Electrically evoked auditory brainstem responses in cochlear implant patients.

Electrically evoked auditory brainstem responses (EABR) were recorded in completely deaf patients implanted with Ineraid multichannel cochlear implants. Clear and reproducible EABR were obtained from all patients. Parametric differences with auditory brainstem responses (ABR) were demonstrated and can be explained by the different natures of both types of stimulations (electric versus acoustic). Evidence is given that other well-known properties of auditory evoked responses, like 'binaural interaction' or suppression of responses in a forward masking paradigm, can be observed in EABR of implanted patients.     

Electrically evoked auditory steady-state responses in a guinea pig model: latency estimates and effects of stimulus parameters

Cochlear implant speech processors typically extract envelope information of speech signals for presentation to the auditory nerve as modulated trains of electric pulses. Recent studies showed the feasibility of recording, at the scalp, the electrically evoked auditory steady-state response using amplitude-modulated electric stimuli. Sinusoidally amplitude-modulated electric stimuli were used to elicit such responses from guinea pigs in order to characterize this response. Response latencies were derived to provide insight regarding neural generator sites. Two distinct sites, one cortical and another more peripheral, were indicated by latency estimates of 22 and 2 ms, respectively, with the former evoked by lower (13-49 Hz) and the latter by higher (55-320 Hz) modulation frequencies. Furthermore, response amplitudes declined with increasing carrier frequency, exhibited a compressive growth with increasing modulation depths, and were sensitive to modulation depths to as low as 5%.     

Electrically evoked auditory nerve responses in the cochlea with normal outer hair cells

As hybrid cochlear implant devices are increasingly used for restoring hearing in patients with residual hearing, it is important to understand electrically evoked responses in cochleae having functional hair cells. To test the hypothesis that extracochlear electrical stimulation (EES) from sinusoidal current can provoke an auditory nerve response with normal frequency selectivity, the EES-evoked compound action potential(ECAP) was investi-gated in this study. Brief sinusoidal electrical currents, delivered via a round window electrode, were used to e-voke ECAP. The ECAP waveform was observed to be the same as the acoustically evoked CAP(ACAP), except for a shorter latency. The input/output and intensity/latency functions of ACAPs and ECAPs were also similar. The maximum acoustic masking for both ACAP and ECAP occurred near probe frequencies. Since the masked tuning curve of a CAP reflects the frequency selectivity of neural excitation, these data demonstrate a highly specific acti-vation of the auditory nerve, which would result in high degree of frequency selectivity. This frequency selectivity likely results from the cochlear traveling wave caused by electrically stimulated outer hair cells.     

Human auditory steady-state responses

Steady-state evoked potentials can be recorded from the human scalp in response to auditory stimuli presented at rates between 1 and 200 Hz or by periodic modulations of the amplitude and/or frequency of a continuous tone. Responses can be objectively detected using frequency-based analyses. In waking subjects, the responses are particularly prominent at rates near 40 Hz. Responses evoked by more rapidly presented stimuli are less affected by changes in arousal and can be evoked by multiple simultaneous stimuli without significant loss of amplitude. Response amplitude increases as the depth of modulation or the intensity increases. The phase delay of the response increases as the intensity or the carrier frequency decreases. Auditory steady-state responses are generated throughout the auditory nervous system, with cortical regions contributing more than brainstem generators to responses at lower modulation frequencies. These responses are useful for objectively evaluating auditory thresholds, assessing suprathreshold hearing, and monitoring the state of arousal during anesthesia.     

Effect of noise on auditory evoked responses in awake guinea pigs

Changes in the auditory nerve action potential (AP), evoked responses from the inferior colliculus (IC-ER) and auditory cortex (AC-ER) were assessed after exposure to white noise of 120 dB SPL for 1 h in awake guinea pigs. Auditory thresholds were estimated with the aid of averaged AP, IC-ER and AC-ER, besides the threshold shifts also the changes in amplitude-intensity functions were evaluated. Auditory thresholds for tone pips and clicks increased by 20-30 dB 1 h after exposure and were similar in all the three investigated structures. The maximum threshold shifts for tone pips were observed at 8 kHz and were 33.2 +/- 12.9 dB for AP, 30.4 +/- 12.7 dB for IC-ER and 30.8 +/- 13.0 dB for AC-ER (n = 20). The thresholds recovered to preexposure levels within one week. Reduction in AP and IC-ER amplitudes 1 h after exposure was similar, the amplitude-intensity functions were shifted by 20-40 dB. In contrast, the amplitude-intensity functions in the auditory cortex 1 h after exposure were steeper than before exposure and this amplitude enhancement was present for 24 h after exposure. The enhancement of the AC-ER which resembles recruitment and which may be a sign of hypersensitivity of the animal to auditory stimuli was present only when the animals exposed to noise were awake. The noise exposure in animals anaesthetized with urethane reduced the amplitude-intensity functions of all three recorded potentials.     

