dB pSPL Research Articles

Effects of Age on the Frequency Amplitude Ratio of Cervical and Ocular Vestibular Evoked Myogenic Potentials.

An increase in the 1000/500 Hz frequency amplitude ratio (FAR) of the cervical and ocular vestibular evoked myogenic potentials (cVEMP and oVEMP, respectively) may serve as a potential biomarker for diagnosing Meniere's disease (MD). However, the aging process can also result in an increased FAR for VEMPs. In older patients, distinguishing whether changes in VEMP FAR are due to MD or aging processes becomes difficult. We aimed to investigate the effects of age on VEMP FARs and establish a FAR-normative range for different age groups. cVEMP and oVEMP were recorded from a total of 106 participants grouped as young, middle-aged, and older adults using air-conducted tone bursts at 500, 750, and 1000 Hz at 125 dB pSPL. The FAR was calculated for the cVEMP and oVEMP for the following frequencies: FAR1 = 1000/500, FAR2 = 1000/750, and FAR3 = 750/500. A significant age-related effect was observed on the cVEMP FAR. Although the oVEMP FAR showed an increasing trend with age, it was not statistically significant. Age-based normative FAR values are provided. Drawing from the normative FAR from this study, there is evidence that the existing MD diagnostic criteria would misidentify a considerable number of older adults. Therefore, to reduce false positives, we recommend a more stringent cVEMP and oVEMP FAR criterion in older adults.

Comparison of two acoustic test fixtures for measuring impulse level dependent attenuation

In the American National Standards Institute (ANSI) S12.42-2010 standard for measuring insertion loss of hearing protection devices (HPDs) in impulsive noise, the range of peak sound pressure levels for the impulses is 132 to 168 dB peak sound pressure level (dB pSPL). The specification of the acoustic test fixtures (ATFs) included an IEC 60318-4 ear simulator fitted with a microphone. The microphones typically used are a ¼” cartridge and have a dynamic range up to about 169 dB pSPL. For most small caliber firearms, the peak SPLs are less than 170 dB SPL at the location of the shooters ear (Schulz et al. 2013). For some military weapon systems that produce impulses greater than 170 dB pSPL, impulse insertion loss cannot be assessed without exceeding the microphone maximum dynamic range. Some condenser microphones have maximum dynamic ranges of 190 dB pSPL. This paper compares insertion losses for HPDs measured on two GRAS 45CB ATFs with microphones with maximum dynamic ranges of 169 and 193 dB pSPL. Waveform distortion, field probe to unoccluded transfer functions between the ATF and field probe will be examined for distortion and accuracy when estimating the impulse level dependent attenuation.

Influence of reference transducer location on hearing protector attenuation metrics for impulse noise

The ANSI/ASA S12.42-2010 standard can be used to estimate the attenuation for impulsive noises between 130 and 170 decibels peak sound pressure level (dB pSPL). The ANSI/ASA S12.42 method uses a complex transfer function between the signal received in the ear of an acoustic test fixture (ATF) and a reference transducer. The reference transducer is at the same radial distance from the impulse source and at less than 30 degrees from the ATF angle. The reference transducer is specified as a pencil-type pressure (> 40.6 cm long). The maximum angle and the minimum pencil probe dimensions could be incompatible near the source, or may introduce artifacts or hazards. In this study, several hearing protectors were evaluated with two rifles (A-Bolt .300 Winchester Magnum and Colt AR-15 5.56 caliber), two ATFs (GRAS 45CB), and five transducers (four ¼” microphones and one surface mount microphone). The ATFs were on opposite sides of the gun at distances for field levels between 180- and 140-dB pSPL. For each location and rifle, S12.42 metrics were calculated for all 20 combinations of ATF ear and reference transducer. Results indicated that S12.42 metrics were minimally affected by the locations of the reference transducers.

Evaluating Fixed Single-Point Parameters When Applied to Vestibular Evoked Myogenic Potentials: The Effect of Single Point and Signal Window.

