Two-tone interactions in the cochlear microphonic

Two-tone interactions are explored for the cochlear microphonic (CM) in the guinea pig. Recordings are made from turns one and three using differential electrodes in the perilymphatic space or pipettes placed in scala media through a fenestra over the stria vascularis. We focus on magnitude changes associated with the introduction of appropriate interference tones and on various types of phase shift concomitant with these magnitude variations that have not received documentation in the literature. Based on extensive parametric data, it is suggested that some features of the gross interference phenomenon may be a consequence of the vectorial summation of outputs from contributing hair cell generators. These spatial effects appear to determine phase behavior and the influence of probe frequency on the frequency of maximal interference. In addition, the apparent interval between our defined best frequency (CF) and the frequency of maximal interference is most likely due to an underestimation of CF resulting from phase cancellation between CM-producing hair cell populations. However, after compensating for these spatial effects, several aspects of the CM interference phenomenon seem to be analogous to two-tone suppression in auditory nerve fibers. A direct one-to-one relationship is not implied since the latter reflect the outputs of inner hair cells while CM interference most likely reflects outer hair cell behavior. As a result, the association between suppression and interference must be sought in the process by which outer hair cells influence inner hair cell transduction.     

Cochlear microphonic potentials: a new recording technique.

A new instrumentation and a particular method for detecting and recording cochlear microphonic potentials (CMPs) are described here. The CMPs were recorded in rats by means of pure tones (4,000, 2,000, 1,000, 500, and 250 Hz) and intraepidermic electrodes; the electrocochleography technique was avoided. An experimental design that included the use of a glutamatergic agonist (kainic acid [KA]) and an aminoglycoside antibiotic (kanamycin [KANA]) was carried out to demonstrate the origin of the recorded potential. Morphological studies showed that KA selectively eliminated the afferent type I dendrites of the spiral ganglion, while the administration of KANA resulted in the absence of outer hair cells. When CMPs were recorded after KA administration, no alterations were detected. In contrast, KANA administration resulted in the absence of any selective electrophysiological activity corresponding to CMPs. All these results were compared with the recording of the compound action potential of the eighth nerve obtained by electrocochleography. These findings and the great specificity of the reproduction of the sound stimulus confirm that the CMPs can be recorded by the new equipment.     

Cochlear microphonic responses of the peripheral auditory system to frequency-varying signals

Cochlear partition displacement responses to rising and falling frequency sweeps were inferred from cochlear microphonic potentials recorded from three basal turn locations in the guinea pig cochlea. Relative phase measures of microphonic potentials recorded from the three locations suggested that displacements of the partition toward either scala vestibuli or scala tympani occurred closely together in time for rising sweeps and were dispersed in time for falling sweeps. These differences in peripheral response patterns to sweeps may explain, in part, asymmetric neural discharges elicited from higher neural centers.     

小儿类听神经病的耳蜗微音电位研究

目的　研究类听神经病（auditory neuropathy spectrum disorder,ANSD）病例的耳蜗微音电位（cochlear microphonic potentials,CMs）特征,探索CMs起源。方法 回顾性分析2007年1月～2010年1月于首都医科大学附属北京同仁医院确诊的ANSD 33例（49耳）,2～75月龄,平均（19±17）月龄,中位数16月龄,依据CMs、畸变产物耳声发射（distortion product otoacoustic emission,DPOAE）和中耳分析仪/颞骨CT检测结果分为3个组,中耳正常且DPOAE引出组26耳,中耳正常且DPOAE未引出组16耳,中耳异常组7耳。结果　当刺激声强度为100 dB nHL时,有DPOAE组CMs幅值（0.45±0.12）μV,无DPOAE组CMs幅值为（0.37±0.08）μV,两组之间有显著性差异（P =0.008）;而中耳异常组全部记录到CMs,且其幅值与DPOAE未引出的中耳正常组无明显差别。结论　在ANSD中部分病例外毛细胞功能会发生损害,表现为OAEs消失、CMs持续存在。而这种情况下的CMs单纯来自于内毛细胞的可能性较小,更可能来自于部分受损外毛细胞与部分或全部内毛细胞。     

Cochlear microphonic audiometry: a new hearing test for objective diagnosis of deafness

