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Electrophysiologic Assessment of Hearing
... Middle and long latency-evoked potentials represent synchronous activity of large groups of neurons at the level of the auditory midbrain and cortex. In clinical practice, however, these are much less used since they are considerably more depending upon attention and subject state (awake, sedated or under anesthesia) compared with the hearing tests mentioned above (Brown 2005). Auditory neuropathy and central auditory processing disorders are two types of central hearing loss that are diagnosed more and more frequently. ...
... In general, it is not surprising that our knowledge of the central auditory system is limited compared with the more accessible peripheral system. Consistent (psycho-) physiological tests (such as middle and long-latency evoked potentials) are more complex towards the auditory cortex and are difficult to interpret, compared with more objective tests (such as OAEs, brainstem audiometry or pure tone audiograms), since these tests are not (yet) fully developed until after approximately 10 years of age (Brown 2005). One particular type of sensorineural hearing loss due to aging (presbyacusis) deserves to be mentioned separately. ...
In this thesis, different aspects of central auditory processing in the inferior colliculus (IC) of young-adult mice and rats are described. With the “in vivo patch-clamp” technique we investigated the contribution of membrane properties and synaptic integration of excitatory and inhibitory inputs to sound processing in an intact auditory system. We describe how biocytin cell injections and vesicular glutamate transporter -1 and -2 stainings can be used to confirm localization of measured cells and to identify the central nucleus of the IC. Next, constant current injections were used to characterize the firing patterns and basic membrane properties of IC neurons. New findings include the presence of electrical synapses (spikelets), the absence of onset firing, the absence of a classic pause in buildup neurons and a description of accelerating cells. In addition, spontaneous excitatory synaptic potentials contributed to the irregularity of spike patterns!
. The clearest mechanism in duration tuning seems to be synaptic integration of excitatory and inhibitory inputs and synaptic adaptation, while AM tuning seems to be more influenced by the presence of calcium-dependent potassium channels and the absence of adaptation. Hyperpolarization-activated voltage-dependent sodium/potassium channel Ih can additionally shape the incoming auditory signal. FM tuning is largely determined by the synaptic integration of excitatory and inhibitory inputs, while membrane properties and ion-channels play a lesser role. By showing how the diversity in membrane properties and synaptic inputs can lead to specific tuning for complex sounds, we provide a cellular explanation for the contribution of the IC to central auditory processing.
... Five to seven peaks occurring within a timeframe of less than 10 msec constitute the ABR. All these waves provide information regarding the neural auditory pathway (18) and provide accurate estimations of the threshold. Toneburst and click ABRs are the most common tests to estimate auditory sensitivity. ...
Background/aims:
Celiac disease (CD) is an autoimmune and genetic disease that is triggered by gluten intolerance. We aimed to investigate whether Celiac disease have any effect on Auditory Brainstem Response (ABR) waves compare to a healthy control group, and present its association with sensorineural hearing loss (SNHL).
Materials and methods:
Thirty-eight patients aged 2 to 16 years old were included in the study. The patients had confirmed diagnosis of Celiac disease through duodenal biopsies and transglutaminase Antibody (Ab) (+). The control group consisted of 18 children aged 3 to 17 years old who were all admitted to the pediatric gastroenterology department due to complaints of constipation and transglutaminase Ab (-).All children underwent Auditory-Brain-Stem-Evoked Responses (ABR). The data were gathered using click stimulus at 10/s frequency 90dB HL.
Results:
The results of ABR examination did not show any difference between the patient group and control group as regards the latency of the waves I, III, V. No difference was observed between the two groups in the interpeak latecies I-III, I-V and III-V. None of the patients was observed to have clinical hearing loss.
Discussion:
The exact pathogenesis of neurological damages observed in Celiac disease is still unknown. Humoral immune mechanisms are the most frequently attributed cause.
Conclusion:
Although no significant difference was found in hearing values between the study group and healthy control group, there is a need for further research on this subject.
... Thorough clinical general and all body systems' examination [10,11] with special emphasis on craniofacial dysmorphism and any other concomitant congenital malformations [12]. ENT examination laying stress on palatal examination and hearing assessment using audiometry [13] and or brain stem auditory evoked potential [14]. Family pedigree construction to elicit consanguinity and its degree if any as well as family history of similar conditions [15]. ...
Neonatal jaundice is a common cause of sensorneural hearing loss in children.
We aimed to detect the neurotoxic effects of pathologic hyperbilirubinemia on brain stem and auditory tract by auditory brain stem evoked response (ABR) which could predict early effects of hyperbilirubinemia.