Several studies have applied a common objective detection algorithm (fixed single point [ Fsp ]) for detection of the vestibular evoked myogenic potential (VEMP). However, fundamental parameters of Fsp , such as establishing the location and duration of a signal window, have not been examined. In addition, Fsp criterion values used for response detection have not been established for cervical VEMPs (cVEMPs) or ocular VEMPs (oVEMPs). The purpose of this article was to investigate the effect of various single points and signal windows on Fsp , as well as determining Fsp criteria to determine response presence for cVEMP and oVEMP in a group of young healthy participants. Twenty young healthy adults under the age of 30 and with no history of hearing or balance concerns were enrolled in the study protocol. Air-conducted cVEMPs and oVEMPs were evoked using 500 Hz tone bursts at 123 dB pSPL recorded at a fixed electromyography activation of 50 µV for cVEMPs and 35° gaze angle for oVEMPs. Responses were analyzed off-line using visual and objective detection. Fsp was applied to cVEMPs and oVEMPs using a range of single points and signal windows. Noise variance was lowest for cVEMPs at the latency of P1, and for oVEMPs noise variance was not significantly different across the single-point latencies. On average, extending the length of the signal window lowered the Fsp value in cVEMPs and oVEMPs. An Fsp value of 2.0 was chosen as the criterion cutoff associated with the 95th percentile during no-response conditions using group data for cVEMPs and oVEMPs, respectively. Fsp values for cVEMPs and oVEMPs were not significantly different from each other. This study established single-point latency and time-window parameters for VEMP-related applications of the Fsp detection algorithm. Fsp criteria values were established for cVEMP and oVEMP. Using these parameters, responses were detected in all participants.

Measuring impulse insertion loss of hearing protection device using high-level impulse noise

The American National Standard, ANSI S12.42-2010, specifies the impulse peak insertion loss (IPIL) for a hearing protection device (HPD) using an acoustic test fixture (ATF) over a range of impulse levels nominally at 132, 150, and 168 dB peak sound pressure level (dB pSPL). The GRAS 45CB ATFs have ear simulators fitted with GRAS 40BP microphones (6.35 mm diameter) that have amplitude limits of about 169 dB SPL (172 dB pSPL). The open ear transfer function measured at the 168-dB level can cause the peak amplitude to exceed the design specification of the microphone. Accordingly, the standard directs the user to measure the 150-dB transfer function between the field microphone and unoccluded ear (HFF,TM) and apply it to the field microphone measurement at 168 dB. We have measured the HFF,TM with GRAS 45CB ATF and with the GRAS 45CB-S2 ATF equipped with GRAS 40BH microphones (193 dB/196 dB pSPL). Impulse peak insertion loss measured with both ATFs will be reported and compared.

Acoustic treatments for indoor and outdoor firing ranges

Small-caliber firearms can produce impulse noises that frequently exceed 150 dB peak sound pressure level (dB pSPL) and can approach 185 dB pSPL. These impulse noises can present a significant risk for noise-induced hearing loss for the unprotected ear and pose a risk for persons wearing hearing protection that is possibly poorly fitted or insufficient. For range safety officers and personnel who work in the firing range on a regular basis, the daily cumulative effects of noise exposure can lead to increased fatigue and stress. Acoustic treatments of the reflective surfaces can mitigate these health risks. This paper will review some community noise guidelines as well as health and safety regulations. As a manufacturer of acoustic range treatments, the Troy System materials will be reviewed with regards to their laboratory performance and their capabilities to reduce noise in various firing ranges. One aspect of performance that may be overlooked is the safety features of the materials which Troy Acoustics provides, such as flammability, ability to be cleaned, and the resistance to moisture and mold.

Neural Presbyacusis in Humans Inferred from Age-Related Differences in Auditory Nerve Function and Structure.

