Click Stimuli Research Articles

PEATE por estímulo chirp em recém-nascidos: uma revisão integrativa

ABSTRACT Purpose: to review the literature available on electrophysiological findings on ABR with chirp stimuli in newborns. Methods: articles were searched in PubMed, MEDLINE, Scopus, Web of Science, LILACS, and SciELO. Papers published in English and Portuguese between 2010 and 2020 were selected, including those that addressed ABR with air-conduction broadband chirp stimuli in newborns, that assessed ABR with a specific frequency, and that compared ABR results with chirp and click stimuli. Articles that assessed only bone-conduction results, duplicates, literature reviews, case reports, letters, and editorials were excluded. Literature review: the search strategy resulted in nine selected articles. Four studies (44.4%) analyzed ABR wave amplitude and latency with chirp stimuli, three studies (33.3%) compared the time of ABR procedures between chirp and click stimuli, two studies (22.2%) analyzed only amplitude, and two (22.2%), verified the specificity of ABR with chirp stimuli in neonatal hearing screening. Conclusion: chirp stimuli elicit responses with greater amplitudes, lower latencies, and shorter examination time than those with click stimuli in newborns.

Comparison of Acoustic Reflex Thresholds Across Different Stimuli

Background: Acoustic reflex (AR) is the contraction in the middle ear muscles in response to severe acoustic stimulation. Thresholds of AR can be obtained using different stimuli and different stimulus parameters. However, the reflexes are often difficult to elicit in hearing-related disorders such as hyperacusis, recruitment, young infants, and children with autism. Comparisons of AR thresholds (ARTs) across different stimuli, such as PT, broadband noise, and clicks at different rates, can provide information on the stimuli optimally used for difficult-to-test populations. Objective: The study aimed to estimate and correlate the ARTs elicited by pure-tones (PT), the low-frequency band (low pass [LP]) and high-frequency band (high pass [HP]), wide-band noise (WB), and clicks at different rates. Materials and Methods: ARTs using different stimuli like PT of frequencies 500, 1 k, 2 k, 4 k Hz, the low-frequency band (LP) (i.e., noise in the frequency range of 125–1600 Hz), the high-frequency band (HP) (i.e., noise in the frequency range of 1600–4000 Hz), wideband noise (WB) (125–4 kHz), and clicks at different click repetition rates as 50/s, 100/s, 150/s, 200/s, 250/s, and 300 clicks/sec was measured on 50 normal-hearing individuals. The ARTs were documented for both ipsilateral and contralateral recording for all test stimuli. Results: The mean ART obtained for 500 Hz PT was between 85 and 95 dB HL, for WB, it was between 80 and 85 dB, and for LP and HP, it was between 75 and 80 dB HL. For click stimulus, a better threshold of 70 dB HL was obtained at 300/s. The mean ART elicited by PT and WB noise was higher than click stimuli. The mean comparison of the ART obtained between PT and WB revealed better thresholds for WB noise. Between WB noise and clicks, better ART was observed for click stimuli. The clicks elicited ART were better than noise stimuli followed by PT. Ipsilateral stimulation yielded better responses than contralateral stimulation for all stimuli. Discussion: The mean ART for click stimulus was better because it stimulated a wider frequency range in cochlea than PT, LP, and HP. Even though WB has a wider frequency range than clicks, the mean ART for click stimulus was much better because of a factor called temporal integration, i.e., stimulation at a higher rate (300/s). Conclusions: The click stimuli at a higher rate can be used effectively to measure ART's for individuals with lower comfortable levels as it can elicit reflex at lower thresholds.

Audiological follow-up of children with congenital Zika syndrome

How does the auditory function of children with congenital Zika syndrome present during the first three years of life? To determine the auditory function of children with congenital Zika syndrome during the first three years of life and estimate the frequency and long-term presentation of hearing loss in this syndrome, an auditory assessment with screening and diagnostic tests was conducted. The screening test consisted of measuring the short latency ABR using click stimuli. If the ABR click indicated hearing loss, confirmation was obtained with a frequency-specific ABR (FS-ABR), in which the stimuli were tone bursts at frequencies of 500 and 2000 Hz by bone and air conduction. This case series included 107 children with confirmed congenital Zika syndrome, and the cumulative incidence of sensorineural hearing loss in the first three years of life was 9.3% (10/107). There were no cases of delayed-onset or progressive deficits in hearing. Early presentation of sensorineural hearing loss seems to occur with a higher frequency in children with congenital Zika syndrome than in the general population. Sensorineural hearing loss resulting from congenital Zika virus infection does not appear to present with delayed onset or with progressive deficits.