This case-control study was performed on newborns with pathologic hyperbilirubinemia. The inclusion criteria were healthy term and near term (35 - 37 weeks) newborns with pathologic hyperbilirubinemia with serum bilirubin values of ≥ 7 mg/dL, ≥ 10 mg/dL and ≥14 mg/dL at the first, second and third-day of life, respectively, and with bilirubin concentration ≥ 18 mg/dL at over 72 hours of life. The exclusion criteria included family history and diseases causing sensorineural hearing loss, use of auto-toxic medications within the preceding five days, convulsion, congenital craniofacial anomalies, birth trauma, preterm newborns < 35 weeks old, birth weight < 1500 g, asphyxia, and mechanical ventilations for five days or more. A total of 48 newborns with hyperbilirubinemia met the enrolment criteria as the case group and 49 healthy newborns as the control group, who were hospitalized in a university educational hospital (22 Bahaman), in a north-eastern city of Iran, Mashhad. ABR was performed on both groups. The evaluated variable factors were latency time, inter peak intervals time, and loss of waves.
The mean latencies of waves I, III and V of ABR were significantly higher in the pathologic hyperbilirubinemia group compared with the controls (P < 0.001). In addition, the mean interpeak intervals (IPI) of waves I-III, I-V and III-V of ABR were significantly higher in the pathologic hyperbilirubinemia group compared with the controls (P < 0.001). For example, the mean latencies time of wave I was significantly higher in right ear of the case group than in controls (2.16 ± 0.26 vs. 1.77 ± 0.15 milliseconds, respectively) (P < 0.001).
Pathologic hyperbilirubinemia causes acute disorder on brain stem function; therefore, early diagnosis of neonatal jaundice for prevention of bilirubin neurotoxic effects is essential. As national neonatal hearing screening in not yet established in Iran, we recommend performing ABR for screening of bilirubin neurotoxicity in all cases with hyperbilirubinemia.
The goal of the present study was to determine, across a large number of studies and participants, the threshold estimation performance of the air-conducted tone-evoked auditory brainstem response (ABR) for adult and infant/child groups with either normal hearing or sensorineural hearing loss (SNHL). Overall, 32 studies were included in this meta-analysis, representing results from a total of 1,203 individual participants (i.r., 524 adults or older children, 679 infants or young children; 815 individuals with normal hearing; and 388 individuals with SNHL). results indicate that tone-evoked ABR thresholds in individuals with normal hearing are typically 10 to 20 dB nHL. Tone-ABR thresholds in participants with SNHL are typically 5 to 15 dB higher than pure-tone behavioural thresholds in adult participants and from 10 dB lower to 10 dB higher than pure-tone behavioural thresholds in infants and young children. Importantly, threshold results are quite consistent across studies, and 95% confidence intervals no larger than +/- 5 dB. These results support the recommendation by current guidelines that tone-evoked ABR thresholds be used to guide the initial fitting of amplification in very young infants.
https://cjslpa.ca/files/2000_JSLPA_Vol_24/No_02_33-92/Stapells_JSLPA_2000.pdf
Notched noise can be used to mask the frequency spread of acoustic energy in the brief tonepips that are used to elicit brainstem evoked potentials. Brainstem responses to tonepips and notched noise can therefore be used to evaluate auditory thresholds at particular frequencies. These thresholds are more frequency-specific than those obtained using tonepips alone, and are accurate to within 20 dB of the conventional audiometric thresholds.
Auditory brainstem potentials were recorded from scalp electrodes in 42 infants ranging in gestational age from 25 to 44 weeks. The latencies of the various potential components decreased with maturation. Wave V, evoked by 65-dB sensation level clicks, changed in latency from 9.9 msec at 26 weeks of gestation of 6.9 msec at 40 weeks of gestation. Central conduction times in the auditory pathway also decreased with maturation from 7.2 msec at 26 weeks to 5.2 msec at 40 weeks. The effects of brainstem and cochlear disorders on auditory brainstem potentials were noted in several abnormal infants. The application of all of these techniques could permit an objective definition of both normal and abnormal sensory processes in newborn infants.
We investigated the relationship between results of preoperative transtympanic electrical promontory stimulation, duration of deafness, postoperative implanted psychophysical results, and postoperative speech and speech sound recognition as indicated by a battery of five tests. Our subjects were 10 patients implanted with the Cochlear Corporation multielectrode implant, 1 year postimplantation, with a minimum of 17 active electrodes programmed in the bipolar + 1 mode. The results indicated that preoperative promontory thresholds, the slope of the threshold function, and the duration of auditory deprivation are excellent predictors of postoperative speech and speech sound recognition in the auditory (processor alone) mode. These results have significant implications for patient selection and counseling.
