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The use of cochlear implants to restore hearing in profoundly deaf children is increasing, with a trend toward earlier implantation. However, little is known about how auditory deprivation and subsequent implant use affects the maturing central auditory system. Previously reported results indicate that stimulation of the auditory system by a cochlear implant is sufficient to restore at least some aspects of central auditory pathway maturation, as reflected by age-related changes in the auditory evoked potentials. We review animal and human studies on sensory deprivation and report new results based on longitudinal evoked potentials data recorded from two individuals. Analyses show that age-related changes in the EPs may asymptote at levels very different from those found in the adult normal-hearing population. These results suggest that maturation of at least some aspects of central auditory system activity is limited by the onset and duration of the period of deafness prior to implantation.

An 18-year follow-up of a case of bilateral Lermoyez's syndrome is presented. The left ear having reached a stabilized hearing loss about 9 years after the onset of the disease, the right ear, apart from some isolated early periods of hearing loss, started to show the full extent of clinical symptoms after about 16 years. Electrocochleographic observations are presented. Studies were performed twice in the right ear during a period of strongly fluctuating hearing thresholds, once in an impaired and once in a relatively good condition. Electrocochleography of the stabilized left ear was performed as well. The data are compared with electrocochleographical observations in the left ear in its early fluctuating stage. Variation of cochlear physiological data during the fluctuating stage of the disease shows remarkable correspondence between the two ears. The stabilized Lermoyez ear is shown to have developed considerable hair cell loss, but may still have preserved its endolymphatic hydrops. These findings in Lermoyez's syndrome fit well into the observations reported in patients with Menière's disease.

Bayes’ theorem was used to establish a probabilistic differential diagnosis between four hearing states :normal hearing, conduction hearing loss, Menière’s disease, and hair-cell damage. Measurements were carried out by electrocochleography (ECoG), action potentials being determined in response to short tone-burst stimulation. This method proved to permit differentiation between normal and abnormal cochleas, but the present state of development does not allow a more detailed diagnosis.

Derived narrow-band brainstem responses were obtained for click levels of 10--60 dB SL in normal hearing subjects. The amplitudes and latencies of the wave I, wave III, and wave V components in the derived BSER were studied as a function of click intensity. Characteristic differences were found between the input-output behavior of waves I and III on one hand and wave V on the other hand, especially for the low-frequency narrow bands (center frequencies of 0.5 and 1.0 kHz). While the wave I and wave III (peak-to-succeeding trough) amplitude showed a small (20--30 dB) dynamic range with saturation effects, the wave V amplitude continued to increase across the intensity range studied. At the high-frequency end (narrow-band center frequencies of 4 and 8 kHz), wave V also showed saturation. It is suggested that this difference across center frequency (place of origin along the cochlear partition) is responsible for the dominance of wave V at low-frequency stimulation (e.g., with tonebursts). The latencies of the three waves studied maintained their constant interwave delays across the observed intensity range in each narrow band. Quite large (up to 3.5 ms) increases in the narrow-band latencies were found for decreasing click levels; this is comparable in value with those for the unmasked BSER although the mechanism seems to be different. The major contribution to the BSER which determines its latencies, originates at 60 dB SL from the 8-kHz region but at low SL (10 and 20 dB) from the 2-kHz region. At these low intensity levels, the contribution from the apical part of the cochlea, however, is still of the same size as that from the high-frequency end.

An auditory sensation follows generally as the result of the sequence stimulus, transduction, coding, transformation and sensation. This is then optionally followed by perception and a reaction. The stimulus is usually airborne sound causing movements of the tympanic membrane, the middle ear ossicles, the inner ear fluids and the basilar membrane. The movements of the basilar membrane are dependent on stimulus frequency: high frequency tones excite only the basal part of the cochlea, regardless of the stimulus intensity; low frequency tones at low levels only excite the so-called place specific region at the apical end but at high levels (above 60–70 dB SPL) cause appreciable movement of the entire basilar membrane. Basilar membrane tuning is as sharp as that of inner hair cells or auditory nerve fibers (Sellick et al., 1982) at least in the basal turn of animals that have a cochlea in physiologically impeccable condition.