A common complaint of older adults is difficulty understanding speech, particularly in challenging listening conditions. Accumulating evidence suggests that these difficulties may reflect a loss and/or dysfunction of auditory nerve (AN) fibers. We used a novel approach to study age-related changes in AN structure and several measures of AN function, including neural synchrony, in 58 older adults and 42 younger adults. AN activity was measured in response to an auditory click (compound action potential; CAP), presented at stimulus levels ranging from 70 to 110 dB pSPL. Poorer AN function was observed for older than younger adults across CAP measures at higher but not lower stimulus levels. Associations across metrics and stimulus levels were consistent with age-related AN disengagement and AN dyssynchrony. High-resolution T2-weighted structural imaging revealed age-related differences in the density of cranial nerve VIII, with lower density in older adults with poorer neural synchrony. Individual differences in neural synchrony were the strongest predictor of speech recognition, such that poorer synchrony predicted poorer recognition of time-compressed speech and poorer speech recognition in noise for both younger and older adults. These results have broad clinical implications and are consistent with an interpretation that age-related atrophy at the level of the AN contributes to poorer neural synchrony and may explain some of the perceptual difficulties of older adults.SIGNIFICANCE STATEMENT Differences in auditory nerve (AN) pathophysiology may contribute to the large variations in hearing and communication abilities of older adults. However, current diagnostics focus largely on the increase in detection thresholds, which is likely because of the absence of indirect measures of AN function in standard clinical test batteries. Using novel metrics of AN function, combined with estimates of AN structure and auditory function, we identified age-related differences across measures that we interpret to represent age-related reductions in AN engagement and poorer neural synchrony. Structure-function associations are consistent with an explanation of AN deficits that arise from age-related atrophy of the AN. Associations between neural synchrony and speech recognition suggest that individual and age-related deficits in neural synchrony contribute to speech recognition deficits.

Efferent-induced shifts in synchronized-spontaneous-otoacoustic-emission magnitude and frequency.

Synchronized-spontaneous otoacoustic emissions (SSOAEs) present as slow-decaying emission energy that persists after the transient-evoked otoacoustic emission (TEOAE). SSOAEs possess high amplitudes and signal-to-noise ratios, making them potentially ideal candidates to assay the medial-olivocochlear reflex (MOCR). The current work quantified MOCR-induced changes to SSOAEs over a 36-dB stimulus level range and compared MOCR effects between TEOAE- and SSOAE-based assays. Otoacoustic emissions were evoked using band limited clicks from 52 to 88 dB peak sound pressure level (pSPL) with and without contralateral-acoustic stimulation (CAS) in 25 normal-hearing, female adults. The CAS was 50-dB sound pressure level (SPL) broadband noise and served to activate the MOCR. The number of SSOAEs increased with the stimulus level through approximately 70 dB pSPL. The presentation of CAS resulted in fewer SSOAEs. SSOAEs exhibited compressive growth and approached saturation for stimulus levels of 70 dB pSPL. The primary effects of CAS were a reduction in the SSOAE magnitude and an upward shift in the SSOAE frequency. These changes were not strongly affected by the stimulus level. Time-domain analysis of the SSOAE revealed an increase in the CAS-induced magnitude shift during the decay portion of the SSOAE. Compared to CAS-induced TEOAE magnitude shifts, SSOAE magnitude shifts were typically 2-3 dB larger. Findings support SSOAEs as a means to assay the MOCR.

Characterizing Insertion Pressure Profiles During Cochlear Implantation: Simultaneous Fluoroscopy and Intracochlear Pressure Measurements.

Combined electrical-acoustical stimulation (EAS) has gained popularity as patients with residual hearing are increasingly undergoing cochlear implantation. Preservation of residual hearing correlates with hearing outcomes, but loss of hearing occurs in a subset of these patients. Several mechanisms have been proposed as causing this hearing loss; we have previously described high amplitude pressure transients, equivalent to high-level noise exposures, in the inner ear during electrode insertion. The source of these transients has not been identified. Cadaveric human heads were prepared with an extended facial recess. Fiber-optic pressure sensors were inserted into the scala vestibuli and scala tympani to measure intracochlear pressures. Two cochlear implant (CI) electrode styles (straight and perimodiolar) were inserted during time-synced intracochlear pressures and video fluoroscopy measurements. CI electrode insertions produced pressure transients in the cochlea up to 160 to 170 dB pSPL equivalent for both styles, consistent with previous results. However, the position of the electrode within the cochlea when transients were generated differed (particularly contact with the medial or lateral walls). These results begin to elucidate the insertion pressure profiles of CI electrodes, which can be used to improve CI electrode designs and facilitate "silent-insertions" to improve chances of hearing preservation.

The Medial Canthus Reference Electrode Is not Electrically Indifferent to the Ocular Vestibular Evoked Myogenic Potential.

