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Lee C, Hartsock JJ, Salt AN, Lichtenhan JT. A Guinea Pig Model Suggests That Objective Assessment of Acoustic Hearing Preservation in Human Ears With Cochlear Implants Is Confounded by Shifts in the Spatial Origin of Acoustically Evoked Potential Measurements Along the Cochlear Length. Ear Hear 2024; 45:666-678. [PMID: 38178312 DOI: 10.1097/aud.0000000000001457] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2024]
Abstract
OBJECTIVES Our recent empirical findings have shown that the auditory nerve compound action potential (CAP) evoked by a low-level tone burst originates from a narrow cochlear region tuned to the tone burst frequency. At moderate to high sound levels, the origins shift to the most sensitive audiometric regions rather than the extended high-frequency regions of the cochlear base. This means that measurements evoked from extended high-frequency sound stimuli can shift toward the apex with increasing level. Here we translate this study to understand the spatial origin of acoustically evoked responses from ears that receive cochlear implants, an emerging area of research and clinical practice that is not completely understood. An essential step is to first understand the influence of the cochlear implant in otherwise naive ears. Our objective was to understand how function of the high-frequency cochlear base, which can be excited by the intense low-frequency sounds that are frequently used for objective intra- and postoperative monitoring, can be influenced by the presence of the cochlear implant. DESIGN We acoustically evoked responses and made measurements with an electrode placed near the guinea pig round window. The cochlear implant was not utilized for either electrical stimulation or recording purposes. With the cochlear implant in situ, CAPs were acoustically evoked from 2 to 16 kHz tone bursts of various levels while utilizing the slow perfusion of a kainic acid solution from the cochlear apex to the cochlear aqueduct in the base, which sequentially reduced neural responses from finely spaced cochlear frequency regions. This cochlear perfusion technique reveals the spatial origin of evoked potential measurements and provides insight on what influence the presence of an implant has on acoustical hearing. RESULTS Threshold measurements at 3 to 11 kHz were elevated by implantation. In an individual ear, thresholds were elevated and lowered as cochlear implant was respectively inserted and removed, indicative of "conductive hearing loss" induced by the implant. The maximum threshold elevation occurred at most sensitive region of the naive guinea pig ear (33.66 dB at 8 kHz), making 11 kHz the most sensitive region to acoustic sounds for guinea pig ears with cochlear implants. Conversely, the acute implantation did not affect the low-frequency, 500 Hz thresholds and suprathreshold function, as shown by the auditory nerve overlapped waveform. As the sound pressure level of the tone bursts increased, mean data show that the spatial origin of CAPs along the cochlear length shifted toward the most sensitive cochlear region of implanted ears, not the extended high-frequency cochlear regions. However, data from individual ears showed that after implantation, measurements from moderate to high sound pressure levels originate in places that are unique to each ear. CONCLUSIONS Alterations to function of the cochlear base from the in situ cochlear implant may influence objective measurements of implanted ears that are frequently made with intense low-frequency sound stimuli. Our results from guinea pigs advance the interpretation of measurements used to understand how and when residual acoustic hearing is lost in human ears receiving a cochlear implant.
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Affiliation(s)
- Choongheon Lee
- Department of Otolaryngology, University of Rochester, Rochester, New York, USA
| | - Jared J Hartsock
- Department of Cochlear Surgery, Turner Scientific, Inc., Jacksonville, Illinois, USA
| | - Alec N Salt
- Department of Pharmacokinetics, Turner Scientific, Inc., Jacksonville, Illinois, USA
| | - Jeffery T Lichtenhan
- Department of Otolaryngology, University of South Florida Morsani School of Medicine, Tampa, Florida, USA
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Tejani VD, Kim JS, Etler CP, Skidmore J, Yuan Y, He S, Hansen MR, Gantz BJ, Abbas PJ, Brown CJ. Longitudinal Electrocochleography as an Objective Measure of Serial Behavioral Audiometry in Electro-Acoustic Stimulation Patients. Ear Hear 2023; 44:1014-1028. [PMID: 36790447 PMCID: PMC10425573 DOI: 10.1097/aud.0000000000001342] [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] [Indexed: 02/16/2023]
Abstract
OBJECTIVE Minimally traumatic surgical techniques and advances in cochlear implant (CI) electrode array designs have allowed acoustic hearing present in a CI candidate prior to surgery to be preserved postoperatively. As a result, these patients benefit from combined electric-acoustic stimulation (EAS) postoperatively. However, 30% to 40% of EAS CI users experience a partial loss of hearing up to 30 dB after surgery. This additional hearing loss is generally not severe enough to preclude use of acoustic amplification; however, it can still impact EAS benefits. The use of electrocochleography (ECoG) measures of peripheral hair cell and neural auditory function have shed insight into the pathophysiology of postimplant loss of residual acoustic hearing. The present study aims to assess the long-term stability of ECoG measures and to establish ECoG as an objective method of monitoring residual hearing over the course of EAS CI use. We hypothesize that repeated measures of ECoG should remain stable over time for EAS CI users with stable postoperative hearing preservation. We also hypothesize that changes in behavioral audiometry for EAS CI users with loss of residual hearing should also be reflected in changes in ECoG measures. DESIGN A pool of 40 subjects implanted under hearing preservation protocol was included in the study. Subjects were seen at postoperative visits for behavioral audiometry and ECoG recordings. Test sessions occurred 0.5, 1, 3, 6, 12 months, and annually after 12 months postoperatively. Changes in pure-tone behavioral audiometric thresholds relative to baseline were used to classify subjects into two groups: one group with stable acoustic hearing and another group with loss of acoustic hearing. At each test session, ECoG amplitude growth functions for several low-frequency stimuli were obtained. The threshold, slope, and suprathreshold amplitude at a fixed stimulation level was obtained from each growth function at each time point. Longitudinal linear mixed effects models were used to study trends in ECoG thresholds, slopes, and amplitudes for subjects with stable hearing and subjects with hearing loss. RESULTS Preoperative, behavioral audiometry indicated that subjects had an average low-frequency pure-tone average (125 to 500 Hz) of 40.88 ± 13.12 dB HL. Postoperatively, results showed that ECoG thresholds and amplitudes were stable in EAS CI users with preserved residual hearing. ECoG thresholds increased (worsened) while ECoG amplitudes decreased (worsened) for those with delayed hearing loss. The slope did not distinguish between EAS CI users with stable hearing and subjects with delayed loss of hearing. CONCLUSIONS These results provide a new application of postoperative ECoG as an objective tool to monitor residual hearing and understand the pathophysiology of delayed hearing loss. While our measures were conducted with custom-designed in-house equipment, CI companies are also designing and implementing hardware and software adaptations to conduct ECoG recordings. Thus, postoperative ECoG recordings can potentially be integrated into clinical practice.
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Affiliation(s)
- Viral D Tejani
- Department of Otolaryngology-Head and Neck Surgery, University Hospitals Cleveland Medical Center, Cleveland, Ohio, USA
- Department of Otolaryngology-Head and Neck Surgery, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa, USA
| | - Jeong-Seo Kim
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa, USA
- Hearing Research Laboratory, Samsung Medical Center, Seoul, South Korea
| | - Christine P Etler
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
| | - Jeffrey Skidmore
- Department of Otolaryngology-Head and Neck Surgery, Eye and Ear Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - Yi Yuan
- Department of Otolaryngology-Head and Neck Surgery, Eye and Ear Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - Shuman He
- Department of Otolaryngology-Head and Neck Surgery, Eye and Ear Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio, USA
| | - Marlan R Hansen
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
- Department of Neurosurgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
- Department of Molecular Physiology and Biophysics, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
| | - Bruce J Gantz
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
- Department of Neurosurgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
| | - Paul J Abbas
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa, USA
| | - Carolyn J Brown
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa, USA
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Haggerty RA, Hutson KA, Riggs WJ, Brown KD, Pillsbury HC, Adunka OF, Buchman CA, Fitzpatrick DC. Assessment of cochlear synaptopathy by electrocochleography to low frequencies in a preclinical model and human subjects. Front Neurol 2023; 14:1104574. [PMID: 37483448 PMCID: PMC10361575 DOI: 10.3389/fneur.2023.1104574] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2022] [Accepted: 06/19/2023] [Indexed: 07/25/2023] Open
Abstract
Cochlear synaptopathy is the loss of synapses between the inner hair cells and the auditory nerve despite survival of sensory hair cells. The findings of extensive cochlear synaptopathy in animals after moderate noise exposures challenged the long-held view that hair cells are the cochlear elements most sensitive to insults that lead to hearing loss. However, cochlear synaptopathy has been difficult to identify in humans. We applied novel algorithms to determine hair cell and neural contributions to electrocochleographic (ECochG) recordings from the round window of animal and human subjects. Gerbils with normal hearing provided training and test sets for a deep learning algorithm to detect the presence of neural responses to low frequency sounds, and an analytic model was used to quantify the proportion of neural and hair cell contributions to the ECochG response. The capacity to detect cochlear synaptopathy was validated in normal hearing and noise-exposed animals by using neurotoxins to reduce or eliminate the neural contributions. When the analytical methods were applied to human surgical subjects with access to the round window, the neural contribution resembled the partial cochlear synaptopathy present after neurotoxin application in animals. This result demonstrates the presence of viable hair cells not connected to auditory nerve fibers in human subjects with substantial hearing loss and indicates that efforts to regenerate nerve fibers may find a ready cochlear substrate for innervation and resumption of function.
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Affiliation(s)
- Raymond A. Haggerty
- Department of Otolaryngology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - Kendall A. Hutson
- Department of Otolaryngology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
| | - William J. Riggs
- Department of Otolaryngology, The Ohio State University, Columbus, OH, United States
| | - Kevin D. Brown
- Department of Otolaryngology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
- University of North Carolina School of Medicine, Chapel Hill, NC, United States
| | - Harold C. Pillsbury
- Department of Otolaryngology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
- University of North Carolina School of Medicine, Chapel Hill, NC, United States
| | - Oliver F. Adunka
- Department of Otolaryngology, The Ohio State University, Columbus, OH, United States
| | - Craig A. Buchman
- Department of Otolaryngology, Washington University in St. Louis, St. Louis, MO, United States
| | - Douglas C. Fitzpatrick
- Department of Otolaryngology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
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Alamri Y, Jennings SG. Computational modeling of the human compound action potential. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2023; 153:2376. [PMID: 37092943 PMCID: PMC10119875 DOI: 10.1121/10.0017863] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Revised: 03/21/2023] [Accepted: 04/04/2023] [Indexed: 05/03/2023]
Abstract
The auditory nerve (AN) compound action potential (CAP) is an important tool for assessing auditory disorders and monitoring the health of the auditory periphery during surgical procedures. The CAP has been mathematically conceptualized as the convolution of a unit response (UR) waveform with the firing rate of a population of AN fibers. Here, an approach for predicting experimentally recorded CAPs in humans is proposed, which involves the use of human-based computational models to simulate AN activity. CAPs elicited by clicks, chirps, and amplitude-modulated carriers were simulated and compared with empirically recorded CAPs from human subjects. In addition, narrowband CAPs derived from noise-masked clicks and tone bursts were simulated. Many morphological, temporal, and spectral aspects of human CAPs were captured by the simulations for all stimuli tested. These findings support the use of model simulations of the human CAP to refine existing human-based models of the auditory periphery, aid in the design and analysis of auditory experiments, and predict the effects of hearing loss, synaptopathy, and other auditory disorders on the human CAP.
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Affiliation(s)
- Yousef Alamri
- Department of Biomedical Engineering, The University of Utah, 390 South, 1530 East, BEHS 1201, Salt Lake City, Utah 84112, USA
| | - Skyler G Jennings
- Department of Communication Sciences and Disorders, The University of Utah, 390 South, 1530 East, BEHS 1201, Salt Lake City, Utah 84112, USA
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Almohammad HA, Chertoff ME, Ferraro JA, Diaz FJ. Auditory nerve phase-locked response recorded from normal hearing adults using electrocochleography. Int J Audiol 2023; 62:172-181. [PMID: 35130459 DOI: 10.1080/14992027.2021.2024283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
OBJECTIVE The auditory nerve overlapped waveform response (ANOW), a new measure that can be recorded non-invasively from humans, holds promise for providing more accurate assessment of low frequency hearing thresholds than currently used objective measures. This research aims to investigate the robustness and the nature of the ANOW response in humans. DESIGN Repeated within-session recordings of the ANOW response using low-frequency Tone Bursts (TBs) were obtained at multiple stimulus levels. ANOW's absolute amplitude and phase locking value (PLV) measures were analysed to obtain normative data and to test the reliability of the ANOW response. STUDY SAMPLE Thirteen normal hearing adults within the age range of 25 to 40 years. RESULTS ANOW response was obtained to both 250 Hz and 500 Hz TBs and was traced down to 30-40 dB nHL. ANOW response showed significantly higher amplitude and stronger phase locking using 250 Hz TB compared to 500 Hz TB. High degree of test retest reliability of the ANOW response was found using 250 Hz TB at presentation levels higher than 40 dB nHL. CONCLUSIONS ANOW response is recordable noninvasively using low-frequency TBs and shows higher robustness as the stimulus frequency decreases.