正常青年人多频稳态听觉诱发反应测试

目的 :测定正常青年人多频稳态听觉诱发反应 (ASSR)阈值 ,为临床诊断提供客观依据。方法 :选正常青年人 2 2例 (4 4耳 ) ,行ASSR阈值测试。结果 :在 0 .2 5～ 8.0kHz频区间 ,ASSR平均阈值约在 4 0～ 6 0dBHL之间 ,从低频到高频其阈值越来越高 ,0 .2 5kHz、0 .5kHz、1.0kHz处的ASSR平均阈值约为 4 0dBHL ,2 .0kHz处约为 4 5dBHL ,4 .0kHz处约为 5 0dBHL ,8.0kHz处约为 6 0dBHL。ASSR阈值与纯音听阈间差值多在2 5～ 5 5dBHL之间 ,从低频到高频其阈差值越来越高 ,0 .2 5kHz处的差值约为 2 5dBHL ,0 .5kHz处约30dBHL ,1.0kHz处约 35dBHL ,2 .0kHz处约 4 0dBHL ,4 .0kHz处约 5 0dBHL ,8.0kHz处约 5 5dBHL。结论 :正常青年人ASSR阈值与纯音听阈间有一定差值。利用这一差值 ,通过测试ASSR阈值可推断出被检查者纯音听阈的阈值     

Aided auditory steady-state responses in infants

Infants with hearing loss routinely receive hearing aids several months before reliable behavioral responses to amplified sound can be observed. This necessitates objective measures to validate hearing-aid fittings. A single report has demonstrated the use of ASSRs to determine aided thresholds in children but data in young infants is still lacking. The current study explored aided ASSR compared to unaided ASSR thresholds and subsequent behavioral thresholds in a group of six young infants with hearing loss who received hearing aids between three and six months of age. Aided ASSR thresholds were obtained in 83% of frequencies where aided behavioral thresholds were obtained, with a mean threshold difference of 13±13 dB. The aided ASSR-based threshold estimates were within 15 dB of behavioral thresholds in 63% of cases, indicating a moderate correlation (r = 0.55). Comparing aided and unaided ASSR measurements revealed an average functional gain of 36±15 dB. These results indicate that ASSRs can provide the first evidence of robust hearing aid benefit in young infants several months before behavioral responses are observed.     

Aided auditory steady-state responses in infants

Infants with hearing loss routinely receive hearing aids several months before reliable behavioral responses to amplified sound can be observed. This necessitates objective measures to validate hearing-aid fittings. A single report has demonstrated the use of ASSRs to determine aided thresholds in children but data in young infants is still lacking. The current study explored aided ASSR compared to unaided ASSR thresholds and subsequent behavioral thresholds in a group of six young infants with hearing loss who received hearing aids between three and six months of age. Aided ASSR thresholds were obtained in 83% of frequencies where aided behavioral thresholds were obtained, with a mean threshold difference of 13+/-13 dB. The aided ASSR-based threshold estimates were within 15 dB of behavioral thresholds in 63% of cases, indicating a moderate correlation (r = 0.55). Comparing aided and unaided ASSR measurements revealed an average functional gain of 36+/-15 dB. These results indicate that ASSRs can provide the first evidence of robust hearing aid benefit in young infants several months before behavioral responses are observed.     