To determine whether a reference electrode placed over the contralateral medical canthus is electrically indifferent to the ocular vestibular evoked myogenic potential (oVEMP). Prospective observational study. Tertiary academic center. Nineteen otologically normal subjects. oVEMPs were recorded using a 500 Hz tone burst at 125 dB pSPL using both a conventional dual infra-orbital derivation and contralateral infraorbital electrode referenced to a medial canthus electrode known as the "belly-tendon" derivation. The belly-tendon derivation produced significantly larger oVEMP amplitudes. This appears to be due to a polarity inversion of the first negative peak that occurs when the reference electrode is placed over the medial canthus. Thus, the belly-tendon derivation was associated with reference contamination, but in this instance the reference contamination produced an augmented oVEMP amplitude. Neither the dual infra-orbital nor belly-tendon electrode montages are electrically neutral. Reference contamination is the source of both a decrease in amplitude using conventional recording techniques and increased amplitude using the belly-tendon montage. The results support the contention that the belly-tendon montage generates a reversed polarity response, i.e., algebraically subtracted (i.e., added in the differential amplifier) from the response recorded at the infraorbital midline enhancing the oVEMP amplitude. It should be noted that the amplitude gained when using the belly-tendon montage may also be due to electromyographic (EMG) generated by extraocular muscles other than the inferior oblique generator, resulting in a loss of specificity. The authors recommend the belly-tendon montage be used in clinical situations where the oVEMP is absent or low in amplitude.

Intracochlear pressure measurements during acoustic shock wave exposure

IntroductionInjuries to the peripheral auditory system are among the most common results of high intensity impulsive acoustic exposure. Prior studies of high intensity sound transmission by the ossicular chain have relied upon measurements in animal models, measurements at more moderate sound levels (i.e. < 130 dB SPL), and/or measured responses to steady-state noise. Here, we directly measure intracochlear pressure in human cadaveric temporal bones, with fiber optic pressure sensors placed in scala vestibuli (SV) and tympani (ST), during exposure to shock waves with peak positive pressures between ∼7 and 83 kPa. MethodsEight full-cephalic human cadaver heads were exposed, face-on, to acoustic shock waves in a 45 cm diameter shock tube. Specimens were exposed to impulses with nominal peak overpressures of 7, 28, 55, & 83 kPa (171, 183, 189, & 192 dB pSPL), measured in the free field adjacent to the forehead. Specimens were prepared bilaterally by mastoidectomy and extended facial recess to expose the ossicular chain. Ear canal (EAC), middle ear, and intracochlear sound pressure levels were measured with fiber-optic pressure sensors. Surface-mounted sensors measured SPL and skull strain near the opening of each EAC and at the forehead. ResultsMeasurements on the forehead showed incident peak pressures approximately twice that measured by adjacent free-field and EAC entrance sensors, as expected based on the sensor orientation (normal vs tangential to the shock wave propagation). At 7 kPa, EAC pressure showed gain, calculated from the frequency spectra, consistent with the ear canal resonance, and gain in the intracochlear pressures (normalized to the EAC pressure) were consistent with (though somewhat lower than) previously reported middle ear transfer functions. Responses to higher intensity impulses tended to show lower intracochlear gain relative to EAC, suggesting sound transmission efficiency along the ossicular chain is reduced at high intensities. Tympanic membrane (TM) rupture was observed following nearly every exposure 55 kPa or higher. ConclusionsIntracochlear pressures reveal lower middle-ear transfer function magnitudes (i.e. reduced gain relative to the ear canal) for high sound pressure levels, thus revealing lower than expected cochlear exposure based on extrapolation from cochlear pressures measured at more moderate sound levels. These results are consistent with lowered transmissivity of the ossicular chain at high intensities, and are consistent with our prior report measuring middle ear transfer functions in human cadaveric temporal bones with high intensity tone pips.

Increased medial olivocochlear reflex strength in normal-hearing, noise-exposed humans.