Spontaneous otoacoustic emissions (SOAEs), which occur in about 40% of normal-hearing humans, do not have a firm explanation in auditory theory nor are their distributional properties well understood. To enhance our understanding of SOAEs, we have pooled data from three reports (Hammel, 1983; Strickland, Burns, & Tubis, 1985; Zurek, 1981) to assemble a large enough sample to assess the relevant hypotheses about the effects of ear and gender on their presence. The results, based on loglinear analyses of the pooled sample of 131 normal-hearing subjects, indicated that (a) the prevalence of SOAEs for female subjects [P(S/F) = .533] was significantly higher than that for male subjects [P(S/M) = .268]; (b) the percentage of right ears with SOAEs (36.6%) was significantly greater than that of left ears (25.2%); and (c) right and left ears were not independent with respect to the presence of SOAEs. These results can be explained by assuming that the (a) tendency to exhibit emissions is inherited, perhaps as a sex-linked trait and (b) ears are asymmetric with respect to the anatomical anomalies of the apical portion of the organ of Corti that may precipitate SOAEs.
The thresholds for the short-latency auditory evoked potentials (SLAEPs) to short-duration tones presented in notched-noise masking were evaluated in 20 normal-hearing and 20 hearing-impaired subjects. The differences (dB) between these thresholds (dB nHL) and the pure-tone behavioral thresholds (dB HL) across all 40 subjects were 11.6, 6.1, 6.3 and 0.8 dB for 500, 1,000, 2,000 and 4,000 Hz, respectively. These differences were significantly smaller for the hearing-impaired subjects than for the normal-hearing subjects. Ninety-eight percent of the SLAEP threshold estimations were within 30 dB of the subjects' pure-tone behavioral thresholds and 91% were within 20 dB.
Steady state responses to the sinusoidal modulation of the amplitude or frequency of a tone were recorded from the human scalp. For both amplitude modulation (AM) and frequency modulation (FM), the responses were most consistent at modulation frequencies between 30 and 50 Hz. However, reliable responses could also be recorded at lower frequencies, particularly at 2-5 Hz for AM and at 3-7 Hz for FM. With increasing modulation depth at 40 Hz, both the AM and FM response increased in amplitude, but the AM response tended to saturate at large modulation depths. Neither response showed any significant change in phase with changes in modulation depth. Both responses increased in amplitude and decreased in phase delay with increasing intensity of the carrier tone, the FM response showing some saturation of amplitude at high intensities. Both responses could be recorded at modulation depths close to the subjective threshold for detecting the modulation and at intensities close to the subjective threshold for hearing the stimulus. The responses were variable but did not consistently adapt over periods of 10 min. The 40-Hz AM and FM responses appear to originate in the same generator, this generator being activated by separate auditory systems that detect changes in either amplitude or frequency.
Transient‐evoked otoacoustic emissions (TEOAEs) were measured in 113 normal‐hearing and hearing‐impaired ears to examine repeatability within a test session, which TEOAE parameter (level, TEOAE level‐to‐noise or reproducibility) best identified hearing loss and if the TEOAE separated into frequency‐specific bands identified hearing loss in a corresponding frequency region. TEOAEs and stimulus levels were found to be very repeatable. For broadband TEOAEs, TEOAE level, TEOAE‐to‐noise, and % reproducibility were found to identify hearing loss equally well, based on measurement of the area underlying relative operator characteristic curves. Analysis for frequency‐specific bands showed that separation of normal‐hearing and hearing‐impaired ears depended on frequency, with best identification at 2000 and 4000 Hz, identification at 1000 Hz slightly worse, and virtually no separation between normal‐hearing and hearing‐impaired ears at 500 Hz. Again, all three parameters were essentially equal in identifying hearing loss. Subjective evaluations of presence or absence of TEOAEs was highly correlated between two judges, with good agreement for TEOAEs at 1000, 2000, and 4000 Hz. The findings from this study suggest that TEOAEs will be valuable for clinical use because of their repeatability and identification of hearing‐impaired ears.
The ac (“microphonic”) cochlear potential and the positive dc “endolymphatic” potential have been recorded simultaneously as the exploring electrode was introduced into scala media or as other parameters were varied. Negative intracellular de potentials were demonstrated in the cells of the organ of Corti. The zone of positive endolymphatic potential is bounded by the reticular lamina, not by the basilar membrane. The cochlear microphonic reverses phase as the exploring electrode penetrates the reticular lamina. A dc polarizing current with the positive pole in scala media (and negative in scala tympani) increases the cochlear microphonic just as it does when the positive pole is located in the scala vestibuli. These facts indicate that the source of the ac (microphonic) potential seems clearly to be at the hair‐bearing end of the hair cells and that the source of the dc endolymphatic potential is probably here also, while Reissner's membrane is not the source of either the ac or the dc potential. No steady dc current flow outside scala media was found such as would be expected if stria vascularis were the dc source and if the hair cells modulated a dc current flow through them. The dc endolymphatic potential may be increased by as much as 10 percent if and while the basilar membrane is displaced toward scala vestibuli and may be decreased to 50 percent or less when and while it is displaced toward scala tympani. Isotonic solutions rich in potassium depressed the ac potential and nerve responses when introduced into scala tympani but not when in scala vestibuli only. The. dc potential, however, was not altered by high potassium concentration in scala tympani.