Detrimental Effects of Traffic Noise in Traffic Policemen as Assessed by Auditory Brainstem Evoked Response: A Cross-sectional Observational Study

Introduction: Loud noise is a global occupational health hazard with substantial social and physiological impacts, especially pronounced in traffic policemen who are engaged at heavy traffic junctions. Apart from its overt effect on sensorineural hearing, loud noise has been also implicated, albeit covertly, as a causative factor for disturbances in sleep, learning and depression. Due to the insidious nature of hearing impairment, manifestations are often masked and hence testing through Auditory Brainstem Evoked Response (ABER) should be resorted to, for assessment of functional status of auditory pathway objectively. Aim: To assess and compare the effect of traffic noise in traffic policemen with age matched apparently healthy males using ABER. Materials and Methods: The present study was a crosssectional, comparative type of observational research conducted in the Department of Physiology, SMS Medical College, Jaipur, Rajasthan, India, from June 2019 to May 2020, on 45 apparently healthy male traffic policemen, aged 25-40 years, engaged at heavy traffic junctions of Jaipur city, with an average field posting of five years or more. An equal number of age and sex matched apparently healthy subjects living in Jaipur city, were recruited as controls. Before commencing with the test procedure, ethical clearance was obtained from the institute’s ethics committee and research review board and written informed consent was obtained from all the participants. ABER assessment was done via RMS EMG SALUS 2C machine on each subject using click stimuli presented mono-aurally via an overhead headphone resulting in harvest of variables in form of absolute wave latencies (I to V) and Interpeak Latencies (IPL) (I-III, I-V and III-V). Unpaired Student’s t-test was used to derive the level of significance using Statistical Package for the Social Sciences (SPSS) version 16.0. Level of significance was set at p-value <0.05. Results: The results obtained in the present study demonstrated pronounced delay (p-value<0.01) in all absolute wave latencies (I to V) in both ears in traffic policemen. A statistically significant delay was also observed in IPL I-V (p-value<0.01) when a comparison of left ABER was made between traffic policemen and controls. Conclusion: The findings of the present study indicate that the hidden footprints of loss in auditory acuity in traffic policemen exposed to traffic noise can be unearthed objectively via using ABER assessment and therefore periodic ABER assessment along with usage of preventive equipment should be the strategy for prevention of imminent hearing loss.

Auditory Brainstem Response in Children with Thalassemia Major under Chelating Therapy.

The present study compared the Auditory Brainstem Response (ABR) of children with thalassemia major and typically developing children. A total of 16 children participated in this study. Group I included 8 children with thalassemia major regularly undergoing blood transfusions and chelating therapy. Group II included 8 age and gender-matched typically developing children. All children in both groups had hearing sensitivity within normal limits. The Auditory Brainstem Response (ABR) was recorded monaurally for click stimuli from both ears. Results showed that the mean latencies of peaks of ABR were similar in both groups. The mean peak amplitude of peaks I and V of the ABR were different between groups, but it was not statistically significant. The present study showed no abnormality in the latency and amplitude of peaks of the ABR in children with thalassemia major with hearing sensitivity within normal limits.

Well Diving is Not Well for Hearing: Sudden Sensory Neural Hearing Loss-A Case Report

Background: Sudden sensory neural hearing loss can be caused by many factors. It may range from minimal to profound degree of hearing loss. Barotrauma is a type of ear damage caused by pressure difference between the atmosphere and the inner ear. This may result in permanent sensory neural hearing loss. Objective: The aim of the study was to use behavioral and electrophysiological assessments to analyze the hearing of a patient who experienced sudden hearing loss following a dive in well. Case Report: A 31 year old male adult who reported sudden hearing loss following a dive in the well was evaluated. Hearing assessment was done. Pure tone audiometry revealed bilateral profound hearing loss. Immittance audiometry showed ‘A’ type tympanogram in both ears and acoustic reflexes absent in both ears. In ABR click stimulus test, no responses were observed till 105dBnHL in both ears. DPOAE’s were also absent in both ears. Vestibular assessments (subjective and objective) were also done. Conclusion: The current case study verifies the importance of audiological assessment for divers and importance of safety measures to be taken.

