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At least 163 records · Page 9Linked to original sources
PubMed1991

[Effects of intravenous injection of salicylate on the spontaneous discharge rate of the cochlear nerve].

This study was aimed to elucidate the effects of salicylate on the cochlear nerve by recording the spontaneous activity in guinea pigs. After guinea pigs were given salicylate (200 mg/kg) intravenously, the transient reduction in cochlear spontaneous activity and the elevation over the subsequent 10-20 minutes were observed in three of four fibers recorded for more than 30 minutes. The mean spontaneous discharge rate of 102 fibers after administration of salicylate (200 mg/kg) was not significantly higher than the control values from 30 to 120 minutes after salicylate administration, while that rate of 112 fibers after administration of salicylate (400 mg/kg) was significantly higher. The observed changes in spontaneous activity due to salicylate administration may represent the evidence of a tinnituslike phenomenon in guinea pigs.

Animals↗
PubMed1996

Direct cochlear nerve action potentials as an aid to hearing preservation in middle fossa acoustic neuroma resection.

A new application of auditory evoked potentials using direct cochlear nerve action potentials (CNAPs) for monitoring middle fossa acoustic neuroma resection with attempted hearing preservation is described. Twenty patients have been studied to date. With this technique, a monitoring electrode is secured between the floor of the internal auditory canal and the dura adjacent to the cochlear nerve in an extradural location. Standard auditory evoked potential techniques with click stimuli and microelectrical recording allow observation of nearfield waveforms in seconds versus several minutes required for farfield potentials recorded from the scalp. Advantages of this technique over auditory brainstem response monitoring may include nearly real time measurement of potentials, improved surgeon learning curve and possibly higher rates of hearing preservation, and applicability to all patients undergoing hearing-preservation surgery independent of presence or absence of ABR tracing. Immediate changes in amplitude and latency of waveforms appear to compare with reversible and irreversible intraoperative auditory system damage, thereby guiding surgical maneuvers.

Acoustic Stimulation↗
PubMed2004

Connections between the facial, vestibular and cochlear nerve bundles within the internal auditory canal.

The vestibular, cochlear and facial nerves have a common course in the internal auditory canal (IAC). In this study we investigated the average number of nerve fibres, the average cross-sectional areas of the nerves and nerve fibres, and the apparent connections between the facial, cochlear and vestibular nerve bundles within the IAC, using light and scanning electron microscopy. The anatomical localization of the nerves within the IAC was not straightforward. The general course showed that the nerves rotated anticlockwise in the right ear from the inner ear end towards the brainstem end and vice versa for the left ear. The average number of fibres forming vestibular, cochlear, and facial nerves was not constant during their courses within the IAC. The superior and the inferior vestibular nerves showed an increase in the number of nerve fibres from the inner ear end towards the brainstem end of the IAC, whereas the facial and the cochlear nerves showed a reduction in the number of fibres. This suggests that some of the superior and inferior vestibular nerve bundles may receive fibres from the facial and/or cochlear nerves. Scanning electron microscopic evaluations showed superior vestibular-facial and inferior vestibular-cochlear connections within the IAC, but no facial-cochlear connections were observed. Connections between the nerves of the IAC can explain the unexpected vestibular disturbances in facial paralysis or persistence of tinnitus after cochlear neurectomy in intractable tinnitus cases. The present study offers morphometric and scanning electron microscopic data on the fibre connections of the nerves of the IAC.

Adult↗
PubMed1992

Morphometric analysis of the cochlear nerve in man.

Fiber diameters were analyzed in the meatal segment of the cochlear nerve from 7 temporal bones obtained from 7 patients. Two patients had normal hearing for their age. Two had sustained noise exposure and one had presbyacusis of predominantly neural type. The cochleae displayed characteristic degeneration patterns. The other two manifested hearing loss of unspecified type. The fiber diameters ranged from 0.5 to 11 microns. The diameter distribution was unimodal in all seven nerves. The means of the diameters ranged from 4.2 to 5.5 microns. They were significantly different between patients with age-related normal hearing on the one hand and patients with noise induced hearing loss and neural presbyacusis on the other. The findings are discussed in relation to changes in nerve conduction speed and hearing loss; a possible correlation between the fiber diameter distribution and the tonotopical arrangement of the cochlea is suggested.