Pediatric cochlear implantation is restricted to patients with stable, bilateral profound sensorineural hearing losses who derive no benefit from conventional amplification. Obtaining reliable audiologic thresholds in a young child with sudden or early-onset hearing loss can be challenging. This study examines the accuracy with which auditory brain-stem response evaluation can predict unaided and aided behavioral thresholds in a child with severe-to-profound hearing loss. Reliable behavioral thresholds were obtained on 119 children who had no measurable click-evoked auditory brainstem responses at instrumentation limits of 100 dB HLn. These data show that an absent auditory brainstem response at 100 dB HLn does not necessarily indicate the absence of measurable unaided hearing for test frequencies ranging from 250 Hz to 4000 Hz. Average aided thresholds of better than 60 dB were present in 43% of the children for 500, 1000, and 2000 Hz and in 53% for 500 and 1000 Hz. Therefore, the absence of a click-evoked auditory brainstem response at 100 dB HLn in a young child is not prima facie evidence of the child's cochlear implant candidacy.
Advances in the diagnosis and intraoperative management of acoustic neuromas have greatly reduced the incidence of neurologic deficits following their removal. Ninety-three patients underwent acoustic tumor removal during a 4½-year period, and hearing preservation was attempted in 20 cases. Hearing was preserved in 65% of the entire series, and excellent results were obtained in tumors less than 1.5 cm. No patient with a tumor greater than 1.5 cm had serviceable hearing preserved when total tumor removal was performed. Two patients, one with neurofibromatosis and one with an acoustic neuroma in an only-hearing ear, had planned partial tumor removal with preservation of hearing. Preoperative auditory brainstem response results were not predictive of postoperative hearing preservation. Intraoperative auditory brainstem response monitoring demonstrated that loss of wave V consistently correlated with loss of hearing postoperatively, whereas persistence of wave V (with a latency prolongation not exceeding 3.00 ms) was predictive of successful hearing preservation regardless of latency increases.
1) To examine the distribution of behavioral hearing thresholds in a group of children who had shown no click-evoked auditory brain stem response (ABR) at maximum presentation levels. 2) To describe the relationship between the 90 Hz steady-state evoked potential (SSEP) and behavioral thresholds in these subjects.
A retrospective study based on clinical findings obtained from 108 infants and young children. Each of these children had shown no recordable ABR to clicks presented at maximum levels (100 dB nHL). SSEP audiograms were obtained using AM/FM tones at the octave frequencies 250 to 4000 Hz. The results of these evoked potential assessments were compared with hearing thresholds established behaviorally.
Click-ABR assessment could not differentiate between the subjects in our sample with total hearing losses and those with useful residual hearing. Although some of the ears were anacusic, more than a quarter showed residual hearing at each of the audiometric frequencies. Furthermore, at least 10% of the behavioral thresholds at each frequency fell within the moderate/severe hearing loss range. A far closer relationship was observed between SSEP and hearing thresholds. On occasions where the SSEP was absent at maximum levels, 99.5% of the ears showed either a total loss or a behavioral threshold within 10 dB of that level. When an SSEP was obtained, the hearing threshold was typically within 5 dB of the SSEP threshold.
The results suggested that in our group of selected subjects, the SSEP technique was able to assess ears with only minimal amounts of residual hearing. Where the brevity of the acoustic click limits both its frequency specificity and its presentation level, the modulated tones used for SSEP testing allow accurate, frequency-specific assessment at high presentation levels.
Ce texte correspond à celui de la lecture du 8 janvier 1861 devant l'Académie de Médecine, bien que le titre ait été modifié.
Thesis (Ph. D.)--University of Washington, 1999. Vita. Includes bibliographical references (leaves [98]-103).
• Correlational analysis was carried out between the auditory brain stem evoked response (BER) threshold, BER latency, and various audiometric indices in 275 ears with varying degrees and configurations of sensorineural hearing loss.
Results confirm the importance of sensitivity in the 1 to 4-kHz region to the brain stem response. Sensitivity over this frequency region is best predicted as 0.6 of the BER threshold. Brain stem evoked response latency in the 70- to 90-dB hearing level range increases about 0.2 ms for each 30-dB increase in the steepness of the audiometric contour between 1 and 4 kHz. Finally, audiometric shape appears to be more important than absolute high-frequency sensitivity in determining BER latency.