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Affiliation(s)
- Hana A Almohammad
- Department of Rehabilitation Sciences, Faculty of Applied Medical Sciences, Jordan University of Science and Technology, Irbid, Jordan
| | - Mark E Chertoff
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, KS, USA
| | - John A Ferraro
- Department of Biostatistics and Data Science, University of Kansas Medical Center, Kansas City, KS, USA
| | - Francisco J Diaz
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, KS, USA
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Round Window Electrocochleography to Low Frequency Tones in Pediatric Cochlear Implant Recipients with and Without Auditory Neuropathy Spectrum Disorder: Separating Hair Cell and Neural Contributions Using a Computational Model. Otol Neurotol 2022; 43:781-788. [PMID: 35763496 PMCID: PMC9329248 DOI: 10.1097/mao.0000000000003568] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
HYPOTHESIS Characterize the contribution of the auditory nerve neurophonic (ANN) to electrocochleography (ECochG) of pediatric cochlear implant (CI) recipients with and without auditory nerve spectrum disorder (ANSD). BACKGROUND ECochG is an emerging technique for predicting outcomes in CI recipients. Its utility may be increased by separating the cochlear microphonic (CM), produced by hair cells, from the ANN, the evoked potential correlate of neural phase-locking, which are mixed in the ongoing portion of the response to low frequency tone bursts. METHODS Responses to tone bursts of different frequency and intensities were recorded from the round window of pediatric CI recipients. Separation of the CM and ANN was performed using a model of the underlying processes that lead to the shapes of the observed waveforms. RESULTS Preoperative mean pure tone amplitudes of the included ANSD (n = 36) and non-ANSD subjects (n = 123), were similar (89.5 and 93.5, p = 0.1). Total of 1,024 ECochG responses to frequency and intensity series were recorded. The mean correlation (r) between the input and the modeled signals was 0.973 ± 0.056 (standard deviation). The ANN magnitudes were higher in the ANSD group (ANOVAs, F = 26.5 for frequency and 21.9 for intensity, df's = 1, p's < 0.001). However, its relative contribution to the overall signal was lower (ANOVAs, F = 25.8 and 12.1, df = 1, p's < 0.001). CONCLUSIONS ANN was detected in low frequency ECochG responses but not high frequency responses in both ANSD and non-ANSD subjects. ANSD subjects, evidence of neural contribution in responses to low frequency stimuli was highly variable and often comparable to signals recorded in non-ANSD subjects. The computational model revealed that on average the ANN comprised a lower proportion of the overall signal than in non-ANSD subjects.
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7
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Jennings SG, Dominguez J. Firing Rate Adaptation of the Human Auditory Nerve Optimizes Neural Signal-to-Noise Ratios. J Assoc Res Otolaryngol 2022; 23:365-378. [PMID: 35254540 PMCID: PMC9085988 DOI: 10.1007/s10162-022-00841-7] [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: 10/28/2021] [Accepted: 02/14/2022] [Indexed: 10/18/2022] Open
Abstract
Several physiological mechanisms act on the response of the auditory nerve (AN) during acoustic stimulation, resulting in an adjustment in auditory gain. These mechanisms include-but are not limited to-firing rate adaptation, dynamic range adaptation, the middle ear muscle reflex, and the medial olivocochlear reflex. A potential role of these mechanisms is to improve the neural signal-to-noise ratio (SNR) at the output of the AN in real time. This study tested the hypothesis that neural SNRs, inferred from non-invasive assessment of the human AN, improve over the duration of acoustic stimulation. Cochlear potentials were measured in response to a series of six high-level clicks embedded in a series of six lower-level broadband noise bursts. This paradigm elicited a compound action potential (CAP) in response to each click and to the onset of each noise burst. The ratio of CAP amplitudes elicited by each click and noise burst pair (i.e., neural SNR) was tracked over the six click/noise bursts. The main finding was a rapid (< 24 ms) increase in neural SNR from the first to the second click/noise burst, consistent with a real-time adjustment in the response of the auditory periphery toward improving the SNR of the signal transmitted to the brainstem. Analysis of cochlear microphonic and ear canal sound pressure recordings, as well as the time course for this improvement in neural SNR, supports the conclusion that firing rate adaptation is likely the primary mechanism responsible for improving neural SNR, while dynamic range adaptation, the middle ear muscle reflex, and the medial olivocochlear reflex played a secondary role on the effects observed in this study. Real-time improvements in neural SNR are significant because they may be essential for robust encoding of speech and other relevant stimuli in the presence of background noise.
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Affiliation(s)
- Skyler G Jennings
- Department of Communication Sciences and Disorders, The University of Utah, 390 South, 1530 East, BEHS 1201, Salt Lake City, UT, 84112, USA.
| | - Juan Dominguez
- Department of Communication Sciences and Disorders, The University of Utah, 390 South, 1530 East, BEHS 1201, Salt Lake City, UT, 84112, USA
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Cheng FY, Xu C, Gold L, Smith S. Rapid Enhancement of Subcortical Neural Responses to Sine-Wave Speech. Front Neurosci 2022; 15:747303. [PMID: 34987356 PMCID: PMC8721138 DOI: 10.3389/fnins.2021.747303] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Accepted: 12/02/2021] [Indexed: 01/15/2023] Open
Abstract
The efferent auditory nervous system may be a potent force in shaping how the brain responds to behaviorally significant sounds. Previous human experiments using the frequency following response (FFR) have shown efferent-induced modulation of subcortical auditory function online and over short- and long-term time scales; however, a contemporary understanding of FFR generation presents new questions about whether previous effects were constrained solely to the auditory subcortex. The present experiment used sine-wave speech (SWS), an acoustically-sparse stimulus in which dynamic pure tones represent speech formant contours, to evoke FFRSWS. Due to the higher stimulus frequencies used in SWS, this approach biased neural responses toward brainstem generators and allowed for three stimuli (/bɔ/, /bu/, and /bo/) to be used to evoke FFRSWSbefore and after listeners in a training group were made aware that they were hearing a degraded speech stimulus. All SWS stimuli were rapidly perceived as speech when presented with a SWS carrier phrase, and average token identification reached ceiling performance during a perceptual training phase. Compared to a control group which remained naïve throughout the experiment, training group FFRSWS amplitudes were enhanced post-training for each stimulus. Further, linear support vector machine classification of training group FFRSWS significantly improved post-training compared to the control group, indicating that training-induced neural enhancements were sufficient to bolster machine learning classification accuracy. These results suggest that the efferent auditory system may rapidly modulate auditory brainstem representation of sounds depending on their context and perception as non-speech or speech.
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Affiliation(s)
- Fan-Yin Cheng
- Department of Speech, Language, and Hearing Sciences, University of Texas at Austin, Austin, TX, United States
| | - Can Xu
- Department of Speech, Language, and Hearing Sciences, University of Texas at Austin, Austin, TX, United States
| | - Lisa Gold
- Department of Speech, Language, and Hearing Sciences, University of Texas at Austin, Austin, TX, United States
| | - Spencer Smith
- Department of Speech, Language, and Hearing Sciences, University of Texas at Austin, Austin, TX, United States
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Lefler SM, Duncan RK, Goodman SS, Guinan JJ, Lichtenhan JT. Measurements From Ears With Endolymphatic Hydrops and 2-Hydroxypropyl-Beta-Cyclodextrin Provide Evidence That Loudness Recruitment Can Have a Cochlear Origin. Front Surg 2021; 8:687490. [PMID: 34676239 PMCID: PMC8523923 DOI: 10.3389/fsurg.2021.687490] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Accepted: 09/02/2021] [Indexed: 11/21/2022] Open
Abstract
Background: Loudness recruitment is commonly experienced by patients with putative endolymphatic hydrops. Loudness recruitment is abnormal loudness growth with high-level sounds being perceived as having normal loudness even though hearing thresholds are elevated. The traditional interpretation of recruitment is that cochlear amplification has been reduced. Since the cochlear amplifier acts primarily at low sound levels, an ear with elevated thresholds from reduced cochlear amplification can have normal processing at high sound levels. In humans, recruitment can be studied using perceptual loudness but in animals physiological measurements are used. Recruitment in animal auditory-nerve responses has never been unequivocally demonstrated because the animals used had damage to sensory and neural cells, not solely a reduction of cochlear amplification. Investigators have thus looked for, and found, evidence of recruitment in the auditory central nervous system (CNS). While studies on CNS recruitment are informative, they cannot rule out the traditional interpretation of recruitment originating in the cochlea. Design: We used techniques that could assess hearing function throughout entire frequency- and dynamic-range of hearing. Measurements were made from two animal models: guinea-pig ears with endolymphatic-sac-ablation surgery to produce endolymphatic hydrops, and naïve guinea-pig ears with cochlear perfusions of 13 mM 2-Hydroxypropyl-Beta-Cyclodextrin (HPBCD) in artificial perilymph. Endolymphatic sac ablation caused low-frequency loss. Animals treated with HPBCD had hearing loss at all frequencies. None of these animals had loss of hair cells or synapses on auditory nerve fibers. Results: In ears with endolymphatic hydrops and those perfused with HPBCD, auditory-nerve based measurements at low frequencies showed recruitment compared to controls. Recruitment was not found at high frequencies (> 4 kHz) where hearing thresholds were normal in ears with endolymphatic hydrops and elevated in ears treated with HPBCD. Conclusions: We found compelling evidence of recruitment in auditory-nerve data. Such clear evidence has never been shown before. Our findings suggest that, in patients suspected of having endolymphatic hydrops, loudness recruitment may be a good indication that the associated low-frequency hearing loss originates from a reduction of cochlear amplification, and that measurements of recruitment could be used in differential diagnosis and treatment monitoring of Ménière's disease.
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Affiliation(s)
- Shannon M Lefler
- Department of Otolaryngology, Washington University School of Medicine in St. Louis, Saint Louis, MO, United States
| | - Robert K Duncan
- Department of Otolaryngology-Head and Neck Surgery, Kresge Hearing Research Institute, University of Michigan, Ann Arbor, MI, United States
| | - Shawn S Goodman
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, United States
| | - John J Guinan
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, United States.,Department of Otolaryngology, Harvard Medical School, Boston, MA, United States
| | - Jeffery T Lichtenhan
- Department of Otolaryngology, Washington University School of Medicine in St. Louis, Saint Louis, MO, United States
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10
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Using electrocochleography to detect sensory and neural damages in a gerbil model. Sci Rep 2021; 11:19557. [PMID: 34599220 PMCID: PMC8486782 DOI: 10.1038/s41598-021-98658-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Accepted: 09/13/2021] [Indexed: 11/09/2022] Open
Abstract
Hearing is one of the five sensory organs that allows us to interact with society and our environment. However, one in eight Americans suffers from sensorineural hearing loss that is great enough to adversely impact their daily life. There is an urgent need to identify what part/degree of the auditory pathway (sensory or neural) is compromised so that appropriate treatment/intervention can be implemented. Single- or two-tone evoked potentials, the electrocochleography (eCochG), were measured along the auditory pathway, i.e., at the round window and remotely at the vertex, with simultaneous recordings of ear canal distortion product otoacoustic emissions. Sensory (cochlear) and neural components in the (remote-) eCochG responses showed distinct level- and frequency-dependent features allowing to be differentiated from each other. Specifically, the distortion products in the (remote-)eCochGs can precisely localize the sensory damage showing that they are effective to determine the sensory or neural damage along the auditory pathway.
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Walia A, Lee C, Hartsock J, Goodman SS, Dolle R, Salt AN, Lichtenhan JT, Rutherford MA. Reducing Auditory Nerve Excitability by Acute Antagonism of Ca 2+-Permeable AMPA Receptors. Front Synaptic Neurosci 2021; 13:680621. [PMID: 34290596 PMCID: PMC8287724 DOI: 10.3389/fnsyn.2021.680621] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 05/31/2021] [Indexed: 11/13/2022] Open
Abstract
Hearing depends on glutamatergic synaptic transmission mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). AMPARs are tetramers, where inclusion of the GluA2 subunit reduces overall channel conductance and Ca2+ permeability. Cochlear afferent synapses between inner hair cells (IHCs) and auditory nerve fibers (ANFs) contain the AMPAR subunits GluA2, 3, and 4. However, the tetrameric complement of cochlear AMPAR subunits is not known. It was recently shown in mice that chronic intracochlear delivery of IEM-1460, an antagonist selective for GluA2-lacking AMPARs [also known as Ca2+-permeable AMPARs (CP-AMPARs)], before, during, and after acoustic overexposure prevented both the trauma to ANF synapses and the ensuing reduction of cochlear nerve activity in response to sound. Surprisingly, baseline measurements of cochlear function before exposure were unaffected by chronic intracochlear delivery of IEM-1460. This suggested that cochlear afferent synapses contain GluA2-lacking CP-AMPARs alongside GluA2-containing Ca2+-impermeable AMPA receptors (CI-AMPARs), and that the former can be antagonized for protection while the latter remain conductive. Here, we investigated hearing function in the guinea pig during acute local or systemic delivery of CP-AMPAR antagonists. Acute intracochlear delivery of IEM-1460 or systemic delivery of IEM-1460 or IEM-1925 reduced the amplitude of the ANF compound action potential (CAP) significantly, for all tone levels and frequencies, by > 50% without affecting CAP thresholds or distortion product otoacoustic emissions (DPOAE). Following systemic dosing, IEM-1460 levels in cochlear perilymph were ~ 30% of blood levels, on average, consistent with pharmacokinetic properties predicting permeation of the compounds into the brain and ear. Both compounds were metabolically stable with half-lives >5 h in vitro, and elimination half-lives in vivo of 118 min (IEM-1460) and 68 min (IEM-1925). Heart rate monitoring and off-target binding assays suggest an enhanced safety profile for IEM-1925 over IEM-1460. Compound potency on CAP reduction (IC50 ~ 73 μM IEM-1460) was consistent with a mixture of GluA2-lacking and GluA2-containing AMPARs. These data strongly imply that cochlear afferent synapses of the guinea pig contain GluA2-lacking CP-AMPARs. We propose these CP-AMPARs may be acutely antagonized with systemic dosing, to protect from glutamate excitotoxicity, while transmission at GluA2-containing AMPARs persists to mediate hearing during the protection.