Conclusions. Objective audiometric tests could constitute a valuable tool for detection of deafness. This could be especially useful in children (universal newborn hearing screening) and non-collaborative patients, who are especially difficult candidates for classic audiometry. The cochlear microphonic audiometry (CMA) technique offers the possibility of obtaining objective audiometric profiles, highly correlated with those obtained by pure tone audiometry (PTA). Therefore, CMA could be used as an alternative test to obtain the audiometric profile of these patients. Objective. The main purpose of the present study was to demonstrate that CMA provides objective audiometric profiles by avoiding active participation by the patient. Subjects and methods. CMA specific equipment, improved for non-invasive recording of cochlear microphonic potentials, was used. This tool plots the recordings obtained as the classic audiogram. Verification of the method was carried out in adult patients by comparing the PTA with the CMA audiometric profiles obtained for each patient. Results. Our findings showed that audiometric profiles obtained from CMA are highly correlated, without statistical differences, to those obtained with PTA. More than 81% of patients explored (91.67% at 250 Hz) exhibited differences below 10 dB(HL) between tests at all exploration frequencies, while a low number of cases showed differences over 20 dB(HL).     

Contrast enhancement in frequency spectra of cochlear microphonic responses to complex stimuli

Cochlear microphonic responses were measured in pigeons and guinea pigs during stimulation with complex sounds. The acoustical stimuli had many component frequency spectra with a more or less undulating envelope. Enhancement of the peak-and-valley structure of the envelope occurred at high stimuli levels, especially if all frequency components in the stimulus had equal (cosine) phase. The observed effects could very well be modelled with a simple passive electronic network, as well as with an analytical expression that describes saturation of the cochlear microphonic at high stimulus levels.     

Cochlear microphonic potentials elicited by biosonar signals in flying bats, Pteronotus p. parnellii

Cochlear microphonic (CM) potentials were recorded from the bat, Pteronotus p. parnellii during tethered flight and during simulated flight on a pendulum. For each emitted signal the frequency of the ca. 61 kHz constant frequency (CF) component was compared with the frequency response characteristics of the animal's ear. The majority of ‘resting pulses’ had CF components with the maximum frequency approximately 200 Hz below the best frequency (BF) of the CM audiogram.Doppler shift compensation occurred only during forward swings of the pendulum and in such a way that the echo CF components were always maintained near the BF, but on the low frequency slope of the CM audiogram.CM responses to emitted pulses were usually small in amplitude and in some animals no responses were seen. Echoes Doppler shifted upward, however, evoked high amplitude potentials. Echo CF components estimated to be at least 43 dB fainter than the emitted pulses evoked higher amplitude CM potentials than the loud emitted pulses. Echoes from large surfaces up to 4.S-S.O meters away evoked CM potentials as high in amplitude as those elicited by emitted pulses, even when there was no Doppler shift. Beats in the CM were observed on many occasions and occurred as a result of pulse-echo and echo-echo interactions.     

Role of suppressive interactions in the cochlear microphonic response to wide-band clicks

Cochlear microphonic responses (CM) were recorded from the guinea pig cochlea with conventional differential electrodes implanted in the first and second turns. The CM frequency functions were determined by calculating the Fast Fourier Transform of responses to wide-band clicks. These frequency functions appeared to be dependent upon the spectrum of the click. This effect was interpreted as resulting from suppressive interactions between the various components of the click. It is suggested that such CM interactions are related to corresponding effects reported previously concerning cochlear nerve responses.     

Vestibular microphonic potentials in pigeons

Electrical responses to acoustic stimuli were measured by placing thin wire electrodes in the vestibular system of a pigeon model. Responses were measured after extirpation of the cochlea and the application of tetrodotoxin to the perilymphatic space. Responses seen were comparable to those of known cochlear microphonic potentials. These findings indicate that acoustic stimuli can evoke microphonic potentials in the vestibular system of the pigeon. We also found that vibrational amplitudes of less than 1 nm were sufficient to evoke a vestibular microphonic potential.     