(Arch Otolaryngol 104:456-461, 1978)
A new auditory phenomenon has been identified in the acoustic impulse response of the human ear. Using a signal averaging technique, a study has been made of the response of the closed external acoustic meatus to acoustic impulses near to the threshold of audibility. Particular attention has been paid to the waveform of the response at post excitation times in excess of 5 ms. No previous worker appears to have extended observations into this region. The response observed after about 5 ms is not a simple extension of the initial response attributable to the middle ear. The oscillatory response decay time constant was found to change from approximately 1 ms to over 12 ms at about this time. The slowly decaying response component was present in all normal ears tested, but was not present in ears with cochlear deafness. This component of the response appears to have its origin in some nonlinear mechanism probably located in the cochlea, responding mechanically to auditory stimulation, and dependent upon the normal functioning of the cochlea transduction process. A cochlear reflection hypothesis received some support from these results.
THE function of the two populations of sensory cells in the mammalian inner ear is not well understood. Anatomical evidence indicates that the inner hair cells (IHCs) and the outer hair cells (OHCs) play separate roles in the transduction of acoustic stimuli1. Furthermore, there have been numerous proposals attributing different roles to the two hair cell populations in the production of the various cochlear potentials2-5. On the other hand, theoretical considerations and the interpretation of data from several experiments have led to suggestions of different types of interaction between the OHCs and IHCs6-8.
A sequence of seven low-amplitude (nanovolt) potentials that occur in the initial 10 msec following click signals can be recorded from scalp electrodes in human subjects using computer averaging techniques. The potentials, termed auditory brain stem responses, are thought to be the far-field reflection of electrical events originating in the auditory pathway during its course through the brain stem. We have studied auditory brain stem responses in a variety of neurological disorders and found them to be of assistance in evaluating the mechanisms of coma, the localization of midbrain and brain stem tumors, the localization of demyelination of the brain stem, and tumors, the localization of demyelination of the brain stem, and the presence of diminished brain stem circulation.
Steady-state evoked potential responses were measured to binaural amplitude-modulated (AM) and combined amplitude- and frequency-modulated (AM/FM) tones. For awake subjects, AM/FM tones produced larger amplitude responses than did AM tones. Awake and sleeping responses to 30-dB HL AM/FM tones were compared. Response amplitudes were lower during sleep and the extent to which they differed from awake amplitudes was dependent on both carrier and modulation frequencies. Background EEG noise at the stimulus modulation frequency was also reduced during sleep and varied with modulation frequency. A detection efficiency function was used to indicate the modulation frequencies likely to be most suitable for electrical estimation of behavioral threshold. In awake subjects, for all carrier frequencies tested, detection efficiency was highest at a modulation frequency of 45 Hz. In sleeping subjects, the modulation frequency regions of highest efficiency varied with carrier frequency. For carrier frequencies of 250 Hz, 500 Hz, and 1 kHz, the highest efficiencies were found in two modulation frequency regions centered on 45 and 90 Hz. For 2 and 4 kHz, the highest efficiencies were at modulation frequencies above 70 Hz. Sleep stage affected both response amplitude and background EEG noise in a manner that depended on modulation frequency. The results of this study suggest that, for sleeping subjects, modulation frequencies above 70 Hz may be best when using steady-state potentials for hearing threshold estimation.
The electrically evoked brainstem response (EABR) was measured in cochlear implant users who had received either the Ineraid multichannel implant or the Nucleus multichannel implant. Although both implants use a multi-electrode array, they are different in a number of ways. In the Ineraid system the electrodes can be accessed directly through a percutaneous plug and stimulation is generally on four different intracochlear electrodes relative to a common ground outside the cochlea. In the Nucleus implant stimulation is accomplished via an internal coil and stimulation is bipolar between pairs along the 22 electrode array. The ABR waveforms were similar for both groups of subjects, consisting of a series of 3 or 4 positive peaks at the highest levels of stimulation. Using the normal stimulation mode (bipolar for Nucleus and monopolar for Ineraid), users of both devices demonstrated an increase in response amplitude and a decrease in response latency with increases in current level. The threshold of response tended to be higher and growth of the response with level tended to be more gradual for Nucleus users than for Ineraid users. However, with bipolar stimulation for both implant types, when the stimulating electrodes were closely spaced the threshold of response was higher and the growth of amplitude with level was more gradual than the case where the electrodes were separated further. When bipolar stimulation and similar electrode spacing was used, the response growth and threshold were similar for both implant types. Results from neither device showed a strong correlation with performance on word recognition tests.
• We describe a child who emitted a continuous audible sound from his left ear. A high-level spontaneous otoacoustic emission was measured at the frequency of 5.64 kHz with an amplitude of 55 dB sound pressure level. A high-frequency hearing loss was measured in both ears; however, it was more pronounced in the emitting ear. The emission failed to synchronize to external click stimuli. This spontaneous emission is probably related to a cochlear defect, but it should not contribute additionally to the child's existing auditory impairment.