Cochlear Nerve↗
PubMed2005

Nonsyndromic isolated unilateral cochlear nerve aplasia without narrow internal auditorymeatus: a previously overlooked cause of unilateral profound deafness in childhood.

OBJECTIVES: Juvenile or adolescent unilateral profound sensorineural deafness (worldwide prevalence, 0.1% to 0.2%) has been attributed to postnatal viral infection, sudden deafness, prenatal and perinatal problems including maternal rubella and viral infections, congenital innerear anomalies, and other factors. Herein, 2 cases are reported and another potentially important cause of unilateral profound hearing loss is proposed. METHODS: Two nonsyndromic cases of a presently "very rare" cause of pediatric unilateral deafness are presented as a retrospective case study. RESULTS: The 2 patients showed isolated aplasia of the cochlear nerve; other branches of the eighth cranial nerve, the seventh nerve, and the inner ear were spared,and there was no anomaly of the internal auditory meatus. Both functional and imaging studies confirmed the isolated lesion (absence) of the cochlear nerve. CONCLUSIONS: Because of the absence of bony abnormalities, such cases may have been overlooked. The authors would like to advocate this isolated anomaly of thecochlear nerve as an important cause of juvenile or adolescent unilateral profound deafness.

Child↗
PubMed1999

The effects of quinine on cochlear nerve fibre activity in the guinea pig.

The effect of quinine on single cochlear nerve fibre activity (n = 38) was measured in four pigmented guinea pigs, which were given 10-30 mg/kg of quinine intravenously. The frequency tuning curves of these fibres exhibited significant increases in the thresholds of both 'tip' and 'tails' regions of the frequency tuning curve, but these changes did not appear to be accompanied by significant changes in tuning, as measured by the Q'10'dB. In comparison with control fibres (n = 178) from 13 untreated animals, significant changes in the proportion of low:high spontaneous rates (SR) were also seen. Using a boundary criterion of 25 sp/s, this rate changed from 26:74% to 47:53% in control and quinine-poisoned fibres, respectively. Independent of changes in the spontaneous rate, significant increases in the mean absolute refractory period from 0.85 to 1 ms were measured following quinine administration. The absence of a significant effect on fibre tuning whilst threshold was elevated indicates that quinine does not affect the integrity of the cochlear amplifier, though appears to affect cochlear sensitivity.

Acoustic Stimulation↗
PubMed2002

Hearing preservation in acoustic neuroma surgery: importance of adhesion between the cochlear nerve and the tumor.

OBJECT: To evaluate the possible prognostic factors for hearing preservation, the authors retrospectively reviewed the results of 30 consecutive acoustic neuroma operations in which hearing preservation was attempted, in a total series of 63 acoustic neuromas. METHODS: Intracanalicular tumors or those that extended less than 3 mm outside the porus acusticus (10 cases) were resected via the middle fossa approach. The retrosigmoid approach was used for tumors exceeding the limits for the middle fossa approach (20 cases). Overall, hearing was preserved (pure tone average < or = 50 dB and speech discrimination score > or = 50%) in 21 patients (70%). There were 11 patients with severe adhesion between the cochlear nerve and tumor capsule, and 19 without. Hearing was preserved postoperatively in only two (18.2%) of 11 patients with severe adhesion, whereas all 19 without severe adhesion had hearing preservation. CONCLUSIONS: The presence or absence of severe adhesion in the interface between the cochlear nerve and the tumor might be the most significant prognostic factor for hearing preservation postsurgery.

Adult↗
PubMed1978

Cochlear nerve in neurilemomas. Audiology and histopathology.

Correlative data between the histopathologic changes in the cochlear nerve and audiologic findings are reported in 16 cases of neurilemomas. Poor speech discrimination, positive or absent recruitment, excessive adaptation, or separation of forward vs reverse continuous tone Bekesy tracings did not correlate with the number of preserved nerve fibers. There were several cases with profound hearing loss in which the nerve fiber population approached normal. Histologically, pathologic changes included dilated fibers and increased interfibrillary collagen. In many specimens the fibers were further apart than normally, especially in the immediate vicinity of the tumor, and many lay between tumor cells. The tumor-nerve interface was usually gradual and no abrupt change appeared at the transition from the nerve to the tumor, the Schwann cells appearing to continue as tumor cells. Nonspecific changes apparently due to specimen handling were seen in some areas of most specimens.