A case of Lermoyez's syndrome was investigated by tone-burst electrocochleography in both a period of impaired hearing and in a period of almost normal hearing. The changes in threshold values, compound action potential waveforms, input-output curves, and amplitude-latency curves for the compound AP, are described. The electrocochleographic data are compared with the psycho-acoustic data for this case and with electrocochleographic results in a group of 22 Meniere cases. Although the symptoms of vertogo and hearing impairment in Lermoyez's syndrome occur in the reverse sequence, as compared with the classical Menière attack, the data obtained in this case of Lermoyez's syndrome do not differ substantially from those obtained in a group of Menière cases.

Twenty patients suffering from Meniere's disease or Lermoyez syndrome were studied with respect to the time course of their hearing loss. Careful history-taking as well as repeated audiometry over long time spans (5–20 years) resulted in a longitudinal study of hearing loss at the standard audiometric frequencies. From these time series, correlation coefficients were computed between the changes in both ears at identical frequencies, and for changes in the same ear at different frequencies. Correlations between changes in hearing loss in both ears were more obvious in bilateral Meniere's disease than in unilateral disease. Correlations between changes in hearing loss at different frequencies were also more pronounced in Meniere's disease ears than in normal ears. If was found that recovery of hearing loss after an attack was nearly identical each time it occurred in the same ear, but differed between ears and patients. This deterministic finding in the otherwise random course of the hearing loss as a function of time may be important in deciding what mechanisms cause fluctuating hearing loss in Meniere's disease.

Cochlear microphonics (CM) were recorded in the guinea pig using differential recording from the first and third cochlear turns as well as by using a 10-electrode array inserted in the scala tympani of the basal turn. The excitation profile as represented by the CM was quantified by amplitude and phase data, and was measured at normal temperature (38 degrees C) and a 10 degrees lower cochlear temperature. It appears that the CM pattern shifts toward the base of the cochlea as a result of cooling. This is explained on the basis of an increased compliance of the basilar membrane with an optional influence of increased viscosity of the perilymph.

Adaptation phenomena in the peripheral hearing organ originate from the properties of the haircell-neuron synaps as revealed by their temperature dependency. In order to verify this hypothesis a model experiment is set up. The model consists of programming on an analog computer the equations describing the reaction kinetics from the frogs myoneural junction. A model neuron is attached to the synapsmodel in which two independent noise sources are incorporated. This noise addition serves to simulate the stochastic behavior of the transmitter release in the synaps resulting in a fluctuating generator potential and independently thereof to reflect the varying threshold of the nerve fiber. The reaction rate constants in the synaptic model were modified with respect to the original ones in order to get a coincidence of in vivo- and model results. The compound model primarily is used to simulate the quite different synchronization between the auditory nerve fibers occurring during intensity changes and during changes of the stimulus repetition rate. These results were known to be different in the animal experiments and were also generated by the model. It is shown clearly that neither synaptic noise alone nor membrane noise alone can account for the observations made in the animal experiments. Therefore a combination of both types of noise is used in this model. The model experiment also visualizes that amplitude changes for compound AP's during adaptation can be explained in toto by a decreasing synchronization, i.e. the broadening of the latency distribution function for the nerve fibers.

The properties of both the compound action potential (AP) and summating potential (SP) were studied in 18 normal human cochleas. The summating potentials were investigated with respect to the input-output behaviour and occurrence of positive and negative summating potentials.The compound action potential is discussed with respect to:a. the amplitude-intensity and latency-intensity behaviour, with special reference to the separation into low and high intensity parts;b. the action potential waveform and particularly the occurrence of a double-peaked N1 and the properties of both peaks;c. the adaptation and masking properties;d. the amplitude-latency and width-latency relations describing the internal synchronization for the compo nents of the compound action potential.A regression analysis was performed for the amplitude-latency scattergrams to provide adequate data reduction for clinical reference. Detailed properties of the two populations of neural units are given, and a morpho-logical substrate ...