(Arch Otolaryngol Head Neck Surg. 1991;117:674-676)
Otoacoustic emissions can be separated into two interrelated classes according to the type of eliciting stimulus. On the basis of this categorization, four discrete subtypes can be recognized that include spontaneous, transiently evoked, stimulus-frequency, and distortion-product otoacoustic emissions. Methods of recording and findings in the ears of normally hearing humans are reviewed for each emission type.
This study describes a method for recording the electrically evoked, whole-nerve action potential (EAP) in users of the Ineraid cochlear implant. The method is an adaptation of one originally used by Charlet de Sauvage et al. [J. Acoust. Soc. Am. 73, 615-627 (1983)] in guinea pigs. The response, recorded from 11 subjects, consists of a single negative peak that occurs with a latency of approximately 0.4 ms. EAP input/output functions are steeply sloping and monotonic. Response amplitudes ranging up to 160 micro V have been recorded. Slope of the EAP input/output function correlates modestly (approximately 0.6-0.69) with results of tests measuring word recognition skills. The refractory properties of the auditory nerve were also assessed. Differences across subjects were found in the rate of recovery from the refractory state. These findings imply that there may be difference across subjects in the accuracy with which rapid temporal cues can be coded at the level of the auditory nerve. Reasonably strong correlations (approximately 0.74-0.85) have been found between the magnitude of the slope of these recovery curves and performance on tests of word recognition.
Electrical auditory brain stem responses (EABR) and electrical middle latency responses (EMLR) were recorded from patients who had received the Nucleus multichannel cochlear implant system. Twenty-five sequential patients had either intraoperative or outpatient EABR testing. We also recorded EMLRs from several outpatients. EABR results were consistent among all patients tested. Wave V mean latencies were the shortest (3.82 msec) for the most apical electrode (E20) and increased slightly for the medial (E12) and basal (E5) electrodes (3.94 and 4.20 msec, respectively). Absolute latencies for all EABR component waves were observed to be 1 to 1.5 msec shorter than typical acoustic auditory brain stem response (ABR) mean latencies. We have examined the relationships between patients' EABR/EMLR and their behavioral responses to electrical stimulation. Generally, the behavioral threshold and comfort current levels were lower than the predicted values based on EABR/EMLR findings. This observation may be due in part to psychophysical loudness differences noted for pulse rates of 10 to 500 pulses per second in some of the patients that we have studied in greater detail.
• Prototypical experimental tests for linking spontaneous otoacoustic emissions with disruptive tinnitus have been described previously. Using similar experimental tests on 96 tinnitus sufferers, an estimate is made here of the prevalence of tinnitus caused by spontaneous otoacoustic emissions: the 95% confidence limits of this estimate are 1.11% and 9.05%.
(Arch Otolaryngol Head Neck Surg. 1990;116:418-423)
The effects of primary-tone separation on the amplitude of distortion-product emissions (DPEs) at the 2f1-f2 frequency were systematically examined in ten ears of five subjects. All individuals had normal hearing and middle-ear function based upon standard clinical measures. Acoustic-distortion products were elicited at 1, 2.5, and 4 kHz by equilevel primaries at 65, 75, and 85 dB SPL, while f2/f1 ratios were varied in 0.02 increments from 1.01-1.41 (4 kHz), 1.01-1.59 (2.5 kHz), or 1.01-1.79 (1 kHz). A principal outcome reflected in the detailed structure of both average and individual ratio functions was a nonmonotonic change in DPE amplitude as the ratio of f2/f1 increased. Despite the presence of amplitude nonmonotonicities, there was clearly a region of f1 and f2 separation that generated a maximum DPE. The effects of primary-tone separation on DPE amplitudes were systematically related to DPE frequency and primary-tone level. For all three levels of stimulation, the f2/f1 ratio was inversely related to DPE frequency. Thus larger ratios reflecting a greater separation of f1 and f2 were more effective in generating DPEs at 1 kHz rather than at 4 kHz. The optimal ratio for 2.5 kHz fell at an intermediate value. Conversely, acoustic distortion-product amplitude as a function of primary-tone level was directly related to the frequency separation of the primary tones. Regardless of the frequency region of the primary tones, smaller f2/f1 ratios were superior in generating DPEs in response to 65-dB stimuli, whereas larger ratios elicited bigger DPEs with primaries at 75 and 85 dB SPL. Within any specific stimulus-parameter combination, individual variability in DPE amplitude was noted. When all stimulus conditions describing the variations in frequency and level were considered, an f2/f1 ratio of 1.22 was most effective in maximizing DPE amplitude.