Early auditory cortical processing predicts auditory speech in noise identification and lipreading

Individuals typically exhibit better cross-sensory perception following unisensory loss, demonstrating improved perception of information available from the remaining senses and increased cross-sensory use of neural resources. Even individuals with no sensory loss will exhibit such changes in cross-sensory processing following temporary sensory deprivation, suggesting that the brain's capacity for recruiting cross-sensory sources to compensate for degraded unisensory input is a general characteristic of the perceptual process. Many studies have investigated how auditory and visual neural structures respond to within- and cross-sensory input. However, little attention has been given to how general auditory and visual neural processing relates to within and cross-sensory perception. The current investigation examines the extent to which individual differences in general auditory neural processing accounts for variability in auditory, visual, and audiovisual speech perception in a sample of young healthy adults. Auditory neural processing was assessed using a simple click stimulus. We found that individuals with a smaller P1 peak amplitude in their auditory-evoked potential (AEP) had more difficulty identifying speech sounds in difficult listening conditions, but were better lipreaders. The results suggest that individual differences in the auditory neural processing of healthy adults can account for variability in the perception of information available from the auditory and visual modalities, similar to the cross-sensory perceptual compensation observed in individuals with sensory loss.

Influence of Stimulus Polarity on the Auditory Brainstem Response From Level-Specific Chirp.

Background and ObjectivesNo known studies have investigated the influence of stimulus polarity on the Auditory Brainstem Response (ABR) elicited from level-specific (LS) chirp. This study is important as it provides a better understanding of the stimulus polarity selection for ABR elicited from LS chirp stimulus. We explored the influence of stimulus polarity on the ABR from LS chirp compared to the ABR from click at 80 dBnHL in normal-hearing adults.Subjects and MethodsNineteen adults with normal hearing participated. The ABRs were acquired using click and LS chirp stimuli using three stimulus polarities (rarefaction, condensation, and alternating) at 80 dBnHL. The ABRs were tested only on the right ear at a stimulus rate of 33.33 Hz. The ABR test was stopped when the recording reached the residual noise level of 0.04 µV. The ABRs amplitudes, absolute latencies, inter-peak latencies (IPLs), and the recorded number of averages were statistically compared among ABRs at different stimulus polarities and stimuli combinations.ResultsRarefaction polarity had the largest ABR amplitudes and SNRs compared with other stimulus polarities in both stimuli. There were marginal differences in the absolute latencies and IPLs among stimulus polarities. No significant difference in the number of averages required to reach the stopping criteria was found.ConclusionsStimulus polarities have a significant influence on the ABR to LS chirp. Rarefaction polarity is recommended for clinical use because of its larger ABR peak I, III, and V amplitudes than those of the other stimulus polarities.

Temperature (but not acclimation) affects hearing in fishes adapted to different temperature regimes

Temperature affects various metabolic and physiological processes in ectothermic animals, including auditory systems. The current study investigates the effect of temperature and thermal acclimation time on hearing sensitivities in a eurythermal and a stenothermal fish possessing accessory hearing structures. Using the auditory evoked potential (AEP) recording technique, we determined thresholds from 0.1 to 4 kHz and peak latencies of AEP-waveforms in response to a click stimulus. The goldfish Carassius auratus was chosen as a model for eurythermal and the Amazonian catfish Megalodoras uranoscopus as a model for stenothermal species. Both species were tested at two different temperatures (C. auratus: 15 °C and 25 °C, M. uranoscopus: 22 °C and 30 °C) and acclimation periods, within 22 h (unacclimated) or three to four weeks (acclimated) after reaching the target temperature. A frequency-dependent increase in auditory sensitivity and a decrease of peak latencies was recorded in both species at higher temperatures, independent of acclimation time. The change in hearing thresholds per degree Celsius was more pronounced in the stenothermal catfish. The data indicate that higher temperatures improved hearing (lower thresholds, shorter latencies), whereas acclimation had no effect on hearing in either species. The latter data contradict previous findings in the eurythermal channel catfish Ictalurus punctatus in which acclimation slightly improved hearing when raising the temperatures. A comparison of changes in hearing sensitivity per degree Celsius of all seven species tested so far revealed no differences between eurythermal and stenothermal species.