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Affiliation(s)
- Amit Walia
- Department of Otolaryngology, Washington University in St. Louis School of Medicine, St. Louis, MO, United States
| | - Choongheon Lee
- Department of Otolaryngology, Washington University in St. Louis School of Medicine, St. Louis, MO, United States
| | - Jared Hartsock
- Department of Otolaryngology, Washington University in St. Louis School of Medicine, St. Louis, MO, United States
| | - Shawn S Goodman
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, United States
| | - Roland Dolle
- Department of Biochemistry and Molecular Biophysics, Washington University Center for Drug Discovery, Washington University in St. Louis School of Medicine, St. Louis, MO, United States
| | - Alec N Salt
- Department of Otolaryngology, Washington University in St. Louis School of Medicine, St. Louis, MO, United States
| | - Jeffery T Lichtenhan
- Department of Otolaryngology, Washington University in St. Louis School of Medicine, St. Louis, MO, United States
| | - Mark A Rutherford
- Department of Otolaryngology, Washington University in St. Louis School of Medicine, St. Louis, MO, United States
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12
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Guinan JJ, Lefler SM, Buchman CA, Goodman SS, Lichtenhan JT. Altered mapping of sound frequency to cochlear place in ears with endolymphatic hydrops provide insight into the pitch anomaly of diplacusis. Sci Rep 2021; 11:10380. [PMID: 34001971 PMCID: PMC8128888 DOI: 10.1038/s41598-021-89902-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 04/26/2021] [Indexed: 11/22/2022] Open
Abstract
A fundamental property of mammalian hearing is the conversion of sound pressure into a frequency-specific place of maximum vibration along the cochlear length, thereby creating a tonotopic map. The tonotopic map makes possible systematic frequency tuning across auditory-nerve fibers, which enables the brain to use pitch to separate sounds from different environmental sources and process the speech and music that connects us to people and the world. Sometimes a tone has a different pitch in the left and right ears, a perceptual anomaly known as diplacusis. Diplacusis has been attributed to a change in the cochlear frequency-place map, but the hypothesized abnormal cochlear map has never been demonstrated. Here we assess cochlear frequency-place maps in guinea-pig ears with experimentally-induced endolymphatic hydrops, a hallmark of Ménière’s disease. Our findings are consistent with the hypothesis that diplacusis is due to an altered cochlear map. Map changes can lead to altered pitch, but the size of the pitch change is also affected by neural synchrony. Our data show that the cochlear frequency-place map is not fixed but can be altered by endolymphatic hydrops. Map changes should be considered in assessing hearing pathologies and treatments.
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Affiliation(s)
- J J Guinan
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, MA, USA.,Department of Otolaryngology, Harvard Medical School, Boston, MA, USA
| | - S M Lefler
- Department of Otolaryngology, School of Medicine, Washington University St. Louis, Campus Box 8115, 660 South Euclid Avenue, Saint Louis, MO, 63110, USA
| | - C A Buchman
- Department of Otolaryngology, School of Medicine, Washington University St. Louis, Campus Box 8115, 660 South Euclid Avenue, Saint Louis, MO, 63110, USA
| | - S S Goodman
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA
| | - J T Lichtenhan
- Department of Otolaryngology, School of Medicine, Washington University St. Louis, Campus Box 8115, 660 South Euclid Avenue, Saint Louis, MO, 63110, USA.
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13
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Tejani VD, Kim JS, Oleson JJ, Abbas PJ, Brown CJ, Hansen MR, Gantz BJ. Residual Hair Cell Responses in Electric-Acoustic Stimulation Cochlear Implant Users with Complete Loss of Acoustic Hearing After Implantation. J Assoc Res Otolaryngol 2021; 22:161-176. [PMID: 33538936 DOI: 10.1007/s10162-021-00785-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 01/03/2021] [Indexed: 11/27/2022] Open
Abstract
Changes in cochlear implant (CI) design and surgical techniques have enabled the preservation of residual acoustic hearing in the implanted ear. While most Nucleus Hybrid L24 CI users retain significant acoustic hearing years after surgery, 6-17 % experience a complete loss of acoustic hearing (Roland et al. Laryngoscope. 126(1):175-81. (2016), Laryngoscope. 128(8):1939-1945 (2018); Scheperle et al. Hear Res. 350:45-57 (2017)). Electrocochleography (ECoG) enables non-invasive monitoring of peripheral auditory function and may provide insight into the pathophysiology of hearing loss. The ECoG response is evoked using an acoustic stimulus and includes contributions from the hair cells (cochlear microphonic-CM) as well as the auditory nerve (auditory nerve neurophonic-ANN). Seven Hybrid L24 CI users with complete loss of residual hearing months after surgery underwent ECoG measures before and after loss of hearing. While significant reductions in CMs were evident after hearing loss, all participants had measurable CMs despite having no measurable acoustic hearing. None retained measurable ANNs. Given histological data suggesting stable hair cell and neural counts after hearing loss (e.g., Quesnel et al. Hear Res. 333:225-234. (2016)), the loss of ECoG and audiometric hearing may reflect reduced synaptic input. This is consistent with the theory that residual CM responses coupled with little to no ANN responses reflect a "disconnect" between hair cells and auditory nerve fibers (Fontenot et al. Ear Hear. 40(3):577-591. 2019). This "disconnection" may prevent proper encoding of auditory stimulation at higher auditory pathways, leading to a lack of audiometric responses, even in the presence of viable cochlear hair cells.
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Affiliation(s)
- Viral D Tejani
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA. .,Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA.
| | - Jeong-Seo Kim
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.,Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA
| | - Jacob J Oleson
- Department of Biostatistics, University of Iowa, Iowa City, IA, USA
| | - Paul J Abbas
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.,Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA
| | - Carolyn J Brown
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.,Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA
| | - Marlan R Hansen
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.,Department of Neurosurgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
| | - Bruce J Gantz
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.,Department of Neurosurgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
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14
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Parida S, Bharadwaj H, Heinz MG. Spectrally specific temporal analyses of spike-train responses to complex sounds: A unifying framework. PLoS Comput Biol 2021; 17:e1008155. [PMID: 33617548 PMCID: PMC7932515 DOI: 10.1371/journal.pcbi.1008155] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 03/04/2021] [Accepted: 02/04/2021] [Indexed: 11/24/2022] Open
Abstract
Significant scientific and translational questions remain in auditory neuroscience surrounding the neural correlates of perception. Relating perceptual and neural data collected from humans can be useful; however, human-based neural data are typically limited to evoked far-field responses, which lack anatomical and physiological specificity. Laboratory-controlled preclinical animal models offer the advantage of comparing single-unit and evoked responses from the same animals. This ability provides opportunities to develop invaluable insight into proper interpretations of evoked responses, which benefits both basic-science studies of neural mechanisms and translational applications, e.g., diagnostic development. However, these comparisons have been limited by a disconnect between the types of spectrotemporal analyses used with single-unit spike trains and evoked responses, which results because these response types are fundamentally different (point-process versus continuous-valued signals) even though the responses themselves are related. Here, we describe a unifying framework to study temporal coding of complex sounds that allows spike-train and evoked-response data to be analyzed and compared using the same advanced signal-processing techniques. The framework uses a set of peristimulus-time histograms computed from single-unit spike trains in response to polarity-alternating stimuli to allow advanced spectral analyses of both slow (envelope) and rapid (temporal fine structure) response components. Demonstrated benefits include: (1) novel spectrally specific temporal-coding measures that are less confounded by distortions due to hair-cell transduction, synaptic rectification, and neural stochasticity compared to previous metrics, e.g., the correlogram peak-height, (2) spectrally specific analyses of spike-train modulation coding (magnitude and phase), which can be directly compared to modern perceptually based models of speech intelligibility (e.g., that depend on modulation filter banks), and (3) superior spectral resolution in analyzing the neural representation of nonstationary sounds, such as speech and music. This unifying framework significantly expands the potential of preclinical animal models to advance our understanding of the physiological correlates of perceptual deficits in real-world listening following sensorineural hearing loss.
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Affiliation(s)
- Satyabrata Parida
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana, United States of America
| | - Hari Bharadwaj
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana, United States of America
- Department of Speech, Language, and Hearing Sciences, Purdue University, West Lafayette, Indiana, United States of America
| | - Michael G. Heinz
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana, United States of America
- Department of Speech, Language, and Hearing Sciences, Purdue University, West Lafayette, Indiana, United States of America
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15
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Valenzuela CV, Lee C, Mispagel A, Bhattacharyya A, Lefler SM, Payne S, Goodman SS, Ortmann AJ, Buchman CA, Rutherford MA, Lichtenhan JT. Is cochlear synapse loss an origin of low-frequency hearing loss associated with endolymphatic hydrops? Hear Res 2020; 398:108099. [PMID: 33125982 DOI: 10.1016/j.heares.2020.108099] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 10/06/2020] [Accepted: 10/19/2020] [Indexed: 01/19/2023]
Abstract
There is a strong association between endolymphatic hydrops and low-frequency hearing loss, but the origin of the hearing loss remains unknown. A reduction in the number of cochlear afferent synapses between inner hair cells and auditory nerve fibres may be the origin of the low-frequency hearing loss, but this hypothesis has not been directly tested in humans or animals. In humans, measurements of hearing loss and postmortem temporal-bone based measurements of endolymphatic hydrops are generally separated by large amounts of time. In animals, there has not been a good objective, physiologic, and minimally invasive measurement of low-frequency hearing. We overcame this obstacle with the combined use of a reliable surgical approach to ablate the endolymphatic sac in guinea pigs and create endolymphatic hydrops, the Auditory Nerve Overlapped Waveform to measure low-frequency hearing loss (≤ 1 kHz), and immunohistofluorescence-based confocal microscopy to count cochlear synapses. Results showed low- and mid-(1-4 kHz) frequency hearing loss at all postoperative days, 1, 4, and 30. There was no statistically significant loss of cochlear synapses, and there was no correlation between synapse loss and hearing function. We conclude that cochlear afferent synaptic loss is not the origin of the low-frequency hearing loss in the early days following endolymphatic sac ablation. Understanding what is, and is not, the origin of a hearing loss can help guide preventative and therapeutic development.
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Affiliation(s)
- Carla V Valenzuela
- Department of Otolaryngology - Head and Neck Surgery, Washington University School of Medicine in St. Louis, 660 South Euclid Avenue, Saint Louis, MO 63110, USA
| | - Choongheon Lee
- Department of Otolaryngology, University of Rochester, Rochester, NY, USA
| | - Abby Mispagel
- Program in Audiology and Communication Sciences, Washington University School of Medicine in St. Louis, St. Louis, MO, USA
| | | | - Shannon M Lefler
- Department of Otolaryngology - Head and Neck Surgery, Washington University School of Medicine in St. Louis, 660 South Euclid Avenue, Saint Louis, MO 63110, USA
| | - Shelby Payne
- Department of Otolaryngology - Head and Neck Surgery, Washington University School of Medicine in St. Louis, 660 South Euclid Avenue, Saint Louis, MO 63110, USA
| | - Shawn S Goodman
- Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA
| | - Amanda J Ortmann
- Department of Otolaryngology - Head and Neck Surgery, Washington University School of Medicine in St. Louis, 660 South Euclid Avenue, Saint Louis, MO 63110, USA; Department of Otolaryngology, University of Rochester, Rochester, NY, USA
| | - Craig A Buchman
- Department of Otolaryngology - Head and Neck Surgery, Washington University School of Medicine in St. Louis, 660 South Euclid Avenue, Saint Louis, MO 63110, USA
| | - Mark A Rutherford
- Department of Otolaryngology - Head and Neck Surgery, Washington University School of Medicine in St. Louis, 660 South Euclid Avenue, Saint Louis, MO 63110, USA
| | - Jeffery T Lichtenhan
- Department of Otolaryngology - Head and Neck Surgery, Washington University School of Medicine in St. Louis, 660 South Euclid Avenue, Saint Louis, MO 63110, USA; Program in Audiology and Communication Sciences, Washington University School of Medicine in St. Louis, St. Louis, MO, USA.
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16
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Simpson MJ, Jennings SG, Margolis RH. Techniques for Obtaining High-quality Recordings in Electrocochleography. Front Syst Neurosci 2020; 14:18. [PMID: 32351368 PMCID: PMC7176302 DOI: 10.3389/fnsys.2020.00018] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Accepted: 03/18/2020] [Indexed: 11/17/2022] Open
Abstract
There are several technical challenges to obtaining high-quality recordings of cochlear potentials in human electrocochleography (ECochG). These challenges include electrical artifacts from devices such as acoustic transducers, biological artifacts from excessive myogenic and electroencephalographic potentials, and issues associated with the placement of a tympanic membrane (TM) electrode on the eardrum. This article presents approaches for dealing with these challenges for ECochG measurement using a TM electrode. Emphasis is placed on eliminating stimulus artifact, optimizing the placement of the electrode, and comparing a custom-made electrode with a commercially-available electrode. This comparison revealed that the custom-made electrode results in greater subject comfort, superior ease of placing the electrode on the eardrum, and larger compound action potential (CAP) amplitudes.