Research suggests that college-aged adults are vulnerable to tinnitus and hearing loss due to exposure to traumatic levels of noise on a regular basis. Recent human studies have associated exposure to high noise exposure background (NEB, i.e., routine noise exposure) with the reduced cochlear output and impaired speech processing ability in subjects with clinically normal hearing sensitivity. While the relationship between NEB and the functions of the auditory afferent neurons are studied in the literature, little is known about the effects of NEB on functioning of the auditory efferent system. The objective of the present study was to investigate the relationship between medial olivocochlear reflex (MOCR) strength and NEB in subjects with clinically normal hearing sensitivity. It was hypothesized that subjects with high NEB would exhibit reduced afferent input to the MOCR circuit which would subsequently lead to reduced strength of the MOCR. In normal-hearing listeners, the study examined (1) the association between NEB and baseline click-evoked otoacoustic emissions (CEOAEs) and (2) the association between NEB and MOCR strength. The MOCR was measured using CEOAEs evoked by 60 dB pSPL linear clicks in a contralateral acoustic stimulation (CAS)-off and CAS-on (a broadband noise at 60 dB SPL) condition. Participants with at least 6 dB signal-to-noise ratio (SNR) in the CAS-off and CAS-on conditions were included for analysis. A normalized CEOAE inhibition index was calculated to express MOCR strength in a percentage value. NEB was estimated using a validated questionnaire. The results showed that NEB was not associated with the baseline CEOAE amplitude (r = -0.112, p = 0.586). Contrary to the hypothesis, MOCR strength was positively correlated with NEB (r = 0.557, p = 0.003). NEB remained a significant predictor of MOCR strength (β = 2.98, t(19) = 3.474, p = 0.003) after the unstandardized coefficient was adjusted to control for effects of smoking, sound level tolerance (SLT) and tinnitus. These data provide evidence that MOCR strength is associated with NEB. The functional significance of increased MOCR strength is discussed.

The Effect of Repetition Rate on Air-Conducted Ocular Vestibular Evoked Myogenic Potentials (oVEMPs).

Ocular vestibular evoked myogenic potentials (oVEMPs) are used to describe utricular/superior vestibular nerve function; however, optimal recording parameters have not been fully established. This study investigated the effect of repetition rate on air-conducted oVEMPs. Ten healthy adults were evaluated using 500-Hz tone bursts (4-ms duration, Blackman gating, 122 dB pSPL). Four repetition rates were used (1.6, 4.8, 8.3, and 26.6 Hz) and resulting oVEMP response presence, amplitude, amplitude asymmetry, and n1/p1 latency were assessed. Response presence was significantly reduced for 26.6 Hz using monaural stimulation and for 8.3 Hz and 26.6 Hz for binaural stimulation. For monaural stimulation using 1.6, 4.8, and 8.3 Hz, no significant differences were noted for amplitude or latency. Responses obtained using binaural stimulation demonstrated a significant effect of rate on amplitude, with 8.3 Hz producing significantly reduced amplitude. Binaural amplitudes were significantly larger than monaural contralateral responses but with reduced response presence. No significant differences were noted for latency or amplitude asymmetry. Using repetition rates of approximately 5 Hz or less may produce more consistent oVEMP response presence with minimal effects on amplitude for monaural or binaural recordings.

Effects of motion sickness severity on the vestibular-evoked myogenic potentials.