Effects of Aging Versus Noise Exposure on Auditory System in Individuals With Normal Audiometric Thresholds.

Background: The study aims at investigating the effect of aging and noise exposure on the auditory system using auditory brainstem responses (ABRs), distortion product otoacoustic emissions (DPOAEs), and contralateral suppression of OAEs (CSOAEs). The objective was to compare DPOAEs, CSOAEs, and ABR in aged and noise-exposed individuals with the normal, to find an indicator for early diagnosis of auditory damage.Methods: Sixty adult male participants were divided into 3 groups. Group 1 included individuals not exposed to occupational noise and group 3 included individuals exposed to occupational noise who were <35 years of age. Group 2 consisted of individuals with an age range of 45-65 years without any occupational noise exposure. DPOAE fine structure was studied at 8 points per octave at different F2 frequencies. Transient evoked otoacoustic emissions (TEOAEs) were measured with and without contralateral broad band noise (BBN) at 30 dB SL (CSOAEs). ABR was recorded using click stimuli at different levels, from 90 dB nHL down to 50 dB nHL. The absolute amplitude and peak latencies for peaks I, III, and V; and the wave V/I amplitude ratio were analyzed.Results: In CSOAEs, group 1 showed greater contralateral suppression when compared to group 2 and group 3. The amplitude of ABR wave I and the wave V/I ratio showed a significant difference between the 3 groups, and there was a reduction in amplitude of wave I for groups 2 and 3.Conclusion: The findings indicate that the functioning of the auditory system is affected by occupational noise exposure and aging. CSOAEs, ABR wave I amplitude, and wave V/I amplitude ratio serve as reliable markers in the identification of hidden hearing loss.

Comparing Simultaneous Electrocochleography and Auditory Brainstem Response Measurements Using Three Different Extratympanic Electrodes.

Various extratympanic recording electrodes have been used to make electrocochleography (ECochG) and auditory brainstem response (ABR) measurements in clinics, translational research, and basic science laboratories. However, differences may exist in ECochG and ABR measurements depending on the different types of extratympanic electrodes that are used. The purpose of this research is to compare simultaneously recorded ECochG and ABR responses using three different extratympanic electrodes. This research helps clinicians and researchers to understand how electrode types and recording sites influence EcochG and ABR results. In addition, our findings could provide more normative data to the ECochG and ABR literature as well as give perspective on a preferred electrode approach when performing simultaneous ECochG and ABR testing. Ours was a repeated-measures study with measurements being made from individual participants on two separate sessions. Twenty young adult females with normal hearing. A three-channel recording system was used to simultaneously record ECochG and ABR measurements in response to alternating polarity click stimuli. In each session, measurements were simultaneously recorded with a TipTrode electrode and one of the tympanic membrane (TM) electrodes. Suprathreshold summating potential (SP) and action potential (AP) of the ECochG and waves I, III, and V of the ABR, and threshold responses (AP and wave V) were identified. Compared with the ear canal TipTrode electrode, TM electrodes yielded suprathreshold amplitudes that were larger than those from the ear canal electrode, smaller SP-AP ratios, lower AP thresholds, and less variability. These findings can help guide choices made by clinicians, translational investigators, and basic science researchers on which type of extra-tympanic electrode to use for their intended purpose.

The difference between Chirp &amp; Click stimulation in Diagnostic Auditory Brainstem Response in assessment of hearing among age group between 1-10 years Iraqi children

