Head and Neck Surgery, Grosshadern Medical Centre, University of Munich, 81377, Munich, Germany
| | - Eike Krause
- German Center for Vertigo and Balance Disorders (IFB), Grosshadern Medical Centre, University of Munich, 81377, Munich, Germany.,Department of Otorhinolaryngology, Head and Neck Surgery, Grosshadern Medical Centre, University of Munich, 81377, Munich, Germany
| | - Markus Drexl
- German Center for Vertigo and Balance Disorders (IFB), Grosshadern Medical Centre, University of Munich, 81377, Munich, Germany. .,Department of Otorhinolaryngology, Head and Neck Surgery, Grosshadern Medical Centre, University of Munich, 81377, Munich, Germany. .,Division of Neurobiology, Department Biology II, University of Munich, 82152, Martinsried, Germany.
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18
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Boothalingam S, Purcell DW. Influence of the stimulus presentation rate on medial olivocochlear system assays. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2015; 137:724-32. [PMID: 25698007 DOI: 10.1121/1.4906250] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Click evoked otoacoustic emissions (CEOAEs) are commonly used both in research and clinics to assay the medial olivocochlear system (MOC). Clicks presented at rates >50 Hz in the contralateral ear have previously been reported to evoke contralateral MOC activity. However, in typical MOC assays, clicks are presented in the ipsilateral ear in conjunction with MOC elicitor (noise) in the contralateral ear. The effect of click rates in such an arrangement is currently unknown. A forward masking paradigm was used to emulate typical MOC assays to elucidate the influence of ipsilateral click presentation rates on MOC inhibition of CEOAEs in 28 normal hearing adults. Influence of five click rates (20.83, 25, 31.25, 41.67, and 62.5 Hz) presented at 55 dB peSPL was tested. Results indicate that click rates as low as 31.25 Hz significantly enhance contralateral MOC inhibition, possibly through the activation of ipsilateral and binaural MOC neurons with potential contributions from the middle ear muscle reflex. Therefore, click rates ≤25 Hz are recommended for use in MOC assays, at least for 55 dB peSPL click level.
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Affiliation(s)
- Sriram Boothalingam
- National Centre for Audiology, Western University, London, Ontario N6G 1H1, Canada
| | - David W Purcell
- National Centre for Audiology, Western University, London, Ontario N6G 1H1, Canada
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19
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Effects of contralateral acoustic stimulation on spontaneous otoacoustic emissions and hearing threshold fine structure. J Assoc Res Otolaryngol 2014; 15:897-914. [PMID: 25245498 DOI: 10.1007/s10162-014-0485-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Accepted: 08/18/2014] [Indexed: 10/24/2022] Open
Abstract
Medial olivocochlear (MOC) influence on cochlear mechanics can be noninvasively, albeit indirectly, explored via the effects of contralateral acoustic stimulation (CAS) on otoacoustic emissions. CAS-mediated effects are particularly pronounced for spontaneous otoacoustic emissions (SOAEs), which are typically reduced in amplitude and shifted upward in frequency by CAS. We investigated whether similar frequency shifts and magnitude reductions were observed behaviorally in the fine structure of pure-tone hearing thresholds, a phenomenon thought to share a common underlying mechanism with SOAEs. In normal-hearing listeners, fine-resolution thresholds were obtained over a narrow frequency range centered on the frequency of an SOAE, both in the absence and presence of 60-dB SPL broadband CAS. While CAS shifted threshold fine structure patterns and SOAEs upward in frequency by a comparable amount, little reduction in the presence or depth of fine structure was observed at frequencies near those of SOAEs. In fact, CAS typically improved thresholds, particularly at threshold minima, and increased fine structure depth when reductions in the amplitude of the associated SOAE were less than 10 dB. Additional measurements made at frequencies distant from SOAEs, or near SOAEs that were more dramatically reduced in amplitude by the CAS, revealed that CAS tended to elevate thresholds and reduce threshold fine structure depth. The results suggest that threshold fine structure is sensitive to MOC-mediated changes in cochlear gain, but that SOAEs complicate the interpretation of threshold measurements at nearby frequencies, perhaps due to masking or other interference effects. Both threshold fine structure and SOAEs may be significant sources of intersubject and intrasubject variability in psychoacoustic investigations of MOC function.