Motion sickness is a common debilitating condition associated with both actual and perceived motion. Despite the commonality, little is known about the underlying physiological mechanisms. One theory proposes that motion sickness arises from a mismatch between reality and past experience in vertical motions. Physiological tests of the vestibular system, however, have been inconclusive regarding the underlying pathogenesis. Cervical vestibular-evoked myogenic potentials (cVEMPs) arise from the saccule, which responds to vertical motion. If vertical motion elicits motion sickness, the cVEMP should be affected. The purpose of this investigation was to determine if cVEMP characteristics differ among individuals with a range of motion sickness susceptibility from negligible to severe. The hypothesis was that individuals with high susceptibility would have larger cVEMP amplitudes and shorter cVEMP latencies relative to those who are resistant to motion sickness. The study had two parts. The first was quasi-experimental in which participants comprised three groups based on susceptibility to motion sickness (low, mild-moderate, high) as identified on the short version of the Motion Sickness Susceptibility Questionnaire (MSSQ-S). The second part of the study was correlational and evaluated the specific relationships between the degree of motion sickness susceptibility and characteristics of the VEMPs. A total of 24 healthy young adults (ages 20-24 yr) were recruited from the university and the community without regard to motion sickness severity. Participants took the MSSQ-S, which quantifies susceptibility to motion sickness. The participants had a range of motion sickness susceptibility with MSSQ raw scores from 0.0-36.6, which correspond to percent susceptibility from 0.0-99.3%. VEMPs were elicited by 500 Hz tone-bursts monaurally in both ears at 120 dB pSPL. MSSQ-S percent scores were used to divide the participants into low, mild-moderate, and high susceptibility groups. A fixed general linear model with repeated-measures analysis of variance tested cVEMP characteristics for the susceptibility groups (between participants) and ears (within participants). A univariate analysis of variance tested the cVEMP interaural amplitudes across groups. The second analysis was a regression of the severity of motion sickness in percent on cVEMP characteristics. Significance was defined as p < 0.05. Participants in the high susceptibility group had significantly higher cVEMP amplitudes than those in the low susceptibility group. cVEMP amplitudes did not differ between ears, and latencies did not differ between the two groups or between ears. Regression analysis on MSSQ-S percent susceptibility by VEMP amplitudes revealed a best-fit cubic function in both ears, with r(2) values of more than 42%. The interaural asymmetry ratio was negatively associated with motion sickness susceptibility (r(2) = 0.389). The current study is the first to report that greater susceptibility to motion sickness is associated with larger cVEMP amplitudes and lower interaural cVEMP asymmetries. Larger interaural asymmetries in cVEMPs did not promote motion sickness susceptibility. The cVEMP findings implicate the saccule and its neural pathways in the production of motion sickness and are consistent with the theory that vertical motions elicit motion sickness. Motion sickness susceptibility may contribute to the variability in normative cVEMP amplitudes.

Effects of Age on the Tuning of the cVEMP and oVEMP

The purpose of the present investigation was to define for young, middle-aged, and older adults the optimal frequency (cies) to record both the cervical vestibular-evoked myogenic potential (cVEMP) and the ocular vestibular-evoked myogenic potential (oVEMP). Further, this study aimed to describe age-related changes in the tuning of these two vestibular-evoked myogenic potentials. This was a prospective study. Participants were 39 healthy adults (mean age 46.3 ± 15.7 years; range = 22 to 78 years; 15 men) equally divided into 3 age groups of 13 participants each: young adult (18 to 39 years), middle age (40 to 59 years), and old adult (≥60 years). cVEMPs and oVEMPs were recorded using air-conduction tone bursts at stimulus frequencies of 125, 250, 500, 750, 1000, 1500, and 2000 Hz presented at 127 dB pSPL. There was a significant main effect of age group and frequency on the amplitude of both the cVEMP and the oVEMP. Amplitudes were largest for the Young adult group for the cVEMP and for the young adult and Middle age group for the oVEMP. The largest average peak-to-peak amplitude occurred in response to a 750 Hz tone burst for both responses. No significant differences in mean amplitude of the cVEMP or oVEMP were observed for 500, 750, or 1000 Hz stimuli. There was a significant interaction of age group and frequency for the cVEMP, suggesting a loss of tuning for the old adult group. Compared with the young adult group, the tuning of the cVEMP and oVEMP for the older adjults appeared to shift to a higher frequency. There is no sharp tuning in the saccule and utricle. Instead, there is a range of best frequencies that may be used to evoke the cVEMP and oVEMP responses. The results of the present investigation also demonstrate that the optimal stimulus frequency to elicit a VEMP may change with age. Accordingly, 500 Hz may not be the ideal frequency to elicit VEMPs for all age groups. For this reason, in cases where the VEMP response is absent at 500 Hz it is recommended that attempts be made to record the VEMP for tone-burst frequencies of 750 or 1000 Hz.