Background: Aim: To compare the response of human auditory brain stem evoked by clicks stimuli and chirps. Patients and Methods: A study of cross-sectional design was chosen to evaluate the objective of the study. Children between 1-10 years were enrolled from the attendants of the Dept. of Surgery and Audiology, Al-Jamhoori Teaching Hospital, Ministry of Health /Nineveh health Directorate, and the outpatient clinics in al-alwiyah teaching hospital for children and done in the privet clinics of the researchers. The data collection extended over the period from 2019 January to 2020 August. A total number of 70 children involved in the study according to the parents’ complaints, full history taken and the clinical examination by otoscopy. The probable conductive problem excluded by using the Tympanometry. Moreover, free field test was done before chirp and click. Paired t-test was used for the statistical analysis. Results: The males represent (44.3%) and the females (55.7%). The mean age of children included was 49 months ± 27.7 SD. Wave V of the chirp shows lower latency means in all intensities in comparison with that of click stimuli. While waves I and III, show longer latency as the intensity go down, but the differences between chirp and click are insignificant. Wave V amplitudes getting lower values as the intensity decreasing in both chirp and click and become significantly higher than that of click. Wave I and III show decreasing amplitudes with the decreasing intensity in both chirp and click, with higher amplitudes in click in comparing with that of chirp, which are insignificant statistically down to below 70 dBnHL. Conclusions: The chirp stimuli are highly significant and more efficient from the click in the detection of hearing loss among the children regarding both latency and amplitude particularly at wave V.

Auditory evoked potentials: Differences by sex, race, and menstrual cycle and correlations with common psychoacoustical tasks.

Auditory brainstem responses (ABRs) and auditory middle-latency responses (AMLRs) to a click stimulus were measured in about 100 subjects. Of interest were the sex differences in those auditory evoked potentials (AEPs), the correlations between the various AEP measures, and the correlations between the AEP measures and measures of otoacoustic emissions (OAEs) and behavioral performance also measured on the same subjects. Also of interest was how the menstrual cycle affected the various AEP measures. Most ABR measures and several AMLR measures exhibited sex differences, and many of the former were substantial. The sex differences tended to be larger for latency than for amplitude of the waves, and they tended to be larger for a weak click stimulus than for a strong click. The largest sex difference was for Wave-V latency (effect size ~1.2). When subjects were dichotomized into Non-Whites and Whites, the race differences in AEPs were small within sex. However, sex and race interacted so that the sex differences often were larger for the White subjects than for the Non-White subjects, particularly for the latency measures. Contrary to the literature, no AEP measures differed markedly across the menstrual cycle. Correlations between various AEP measures, and between AEP and OAE measures, were small and showed no consistent patterns across sex or race categories. Performance on seven common psychoacoustical tasks was only weakly correlated with individual AEP measures (just as was true for the OAEs also measured on these subjects). AMLR Wave Pa unexpectedly did not show the decrease in latency and increase in amplitude typically observed for AEPs when click level was varied from 40 to 70 dB nHL (normal Hearing Level). For the majority of the measures, the variability of the distribution of scores was greater for the males than for the females.

Auditory brainstem response asymmetries in older adults: An exploratory study using click and speech stimuli.

BackgroundSome evidence suggests that young adults exhibit a selective laterality of auditory brainstem response (ABR) elicited with speech stimuli. Little is known about such an auditory laterality in older adults.ObjectiveThe aim of this study was to investigate possible asymmetric auditory brainstem processing between right and left ear presentation in older adults.MethodsSixty-two older adults presenting with normal hearing thresholds according to their age and who were native speakers of Quebec French participated in this study. ABR was recorded using click and a 40-ms /da/ syllable. ABR was elicited through monaural right and monaural left stimulation. Latency and amplitude for click-and speech-ABR components were compared between right and left ear presentations. In addition, for the /da/ syllable, a fast Fourier transform analysis of the sustained frequency-following response (FFR) of the vowel was performed along with stimulus-to-response and right-left ear correlation analyses.ResultsNo significant differences between right and left ear presentation were found for amplitudes and latencies of the click-ABR components. Significantly shorter latencies for right ear presentation as compared to left ear presentation were observed for onset and offset transient components (V, A and O), sustained components (D and E), and voiced transition components (C) of the speech-ABR. In addition, the spectral amplitude of the fundamental frequency (F0) was significantly larger for the left ear presentation than the right ear presentation.ConclusionsResults of this study show that older adults with normal hearing exhibit symmetric encoding for click stimuli at the brainstem level between the right and left ear presentation. However, they present with brainstem asymmetries for the encoding of selective stimulus components of the speech-ABR between the right and left ear presentation. The right ear presentation of a /da/ syllable elicited reduced neural timing for both transient and sustained components compared to the left ear. Conversely, a stronger left ear F0 encoding was observed. These findings suggest that at a preattentive, sensory stage of auditory processing, older adults lateralize speech stimuli similarly to young adults.