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20
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Mishra SK, Lutman ME. Top-down influences of the medial olivocochlear efferent system in speech perception in noise. PLoS One 2014; 9:e85756. [PMID: 24465686 PMCID: PMC3896402 DOI: 10.1371/journal.pone.0085756] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Accepted: 12/01/2013] [Indexed: 11/18/2022] Open
Abstract
One of the putative functions of the medial olivocochlear (MOC) system is to enhance signal detection in noise. The objective of this study was to elucidate the role of the MOC system in speech perception in noise. In normal-hearing human listeners, we examined (1) the association between magnitude of MOC inhibition and speech-in-noise performance, and (2) the association between MOC inhibition and the amount of contralateral acoustic stimulation (CAS)-induced shift in speech-in-noise acuity. MOC reflex measurements in this study considered critical measurement issues overlooked in past work by: recording relatively low-level, linear click-evoked otoacoustic emissions (CEOAEs), adopting 6 dB signal-to-noise ratio (SNR) criteria, and computing normalized CEOAE differences. We found normalized index to be a stable measure of MOC inhibition (mean = 17.21%). MOC inhibition was not related to speech-in-noise performance measured without CAS. However, CAS in a speech-in-noise task caused an SNRSP enhancement (mean = 2.45 dB), and this improvement in speech-in-noise acuity was directly related to their MOC reflex assayed by CEOAEs. Individuals do not necessarily use the available MOC-unmasking characteristic while listening to speech in noise, or do not utilize unmasking to the extent that can be shown by artificial MOC activation. It may be the case that the MOC is not actually used under natural listening conditions and the higher auditory centers recruit MOC-mediated mechanisms only in specific listening conditions-those conditions remain to be investigated.
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Affiliation(s)
- Srikanta K Mishra
- Institute of Sound and Vibration Research, University of Southampton, Southampton, United Kingdom ; Department of Communication Sciences and Disorders, Butler University, Indianapolis, Indiana, United States of America
| | - Mark E Lutman
- Institute of Sound and Vibration Research, University of Southampton, Southampton, United Kingdom
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DPOAE Intensity Increase at Individual Dominant Frequency after Short-Term Auditory Exposure. ISRN OTOLARYNGOLOGY 2013; 2013:379719. [PMID: 24083031 PMCID: PMC3777126 DOI: 10.1155/2013/379719] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Accepted: 08/06/2013] [Indexed: 11/17/2022]
Abstract
Previous experiments suggested the possibility of a short-term sound stimulus-evoked and transient increase in DPOAE amplitudes. This phenomenon is possibly due to the complexity of the outer hair cells and their efferent control system and the different time scales of regulatory processes. A total of 100 healthy subjects ranging from 18 to 40 years of age with normal hearing and normal DPOAE values in the range of 781–4000 Hz were recruited in the study. Diagnostic DPOAE measurements were performed after short-term sound exposure. We proposed a 10 sec, 50 dB sound impulse as the most effective stimulus for clinical practice between 40 and 60 sec poststimulus time to detect the aforementioned transient DPOAE increase. We developed a procedure for detection of this transient increase in DPOAE by the application of a short-term sound exposure. The phenomenon was consistent and well detectable. Based on our findings, a new aspect of cochlear adaptation can be established that might be introduced as a routine clinical diagnostic tool. A mathematical model was provided that summarizes various factors that determine electromotility of OHCs and serves as a possible clinical application using this phenomenon for the prediction of individual noise susceptibility.