Electrically evoked responses in Cochlear implant patients

Highly reproducible recordings of evoked responses elicited by electrical stimulation of the auditory nerve were obtained in a group of 4 totally deaf patients implanted with a multichannel intracochlear prosthesis. They were compared to auditory evoked responses obtained in a normal-hearing subject tested with the same equipment. The most striking observation drawn from these data is certainly the close resemblance, at all latencies, between evoked responses elicited by electrical stimulation and those elicited by acoustic stimulation. The remarkable correspondence of waveform morphology, waveform amplitude and interpeak latencies provides indirect evidence that the same sequence of events is triggered in the central auditory system in both cases. Those aspects of the responses which differ significantly are easily interpreted by the physical and physiological properties of the different types of stimulation.     

Artifactual responses when recording auditory steady-state responses

OBJECTIVE: The goal of this study was to investigate, in hearing-impaired participants who could not hear the stimuli, the possibility of artifactual auditory steady-state responses (ASSRs) when stimuli are presented at high intensities. DESIGN: ASSRs to single (60 dB HL) and multiple (20 to 50 dB HL; 500 to 4000 Hz) bone-conduction stimuli as well as single 114 to 120 dB HL air-conduction stimuli, were obtained using the Rotman MASTER system, using analog-to-digital (A/D) conversion rates of 500, 1000, and 1250 Hz. Responses (p < 0.05) were considered artifactual when their numbers exceeded that expected by chance. In some conditions, we also obtained ASSRs to "alternated" stimuli (stimuli inverted and ASSRs to the two polarities averaged). A total of 17 subjects were tested. RESULTS: Bone conduction results: 500 Hz A/D rate: Large-amplitude (43 to 1558 nV) artifactual ASSRs were seen at 40 and 50 dB HL for the 500 Hz carrier frequency. Smaller responses (28 to 53 nV) were also recorded at 20 dB HL for the 500 Hz carrier frequency. Artifactual ASSRs (17 to 62 nV) were seen at 40 dB HL and above for the 1000 Hz carrier frequency and at 50 dB HL for the 2000 Hz carrier frequency. Alternating the stimulus polarity decreased the amplitude and occurrence of these artifactual responses but did not eliminate responses for the 500 Hz carrier frequency at 40 dB HL and above. No artifactual responses were recorded for 4000 Hz stimuli for any condition. 1000 Hz A/D rate: Artifactual ASSRs (15 to 523 nV) were seen at 50 dB HL and above for the 500 Hz carrier frequency and 40 dB HL and above for the 1000 Hz carrier frequency. Artifactual responses were also obtained at 50 dB HL for a 2000 Hz carrier frequency but not at lower levels. Artifactual responses were not seen for the 4000 Hz carrier frequency. Alternating the stimulus polarity removed the responses for the 1000 and 2000 Hz carrier frequencies but did not change the results for the 500 Hz carrier frequency. 1250 Hz A/D rate: Artifactual ASSRs (16 to 220 nV) were seen at 50 dB HL and above for the 500 Hz carrier frequency and 60 dB HL and above for the 1000 Hz carrier frequency. Alternating the stimulus polarity removed the responses for the 1000 Hz carrier frequency but did not change the results for the 500 Hz carrier frequency. There were no artifactual responses at 2000 and 4000 Hz. Air conduction results: 500 Hz A/D rate: Artifactual ASSRs (49 to 153 nV) were seen for 114 to 120 dB HL stimuli for 500 and 1000 Hz carrier frequencies. Alternating the stimulus polarity removed these responses. There were no artifactual responses at 2000 and 4000 Hz. 1000 and 1250 Hz A/D rates: Artifactual ASSRs (19 to 55 nV) were seen for a 120 dB HL stimulus for a 1000 Hz carrier. Alternating the stimulus polarity removed these responses. CONCLUSIONS: High-intensity air- or bone-conduction stimuli can produce spurious ASSRs, especially for 500 and 1000 Hz carrier frequencies. High-amplitude stimulus artifact can result in energy that is aliased to exactly the modulation frequency. Choice of signal conditioning (electroencephalogram filter slope and low-pass cutoff) and processing (A/D rate) can avoid spurious responses due to aliasing. However, artifactual responses due to other causes may still occur for bone-conduction stimuli 50 dB HL and higher (and possibly for high-level air conduction). Because the phases of these spurious responses do not invert with inversion of stimulus, the possibility of nonauditory physiologic responses cannot be ruled out. The clinical implications of these results are that artifactual responses may occur for any patient for bone-conduction stimuli at levels greater than 40 dB HL and for high-intensity air-conduction stimuli used to assess patients with profound hearing loss.     