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Affiliation(s)
- Michael J Simpson
- Department of Communication Sciences and Disorders, University of Utah, Salt Lake City, UT, United States
| | - Skyler G Jennings
- Department of Communication Sciences and Disorders, University of Utah, Salt Lake City, UT, United States
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17
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Lee C, Valenzuela CV, Goodman SS, Kallogjeri D, Buchman CA, Lichtenhan JT. Early Detection of Endolymphatic Hydrops using the Auditory Nerve Overlapped Waveform (ANOW). Neuroscience 2020; 425:251-266. [PMID: 31809731 PMCID: PMC6935415 DOI: 10.1016/j.neuroscience.2019.11.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Revised: 10/30/2019] [Accepted: 11/04/2019] [Indexed: 01/14/2023]
Abstract
Endolymphatic hydrops is associated with low-frequency sensorineural hearing loss, with a large body of research dedicated to examining its putative causal role in low-frequency hearing loss. Investigations have been thwarted by the fact that hearing loss is measured in intact ears, but gold standard assessments of endolymphatic hydrops are made postmortem only; and that no objective low-frequency hearing measure has existed. Yet the association of endolymphatic hydrops with low-frequency hearing loss is so strong that it has been established as one of the important defining features for Ménière's disease, rendering it critical to detect endolymphatic hydrops early, regardless of whether it serves a causal role or is the result of other disease mechanisms. We surgically induced endolymphatic hydrops in guinea pigs and employed our recently developed objective neural measure of low-frequency hearing, the Auditory Nerve Overlapped Waveform (ANOW). Hearing loss and endolymphatic hydrops were assessed at various time points after surgery. The ANOW detected low-frequency hearing loss as early as the first day after surgery, well before endolymphatic hydrops was found histologically. The ANOW detected low-frequency hearing loss with perfect sensitivity and specificity in all ears after endolymphatic hydrops developed, where there was a strong linear relationship between degree of endolymphatic hydrops and severity of low-frequency hearing loss. Further, histological data demonstrated that endolymphatic hydrops is seen first in the high-frequency cochlear base, though the ANOW demonstrated that dysfunction begins in the low-frequency apical cochlear half. The results lay the groundwork for future investigations of the causal role of endolymphatic hydrops in low-frequency hearing loss.
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Affiliation(s)
- C Lee
- Washington University School of Medicine in St. Louis, Department of Otolaryngology, Saint Louis, MO, USA
| | - C V Valenzuela
- Washington University School of Medicine in St. Louis, Department of Otolaryngology, Saint Louis, MO, USA
| | - S S Goodman
- University of Iowa, Department of Communication Sciences and Disorders, Iowa City, IA, USA
| | - D Kallogjeri
- Washington University School of Medicine in St. Louis, Department of Otolaryngology, Saint Louis, MO, USA
| | - C A Buchman
- Washington University School of Medicine in St. Louis, Department of Otolaryngology, Saint Louis, MO, USA
| | - J T Lichtenhan
- Washington University School of Medicine in St. Louis, Department of Otolaryngology, Saint Louis, MO, USA.
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18
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Goodman SS, Lee C, Guinan JJ, Lichtenhan JT. The Spatial Origins of Cochlear Amplification Assessed by Stimulus-Frequency Otoacoustic Emissions. Biophys J 2020; 118:1183-1195. [PMID: 31968228 DOI: 10.1016/j.bpj.2019.12.031] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Revised: 12/04/2019] [Accepted: 12/27/2019] [Indexed: 10/25/2022] Open
Abstract
Cochlear amplification of basilar membrane traveling waves is thought to occur between a tone's characteristic frequency (CF) place and within one octave basal of the CF. Evidence for this view comes only from the cochlear base. Stimulus-frequency otoacoustic emissions (SFOAEs) provide a noninvasive alternative to direct measurements of cochlear motion that can be measured across a wide range of CF regions. Coherent reflection theory indicates that SFOAEs arise mostly from the peak region of the traveling wave, but several studies using far-basal suppressor tones claimed that SFOAE components originate many octaves basal of CF. We measured SFOAEs while perfusing guinea pig cochleas from apex to base with salicylate or KCl solutions that reduced outer-hair-cell function and SFOAE amplification. Solution effects on inner hair cells reduced auditory nerve compound action potentials (CAPs) and provided reference times for when solutions reached the SFOAE-frequency CF region. As solution flowed from apex to base, SFOAE reductions generally occurred later than CAP reductions and showed that the effects of cochlear amplification usually peaked ∼1/2 octave basal of the CF region. For tones ≥2 kHz, cochlear amplification typically extended ∼1.5 octaves basal of CF, and the data are consistent with coherent reflection theory. SFOAE amplification did not extend to the basal end of the cochlea, even though reticular lamina motion is amplified in this region, which indicates that reticular lamina motion is not directly coupled to basilar membrane traveling waves. Previous reports of SFOAE-frequency residuals produced by suppressor frequencies far above the SFOAE frequency are most likely due to additional sources created by the suppressor. For some tones <2 kHz, SFOAE amplification extended two octaves apical of CF, which highlights that different vibratory motions produce SFOAEs and CAPs, and that the amplification region depends on the cochlear mode of motion considered. The concept that there is a single "cochlear amplification region" needs to be revised.
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Affiliation(s)
- Shawn S Goodman
- Communication Sciences and Disorders, University of Iowa, Iowa City, Iowa
| | - Choongheon Lee
- Department of Otolaryngology, Washington University School of Medicine in St. Louis, St. Louis, Missouri
| | - John J Guinan
- Department of Otolaryngology, Harvard Medical School, Boston, Massachusetts; Eaton-Peabody Laboratories, Massachusetts Eye and Ear, Boston, Massachusetts
| | - Jeffery T Lichtenhan
- Department of Otolaryngology, Washington University School of Medicine in St. Louis, St. Louis, Missouri.
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19
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Residual Cochlear Function in Adults and Children Receiving Cochlear Implants: Correlations With Speech Perception Outcomes. Ear Hear 2019; 40:577-591. [PMID: 30169463 DOI: 10.1097/aud.0000000000000630] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
OBJECTIVES Variability in speech perception outcomes with cochlear implants remains largely unexplained. Recently, electrocochleography, or measurements of cochlear potentials in response to sound, has been used to assess residual cochlear function at the time of implantation. Our objective was to characterize the potentials recorded preimplantation in subjects of all ages, and evaluate the relationship between the responses, including a subjective estimate of neural activity, and speech perception outcomes. DESIGN Electrocochleography was recorded in a prospective cohort of 284 candidates for cochlear implant at University of North Carolina (10 months to 88 years of ages). Measurement of residual cochlear function called the "total response" (TR), which is the sum of magnitudes of spectral components in response to tones of different stimulus frequencies, was obtained for each subject. The TR was then related to results on age-appropriate monosyllabic word score tests presented in quiet. In addition to the TR, the electrocochleography results were also assessed for neural activity in the forms of the compound action potential and auditory nerve neurophonic. RESULTS The TR magnitude ranged from a barely detectable response of about 0.02 µV to more than 100 µV. In adults (18 to 79 years old), the TR accounted for 46% of variability in speech perception outcome by linear regression (r = 0.46; p < 0.001). In children between 6 and 17 years old, the variability accounted for was 36% (p < 0.001). In younger children, the TR accounted for less of the variability, 15% (p = 0.012). Subjects over 80 years old tended to perform worse for a given TR than younger adults at the 6-month testing interval. The subjectively assessed neural activity did not increase the information compared with the TR alone, which is primarily composed of the cochlear microphonic produced by hair cells. CONCLUSIONS The status of the auditory periphery, particularly of hair cells rather than neural activity, accounts for a large fraction of variability in speech perception outcomes in adults and older children. In younger children, the relationship is weaker, and the elderly differ from other adults. This simple measurement can be applied with high throughput so that peripheral status can be assessed to help manage patient expectations, create individually-tailored treatment plans, and identify subjects performing below expectations based on residual cochlear function.
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20
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Impact of stimulus frequency and recording electrode on electrocochleography in Hybrid cochlear implant users. Hear Res 2019; 384:107815. [PMID: 31678892 DOI: 10.1016/j.heares.2019.107815] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Revised: 10/02/2019] [Accepted: 10/09/2019] [Indexed: 11/21/2022]
Abstract
This report explores the impact of recording electrode position and stimulus frequency on intracochlear electrocochleography (ECoG) responses recorded from six Nucleus L24 Hybrid CI users. Acoustic tone bursts (250 Hz, 500 Hz, 750 Hz, and 1000 Hz) were presented to the implanted ear via an insert earphone. Recordings were obtained from intracochlear electrodes 6 (most basal), 8, 10, 12, 14, 16, 18, 20, and 22 (most apical). Responses to condensation and rarefaction stimuli were subtracted from one another to emphasize hair cell responses (CM/DIF) and added to one another to emphasize neural responses (ANN/SUM). For a fixed stimulus frequency, the CM/DIF and ANN/SUM magnitudes increased as the recording electrode moved apically. For a fixed recording electrode, as the stimulus frequency was lowered, response magnitudes increased. The CM/DIF and ANN/SUM response phase were generally stable across recording electrodes, although substantial phase shifts were noted for a few conditions. Given the recent interest in ECoG for assessing peripheral auditory function in CI users, the impact of stimulus frequency and recording electrode position on response magnitude should be considered. Results suggest optimal ECoG responses are obtained using the most apical recording electrode and a low frequency acoustic stimulus (250 Hz or 500 Hz).
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21
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Lee C, Guinan JJ, Rutherford MA, Kaf WA, Kennedy KM, Buchman CA, Salt AN, Lichtenhan JT. Cochlear compound action potentials from high-level tone bursts originate from wide cochlear regions that are offset toward the most sensitive cochlear region. J Neurophysiol 2019; 121:1018-1033. [PMID: 30673362 DOI: 10.1152/jn.00677.2018] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Little is known about the spatial origins of auditory nerve (AN) compound action potentials (CAPs) evoked by moderate to intense sounds. We studied the spatial origins of AN CAPs evoked by 2- to 16-kHz tone bursts at several sound levels by slowly injecting kainic acid solution into the cochlear apex of anesthetized guinea pigs. As the solution flowed from apex to base, it sequentially reduced CAP responses from low- to high-frequency cochlear regions. The times at which CAPs were reduced, combined with the cochlear location traversed by the solution at that time, showed the cochlear origin of the removed CAP component. For low-level tone bursts, the CAP origin along the cochlea was centered at the characteristic frequency (CF). As sound level increased, the CAP center shifted basally for low-frequency tone bursts but apically for high-frequency tone bursts. The apical shift was surprising because it is opposite the shift expected from AN tuning curve and basilar membrane motion asymmetries. For almost all high-level tone bursts, CAP spatial origins extended over 2 octaves along the cochlea. Surprisingly, CAPs evoked by high-level low-frequency (including 2 kHz) tone bursts showed little CAP contribution from CF regions ≤ 2 kHz. Our results can be mostly explained by spectral splatter from the tone-burst rise times, excitation in AN tuning-curve "tails," and asynchronous AN responses to high-level energy ≤ 2 kHz. This is the first time CAP origins have been identified by a spatially specific technique. Our results show the need for revising the interpretation of the cochlear origins of high-level CAPs-ABR wave 1. NEW & NOTEWORTHY Cochlear compound action potentials (CAPs) and auditory brain stem responses (ABRs) are routinely used in laboratories and clinics. They are typically interpreted as arising from the cochlear region tuned to the stimulus frequency. However, as sound level is increased, the cochlear origins of CAPs from tone bursts of all frequencies become very wide and their centers shift toward the most sensitive cochlear region. The standard interpretation of CAPs and ABRs from moderate to intense stimuli needs revision.
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Affiliation(s)
- C Lee
- Department of Otolaryngology, Washington University School of Medicine in St. Louis , St. Louis, Missouri
| | - J J Guinan
- Eaton-Peabody Laboratories, Massachusetts Eye and Ear, and Department of Otolaryngology, Harvard Medical School , Boston, Massachusetts
| | - M A Rutherford
- Department of Otolaryngology, Washington University School of Medicine in St. Louis , St. Louis, Missouri
| | - W A Kaf
- Communication Sciences and Disorders Department, Missouri State University , Springfield, Missouri
| | - K M Kennedy
- Department of Otolaryngology, Washington University School of Medicine in St. Louis , St. Louis, Missouri.,Communication Sciences and Disorders Department, Missouri State University , Springfield, Missouri
| | - C A Buchman
- Department of Otolaryngology, Washington University School of Medicine in St. Louis , St. Louis, Missouri
| | - A N Salt
- Department of Otolaryngology, Washington University School of Medicine in St. Louis , St. Louis, Missouri
| | - J T Lichtenhan
- Department of Otolaryngology, Washington University School of Medicine in St. Louis , St. Louis, Missouri
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22
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Tejani VD, Abbas PJ, Brown CJ, Woo J. An improved method of obtaining electrocochleography recordings from Nucleus Hybrid cochlear implant users. Hear Res 2019; 373:113-120. [PMID: 30665078 DOI: 10.1016/j.heares.2019.01.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Revised: 12/26/2018] [Accepted: 01/04/2019] [Indexed: 11/16/2022]
Abstract
Interest in electrocochleography (ECoG) has recently resurged as a potential tool to assess peripheral auditory function in cochlear implant (CI) users. ECoG recordings can be evoked using acoustic stimulation and recorded from an extra- or intra-cochlear electrode in CI users. Recordings reflect contributions from cochlear hair cells and the auditory nerve. We recently demonstrated the feasibility of using Custom Sound EP (clinically available software) to record ECoG responses in Nucleus Hybrid CI users with preserved acoustic hearing in the implanted ear (Abbas et al, 2017). While successful, the recording procedures were time intensive, limiting clinical applications. The current report describes how we improved data collection efficiency by writing custom software using Python programming language. The software interfaced with Nucleus Implant Communicator (NIC) routines to record responses from an intracochlear electrode. ECoG responses were recorded in eight CI users with preserved acoustic hearing using Custom Sound EP and the Python-based software. Responses were similar across both recording systems, but the recording time decreased significantly using the Python-based software. Seven additional CI users underwent repeated testing using the Python-based software and showed high test-retest reliability. The improved efficiency and high reliability increases the likelihood of translating intracochlear ECoG to clinical practice.