(1) In response to stimulus trains, the amplitude, latency and width of the N1 component of the round-window-recorded action potentials (AP) reach an equilibrium value after about 5 stimuli. This final value is expressed in percent of the first response and depends on the stimulus intensity, stimulus duration and interstimulus interval (ISI). The equilibrium value is generally reached in an exponential way, the time constant of which also depends on the various stimulus parameters.(2) The adaptation properties of the AP (i.e., those depending on the ISI) measured in this way are identical to those of action potentials recorded in single-nerve-fiber experiments. It is concluded that the AP reflects the properties of the nerve-fiber population by means of a weighted sum of the single-nerve-fiber contributions.(3) It is possible to describe the N1 component of the AP as sum of two partly overlappling Gaussian distribution functions. These two functions reflect the properties of two populations of nerve fiber...

(1) In response to stimulus trains, the amplitude, latency and width of the N1 component of the round-window-recorded action potentials (AP) reach an equilibrium value after about 5 stimuli. This final value is expressed in percent of the first response and depends on the stimulus intensity, stimulus duration and interstimulus interval (ISI). The equilibrium value is generally reached in an exponential way, the time constant of which also depends on the various stimulus parameters.(2) The adaptation properties of the AP (i.e., those depending on the ISI) measured in this way are identical to those of action potentials recorded in single-nerve-fiber experiments. It is concluded that the AP reflects the properties of the nerve-fiber population by means of a weighted sum of the single-nerve-fiber contributions.(3) It is possible to describe the N1 component of the AP as sum of two partly overlappling Gaussian distribution functions. These two functions reflect the properties of two populations of nerve fiber...

The amplitude, AN1, and the latency, τN1, of the N1 component of round-window-recorded APs in the guinea pig are modified by simultaneous background noise and also for some time afterward by a preceding noise burst ('forward masking') White-noise masking acts differently below and above 60 dB with respect to its influence on AN1 and τN1.Forward masking is more effective if the delay time is short. On the basis of different slopes of the curves relating AN1 to noise intensity, the time during which forward masking has an effect can be subdivided into three periods. The period of shor delay is dominated by refractory mechanisms; during the period with long delays only adaptive mechanisms cause the masking; in the middle period both mechanisms are at work.Adaptation experiments performed in the presence of masking noise indicate a competitive action between masking and adaptation. At equal stimulus intensities there is a definite relation between S/N value and ISI value.The results of masking of the compound...

Action potentials were picked up from the round window of guinea pigs. By averaging the cochlear responses to tone bursts, the sine wave polarity of which was reversed in half of the presentations, the CM was cancelled out. During steady tones of various frequencies and various intensities, the AP thresholds for short tone bursts of different frequencies were determined. In some experiments the short tone burst was presented shortly after a long tone burst: forward masking.The masking curves of the steady pure tones are compared with the psycho-acoustic masking curves as given in the literature. Another curve is the frequency response curve of a certain location of the cochlea measured by de Boer with the method of reverse correlation. The frequency response curve gives the ability of the cochlea to initiate nerve impulses for various frequencies. The shapes of all these curves are similar and they point to a rather high frequency-selectivity in the cochlea. Tuning curves of single nerve fibers have the s...

In 45 patients with surgically proven pontine angle tumors, compound action potential (AP) and summating potential (SP) were recorded with transtympanic electrocochleography (ECochG) together with brainstem electric responses (BSER). The aims were to quantify the mechanism by which tumors cause hearing loss and to evaluate the diagnostic potentials of ECochG and BSER for detecting eighth nerve and brainstem tumors. Except for AP latency and narrow band AP waveform, response parameters recorded by ECochG are uncor-related. Four uncorrelated parameters were abnormal in only 10% of the cases, three in 25%, two in 40%, and one in 90%. The BSER criterion was the latency delay between waves I and V and resulted in about 90% detection, improving to 95% when used in combination with the interaural wave V delay criterion. ECochG results provide evidence that, for hearing losses up to 60 dB HL, the origin is cochlear, resembling that caused by Menière's disease. Evidence is presented that the increase in I-V delay in the BSERs is caused by differential action of the tumor upon low and high frequency fibers in the auditory nerve and that desynchronization of the firings of the nerve fibers is of more importance than an increase in neural conduction time. ECochG as the sole test for detection of pontine angle tumors appears to be of limited value. Brainstem response on its own has great merits; however, it should be emphasized that no wave I was detected in about 30% of the cases. The 95% detection score obtained with BSER depends on specifying the latency of wave I. For these cases, we substituted the latency of the AP recorded by ECochG.