Vestibular microphonic potentials in pigeons

Summary Electrical responses to acoustic stimuli were measured by placing thin wire electrodes in the vestibular system of a pigeon model. Responses were measured after extirpation of the cochlea and the application of tetrodotoxin to the perilymphatic space. Responses seen were comparable to those of known cochlear microphonic potentials. These findings indicate that acoustic stimuli can evoke microphonic potentials in the vestibular system of the pigeon. We also found that vibrational amplitudes of less than 1 nm were sufficient to evoke a vestibular microphonic potential.Presented at the 22nd Workshop on Inner Ear Biology, Würzburg, Federal Republic of Germany, 15–18 September 1985     

两例听神经病患者的人工耳蜗植入分析

目的回顾分析听神经病患者的人工耳蜗植入的效果与风险,以及可能的预后判断方法。方法对2例临床诊断听神经病的患者行人工耳蜗植入,术中检测电诱发听神经复合动作电位,术后常规调机和检测言语识别率。结果2岁的语前聋患儿引出电诱发听神经复合动作电位,另一例18岁的语后聋患者未引出。术后前者的言语识别率优于后者。结论听神经病患者的耳蜗植入疗效可能因病变部位不同而有差异,目前还缺乏准确的术前检查进行鉴别。     

Cochlear receptor (microphonic and summating potentials, otoacoustic emissions) and auditory pathway (auditory brain stem potentials) activity in auditory neuropathy

OBJECTIVE: To define both auditory nerve and cochlear receptor functions in subjects with auditory neuropathy (AN). DESIGN: We tested 33 AN subjects (66 ears) and compared them with 21 healthy subjects (28 ears). In AN subjects, the average pure-tone (1, 2, and 4 kHz) threshold loss was 57 dB HL. Click stimuli were used to elicit transient evoked otoacoustic emissions (TEOAEs), cochlear microphonics (CMs), and auditory brain stem responses (ABRs). Both cochlear and ABR potentials were recorded from surface electrodes (vertex-ipsilateral mastoid) using averaging procedures. The amplitudes and latencies of CMs and ABRs and the amplitude of the TEOAEs were analyzed. RESULTS: CM amplitudes recorded from normal ears decreased as a function of subject age. CMs recorded from AN subjects fell within the normal age-adjusted range in 60% of the subjects and were >2 SEEs (standard error of estimate) above the age-adjusted normal regression in 40% of the subjects. TEOAEs were absent in 19 (30%) AN ears (bilaterally in eight, and unilaterally in three subjects) and were present in 44 ears. In AN subjects, correlations among CM amplitude, TEOAE amplitude, and pure-tone average thresholds were not significantly related. CM amplitudes were not significantly different whether TEOAEs or ABRs were present or absent. The ABR was present in 21% of AN subjects and consisted of a low-amplitude Wave V without a preceding Wave I. Measures of CM amplitude and PTA hearing loss were not significantly different in those AN ears with a preserved ABR compared with ears with absent ABRs. Summating potentials to transient click stimuli were of small amplitude (<0.1 microV) and detectable in approximately 50% of the AN and healthy control subjects limiting formal analysis of summating potentials. CONCLUSIONS: In a significant proportion of AN subjects, we found abnormalities of cochlear receptor function, including elevated CM amplitudes and absence of TEOAEs. These two abnormalities occurred independently of each other. A low amplitude Wave V of the ABR was found in approximately one-fifth of AN subjects, evidence that neural synchrony can be partially preserved in some subjects with this disorder.     

Increase in cochlear microphonic potential after toluene administration

Human and animal studies have shown that toluene can cause hearing loss. In the rat, the outer hair cells are first disrupted by the ototoxicant. Because of their particular sensitivity to toluene, the cochlear microphonic potential (CMP) was used for monitoring the cochlea activity of anesthetized rats exposed to both noise (band noise centered at 4 kHz) and toluene. In the present experiment, the conditions were specifically designed to study the toluene effects on CMP and not those of its metabolites. To this end, 100-μL injections of a vehicle containing different concentrations of solvent were made into the carotid artery connected to the tested cochlea. Interestingly, an injection of 116.2-mM toluene dramatically increased in the CMP amplitude (4 dB) in response to an 85-dB SPL noise. Moreover, the rise in CMP magnitude was intensity dependent at this concentration suggesting that toluene could inhibit the auditory efferent system involved in the inner-ear or/and middle-ear acoustic reflexes. Because acetylcholine is the neurotransmitter mediated by the auditory efferent bundles, injections of antagonists of cholinergic receptors (AchRs) such as atropine, 4-diphenylacetoxy-N-methylpiperidine-methiodide (mAchR antagonist) and dihydro-β-erythroidine (nAchR antagonist) were also tested in this investigation. They all provoked rises in CMP having amplitudes as large as those obtained with toluene. The results showed for the first time in an in vivo study that toluene mimics the effects of AchR antagonists. It is likely that toluene might modify the response of protective acoustic reflexes.