Tone Burst Masseter Vestibular Evoked Myogenic Potentials: Normative Values and Test-Retest Reliability.

Masseter vestibular evoked myogenic potential (mVEMP) is a recent tool for the assessment of vestibular and trigeminal pathways. Though a few studies have recorded mVEMP using click stimuli, there are no reports of these potentials using the more conventional VEMP eliciting stimuli, the tone bursts. The aim of the study is to establish normative values and determine the test-retest reliability of tone burst evoked mVEMP. The research design type is normative study design. Forty-four healthy participants without hearing and vestibular deficits in the age range of 18 to 50 years participated in the study. All participants underwent mVEMP testing using 500 Hz tone-burst stimuli at 125 dB peSPL. Ten participants underwent second mVEMP testing within 1 month of the initial testing to estimate the test-retest reliability. Tone burst mVEMP showed robust responses in all participants. There were no significant ear and sex differences on any mVEMP parameter (p > 0.05); however, males had significantly higher EMG normalized peak-to-peak amplitude than females. Intraclass correlation coefficient (ICC) values of tone burst mVEMP showed excellent test-retest reliability (ICC >0.75) for ipsilateral and contralateral p11 latency, ipsilateral EMG normalized p11-n21 peak to peak amplitude, and amplitude asymmetry ratio. Fair and good test-retest reliability (0.4 < ICC > 0.75) was observed for ipsilateral and contralateral n21 latency, contralateral EMG normalized peak-to-peak amplitude, and amplitude asymmetry ratio. Tone burst mVEMP is a robust and reliable test for evaluating the functional integrity of the vestibulomasseteric reflex pathway.

Time-domain and frequency-domain effects of tensor tympani contraction on middle ear sound transmission in gerbil

The middle ear is a high-fidelity, broadband impedance transformer that transmits acoustic stimuli at the eardrum to the inner ear. It is home to the two smallest muscles in mammalian species, which modulate middle ear transmission. Of this pair, the function of the tensor tympani muscle (TTM) has remained obscure. We investigated the acoustic effects of this muscle in young adult gerbils. We measured changes in middle ear vibration produced by pulse-train-elicited TTM contraction – in the time-domain with a click stimulus and in the frequency-domain with multitone zwuis stimuli. In our click experiments, there was generally a small reduction in the primary peak of the response and a slight increase in the subsequent ringing, but there was essentially no change in the delay of the click response at the umbo (less than 1 µs change). In our multitone experiments, there were consistent patterns of attenuation and enhancement in the velocity responses at the umbo and ossicles. TTM contraction produced a narrow band of enhancement around 6 kHz (maximally ~5 dB) that can be modeled with an increased stiffness of an overdamped spring-mass resonance. At frequencies below 2 kHz and above 35 kHz, TTM contraction attenuated middle ear vibrations by as much as fivefold.

Auditory Sensory Gating of Speech and Nonspeech Stimuli.

Purpose Auditory sensory gating is a neural measure of inhibition and is typically measured with a click or tonal stimulus. This electrophysiological study examined if stimulus characteristics and the use of speech stimuli affected auditory sensory gating indices. Method Auditory event-related potentials were elicited using natural speech, synthetic speech, and nonspeech stimuli in a traditional auditory gating paradigm in 15 adult listeners with normal hearing. Cortical responses were recorded at 64 electrode sites, and peak amplitudes and latencies to the different stimuli were extracted. Individual data were analyzed using repeated-measures analysis of variance. Results Significant gating of P1-N1-P2 peaks was observed for all stimulus types. N1-P2 cortical responses were affected by stimulus type, with significantly less neural inhibition of the P2 response observed for natural speech compared to nonspeech and synthetic speech. Conclusions Auditory sensory gating responses can be measured using speech and nonspeech stimuli in listeners with normal hearing. The results of the study indicate the amount of gating and neural inhibition observed is affected by the spectrotemporal characteristics of the stimuli used to evoke the neural responses.

Laminar Profile of Auditory Steady-State Response in the Auditory Cortex of Awake Mice.