The auditory system as a whole can only be studied by behavioral tests. When we speak of hearing, we are considering something that leads to a motor response, either an orientation toward the sound source or an answer to it. Hearing involves localization and identification of the sound. Electrophysiological methods can never describe the system completely, since it is impossible to determine with these methods whether a sound was actually heard. Thus, an electrophysiologically normal system is a necessary condition for normal hearing, but it is not a sufficient condition. Depending on the recording site, one can only test the system up to that point. By testing various stations along the auditory pathway, one may obtain time courses of development at all these points. This allows one, for example, to distinguish between maturation at the cochlear level and maturation of the central nervous system.

In electrococholegraphy, compound action potentials (AP) are recorded from the human promontory and the guinea pig round window. High‐pass noise masking and subtraction of AP responses at various high‐pass cutoff frequencies give the narrow‐band contributions to the whole nerve AP. Although the narrow‐band contributions recorded from human and guinea pig ears differ essentially, this narrow‐band concept makes it possible to derive a response area for a given type of stimulus, e.g., tone bursts. Within the response area, any combination of stimulus intensity and site on the cochlear partition evokes a detectable narrow‐band response contributing to the whole‐nerve AP. The main part of this contribution shifts basally the higher the stimulus intensity. Latency differences between responses from the various narrow bands are used to calcuate the traveling‐wave velocity for the human cochlea, which ranges from about 20 m/sec at 10 kHz to 1 m/sec at 500 Hz. The amplitude and width of the narrow‐band responses a...

With a dual-electrode configuration separable few-unit activity was recorded both on one electrode as well as on two electrodes in the auditory midbrain of the grassfrog to a large variety of stimuli. Activity recorded on one electrode was separated by a pattern recognition technique through the use of features of the action potential waveform. Functional connections between units were established on basis of cross-correlation histograms of pairs of simultaneously recorded units. A hierarchical scheme was adopted to describe the various manifestations of neural correlation. If a peak or trough was observed in the simultaneous cross-correlation histogram, irrespective of stimulus conditions, this was called neural synchrony. If this peak or trough was not equal to its shift predictor estimating the stimulus contribution, neural correlation was considered to be present. About 60% of the pairs exhibited neural synchrony, mostly due to shared stimulus influences, independent of mutual distance of units. About 15% of the unit pairs showed neural correlation indicating a functional neural connection. Neural correlation was observed only in units with a distance smaller than 300 micron. The majority (approximately 85%) of the cases showing neural correlation could be ascribed to neural shared input. Unidirectional excitation was observed only in unit pairs recorded on the same electrode. Unidirectional inhibition could not be demonstrated. The dependency of occurrence of neural correlation on unit distance has implications for models of the functional organization of the auditory midbrain. About half of the neurally correlated pairs showed stimulus dependencies of their functional connections. Together with the observed lack of stimulus invariance of single-unit spectrotemporal sensitivities this indicates a dynamic stimulus dependency of functional neuronal organization in the auditory midbrain of the grassfrog. Neuron pairs with a large overlap of their spectrotemporal sensitivities on average had neurally correlated activities more often than pairs with a smaller amount of overlap. In comparison to single-unit coding, ensemble coding by populations of neurons may show an enhanced selectivity to stimulus characteristics.

Cochlear adaptation is postulated to arise in the haircell-first auditory neuron junction due to steady-state reactions between transmitter quanta and receptor sites, thus forming transmitter-receptor complexes which are destroyed enzymatically. The striking resemblance between this mechanism and the occupation and liberation of lines in telephone exchanges led us to apply a well-established stochastic theory for the latter to the adaptation phenomena in the peripheral hearing organ. The theory is evaluated by comparison with experimental data from forward-masking experiments using the compound action potential as a sensor and also with single-nerve fibre data from the literature.