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Affiliation(s)
- Viral D Tejani
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA; Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
| | - Paul J Abbas
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA; Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
| | - Carolyn J Brown
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA; Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
| | - Jihwan Woo
- Department of Biomedical Engineering, University of Ulsan, Ulsan, Republic of Korea.
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23
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Charaziak KK, Siegel JH, Shera CA. Spectral Ripples in Round-Window Cochlear Microphonics: Evidence for Multiple Generation Mechanisms. J Assoc Res Otolaryngol 2018; 19:401-419. [PMID: 30014309 DOI: 10.1007/s10162-018-0668-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Accepted: 04/08/2018] [Indexed: 11/30/2022] Open
Abstract
The cochlear microphonic (CM) results from the vector sum of outer hair cell transduction currents excited by a stimulus. The classical theory of CM generation-that the response measured at the round window is dominated by cellular sources located within the tail region of the basilar membrane (BM) excitation pattern-predicts that CM amplitude and phase vary little with stimulus frequency. Contrary to expectations, CM amplitude and phase-gradient delay measured in response to low-level tones in chinchillas demonstrate a striking, quasiperiodic pattern of spectral ripples, even at frequencies > 5 kHz, where interference with neurophonic potentials is unlikely. The spectral ripples were reduced in the presence of a moderate-level saturating tone at a nearby frequency. When converted to the time domain, only the delayed CM energy was diminished in the presence of the saturator. We hypothesize that the ripples represent an interference pattern produced by CM components with different phase gradients: an early-latency component originating within the tail region of the BM excitation and two delayed components that depend on active cochlear processing near the peak region of the traveling wave. Using time windowing, we show that the early, middle, and late components have delays corresponding to estimated middle-ear transmission, cochlear forward delays, and cochlear round-trip delays, respectively. By extending the classical model of CM generation to include mechanical and electrical irregularities, we propose that middle components are generated through a mechanism of "coherent summation" analogous to the production of reflection-source otoacoustic emissions (OAEs), while the late components arise through a process of internal cochlear reflection related to the generation of stimulus-frequency OAEs. Although early-latency components from the passive tail region typically dominate the round-window CM, at low stimulus levels, substantial contributions from components shaped by active cochlear processing provide a new avenue for improving CM measurements as assays of cochlear health.
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Affiliation(s)
- Karolina K Charaziak
- Auditory Research Center, Caruso Department of Otolarygnology, University of Southern California, Los Angeles, CA, USA.
| | - Jonathan H Siegel
- Hugh Knowles Center, Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, USA
| | - Christopher A Shera
- Auditory Research Center, Caruso Department of Otolarygnology, University of Southern California, Los Angeles, CA, USA.,Department of Physics and Astronomy, University of Southern California, Los Angeles, CA, USA
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24
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Patterns Seen During Electrode Insertion Using Intracochlear Electrocochleography Obtained Directly Through a Cochlear Implant. Otol Neurotol 2018; 38:1415-1420. [PMID: 28953607 DOI: 10.1097/mao.0000000000001559] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
HYPOTHESIS Intraoperative, intracochlear electrocochleography (ECochG) will provide a means to monitor cochlear hair cell and neural response during cochlear implant (CI) electrode insertion. Distinct patterns in the insertion track can be characterized. BACKGROUND Conventional CI surgery is performed without a means of actively monitoring cochlear hair cell and neural responses. Intracochlear ECochG obtained directly through the CI may be a source of such feedback. Understanding the patterns observed in the "insertion track" is an essential step toward refining intracochlear ECochG as a tool that can be used to assist in intraoperative decision making and prognostication of hearing preservation. METHODS Intracochlear ECochG was performed in 17 patients. During electrode insertion, a 50-ms tone burst acoustic stimulus was delivered with a frequency of 500 Hz at 110 dB SPL. The ECochG response was monitored from the apical-most electrode. The amplitude of the first harmonic was plotted and monitored in near real time by the audiologist-surgeon team during CI electrode insertion. RESULTS Three distinct patterns in first harmonic amplitude change were observed across subjects during insertion: Type A (52%), overall increase in amplitude from the beginning of insertion until completion; Type B (11%), a maximum amplitude at the beginning of insertion, with a decrease in amplitude as insertion progressed to completion; and Type C (35%), comparable amplitudes at the beginning and completion of the insertion with the maximum amplitude mid-insertion. CONCLUSION Three ECochG patterns were observed during electrode advancement into the cochlea. Ongoing and future work will broaden our scope of knowledge regarding the relationship among these patterns, the presence of cochlear trauma, and functional outcomes related to hearing preservation.
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25
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Abbas PJ, Tejani VD, Scheperle RA, Brown CJ. Using Neural Response Telemetry to Monitor Physiological Responses to Acoustic Stimulation in Hybrid Cochlear Implant Users. Ear Hear 2018; 38:409-425. [PMID: 28085738 PMCID: PMC5482777 DOI: 10.1097/aud.0000000000000400] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE This report describes the results of a series of experiments where we use the neural response telemetry (NRT) system of the Nucleus cochlear implant (CI) to measure the response of the peripheral auditory system to acoustic stimulation in Nucleus Hybrid CI users. The objectives of this study were to determine whether they could separate responses from hair cells and neurons and to evaluate the stability of these measures over time. DESIGN Forty-four CI users participated. They all had residual acoustic hearing and used a Nucleus Hybrid S8, S12, or L24 CI or the standard lateral wall CI422 implant. The NRT system of the CI was used to trigger an acoustic stimulus (500-Hz tone burst or click), which was presented at a low stimulation rate (10, 15, or 50 per second) to the implanted ear via an insert earphone and to record the cochlear microphonic, the auditory nerve neurophonic and the compound action potential (CAP) from an apical intracochlear electrode. To record acoustically evoked responses, a longer time window than is available with the commercial NRT software is required. This limitation was circumvented by making multiple recordings for each stimulus using different time delays between the onset of stimulation and the onset of averaging. These recordings were then concatenated off-line. Matched recordings elicited using positive and negative polarity stimuli were added off-line to emphasize neural potentials (SUM) and subtracted off-line to emphasize potentials primarily generated by cochlear hair cells (DIF). These assumptions regarding the origin of the SUM and DIF components were tested by comparing the magnitude of these derived responses recorded using various stimulation rates. Magnitudes of the SUM and DIF components were compared with each other and with behavioral thresholds. RESULTS SUM and DIF components were identified for most subjects, consistent with both hair cell and neural responses to acoustic stimulation. For a subset of the study participants, the DIF components grew as stimulus level was increased, but little or no SUM components were identified. Latency of the CAPs in response to click stimuli was long relative to reports in the literature of recordings obtained using extracochlear electrodes. This difference in response latency and general morphology of the CAPs recorded was likely due to differences across subjects in hearing loss configuration. The use of high stimulation rates tended to decrease SUM and CAP components more than DIF components. We suggest this effect reflects neural adaptation. In some individuals, repeated measures were made over intervals as long as 9 months. Changes over time in DIF, SUM, and CAP thresholds mirrored changes in audiometric threshold for the subjects who experienced loss of acoustic hearing in the implanted ear. CONCLUSIONS The Nucleus NRT software can be used to record peripheral responses to acoustic stimulation at threshold and suprathreshold levels, providing a window into the status of the auditory hair cells and the primary afferent nerve fibers. These acoustically evoked responses are sensitive to changes in hearing status and consequently could be useful in characterizing the specific pathophysiology of the hearing loss experienced by this population of CI users.
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Affiliation(s)
- Paul J Abbas
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
| | - Viral D Tejani
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
| | - Rachel A. Scheperle
- Department of Communication Sciences and Disorders, Montclair State University, Bloomfield, NJ, USA
| | - Carolyn J. Brown
- Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA, USA
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26
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Pienkowski M, Adunka OF, Lichtenhan JT. Editorial: New Advances in Electrocochleography for Clinical and Basic Investigation. Front Neurosci 2018; 12:310. [PMID: 29867322 PMCID: PMC5951982 DOI: 10.3389/fnins.2018.00310] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Accepted: 04/20/2018] [Indexed: 12/22/2022] Open
Affiliation(s)
| | - Oliver F Adunka
- Wexner Medical Center, The Ohio State University, Columbus, OH, United States
| | - Jeffery T Lichtenhan
- School of Medicine, Washington University in St. Louis, St. Louis, MO, United States
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27
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Abstract
OBJECTIVE To determine whether tympanic membrane (TM) electrodes induce behavioral pure-tone threshold shifts. DESIGN Pure-tone thresholds (250 to 8000 Hz) were measured twice in test (n = 18) and control (n = 10) groups. TM electrodes were placed between first and second threshold measurements in the test group, whereas the control group did not receive electrodes. Pure-tone threshold shifts were compared between groups. The effect of TM electrode contact location on threshold shifts was evaluated in the test group. RESULTS TM electrodes significantly increased average low-frequency thresholds, 7.5 dB at 250 Hz and 4.2 dB at 500 Hz, and shifts were as large as 25 dB in individual ears. Also, threshold shifts did not appear to vary at any frequency with TM electrode contact location. CONCLUSIONS Low-frequency threshold shifts occur when using TM electrodes and insert earphones. These findings are relevant to interpreting electrocochleographic responses to low-frequency stimuli.
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28
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Fontenot TE, Giardina CK, Fitzpatrick DC. A Model-Based Approach for Separating the Cochlear Microphonic from the Auditory Nerve Neurophonic in the Ongoing Response Using Electrocochleography. Front Neurosci 2017; 11:592. [PMID: 29123468 PMCID: PMC5662900 DOI: 10.3389/fnins.2017.00592] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Accepted: 10/09/2017] [Indexed: 12/02/2022] Open
Abstract
Electrocochleography (ECochG) is a potential clinically valuable technique for predicting speech perception outcomes in cochlear implant (CI) recipients, among other uses. Current analysis is limited by an inability to quantify hair cell and neural contributions which are mixed in the ongoing part of the response to low frequency tones. Here, we used a model based on source properties to account for recorded waveform shapes and to separate the combined signal into its components. The model for the cochlear microphonic (CM) was a sinusoid with parameters for independent saturation of the peaks and the troughs of the responses. The model for the auditory nerve neurophonic (ANN) was the convolution of a unit potential and population cycle histogram with a parameter for spread of excitation. Phases of the ANN and CM were additional parameters. The average cycle from the ongoing response was the input, and adaptive fitting identified CM and ANN parameters that best reproduced the waveform shape. Test datasets were responses recorded from the round windows of CI recipients, from the round window of gerbils before and after application of neurotoxins, and with simulated signals where each parameter could be manipulated in isolation. Waveforms recorded from 284 CI recipients had a variety of morphologies that the model fit with an average r2 of 0.97 ± 0.058 (standard deviation). With simulated signals, small systematic differences between outputs and inputs were seen with some variable combinations, but in general there were limited interactions among the parameters. In gerbils, the CM reported was relatively unaffected by the neurotoxins. In contrast, the ANN was strongly reduced and the reduction was limited to frequencies of 1,000 Hz and lower, consistent with the range of strong neural phase-locking. Across human CI subjects, the ANN contribution was variable, ranging from nearly none to larger than the CM. Development of this model could provide a means to isolate hair cell and neural activity that are mixed in the ongoing response to low-frequency tones. This tool can help characterize the residual physiology across CI subjects, and can be useful in other clinical settings where a description of the cochlear physiology is desirable.