Comparing auditory steady-state responses amplitude evoked by simultaneous air- and bone-conducted stimulation in newborns

Objective: The aim of this study was to evaluate the potential interactions of the simultaneous presentation of air- and bone-conducted stimuli on auditory steady-state responses (ASSR) amplitude in newborns. Design: Bone- and air-conducted stimuli were sinusoidal carrier tones of 500 and 2000?Hz respectively modulated in amplitude (95% depth). Air- and bone- conducted stimuli were either simultaneously recorded in the same ear using insert earphones and bone vibrator respectively, or recorded individually (single stimulation). Study sample: Sixty-nine well babies (135 ears) with ages ranging from 1 to 16 days (mean of 9.2?±?7.9 days) were tested in this study. Results: No significant changes in ASSR amplitude by air-conducted stimuli were observed when evoked by simultaneous or single stimulation. The same trend prevailed for ASSR amplitudes evoked by bone-conducted stimuli. Conclusions: The results of this study suggest that the simultaneous stimulation of air-and bone-conducted stimuli does not alter ASSR amplitude values in well babies. Therefore, the results support the use of this technique as a potential hearing screening tool to discriminate between conductive and sensorineural hearing loss.     

Electrically evoked middle-latency auditory potentials in cochlear implant candidates

Electric middle-latency auditory evoked responses (EMLRs) to transtympanic promontory stimulation were obtained from 19 of 22 ears of profoundly hearing-impaired patients evaluated for cochlear implant candidacy. The EMLRs were characterized by positive polarity peaks with latencies ranging from 20 to 30 ms, with the majority of responses exhibiting peaks in the range of 26 to 30 ms. Generally, the configuration of the EMLRs closely resembled the configuration of acoustic MLRs. While in most cases, behavioral thresholds to identical promontory stimulation were slightly lower, EMLR thresholds closely approximated behavioral electrical promontory thresholds. The EMLR thresholds correlated positively with implanted thresholds and exhibited a negative correlation with implanted dynamic current ranges.     

Recording auditory steady-state responses in young infants

OBJECTIVES: This study examined the auditory steady-state responses evoked by amplitude-modulated (AM), mixed-modulated (MM), exponentially-modulated (AM2), and frequency-modulated (FM) tones in 50 newborn infants (within 3 days of birth) and in 20 older infants (within 3-15 wk of birth). Our hypothesis was that MM and AM2 tonal stimuli would evoke larger responses than either the AM or FM tones, and that this increased size would make the responses more readily detectable. DESIGN: Multiple auditory steady-state responses were recorded to four tonal stimuli presented simultaneously to each ear at 50 dB SPL. The carrier frequencies of the stimuli were 500, 1000, 2000, and 4000 Hz and the modulation rates were between 78 and 95 Hz. Recordings lasting 12 minutes were obtained for each of the three types of modulation: 100% AM, MM (100% AM and 20% FM) and AM2. In six infants, responses to 20% FM were also recorded. RESULTS: In newborn infants, MM and AM2 stimuli produced responses that were on average 15% larger than AM stimuli. For AM, MM, and AM2 stimuli, the percentage of significant responses was 67%, 73%, 76%, respectively. Responses to FM stimuli were clearly evident in newborn infants and were about half the amplitude of the AM responses. Responses recorded in the older infants were 17% larger when evoked by MM and AM2 stimuli, rather than AM stimuli. Responses in the older infants were, on average, 32% larger and showed a higher incidence of significant responses than for infants in the first 3 days of life. For AM, MM, and AM2 stimuli, the percentage of significant responses was 82%, 82%, 84%, respectively. In both newborn and older infants, the overall percentage of significant responses was decreased by the 500 Hz results, which showed lower amplitudes and were less frequently detected than responses evoked by other frequencies. CONCLUSIONS: The responses to MM and AM2 tones were larger than those evoked by AM tones. Using these stimuli will increase the reliability and efficiency of evoked potential audiometry in infancy. Responses at 50 dB SPL are more easily detected at 3-15 wk of age than in the first few days after birth. Comprehensive frequency-specific testing of hearing using steady-state responses will likely be more accurate if postponed until after the immediate neonatal period.     