Responses were obtained from 112 auditory neurons in the midbrain of the grass frog in response to sequences of tones. Their spectro-temporal sensitivities (STS) were determined by a second-order cross-correlation technique. For the majority of units the shape of their action potentials, the degree of timelock to the stimulus and the recording sites were obtained. Two stages of information processing could be distinguished. One was characterized by short latencies (less than 30 ms), strong timelock to the stimulus and many of these units had axon-like action potential waveforms. They were localised in the ventral part of the principal nucleus from the torus semicircularis and in the transition region between laminar and principal nucleus. The other stage comprised units, found all over the torus, with longer latencies, and a weaker timelock to the stimulus. Several units which were predominantly found in the central part of the torus, especially the magnocellular nucleus, showed a broad or multiple STS. Within the principal nucleus a weak tonotopy was found, the dorsoposterior part being sensitive to lower frequencies, the ventroanterior part to the higher frequencies. Binaural-interaction properties are discussed with respect to the eardrum coupling through the mouth cavity. An organisational plan for the torus semicircularis is proposed.

Using a tone‐on‐tone masking procedure to just mask a compound actionpotential (AP) evoked by a 10 dB SL short toneburst yields frequency‐intensity combinations for the tonal masker called AP tuning curves. This procedure is used in addition to the standard electrocochleography procedure to obtain information about the peripheral frequency selectivity. Both methods were performed on a (normal) group of patients having normal or nearly normal (within 15 dB) thresholds for frequencies above and including 1 kHz, and in patients having hearing losses of sensorineural origin exceeding 40 dB HL. In normal ears, the characteristic two‐segment tuning curves are obtained. For pathological ears having a hearing loss of cochlear origin, tuning curves broadening by the loss of their sharp tips are obtained. There is some indication that in predominant neural hearing loss most of the sharp tuning is preserved. The changes in tuning associated with recovery from sudden deafness to almost normal hearing are reported. Th...

Action potentials from the human cochlea in response to short-tone bursts of different frequencies were recorded by means of a transtympanic needle electrode placed on the promontory. The input-output relations for amplitude (AN1) and peak latency (τN1) of the N1 deflecetion have been studied in a large number of human cochleas and are compared with similar results obtained by round window recording in guinea pigs. The amplitude-intensity relation is qualitatively the same for normal human and guinea pig cochleas. At high stimulus intensities, the peak latencies are the same for human and guinea pig cochleas. At high stimulus intensities, the peak latencies are the same for human and guinea pig cochlear action potentials, but at threshold, the human τN1 is about 3 msec longer than for the guinea pig. In recruiting ears, the input-output relation have been measured for both AN1 and τN1 and compared to those obtained from guinea pig cochleas suffering a high-frequency sensorineural hearing loss.On the basis...

The problem of the location of the adaptation mechanism in the peripheral hearing organ is studied using the temperature dependency of adaptation and masking of round window recorded AP in the guinea pigAt first, the influence of temperature on the synchronization conditions in the auditory nerve is investigated by observing the behaviour of the width-latency relation for the N1. It is shown that cooling does not act in the same way as attenuating the stimulus but that the desynchronization caused is comparable to that by lowering the interstimulus interval (ISI). The competitive desynchronizing action of cooling on one side and adaptation and masking on the other side is discussedSecondly, the temperature dependency of the An1-ISI and An1-S/N relations is studied. It became clear that, while the recovery time is not influenced by temperature, the decay time of the An1 to its final value during a series of tone bursts is increased by lowering the temperatureThe temperature dependency of synaptic mechanism...

Human electrocochleography is reviewed and the significance of the recorded potentials is discussed with special reference to the recording site. The response amplitude and threshold values for transtympanic AP recording are compared for various recording sites. The recorded AP amplitude varies with the inverse distance to the cochlear wall, resulting in an AP threshold increase which is nearly exponential with increasing distance from the cochlea.The click and tone-burst results arc compared with respect to frequency specificity and accordance with the subjective threshold. The Leiden method combining the promontory recording with short tone-bursts as stimuli proved to permit accurate determination of threshold for frequencies of 500 Hz and upwards, and provides detailed frequency-specific supraliminal information (e.g. about recruitment).