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Affiliation(s)
- Tatyana E Fontenot
- Otolaryngology-Head and Neck Surgery, University of North Carolina, Chapel Hill, NC, United States
| | | | - Douglas C Fitzpatrick
- Otolaryngology-Head and Neck Surgery, University of North Carolina, Chapel Hill, NC, United States.,School of Medicine, University of North Carolina, Chapel Hill, NC, United States
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29
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Cook AM, Allsop AJ, O'Beirne GA. Putative Auditory-Evoked Neurophonic Measurements Using a Novel Signal Processing Technique: A Pilot Case Study. Front Neurosci 2017; 11:472. [PMID: 28970782 PMCID: PMC5609548 DOI: 10.3389/fnins.2017.00472] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Accepted: 08/09/2017] [Indexed: 11/22/2022] Open
Abstract
With changes to cochlear implant candidacy and improvements in surgical technique, there is a need for accurate intraoperative assessment of low-frequency hearing thresholds during cochlear implantation. In electrocochleography, onset compound action potentials (CAPs) typically allow estimation of auditory threshold for frequencies above 1 kHz, but they are less accurate at lower frequencies. Auditory nerve neurophonic (ANN) waveforms, on the other hand, may overcome this limitation by allowing phase-locked neural activity to be tracked during a prolonged low-frequency stimulus rather than just at its onset (Henry, 1995). Lichtenhan et al. (2013) have used their auditory nerve overlapped waveform (ANOW) technique to measure these potentials from the round windows of cats and guinea pigs, and reported that in guinea pigs these potentials originate in the cochlear apex for stimuli below 70 dB SPL (Lichtenhan et al., 2014). Human intraoperative round window neurophonic measurements have been reported by Choudhury et al. (2012). We have done the same in hearing impaired awake participants, and present here the results of a pilot study in which we recorded responses evoked by 360, 525, and 725 Hz tone bursts from the cochlear promontory of one participant. We also present a modification to the existing measurement technique which halves recording time, extracting the auditory neurophonic by recording a single averaged waveform, and then subtracting from it a 180° group-delayed version of itself, rather than using alternating condensation and rarefaction sound stimuli. We cannot conclude that the waveforms we measured were purely neural responses originating from the apex of the cochlea: as with all neurophonic measurement procedures, the neural responses of interest cannot be separated from higher harmonics of the cochlear microphonic without forward masking, regardless of electrode location, stimuli or post-processing algorithm. In conclusion, the extraction of putative neurophonic waveforms can easily be incorporated into existing electrocochleographic measurement paradigms, but at this stage such measurements should be interpreted with caution.
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Affiliation(s)
- Alison M Cook
- New Zealand Institute of Language Brain and Behaviour, University of CanterburyChristchurch, New Zealand.,Eisdell Moore CentreAuckland, New Zealand
| | - Ashleigh J Allsop
- New Zealand Institute of Language Brain and Behaviour, University of CanterburyChristchurch, New Zealand
| | - Greg A O'Beirne
- New Zealand Institute of Language Brain and Behaviour, University of CanterburyChristchurch, New Zealand.,Eisdell Moore CentreAuckland, New Zealand
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30
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Kennedy AE, Kaf WA, Ferraro JA, Delgado RE, Lichtenhan JT. Human Summating Potential Using Continuous Loop Averaging Deconvolution: Response Amplitudes Vary with Tone Burst Repetition Rate and Duration. Front Neurosci 2017; 11:429. [PMID: 28798660 PMCID: PMC5529347 DOI: 10.3389/fnins.2017.00429] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Accepted: 07/12/2017] [Indexed: 11/13/2022] Open
Abstract
Electrocochleography (ECochG) to high repetition rate tone bursts may have advantages over ECochG to clicks with standard slow rates. Tone burst stimuli presented at a high repetition rate may enhance summating potential (SP) measurements by reducing neural contributions resulting from neural adaptation to high stimulus repetition rates. To allow for the analysis of the complex ECochG responses to high rates, we deconvolved responses using the Continuous Loop Averaging Deconvolution (CLAD) technique. We examined the effect of high stimulus repetition rate and stimulus duration on SP amplitude measurements made with extratympanic ECochG to tone bursts in 20 adult females with normal hearing. We used 500 and 2,000 Hz tone bursts of various stimulus durations (12, 6, 3 ms) and repetition rates (five rates ranging from 7.1 to 234.38/s). A within-subject repeated measures (rate x duration) analysis of variance was conducted. We found that, for both 500 and 2,000 Hz stimuli, the mean deconvolved SP amplitudes were larger at faster repetition rates (58.59 and 97.66/s) compared to slower repetition rates (7.1 and 19.53/s), and larger at shorter stimulus duration compared longer stimulus duration. Our concluding hypothesis is that large SP amplitude to short duration stimuli may originate primarily from neural excitation, and large SP amplitudes to long duration, fast repetition rate stimuli may originate from hair cell responses. While the hair cell or neural origins of the SP to various stimulus parameters remains to be validated, our results nevertheless provide normative data as a step toward applying the CLAD technique to understanding diseased ears.
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Affiliation(s)
- Alana E Kennedy
- Department of Communication Sciences and Disorders, Missouri State UniversitySpringfield, MO, United States
| | - Wafaa A Kaf
- Department of Communication Sciences and Disorders, Missouri State UniversitySpringfield, MO, United States
| | - John A Ferraro
- Department of Hearing and Speech, University of Kansas Medical CenterKansas City, KS, United States
| | - Rafael E Delgado
- Department of Biomedical Engineering, University of MiamiCoral Gables, FL, United States
| | - Jeffery T Lichtenhan
- Department of Otolaryngology, Washington University School of MedicineSt. Louis, MO, United States
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31
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Riggs WJ, Roche JP, Giardina CK, Harris MS, Bastian ZJ, Fontenot TE, Buchman CA, Brown KD, Adunka OF, Fitzpatrick DC. Intraoperative Electrocochleographic Characteristics of Auditory Neuropathy Spectrum Disorder in Cochlear Implant Subjects. Front Neurosci 2017; 11:416. [PMID: 28769753 PMCID: PMC5515907 DOI: 10.3389/fnins.2017.00416] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Accepted: 07/04/2017] [Indexed: 11/13/2022] Open
Abstract
Auditory neuropathy spectrum disorder (ANSD) is characterized by an apparent discrepancy between measures of cochlear and neural function based on auditory brainstem response (ABR) testing. Clinical indicators of ANSD are a present cochlear microphonic (CM) with small or absent wave V. Many identified ANSD patients have speech impairment severe enough that cochlear implantation (CI) is indicated. To better understand the cochleae identified with ANSD that lead to a CI, we performed intraoperative round window electrocochleography (ECochG) to tone bursts in children (n = 167) and adults (n = 163). Magnitudes of the responses to tones of different frequencies were summed to measure the "total response" (ECochG-TR), a metric often dominated by hair cell activity, and auditory nerve activity was estimated visually from the compound action potential (CAP) and auditory nerve neurophonic (ANN) as a ranked "Nerve Score". Subjects identified as ANSD (45 ears in children, 3 in adults) had higher values of ECochG-TR than adult and pediatric subjects also receiving CIs not identified as ANSD. However, nerve scores of the ANSD group were similar to the other cohorts, although dominated by the ANN to low frequencies more than in the non-ANSD groups. To high frequencies, the common morphology of ANSD cases was a large CM and summating potential, and small or absent CAP. Common morphologies in other groups were either only a CM, or a combination of CM and CAP. These results indicate that responses to high frequencies, derived primarily from hair cells, are the main source of the CM used to evaluate ANSD in the clinical setting. However, the clinical tests do not capture the wide range of neural activity seen to low frequency sounds.
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Affiliation(s)
- William J Riggs
- Department of Otolaryngology/Head and Neck Surgery, Ohio State University College of MedicineColumbus, OH, United States
| | - Joseph P Roche
- Lab Department of Otolaryngology/Head and Neck Surgery, University of Wisconsin School of MedicineMadison, WI, United States
| | - Christopher K Giardina
- Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina at Chapel Hill School of MedicineChapel Hill, NC, United States
| | - Michael S Harris
- Department of Otolaryngology/Head and Neck Surgery, Ohio State University College of MedicineColumbus, OH, United States
| | - Zachary J Bastian
- Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina at Chapel Hill School of MedicineChapel Hill, NC, United States
| | - Tatyana E Fontenot
- Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina at Chapel Hill School of MedicineChapel Hill, NC, United States
| | - Craig A Buchman
- Department of Otolaryngology/Head and Neck Surgery, Washington University School of Medicine in St. LouisSt. Louis, MO, United States
| | - Kevin D Brown
- Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina at Chapel Hill School of MedicineChapel Hill, NC, United States
| | - Oliver F Adunka
- Department of Otolaryngology/Head and Neck Surgery, Ohio State University College of MedicineColumbus, OH, United States
| | - Douglas C Fitzpatrick
- Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina at Chapel Hill School of MedicineChapel Hill, NC, United States
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32
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Lichtenhan JT, Lee C, Dubaybo F, Wenrich KA, Wilson US. The Auditory Nerve Overlapped Waveform (ANOW) Detects Small Endolymphatic Manipulations That May Go Undetected by Conventional Measurements. Front Neurosci 2017; 11:405. [PMID: 28769744 PMCID: PMC5513905 DOI: 10.3389/fnins.2017.00405] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Accepted: 06/29/2017] [Indexed: 11/13/2022] Open
Abstract
Electrocochleography (ECochG) has been used to assess Ménière's disease, a pathology associated with endolymphatic hydrops and low-frequency sensorineural hearing loss. However, the current ECochG techniques are limited for use at high-frequencies only (≥1 kHz) and cannot be used to assess and understand the low-frequency sensorineural hearing loss in ears with Ménière's disease. In the current study, we use a relatively new ECochG technique to make measurements that originate from afferent auditory nerve fibers in the apical half of the cochlear spiral to assess effects of endolymphatic hydrops in guinea pig ears. These measurements are made from the Auditory Nerve Overlapped Waveform (ANOW). Hydrops was induced with artificial endolymph injections, iontophoretically applied Ca2+ to endolymph, and exposure to 200 Hz tones. The manipulations used in this study were far smaller than those used in previous investigations on hydrops. In response to all hydropic manipulations, ANOW amplitude to moderate level stimuli was markedly reduced but conventional ECochG measurements of compound action potential thresholds were unaffected (i.e., a less than 2 dB threshold shift). Given the origin of the ANOW, changes in ANOW amplitude likely reflect acute volume disturbances accumulate in the distensible cochlear apex. These results suggest that the ANOW could be used to advance our ability to identify initial stages of dysfunction in ears with Ménière's disease before the pathology progresses to an extent that can be detected with conventional measures.
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Affiliation(s)
- Jeffery T Lichtenhan
- Department of Otolaryngology Washington University School of MedicineSaint Louis, MO, United States
| | - Choongheon Lee
- Department of Otolaryngology Washington University School of MedicineSaint Louis, MO, United States
| | - Farah Dubaybo
- Department of Otolaryngology Washington University School of MedicineSaint Louis, MO, United States
| | - Kaitlyn A Wenrich
- Department of Otolaryngology Washington University School of MedicineSaint Louis, MO, United States
| | - Uzma S Wilson
- Department of Communication Sciences and Disorders, Northwestern UniversityEvanston, IL, United States
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Real-Time Intracochlear Electrocochleography Obtained Directly Through a Cochlear Implant. Otol Neurotol 2017; 38:e107-e113. [DOI: 10.1097/mao.0000000000001425] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Koka K, Litvak LM. Feasibility of Using Electrocochleography for Objective Estimation of Electro-Acoustic Interactions in Cochlear Implant Recipients with Residual Hearing. Front Neurosci 2017; 11:337. [PMID: 28674482 PMCID: PMC5475389 DOI: 10.3389/fnins.2017.00337] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Accepted: 05/29/2017] [Indexed: 11/18/2022] Open
Abstract
Although cochlear implants (CI) traditionally have been used to treat individuals with bilateral profound sensorineural hearing loss, a recent trend is to implant individuals with residual low-frequency hearing. Patients who retain some residual acoustic hearing after surgery often can benefit from electro-acoustic stimulation (EAS) technologies, which combine conventional acoustic amplification with electrical stimulation. However, interactions between acoustic and electrical stimulation may affect outcomes adversely and are time-consuming and difficult to assess behaviorally. This study demonstrated the feasibility of using the Advanced Bionics HiRes90K Advantage implant electronics and HiFocus Mid Scala/1j electrode to measure electrocochleography (ECochG) responses in the presence of electrical stimulation to provide an objective estimate of peripheral physiologic EAS interactions. In general, electrical stimulation reduced ECochG response amplitudes to acoustic stimulation. The degree of peripheral EAS interaction varied as a function of acoustic pure tone frequency and the intra-cochlear location of the electrically stimulated electrode. Further development of this technique may serve to guide and optimize clinical EAS system fittings in the future.
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Affiliation(s)
- Kanthaiah Koka
- Research and Technology, Advanced Bionics LLCValencia, CA, United States
| | - Leonid M Litvak
- Research and Technology, Advanced Bionics LLCValencia, CA, United States
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Koka K, Saoji AA, Attias J, Litvak LM. An Objective Estimation of Air-Bone-Gap in Cochlear Implant Recipients with Residual Hearing Using Electrocochleography. Front Neurosci 2017; 11:210. [PMID: 28458630 PMCID: PMC5394163 DOI: 10.3389/fnins.2017.00210] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Accepted: 03/28/2017] [Indexed: 11/17/2022] Open
Abstract
Although, cochlear implants (CI) traditionally have been used to treat individuals with bilateral profound sensorineural hearing loss, a recent trend is to implant individuals with residual low-frequency hearing. Notably, many of these individuals demonstrate an air-bone gap (ABG) in low-frequency, pure-tone thresholds following implantation. An ABG is the difference between audiometric thresholds measured using air conduction (AC) and bone conduction (BC) stimulation. Although, behavioral AC thresholds are straightforward to assess, BC thresholds can be difficult to measure in individuals with severe-to-profound hearing loss because of vibrotactile responses to high-level, low-frequency stimulation and the potential contribution of hearing in the contralateral ear. Because of these technical barriers to measuring behavioral BC thresholds in implanted patients with residual hearing, it would be helpful to have an objective method for determining ABG. This study evaluated an innovative technique for measuring electrocochleographic (ECochG) responses using the cochlear microphonic (CM) response to assess AC and BC thresholds in implanted patients with residual hearing. Results showed high correlations between CM thresholds and behavioral audiograms for AC and BC conditions, thereby demonstrating the feasibility of using ECochG as an objective tool for quantifying ABG in CI recipients.