ObjectiveAuditory steady-state response (ASSR) is a gamma oscillation evoked by periodic auditory stimuli, which is commonly used in clinical electroencephalographic examination to evaluate the neurological functions. Though it has been suggested that auditory cortex is the origin of ASSR, how the laminar architecture of the neocortex contributes to the ASSR recorded from the brain surface remains unclear.MethodsWe used a 16-channel silicon probe to record the local field potential and the single-unit spike activity in the different layers of the auditory cortex of unanesthetized mice. Click-trains with a repetition rate at 40-Hz were present as sound stimuli to evoke ASSR.ResultsWe found that the LFPs of all cortical layers showed a stable ASSR synchronizing to the 40-Hz click stimuli, while the ASSR was strongest in the granular (thalamorecipient) layer. Furthermore, time-frequency analyses also revealed the strongest coherence between the signals recorded from the granular layer and pial surface.ConclusionOur results reveal that the 40-Hz ASSR primarily shows the evoked gamma oscillation of thalamorecipient layers in the neocortex, and that the ASSR may be a biomarker to detect the cognitive deficits associated with impaired thalamo-cortical connection.

Use of an Extra-Tympanic Membrane Electrode to Record Cochlear Microphonics with Click, Tone Burst and Chirp Stimuli

This study determined electrocochleography (ECochG) parameter settings to obtain cochlear microphonics (CM) with less invasive flexible extra-tympanic membrane electrodes. In 24 adult normal-hearing subjects, CMs were elicited by presenting click stimuli at 100 dBnHL, tone bursts (2 kHz) and broadband (BB) CE-chirps® LS (Interacoustics, Middelfart, Denmark), both at 80 dBnHL. Different high-pass filters (HPFs) (3.3 Hz and 100 Hz, respectively) were used to investigate response quality of the CM. CMs were successfully obtained in 92–100% with click-, 75–83% with 2 kHz tone burst- and 58–63% with CE-chirp®-LS stimuli. Click stimuli elicited significantly larger CM amplitudes compared to 2 kHz tone bursts and BB CE-chirp® LS (Interacoustics, Middelfart, Denmark). No significant differences were found between the two different high-pass filter (HPF) settings. The present study shows that it is possible to obtain clear CMs with the flexible extra-tympanic membrane electrodes using click stimuli. In contrast to 2 kHz tone bursts and CE-chirp® (Interacoustics, Middelfart, Denmark) LS, clicks show a significantly higher success rate and are the preferred stimuli to confirm the presence or absence of CMs.

Medial olivocochlear reflex effects on amplitude growth functions of long- and short-latency components of click-evoked otoacoustic emissions in humans.

Functional outcomes of medial olivocochlear reflex (MOCR) activation, such as improved hearing in background noise and protection from noise damage, involve moderate to high sound levels. Previous noninvasive measurements of MOCR in humans focused primarily on otoacoustic emissions (OAEs) evoked at low sound levels. Interpreting MOCR effects on OAEs at higher levels is complicated by the possibility of the middle-ear muscle reflex and by components of OAEs arising from different locations along the length of the cochlear spiral. We overcame these issues by presenting click stimuli at a very slow rate and by time-frequency windowing the resulting click-evoked (CE)OAEs into short-latency (SL) and long-latency (LL) components. We characterized the effects of MOCR on CEOAE components using multiple measures to more comprehensively assess these effects throughout much of the dynamic range of hearing. These measures included CEOAE amplitude attenuation, equivalent input attenuation, phase, and slope of growth functions. Results show that MOCR effects are smaller on SL components than LL components, consistent with SL components being generated slightly basal of the characteristic frequency region. Amplitude attenuation measures showed the largest effects at the lowest stimulus levels, but slope change and equivalent input attenuation measures did not decrease at higher stimulus levels. These latter measures are less commonly reported and may provide insight into the variability in listening performance and noise susceptibility seen across individuals.NEW & NOTEWORTHY The auditory efferent system, operating at moderate to high sound levels, may improve hearing in background noise and provide protection from noise damage. We used otoacoustic emissions to measure these efferent effects across a wide range of sound levels and identified level-dependent and independent effects. Previous reports have focused on level-dependent measures. The level-independent effects identified here may provide new insights into the functional relevance of auditory efferent activity in humans.