The electrically evoked brainstem potential was measured in cochlear implant patients with Symbion multichannel electrode system. In the first experiment, electrodes within the implant were stimulated individually and the responses and sensitivity across electrodes and across subjects were evaluated. The typical response waveform consisted of a series of three peaks, the most prominent occurring at approximately 4 ms after stimulus onset. The amplitude of the largest peak typically showed an orderly increase with increasing current level while latency changes were relatively small. In the second experiment, two electrodes were stimulated simultaneously in order to evaluate the relative independence of the neural populations being stimulated by the different electrode pairs. The responses were compared when two electrode pairs were stimulated simultaneously with current pulses in phase and when the same electrodes were stimulated with current pulses inverted relative to each other. Both stimulation conditions showed similar growth in response amplitude with level but different sensitivity. The differences in sensitivity between these two conditions may be indicative of the degree of overlap in the stimulated neural populations.
• Four types of evidence indicate that spontaneous otoacoustic emissions (SOAEs) might be the basis of one patient's problematic tinnitus. First, when SOAEs were suppressed, the tinnitus was inaudible. Second, pitch matches to the lowest pitch of the tinnitus corresponded to the lowest frequency of the SOAE. Third, there was a more intense multicomponent SOAE in the right than in the left ear, and patient claimed that the tinnitus was louder in the right ear. Fourth, the patient's SOAEs were unstable and for this reason they might be audible. One practical consequences of this research is that patients with pathological tinnitus (which keeps them awake at night and interferes with concentration) should be tested for SOAEs. Because SOAEs are abolished by aspirin, it is possible that some unusual cases of problematic tinnitus could be easily treated.
(Arch Otolaryngol Head Neck Surg 1988;114:150-153)
Auditory brainstem responses were recorded from 20 normally hearing subjects using tone-burst stimuli that were gated with cosine-squared functions. Clear responses were observed over a wide range of frequencies and levels. These responses were highly reproducible within individual subjects and were reliably measured by two independent examiners. ABR thresholds were higher than behavioral thresholds for all frequencies, especially for lower frequencies. Intersubject variability also was greater for lower frequencies. Wave-V latencies decreased with increases in both frequency and level for frequencies from 250 to 8000 Hz and for levels from 20 to 100 dB SPL. The standard deviations seldom exceeded 10% of the mean wave-V latency for any combination of level and frequency. These latencies can be viewed as the sum of both a peripheral and a central component. Assuming that the central component is relatively independent of both frequency and level, changes of wave V latency must be related to peripheral factors, such as travel time along the cochlear partition, and to stimulus characteristics, such as rise time.
Noninvasive, extratympanic electrocochleography (ECoG) was performed on 13 normal-hearing subjects with three different types of ECoG electrodes. Two of these electrodes, the Life-Tech and Axonics-3M designs are commercially available, and widely used clinically. The third electrode, the TM electrode, is a newly designed system intended to be placed directly onto the tympanic membrane. The purpose of this study was to assess the clinical performance of these different electrodes with particular attention to response amplitudes, response variability, and practical ease of use. The results indicate that the TM electrode provides improved ECoG response amplitudes while minimizing clinical preparation time.
None of the current electrical audiometric procedures, alone or in combination, has yet achieved the precision of conventional audiometric testing that is used to assess hearing in verbally capable children and adults. The reason for this, in part, lies in the use of stimuli which have a wide frequency content. We have measured scalp potentials which follow the envelopes of sinusoidally amplitude-modulated tones: a frequency-specific stimulus. In normal subjects such amplitude-modulation following responses (AMFRs) appear to be generated by two sources. One source has a latency of about 30 ms, generates large responses and is only observed at modulations below 55 Hz, while the other source has a latency of 7-9 ms, generates smaller responses, and is only observed at modulations from 100-350 Hz. The latencies of these two sources are consistent with origins in the cortex and midbrain, respectively. We examined AMFRs to low frequency (50 Hz) modulations as a possible audiometric tool. In normal subjects, the amplitude of the AMFR increased as a function of intensity, decreased as a function of carrier frequency, and could be evoked across the whole audiometric range (250-8000 Hz). In hearing-impaired subjects, the AMFR amplitudes as a function of carrier frequency accurately reflected the pattern of hearing loss on a frequency-by-frequency basis. In most subjects, the threshold for evoking the AMFR was within 0-25 dB of hearing threshold. It therefore appears that the AMFR may be a potentially useful tool to assess hearing in those unable to undergo conventional audiometric testing.
The middle cranial fossa surgical approach has been used for the removal of acoustic neuromas in 43 patients at the University of Iowa since 1974. Hearing was maintained in 50% of patients with tumors 1.5 cm or less outside the porus acusticus. Postoperative hearing, facial nerve function, and complications were similar to reports using the suboccipital or retrosigmoid approach to preserve hearing for this size tumor. The character of the tumor appears to dictate the postoperative outcome rather than the surgical approach.