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Affiliation(s)
- Kanthaiah Koka
- Research and Technology, Advanced BionicsValencia, CA, USA
| | - Aniket A Saoji
- Research and Technology, Advanced BionicsValencia, CA, USA
| | - Joseph Attias
- Research and Technology, Advanced BionicsValencia, CA, USA.,Schneider Children's Medical Center of Israel and Rabin Medical CenterPetach Tikva, Israel
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Lichtenhan JT, Hirose K, Buchman CA, Duncan RK, Salt AN. Direct administration of 2-Hydroxypropyl-Beta-Cyclodextrin into guinea pig cochleae: Effects on physiological and histological measurements. PLoS One 2017; 12:e0175236. [PMID: 28384320 PMCID: PMC5383289 DOI: 10.1371/journal.pone.0175236] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 03/22/2017] [Indexed: 12/26/2022] Open
Abstract
2-Hydroxypropyl-Beta-Cyclodextrin (HPβCD) can be used to treat Niemann-Pick type C disease, Alzheimer's disease, and atherosclerosis. But, a consequence is that HPβCD can cause hearing loss. HPβCD was recently found to be toxic to outer hair cells (OHCs) in the organ of Corti. Previous studies on the chronic effects of in vivo HPβCD toxicity did not know the intra-cochlear concentration of HPβCD and attributed variable effects on OHCs to indirect drug delivery to the cochlea. We studied the acute effects of known HPβCD concentrations administered directly into intact guinea pig cochleae. Our novel approach injected solutions through pipette sealed into scala tympani in the cochlear apex. Solutions were driven along the length of the cochlear spiral toward the cochlear aqueduct in the base. This method ensured that therapeutic levels were achieved throughout the cochlea, including those regions tuned to mid to low frequencies and code speech vowels and background noise. A wide variety of measurements were made. Results were compared to measurements from ears treated with the HPβCD analog methyl-β-cyclodextrin (MβCD), salicylate that is well known to attenuate the gain of the cochlear amplifier, and injection of artificial perilymph alone (controls). Histological data showed that OHCs appeared normal after treatment with a low dose of HPβCD, and physiological data was consistent with attenuation of cochlear amplifier gain and disruption of non-linearity associated with transferring acoustic sound into neural excitation, an origin of distortion products that are commonly used to objectively assess hearing and hearing loss. A high dose of HPβCD caused sporadic OHC losses and markedly affected all physiologic measurements. MβCD caused virulent destruction of OHCs and physiologic responses. Toxicity of HPβCD to OHC along the cochlear length is variable even when a known intra-cochlear concentration is administered, at least for the duration of our acute studies.
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Affiliation(s)
- J. T. Lichtenhan
- Washington University School of Medicine Department of Otolaryngology Saint Louis, Missouri, United States of America
| | - K. Hirose
- Washington University School of Medicine Department of Otolaryngology Saint Louis, Missouri, United States of America
| | - C. A. Buchman
- Washington University School of Medicine Department of Otolaryngology Saint Louis, Missouri, United States of America
| | - R. K. Duncan
- University of Michigan Kresge Hearing Research Institute Department of Otolaryngology-Head and Neck Surgery Ann Arbor, Michigan, United States of America
| | - A. N. Salt
- Washington University School of Medicine Department of Otolaryngology Saint Louis, Missouri, United States of America
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Charaziak KK, Shera CA, Siegel JH. Using Cochlear Microphonic Potentials to Localize Peripheral Hearing Loss. Front Neurosci 2017; 11:169. [PMID: 28420953 PMCID: PMC5378797 DOI: 10.3389/fnins.2017.00169] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Accepted: 03/14/2017] [Indexed: 11/13/2022] Open
Abstract
The cochlear microphonic (CM) is created primarily by the receptor currents of outer hair cells (OHCs) and may therefore be useful for identifying cochlear regions with impaired OHCs. However, the CM measured across the frequency range with round-window or ear-canal electrodes lacks place-specificity as it is dominated by cellular sources located most proximal to the recording site (e.g., at the cochlear base). To overcome this limitation, we extract the "residual" CM (rCM), defined as the complex difference between the CM measured with and without an additional tone (saturating tone, ST). If the ST saturates receptor currents near the peak of its excitation pattern, then the rCM should reflect the activity of OHCs in that region. To test this idea, we measured round-window CMs in chinchillas in response to low-level probe tones presented alone or with an ST ranging from 1 to 2.6 times the probe frequency. CMs were measured both before and after inducing a local impairment in cochlear function (a 4-kHz notch-type acoustic trauma). Following the acoustic trauma, little change was observed in the probe-alone CM. In contrast, rCMs were reduced in a frequency-specific manner. When shifts in rCM levels were plotted vs. the ST frequency, they matched well the frequency range of shifts in neural thresholds. These results suggest that rCMs originate near the cochlear place tuned to the ST frequency and thus can be used to assess OHC function in that region. Our interpretation of the data is supported by predictions of a simple phenomenological model of CM generation and two-tone interactions. The model indicates that the sensitivity of rCM to acoustic trauma is governed by changes in cochlear response at the ST tonotopic place rather than at the probe place. The model also suggests that a combination of CM and rCM measurements could be used to assess both the site and etiology of sensory hearing loss in clinical applications.
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Affiliation(s)
- Karolina K Charaziak
- Caruso Department of Otolaryngology, Keck School of Medicine, University of Southern CaliforniaLos Angeles, CA, USA.,Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Hugh Knowles Center, Northwestern UniversityEvanston, IL, USA
| | - Christopher A Shera
- Caruso Department of Otolaryngology, Keck School of Medicine, University of Southern CaliforniaLos Angeles, CA, USA
| | - Jonathan H Siegel
- Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Hugh Knowles Center, Northwestern UniversityEvanston, IL, USA
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Eggermont JJ. Ups and Downs in 75 Years of Electrocochleography. Front Syst Neurosci 2017; 11:2. [PMID: 28174524 PMCID: PMC5259695 DOI: 10.3389/fnsys.2017.00002] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 01/11/2017] [Indexed: 11/13/2022] Open
Abstract
Before 1964, electrocochleography (ECochG) was a surgical procedure carried out in the operating theatre. Currently, the newest application is also an intra-operative one, often carried out in conjunction with cochlear implant surgery. Starting in 1967, the recording methods became either minimal- or not-invasive, i.e., trans-tympanic (TT) or extra tympanic (ET), and included extensive studies of the arguments pro and con. I will review several valuable applications of ECochG, from a historical point of view, but covering all 75 years if applicable. The main topics will be: (1) comparing human and animal cochlear electrophysiology; (2) the use in objective audiometry involving tone pip stimulation-currently mostly pre cochlear implantation but otherwise replaced by auditory brainstem response (ABR) recordings; (3) attempts to diagnose Ménière's disease and the role of the summating potential (SP); (4) early use in diagnosing vestibular schwannomas-now taken over by ABR screening and MRI confirmation; (5) relating human electrophysiology to the effects of genes as in auditory neuropathy; and (6) intracochlear recording using the cochlear implant electrodes. The last two applications are the most recently added ones. The "historical aspects" of this review article will highlight the founding years prior to 1980 when relevant. A survey of articles on Pubmed shows several ups and downs in the clinical interest as reflected in the publication counts over the last 75 years.
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Affiliation(s)
- Jos J. Eggermont
- Department of Psychology, University of CalgaryCalgary, AB, Canada
- Department of Physiology and Pharmacology, University of CalgaryCalgary, AB, Canada
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Mass Potentials Recorded at the Round Window Enable the Detection of Low Spontaneous Rate Fibers in Gerbil Auditory Nerve. PLoS One 2017; 12:e0169890. [PMID: 28085968 PMCID: PMC5234781 DOI: 10.1371/journal.pone.0169890] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Accepted: 12/22/2016] [Indexed: 11/19/2022] Open
Abstract
Auditory nerve fibers (ANFs) transmit acoustic information from the sensory hair cells to the cochlear nuclei. In experimental and clinical audiology, probing the whole ANF population remains a difficult task, as the ANFs differ greatly in their threshold and onset response to sound. Thus, low spontaneous rate (SR) fibers, which have rather higher thresholds, delay and larger jitter in their first spike latency are not detectable in the far-field compound action potential of the auditory nerve. Here, we developed a new protocol of acoustic stimulation together with electrophysiological signal processing to track the steady state activity of ANFs. Mass potentials at the round window were recorded in response to repetitive 300-ms bursts of 1/3 octave band noise centered on a frequency probe. Analysis was assessed during the last 200-ms of the response to capture the steady-state response of ANFs. To eliminate the microphonic component reflecting the sensory cells activity, repetitive pairs of sounds of opposite polarities were used. The spectral analysis was calculated on the average of two consecutive responses, and the neural gain was calculated by dividing point-by-point the spectrum to sound over unstimulated condition. In response to low-sound-level stimulation, neural gain predominated in the low-frequency cochlear regions, while a second component of responses centered on higher cochlear frequency regions appeared beyond 30 dB SPL. At 60 dB SPL, neural gain showed a bimodal shape, with a notch near 5.6 kHz. In addition to correlate with the functional mapping of ANFs along the tonotopic axis, the deletion of low-SR fibers leads to a reduction in the high-frequency response, where the low-SR fibers are preferentially located. Thus, mass potentials at the round window may provide a useful tool to probe the SR-based distribution of ANFs in humans and in other species in which direct single-unit recordings are difficult to achieve or not feasible.
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41
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Heil P, Peterson AJ. Spike timing in auditory-nerve fibers during spontaneous activity and phase locking. Synapse 2016; 71:5-36. [DOI: 10.1002/syn.21925] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 07/20/2016] [Accepted: 07/24/2016] [Indexed: 12/22/2022]
Affiliation(s)
- Peter Heil
- Department of Systems Physiology of Learning; Leibniz Institute for Neurobiology; Magdeburg 39118 Germany
- Center for Behavioral Brain Sciences; Magdeburg Germany
| | - Adam J. Peterson
- Department of Systems Physiology of Learning; Leibniz Institute for Neurobiology; Magdeburg 39118 Germany
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42
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Lichtenhan JT, Hartsock J, Dornhoffer JR, Donovan KM, Salt AN. Drug delivery into the cochlear apex: Improved control to sequentially affect finely spaced regions along the entire length of the cochlear spiral. J Neurosci Methods 2016; 273:201-209. [PMID: 27506463 DOI: 10.1016/j.jneumeth.2016.08.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Revised: 08/03/2016] [Accepted: 08/05/2016] [Indexed: 10/21/2022]
Abstract
BACKGROUND Administering pharmaceuticals to the scala tympani of the inner ear is a common approach to study cochlear physiology and mechanics. We present here a novel method for in vivo drug delivery in a controlled manner to sealed ears. NEW METHOD Injections of ototoxic solutions were applied from a pipette sealed into a fenestra in the cochlear apex, progressively driving solutions along the length of scala tympani toward the cochlear aqueduct at the base. Drugs can be delivered rapidly or slowly. In this report we focus on slow delivery in which the injection rate is automatically adjusted to account for varying cross sectional area of the scala tympani, therefore driving a solution front at uniform rate. RESULTS Objective measurements originating from finely spaced, low- to high-characteristic cochlear frequency places were sequentially affected. Comparison with existing methods(s): Controlled administration of pharmaceuticals into the cochlear apex overcomes a number of serious limitations of previously established methods such as cochlear perfusions with an injection pipette in the cochlear base: The drug concentration achieved is more precisely controlled, drug concentrations remain in scala tympani and are not rapidly washed out by cerebrospinal fluid flow, and the entire length of the cochlear spiral can be treated quickly or slowly with time. CONCLUSIONS Controlled administration of solutions into the cochlear apex can be a powerful approach to sequentially effect objective measurements originating from finely spaced cochlear regions and allows, for the first time, the spatial origin of CAPs to be objectively defined.
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Affiliation(s)
- J T Lichtenhan
- Washington University School of Medicine, Department of Otolaryngology, Saint Louis, MO 63110, USA.
| | - J Hartsock
- Washington University School of Medicine, Department of Otolaryngology, Saint Louis, MO 63110, USA
| | - J R Dornhoffer
- University of Arkansas School of Medicine, Little Rock, AR 72205, USA
| | - K M Donovan
- Program in Audiology and Communication Sciences, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - A N Salt
- Washington University School of Medicine, Department of Otolaryngology, Saint Louis, MO 63110, USA
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Wilson US, Kaf WA, Danesh AA, Lichtenhan JT. Assessment of low-frequency hearing with narrow-band chirp-evoked 40-Hz sinusoidal auditory steady-state response. Int J Audiol 2016; 55:239-47. [PMID: 26795555 DOI: 10.3109/14992027.2015.1122238] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Objective To determine the clinical utility of narrow-band chirp-evoked 40-Hz sinusoidal auditory steady state responses (s-ASSR) in the assessment of low-frequency hearing in noisy participants. Design Tone bursts and narrow-band chirps were used to respectively evoke auditory brainstem responses (tb-ABR) and 40-Hz s-ASSR thresholds with the Kalman-weighted filtering technique and were compared to behavioral thresholds at 500, 2000, and 4000 Hz. A repeated measure ANOVA and post-hoc t-tests, and simple regression analyses were performed for each of the three stimulus frequencies. Study sample Thirty young adults aged 18-25 with normal hearing participated in this study. Results When 4000 equivalent response averages were used, the range of mean s-ASSR thresholds from 500, 2000, and 4000 Hz were 17-22 dB lower (better) than when 2000 averages were used. The range of mean tb-ABR thresholds were lower by 11-15 dB for 2000 and 4000 Hz when twice as many equivalent response averages were used, while mean tb-ABR thresholds for 500 Hz were indistinguishable regardless of additional response averaging. Conclusion Narrow-band chirp-evoked 40-Hz s-ASSR requires a ∼15 dB smaller correction factor than tb-ABR for estimating low-frequency auditory threshold in noisy participants when adequate response averaging is used.