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Skoe E, Krizman J, Spitzer E, Kraus N. The auditory brainstem is a barometer of rapid auditory learning. Neuroscience 2013; 243:104-14. [DOI: 10.1016/j.neuroscience.2013.03.009] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Revised: 03/11/2013] [Accepted: 03/12/2013] [Indexed: 10/27/2022]
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Abstract
PURPOSE OF REVIEW This review covers the articles published between 2010 and early 2011 that presented new findings on inner-ear efferents and their ability to modulate hair cell function. RECENT FINDINGS Studies published within the review period have increased our understanding of efferent mechanisms on hair cells in the cochlear and vestibular sensory epithelium and provide insights on efferent contributions to the plasticity of bilateral auditory processing. The central nervous system controls the sensitivity of hair cells to physiological stimuli by regulating the gain of hair cell electromechanical amplification and modulating the efficiency of hair cell-eighth nerve transmission. A notable advance in the last year has been animal and human studies that have examined the contribution of the olivocochlear efferents to sound localization, particularly in a noisy environment. SUMMARY Acoustic activation of olivocochlear fibers provides a clinical test for the integrity of the peripheral auditory system and has provided new understanding about the function and limitations of the cochlear amplifier. Although similar tests may be possible in the efferent vestibular system, they have not yet been developed. The structural and functional similarities of the sensory epithelia in the inner ear offer hope that testing procedures may be developed that will allow reliable testing of the vestibular hair cell function.
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Zhao W, Dhar S. Frequency tuning of the contralateral medial olivocochlear reflex in humans. J Neurophysiol 2012; 108:25-30. [PMID: 22457463 DOI: 10.1152/jn.00051.2012] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Activation of the medial olivocochlear (MOC) efferents attenuates cochlear gain and reduces the amplitudes of mechanical, electrical, and neural cochlear outputs. The functional roles of the MOC efferents are not fully understood, especially in humans, despite postulations that they are involved in protection against acoustic trauma, facilitation of transient-sound perception, etc. Delineating the frequency tuning properties of the MOC efferents would provide critical evidence to support or refute these postulated functional roles. By utilizing spontaneous otoacoustic emissions (SOAEs), a cochlear measure sensitive to MOC modulation, we systematically demonstrate in humans that the contralateral MOC reflex is tuned to a fixed frequency band between 500 and 1,000 Hz independent of SOAE frequency. Our results question the role of the MOC reflex in protection against acoustic trauma or facilitation of transient-sound perception.
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Affiliation(s)
- Wei Zhao
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston, Illinois, USA.
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Lilaonitkul W, Guinan JJ. Frequency tuning of medial-olivocochlear-efferent acoustic reflexes in humans as functions of probe frequency. J Neurophysiol 2011; 107:1598-611. [PMID: 22190630 DOI: 10.1152/jn.00549.2011] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The medial-olivocochlear (MOC) acoustic reflex is thought to provide frequency-specific feedback that adjusts the gain of cochlear amplification, but little is known about how frequency specific the reflex actually is. We measured human MOC tuning through changes in stimulus frequency otoacoustic emissions (SFOAEs) from 40-dB-SPL tones at probe frequencies (f(p)s) near 0.5, 1.0, and 4.0 kHz. MOC activity was elicited by 60-dB-SPL ipsilateral, contralateral, or bilateral tones or half-octave noise bands, with elicitor frequency (f(e)) varied in half-octave steps. Tone and noise elicitors produced similar results. At all probe frequencies, SFOAE changes were produced by a wide range of elicitor frequencies with elicitor frequencies near 0.7-2.0 kHz being particularly effective. MOC-induced changes in SFOAE magnitude and SFOAE phase were surprisingly different functions of f(e): magnitude inhibition largest for f(e) close to f(p), phase change largest for f(e) remote from f(p). The metric ΔSFOAE, which combines both magnitude and phase changes, provided the best match to reported (cat) MOC neural inhibition. Ipsilateral and contralateral MOC reflexes often showed dramatic differences in plots of MOC effect vs. elicitor frequency, indicating that the contralateral reflex does not give an accurate picture of ipsilateral-reflex properties. These differences in MOC effects appear to imply that ipsilateral and contralateral reflexes have different actions in the cochlea. The implication of these results for MOC function, cochlear mechanics, and the production of SFOAEs are discussed.
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Affiliation(s)
- Watjana Lilaonitkul
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, USA
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