Vestibular evoked myogenic potentials (VEMPS) from upper limb muscles

Vestibular evoked myogenic potentials (VEMPS) from upper limb muscles

Reduction in Impulse Noise-Induced Permanent Threshold Shift with Intracochlear Application of an NADPH Oxidase Inhibitor

Toxic levels of reactive oxygen species are key contributors to the lesion of dead outer hair cells (OHCs) seen in the cochlea after noise exposure. The current study follows previous work in which paraquat was used to demonstrate that NADPH oxidase is active in the cochlea and can contribute to cochlear reactive oxygen species formation and hair cell loss. The current study was undertaken to test whether pharmacological blockade of NADPH oxidase in the cochlea would lead to reduced noise-induced hearing loss and OHC death. A total of 18 chinchillas (36 ears) were assessed in the study. AEBSF (4-[2-aminoethyl]benzenesulfonyl fluoride), an inhibitor of NADPH oxidase activation, was dissolved in distilled water and delivered into the cochlea via diffusion across the round window membrane. The contralateral ears received distilled water as a vehicle control. Following treatment, chinchillas were exposed to one of two noises: a 4 kHz octave band noise at 106 dB SPL for 6 hr or an impulse noise that consisted of 75 pairs of 155 dB pSPL impulses. Pre- and post-noise exposure, thresholds of the auditory brainstem response at 2-8 kHz were measured. Postmortem OHC counts were conducted at the conclusion of the study. Two- and three-factor ANOVAs were used for statistical analysis of the OHC losses and ABR threshold shifts induced by the noise exposures. Permanent threshold shift from the impulse noise was reduced in the ears treated with the NADPH oxidase inhibitor, but no differences were found in the groups exposed to the continuous noise. OHC losses were not statistically different between the treated and untreated ears for either noise exposure. The results suggest that NADPH oxidase-mediated superoxide has a role in cochlear damage from impulse noise, and pharmacologic inhibition of NADPH oxidase can reduce cochlear susceptibility to noise damage. The lack of protection from the longer-duration continuous noise can be attributed to a number of possibilities related to dose level and delivery schedule.

The Effect of Muscle Contraction Level on the Cervical Vestibular Evoked Myogenic Potential (cVEMP): Usefulness of Amplitude Normalization

The cervical vestibular evoked myogenic potential (cVEMP) is a reflexive change in sternocleidomastoid (SCM) muscle contraction activity thought to be mediated by a saccular vestibulo-collic reflex. CVEMP amplitude varies with the state of the afferent (vestibular) limb of the vestibulo-collic reflex pathway, as well as with the level of SCM muscle contraction. It follows that in order for cVEMP amplitude to reflect the status of the afferent portion of the reflex pathway, muscle contraction level must be controlled. Historically, this has been accomplished by volitionally controlling muscle contraction level either with the aid of a biofeedback method, or by an a posteriori method that normalizes cVEMP amplitude by the level of muscle contraction. A posteriori normalization methods make the implicit assumption that mathematical normalization precisely removes the influence of the efferent limb of the vestibulo-collic pathway. With the cVEMP, however, we are violating basic assumptions of signal averaging: specifically, the background noise and the response are not independent. The influence of this signal-averaging violation on our ability to normalize cVEMP amplitude using a posteriori methods is not well understood. The aims of this investigation were to describe the effect of muscle contraction, as measured by a prestimulus electromyogenic estimate, on cVEMP amplitude and interaural amplitude asymmetry ratio, and to evaluate the benefit of using a commonly advocated a posteriori normalization method on cVEMP amplitude and asymmetry ratio variability. Prospective, repeated-measures design using a convenience sample. Ten healthy adult participants between 25 and 61 yr of age. cVEMP responses to 500 Hz tone bursts (120 dB pSPL) for three conditions describing maximum, moderate, and minimal muscle contraction. Mean (standard deviation) cVEMP amplitude and asymmetry ratios were calculated for each muscle-contraction condition. Repeated measures analysis of variance and t-tests compared the variability in cVEMP amplitude between sides and conditions. Linear regression analyses compared asymmetry ratios. Polynomial regression analyses described the corrected and uncorrected cVEMP amplitude growth functions. While cVEMP amplitude increased with increased muscle contraction, the relationship was not linear or even proportionate. In the majority of cases, once muscle contraction reached a certain "threshold" level, cVEMP amplitude increased rapidly and then saturated. Normalizing cVEMP amplitudes did not remove the relationship between cVEMP amplitude and muscle contraction level. As muscle contraction increased, the normalized amplitude increased, and then decreased, corresponding with the observed amplitude saturation. Abnormal asymmetry ratios (based on values reported in the literature) were noted for four instances of uncorrected amplitude asymmetry at less than maximum muscle contraction levels. Amplitude normalization did not substantially change the number of observed asymmetry ratios. Because cVEMP amplitude did not typically grow proportionally with muscle contraction level, amplitude normalization did not lead to stable cVEMP amplitudes or asymmetry ratios across varying muscle contraction levels. Until we better understand the relationships between muscle contraction level, surface electromyography (EMG) estimates of muscle contraction level, and cVEMP amplitude, the application of normalization methods to correct cVEMP amplitude appears unjustified.