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Affiliation(s)
- Uzma S Wilson
- a Communication Sciences and Disorders, Missouri State University , Springfield , Missouri , USA .,c Department of Otolaryngology , Washington University School of Medicine in Saint Louis , Saint Louis , Missouri , USA
| | - Wafaa A Kaf
- a Communication Sciences and Disorders, Missouri State University , Springfield , Missouri , USA
| | - Ali A Danesh
- b Communication Sciences and Disorders, Florida Atlantic University , Boca Raton , Florida , USA , and
| | - Jeffery T Lichtenhan
- c Department of Otolaryngology , Washington University School of Medicine in Saint Louis , Saint Louis , Missouri , USA
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Chertoff ME, Kamerer AM, Peppi M, Lichtenhan JT. An analysis of cochlear response harmonics: Contribution of neural excitation. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2015; 138:2957-63. [PMID: 26627769 PMCID: PMC4644149 DOI: 10.1121/1.4934556] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Revised: 09/30/2015] [Accepted: 10/12/2015] [Indexed: 05/29/2023]
Abstract
In this report an analysis of cochlear response harmonics is developed to derive a mathematical function to estimate the gross mechanics involved in the in vivo transfer of acoustic sound into neural excitation (f(Tr)). In a simulation it is shown that the harmonic distortion from a nonlinear system can be used to estimate the nonlinearity, supporting the next phase of the experiment: Applying the harmonic analysis to physiologic measurements to derive estimates of the unknown, in vivo f(Tr). From gerbil ears, estimates of f(Tr) were derived from cochlear response measurements made with an electrode at the round window niche from 85 Hz tone bursts. Estimates of f(Tr) before and after inducing auditory neuropathy-loss of auditory nerve responses with preserved hair cell responses from neurotoxic treatment with ouabain-showed that the neural excitation from low-frequency tones contributes to the magnitude of f(Tr) but not the sigmoidal, saturating, nonlinear morphology.
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Affiliation(s)
- M E Chertoff
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
| | - A M Kamerer
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
| | - M Peppi
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
| | - J T Lichtenhan
- Department of Otolaryngology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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Berezina-Greene MA, Guinan JJ. Stimulus Frequency Otoacoustic Emission Delays and Generating Mechanisms in Guinea Pigs, Chinchillas, and Simulations. J Assoc Res Otolaryngol 2015; 16:679-94. [PMID: 26373935 DOI: 10.1007/s10162-015-0543-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Accepted: 08/30/2015] [Indexed: 11/30/2022] Open
Abstract
According to coherent reflection theory (CRT), stimulus frequency otoacoustic emissions (SFOAEs) arise from cochlear irregularities coherently reflecting energy from basilar membrane motion within the traveling-wave peak. This reflected energy arrives in the ear canal predominantly with a single delay at each frequency. However, data from humans and animals indicate that (1) SFOAEs can have multiple delay components, (2) low-frequency SFOAE delays are too short to be accounted for by CRT, and (3) "SFOAEs" obtained with a 2nd ("suppressor") tone ≥2 octaves above the probe tone have been interpreted as arising from the area basal to the region of cochlear amplification. To explore these issues, we collected SFOAEs by the suppression method in guinea pigs and time-frequency analyzed these data, simulated SFOAEs, and published chinchilla SFOAEs. Time-frequency analysis revealed that most frequencies showed only one SFOAE delay component while other frequencies had multiple components including some with short delays. We found no systematic patterns in the occurrence of multiple delay components. Using a cochlear model that had significant basilar membrane motion only in the peak region of the traveling wave, simulated SFOAEs had single and multiple delay components similar to the animal SFOAEs. This result indicates that multiple components (including ones with short delays) can originate from cochlear mechanical irregularities in the SFOAE peak region and are not necessarily indicative of SFOAE sources in regions ≥2 octaves basal of the SFOAE peak region. We conclude that SFOAEs obtained with suppressors close to the probe frequency provide information primarily about the mechanical response in the region that receives amplification, and we attribute the too-short SFOAE delays at low frequencies to distortion-source SFOAEs and coherent reflection from multiple cochlear motions. Our findings suggest that CRT needs revision to include reflections from multiple motions in the cochlear apex.
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Affiliation(s)
- Maria A Berezina-Greene
- Eaton-Peabody Lab, Mass. Eye and Ear Infirmary, 243 Charles St, Boston, MA, 02114, USA. .,Harvard-MIT HST Speech and Hearing Bioscience and Technology Program, Cambridge, MA, USA.
| | - John J Guinan
- Eaton-Peabody Lab, Mass. Eye and Ear Infirmary, 243 Charles St, Boston, MA, 02114, USA. .,Harvard-MIT HST Speech and Hearing Bioscience and Technology Program, Cambridge, MA, USA. .,Harvard Medical School, Boston, MA, USA.
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46
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Abstract
In the diverse mechanosensory systems that animals evolved, the waveform of stimuli can be encoded by phase locking in spike trains of primary afferents. Coding of the fine structure of sounds via phase locking is thought to be critical for hearing. The upper frequency limit of phase locking varies across species and is unknown in humans. We applied a method developed previously, which is based on neural adaptation evoked by forward masking, to analyze mass potentials recorded on the cochlea and auditory nerve in the cat. The method allows us to separate neural phase locking from receptor potentials. We find that the frequency limit of neural phase locking obtained from mass potentials was very similar to that reported for individual auditory nerve fibers. The results suggest that this is a promising approach to examine neural phase locking in humans with normal or impaired hearing or in other species for which direct recordings from primary afferents are not feasible.
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47
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Chertoff ME, Earl BR, Diaz FJ, Sorensen JL, Thomas MLA, Kamerer AM, Peppi M. Predicting the location of missing outer hair cells using the electrical signal recorded at the round window. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2014; 136:1212. [PMID: 25190395 PMCID: PMC4165229 DOI: 10.1121/1.4890641] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Revised: 06/27/2014] [Accepted: 07/07/2014] [Indexed: 06/01/2023]
Abstract
The electrical signal recorded at the round window was used to estimate the location of missing outer hair cells. The cochlear response was recorded to a low frequency tone embedded in high-pass filtered noise conditions. Cochlear damage was created by either overexposure to frequency-specific tones or laser light. In animals with continuous damage along the partition, the amplitude of the cochlear response increased as the high-pass cutoff frequency increased, eventually reaching a plateau. The cochlear distance at the onset of the plateau correlated with the anatomical onset of outer hair cell loss. A mathematical model replicated the physiologic data but was limited to cases with continuous hair cell loss in the middle and basal turns. The neural contribution to the cochlear response was determined by recording the response before and after application of Ouabain. Application of Ouabain eliminated or reduced auditory neural activity from approximately two turns of the cochlea. The amplitude of the cochlear response was reduced for moderate signal levels with a limited effect at higher levels, indicating that the cochlear response was dominated by outer hair cell currents at high signal levels and neural potentials at low to moderate signal levels.
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MESH Headings
- Animals
- Audiometry, Pure-Tone
- Auditory Threshold
- Cochlear Microphonic Potentials/drug effects
- Disease Models, Animal
- Female
- Gerbillinae
- Hair Cells, Auditory, Outer/drug effects
- Hair Cells, Auditory, Outer/pathology
- Hearing Loss, Noise-Induced/etiology
- Hearing Loss, Noise-Induced/pathology
- Hearing Loss, Noise-Induced/physiopathology
- Lasers
- Models, Biological
- Ouabain/pharmacology
- Round Window, Ear/injuries
- Round Window, Ear/innervation
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Affiliation(s)
- Mark E Chertoff
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, Kansas 66160
| | - Brian R Earl
- Department of Communication Sciences and Disorders, University of Cincinnati, Cincinnati, Ohio 45267
| | - Francisco J Diaz
- Department of Biostatistics, University of Kansas Medical Center, Kansas City, Kansas 66160
| | - Janna L Sorensen
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, Kansas 66160
| | - Megan L A Thomas
- Hearing and Balance Center, Boys Town National Research Hospital, Omaha, Nebraska 68131
| | - Aryn M Kamerer
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, Kansas 66160
| | - Marcello Peppi
- Department of Hearing and Speech, University of Kansas Medical Center, Kansas City, Kansas 66160
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48
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Verschooten E, Joris PX. Estimation of neural phase locking from stimulus-evoked potentials. J Assoc Res Otolaryngol 2014; 15:767-87. [PMID: 24890715 DOI: 10.1007/s10162-014-0465-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Accepted: 05/07/2014] [Indexed: 11/24/2022] Open
Abstract
The frequency extent over which fine structure is coded in the auditory nerve has been physiologically characterized in laboratory animals but is unknown in humans. Knowledge of the upper frequency limit in humans would inform the debate regarding the role of fine structure in human hearing. Of the presently available techniques, only the recording of mass neural potentials offers the promise to provide a physiological estimate of neural phase locking in humans. A challenge is to disambiguate neural phase locking from the receptor potentials. We studied mass potentials recorded on the cochlea and auditory nerve of cat and used several experimental manipulations to isolate the neural contribution to these potentials. We find a surprisingly large neural contribution in the signal recorded on the cochlear round window, and this contribution is in many aspects similar to the potential measured on the auditory nerve. The results suggest that recording of mass potentials through the middle ear is a promising approach to examine neural phase locking in humans.
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Affiliation(s)
- Eric Verschooten
- Laboratory of Auditory Neurophysiology, KU Leuven, Herestraat 49 bus 1021, 3000, Leuven, Belgium,
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The auditory nerve overlapped waveform (ANOW) originates in the cochlear apex. J Assoc Res Otolaryngol 2014; 15:395-411. [PMID: 24515339 DOI: 10.1007/s10162-014-0447-y] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2013] [Accepted: 01/23/2014] [Indexed: 10/25/2022] Open
Abstract
Measurements of cochlear function with compound action potentials (CAPs), auditory brainstem responses, and otoacoustic emissions work well with high-frequency sounds but are problematic at low frequencies. We have recently shown that the auditory nerve overlapped waveform (ANOW) can objectively quantify low-frequency (<1 kHz) auditory sensitivity, as thresholds for ANOW at low frequencies and for CAP at high frequencies relate similarly to single auditory nerve fiber thresholds. This favorable relationship, however, does not necessarily mean that ANOW originates from auditory nerve fibers innervating low-frequency regions of the cochlear apex. In the present study, we recorded the cochlear response to tone bursts of low frequency (353, 500, and 707 Hz) and high frequency (2 to 16 kHz) during administration of tetrodotoxin (TTX) to block neural function. TTX was injected using a novel method of slow administration from a pipette sealed into the cochlear apex, allowing real-time measurements of systematic neural blocking from apex to base. The amplitude of phase-locked (ANOW) and onset (CAP) neural firing to moderate-level, low-frequency sounds were markedly suppressed before thresholds and responses to moderate-level, high-frequency sounds were affected. These results demonstrate that the ANOW originates from responses of auditory nerve fibers innervating cochlear apex, confirming that ANOW provides a valid physiological measure of low-frequency auditory nerve function.
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Forgues M, Koehn HA, Dunnon AK, Pulver SH, Buchman CA, Adunka OF, Fitzpatrick DC. Distinguishing hair cell from neural potentials recorded at the round window. J Neurophysiol 2013; 111:580-93. [PMID: 24133227 DOI: 10.1152/jn.00446.2013] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Almost all patients who receive cochlear implants have some acoustic hearing prior to surgery. Electrocochleography (ECoG), or electrophysiological measures of cochlear response to sound, can identify remaining auditory nerve activity that is the basis for this residual hearing and can record potentials from hair cells that are no longer functionally connected to nerve fibers. The ECoG signal is therefore complex, being composed of both hair cell and neural signals. To identify signatures of different sources in the recorded potentials, we collected ECoG data across frequency and intensity from the round window of gerbils before and after treatment with kainic acid, a neurotoxin. Distortions in the recorded waveforms were produced by different sources over different ranges of frequency and intensity. In response to tones at low frequencies and low-to-moderate intensities, the major source of distortion was from neural phase-locking that was sensitive to kainic acid. At high intensities at all frequencies, the distortion was not sensitive to kainic acid and was consistent with asymmetric saturation of the hair cell transducer current. In addition to loss of phase-locking, changes in the envelope after kainic acid treatment indicate that sustained neural firing combines with receptor potentials from hair cells to produce the envelope of the response to tones. These results provide baseline data to interpret comparable recordings from human cochlear implant recipients.
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Affiliation(s)
- Mathieu Forgues
- Department of Otolaryngology/Head and Neck Surgery, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina
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