Pure-tone hearing sensitivity at 2000, 3000, and 4000 Hz and ABR results were reviewed for 458 patients with cochlear hearing loss. Wave V latency and waveform morphology data from the 916 ears yielded percentages of abnormal ABR results as a function of degree and slope of hearing loss. Threshold sensitivity at all three frequencies influenced ABR latency or waveform. A higher incidence of abnormal ABR results was observed when 3000 Hz thresholds were elevated than when 4000 Hz thresholds were elevated to the same levels. ABR results for various audiometric configurations are reported.
Aspects of auditory brain stem responses (ABR) and pure-tone behavioral audiograms were compared in patients with cochlear hearing loss. Click-evoked ABR thresholds appeared to be related most closely to the audiometric thresholds at 2000 and 4000 Hz, with relatively poor agreement at either 1000 or 8000 Hz. These results were related to the amplitude spectrum of the eliciting stimulus. The slope of the wave V latency-intensity function appeared to be related to the configuration of the hearing loss. Patients with high-frequency sensorineural losses had steeper slopes than normal subjects, whereas patients with flat sensorineural losses had shallower slopes. These results were related to the principle that response latency is determined by the cochlear region that predominates the ABR for different stimulus intensities.
Brain stem evoked potentials were recorded by conventional scalp electrodes in infants (3 weeks to 3 years of age) and adults. The latency of one of the major response components (wave V) is shown to be a function both of click intensity and the age of the subject; this latency at a given signal strength shortens postnatally to reach the adult value (about 6 msec) by 12 to 18 months of age. The demonstrated reliability and limited variability of these brain stem electrophysiological responses provide the basis for an optimistic estimate of their usefulness as an objective method for assessing hearing in infants and adults.
This paper is the second in a series of three concerning audiological tests and test batteries designed to differentiate cochlear from retrocochlear site-of-lesion. The first paper discussed the application of clinical decision analysis to diagnostic tests, particularly audiological tests. This paper uses the techniques of clinical decision analysis to evaluate the clinical performance of audiological, vestibular, and radiological tests based on data derived from the last 15 years of the clinical literature. Using calculated measures of test performance, we compared and divided the test into four groups.
Tuning curves were obtained from 100 to 150 auditory-nerve fibers spanning the range of characteristic frequencies (CFs) in each of eight cases of permanent noise-induced and three cases of permanent kanamycin-induced threshold shift. In each ear, from one to six neurons were intracellularly labeled with horseradish peroxidase. Locating the labeled terminals in plastic-embedded surface preparations of the cochlea enabled us to accurately correlate particular tuning-curve abnormalities with the condition of the sensory cells generating them. The correlations between structural and functional changes suggest that a normal tuning-curve tip requires that the stereocilia on both the IHCs and OHCs (especially those from the first row) be normal. Selective damage to the OHCs is associated with elevation of the tips and hypersensitivity of the tuning-curve tails. This tuning-curve pattern also originates from cochlear regions at the basal border of hair cell lesions where the local hair cells (and their stereocilia) appear completely normal at the light-microscopic level. Total destruction of the OHCs in a region in which the IHCs appear normal (as can happen in cases of kanamycin poisoning) is associated with bowl-shaped tuning curves which appear to lack a tip. Combined damage to the IHCs and OHCs (as typically happens in cases of acoustic trauma) is invariably associated with elevation of both tips and tails on the tuning curve. A framework for the interpretation of the results is suggested in which the activity of the OHCs is transmitted via the tectorial membrane to the tall row of stereocilia on the IHCs.
The case notes of 841 subjects who had had ECochG carried out between January 1972 and December 1980, were examined and the results compared with PTA results in 263 cases in which these were available. ECochG was found to be a good predictor of peripheral hearing as long as its limitations were recognized, and some of these are discussed. BSER, which has similar limitations, was also found to be a good predictor of peripheral hearing, although slightly less sensitive, and sometimes gave additional information on the hearing loss and the clinical state of the patient.
We performed a brainstem evoked response (BSER) study to evaluate the extent to which electrical stimulation of the cochlea was conducted centrally by facial, vestibular, and cochlear nerves. Short-term experiments were performed in three monkeys: via a postauricular approach to the round window, a molded Silastic multielectrode prosthesis was placed in the scala tympani. The BSER was recorded to threshold and suprathreshold biphasic electrical pulses delivered to the implant electrodes. A middle cranial fossa dissection was then carried out, exposing the nerves of the internal auditory canal from above. Facial and vestibular neurotomy had no significant effect on BSER, while cochlear nerve section abolished the response. In one animal, blunt pressure on the cochlear nerve caused a reversible loss of electrically evoked BSER. Electrically evoked BSER probably depends on propagated impulses in the cochlear nerve.