Mapping auditory nerve firing density using high-level compound action potentials and high-pass noise masking

Future implementation of regenerative treatments for sensorineural hearing loss may be hindered by the lack of diagnostic tools that specify the target(s) within the cochlea and auditory nerve for delivery of therapeutic agents. Recent research has indicated that the amplitude of high-level compound action potentials (CAPs) is a good predictor of overall auditory nerve survival, but does not pinpoint the location of neural damage. A location-specific estimate of nerve pathology may be possible by using a masking paradigm and high-level CAPs to map auditory nerve firing density throughout the cochlea. This initial study in gerbil utilized a high-pass masking paradigm to determine normative ranges for CAP-derived neural firing density functions using broadband chirp stimuli and low-frequency tonebursts, and to determine if cochlear outer hair cell (OHC) pathology alters the distribution of neural firing in the cochlea. Neural firing distributions for moderate-intensity (60 dB pSPL) chirps were affected by OHC pathology whereas those derived with high-level (90 dB pSPL) chirps were not. These results suggest that CAP-derived neural firing distributions for high-level chirps may provide an estimate of auditory nerve survival that is independent of OHC pathology.

Auditory brainstem responses in aged budgerigars

Event Abstract Back to Event Auditory brainstem responses in aged budgerigars Ryan Simmons1 and Beth Brittan-Powell1* 1 University of Maryland College Park, United States Numerous studies in humans and other mammals show marked changes in hearing sensitivity with age due to deterioration of the peripheral and/or central auditory system. Birds, on the other hand, regenerate hair cells as well as defective sensory epithelium. In fact, Langemann et al. in 1999 showed no hearing loss when comparing behavioral thresholds in young and old European starlings. As far as we know, this has not been documented in other species of birds. In our study, we measured hearing sensitivity in six one-year old and eight 10-year old budgerigars using the auditory brainstem response (ABR). The ABR is a population response resulting from synchronous neural discharge and represents the progressive propagation of auditory neural activity through the ascending auditory pathway. We wanted to determine whether age negatively affected the ability of the peripheral auditory system to synchronize to tone bursts as evidenced by decreased amplitude, increased latency, and higher thresholds as compared to young birds. Subjects were presented with both rectangular-pulse clicks and tone burst stimuli. Clicks were 0.1 ms in duration and presented in ascending order between 10-100 dB pSPL. Tone bursts were 5 ms in duration with a 1 ms rise/fall, presented at frequencies ranging from 500 - 8000 Hz at intensities of 10-100 dB SPL. Hearing sensitivity for younger birds was 5-10 dB better across most frequencies tested. Preliminary analyses suggest there is no difference in latency for peak 1 or 2 of the ABR response between age groups, but there are, on average, reduced amplitude responses exhibited by the older birds, especially at suprathreshold levels – 30 to 40 dB above threshold. Keywords: auditory brainstem response, Ageing, avian, audition, Evoked Potentials Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster Presentation (see alternatives below as well) Topic: Sensory: Audition Citation: Simmons R and Brittan-Powell B (2012). Auditory brainstem responses in aged budgerigars. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00008 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Jul 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Beth Brittan-Powell, University of Maryland College Park, College Park, Maryland, 20742, United States, ebrittan@umd.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Ryan Simmons Beth Brittan-Powell Google Ryan Simmons Beth Brittan-Powell Google Scholar Ryan Simmons Beth Brittan-Powell PubMed Ryan Simmons Beth Brittan-Powell Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.