Comparison of auditory steady-state responses and tone-burst auditory brainstem responses in normal babies

OBJECTIVE: To follow the development of tone-burst auditory brainstem response (TB-ABR) and auditory steady-state response (ASSR) thresholds in a group of normal babies through the first 6 wk of life. DESIGN: This longitudinal study involved assessment at four data-collection points. TB-ABR and ASSR thresholds to 500-Hz and 4-kHz stimuli were established in 17 full-term subjects at 0, 2, 4, and 6 wk of age. Stimulus-modulation rates for ASSR assessment were 74 Hz (for 500-Hz tones) and 95 Hz (for 4-kHz tones). TB-ABR responses were recorded to stimuli presented at 39.1 Hz. RESULTS: Mean ASSR thresholds (calibrated in dBHL) at 500 Hz ranged from 44.4 to 39.7 dB HL across the recording period, and at 4 kHz they ranged from 37.9 to 32.1 dB HL. TB-ABR thresholds (calibrated in dBnHL) were significantly lower, ranging from 36.8 to 36.2 dB nHL at 500 Hz and from 16.5 to 15.9 dB nHL at 4 kHz. However, when the stimuli used for each test were calibrated in the same units (peak equivalent dB SPL), the results were similar. That is, the differences between the two techniques were only an artifact of the calibration. ASSR thresholds were more variable than TB-ABR, particularly at the neonatal measurement point. Within-subject changes across the test period were observed for ASSR thresholds but not for TB-ABR. CONCLUSIONS: The longitudinal findings presented in this study suggest that for normal neonates, the TB-ABR technique may offer a more reliable basis for prediction of hearing levels than ASSR assessment. This is not because TB-ABR thresholds (calibrated in dBnHL) are lower, but because the response is less affected by maturational development in the first weeks of life and is less variable across subjects.     

Effect on brainstem auditory evoked responses of posterior semicircular canal occlusion in guinea pigs

The site of origin of benign paroxysmal positional vertigo is the posterior semicircular canal and when persistent, the condition is known as cupulolithiasis. Singular neurectomy is the current procedure of choice for the treatment of incapacitating cupulolithiasis. The neurectomy is difficult to learn and carries a significant risk of hearing loss. An alternative procedure, whereby the posterior canal is occluded, is discussed. This was performed on 11 guinea pigs and the effect on hearing was measured using brainstem evoked audiometry. Eight animals showed no hearing loss while the other three had a mild to moderate loss of hearing due to intra-operative complications. The effect of canal plugging on hearing compares favorably with the hearing results obtained with singular neurectomy. Posterior semicircular canal occlusion is suggested as a safer and technically easier treatment for incapacitating cupulolithiasis.     

Electrically evoked auditory brain stem responses for lateral and medial placement of the Clarion HiFocus electrode

OBJECTIVE: The purpose of this study was to compare the electrically evoked auditory brain stem response (EABR) for lateral and medial placement of the Clarion HiFocus cochlear implant electrode array via the electrode positioning system (EPS). DESIGN: Twenty-five adult and pediatric cochlear implant recipients participated in the study. Intraoperatively recorded EABRs were evoked by stimuli via three intracochlear electrodes representing apical, medial, and basal locations, and responses were elicited before and after positioner insertion. Evoked potential measures of wave V amplitude and threshold were examined for statistical significance using ANOVA for repeated measures and Chi-Square methods. RESULTS: For a given supra-threshold stimulus level, the increase in EABR wave V amplitude was significantly larger after EPS placement compared to before EPS placement for electrodes 1 (apical) and 13 (basal). Likewise, when the stimulus was decreased to obtain a minimal amplitude, the wave V threshold was significantly lower after EPS placement for electrodes 7 (medial) and 13. The number of measurements that showed decreased wave V threshold after EPS insertion was significantly dependent on intracochlear electrode location. CONCLUSIONS: Placement of the Clarion Electrode Positioning System following HiFocus electrode insertion resulted in a reduction in the electrical current required to activate the auditory system. The effect of the EPS was greatest for the basal location, demonstrated by lower wave V thresholds and a larger percentage increase in wave V amplitude. The EABR reflected electrophysiologic changes relative to lateral-to-medial changes in intracochlear electrode position due to the EPS.