Adult↗
PubMed1978

Cochlear travelling wave velocities calculated from the derived components of the cochlear nerve and brainstem evoked responses of the human auditory system.

From the latency difference between corresponding components of the different derived cochlear nerve and brainstem evoked responses (CBER) and the cochlear location difference between the appropriate derived band centre frequencies (CF), estimates of the travelling wave velocity at various locations along the cochlear partition were calculated. Calculated velocities compared favourably with velocity data obtained using widely contrasting techniques. Derived CBER waveforms were therefore considered to truly represent neural activity initiated by activity at specific frequency regions along the cochlear partition.

Audiometry, Evoked Response↗
PubMed1990

Quantitative evaluation of the human cochlear nerve.

In 18 human temporal bones of patients with normal hearing or sensory neural deafness, the cochlear neurons were evaluated at the level of the peripheral axons in the osseous spiral lamina, the ganglion cells in the spiral ganglion and the central axons in the cochlear nerve in the inner acoustic meatus. The total number and the segmental distribution were both determined.

Adult↗
PubMed1982

Boundaries of two-tone rate suppression of cochlear-nerve activity.

Two-tone rate suppression was examined in the responses of single cochlear-nerve fibers in Mongolian gerbils. The iso-rate tracking algorithm developed by Kiang and Moxon (Kiang, N.Y.-S. and Moxon, E.C. (1974): J. Acoust Soc. Am. 55, 620-630) for obtaining tuning curves was modified to track iso-rate suppression boundaries as a function of frequency with the excitor tone fixed at the characteristic frequency (CF) of the fiber. Lower threshold boundaries of the areas of suppression flanking the tuning curve above and below CF were outlined for fibers over a large CF range. It was found that the boundaries of rate suppression obtained below CF were very stable in their absolute positions on the intensity-frequency plane. This stability was evident both as a function of fiber CF (0.6-15 kHz) and as a function of the shape of the tuning curve at a given CF. In other words, the suppression boundary obtained below CF was largely independent of the tuning curve. In a second series of experiments tuning curves were taken in the presence of a fixed tone placed in the suppression area located above the fiber CF. The fixed tone by itself was not excitatory. These tuning curves were compared to tuning curves obtained with a single tone. It was found that frequencies around the fiber CF were most affected (suppressed) by the presence of the second tone, and that the low-frequency tail of the tuning curve tended to shift toward the boundary of the suppression area below CF. Because this suppression boundary lies below the threshold of the normal tail of the tuning curve for many mid- and high-CF fibers, these fibers often became hypersensitive at low frequencies in the presence of the second tone above CF.

Acoustic Stimulation↗
PubMed2006

Internal auditory canal morphology in children with cochlear nerve deficiency.

OBJECTIVE: To describe the internal auditory canal (IAC) and inner ear morphologic characteristics of children with cochlear nerve (CN) deficiency. STUDY DESIGN: Retrospective case series. SETTING: Tertiary referral center. PATIENTS: Fourteen children with small or absent (deficient) CNs have been identified by means of high-resolution magnetic resonance imaging (MRI). INTERVENTIONS: MRI of the brain. Clinical evaluation. MAIN OUTCOME MEASURES: Review of medical records, audiological testing results, and imaging studies. Images were evaluated for the structure of the cochlear, vestibular and facial nerves, IACs and inner ears. Audiometric thresholds were evaluated in all subjects. METHODS: Fourteen children with small or absent (deficient) CNs have been identified by means of high-resolution MRI. A review of the medical records, audiologic testing results, and imaging studies was undertaken. The images were evaluated for the structure of the cochlear, vestibular and facial nerves, IACs, and inner ears. The audiometric thresholds were evaluated in all subjects. RESULTS: Among the 14 patients, 5 had known syndromes. MRI allowed an exact specification of the nervous structures within all ears with normal-size IACs. Precise characterization of the nerves in ears with small IACs was more difficult, requiring a consideration of both imaging findings and functional parameters. Five children had bilateral deficient CNs, whereas the remaining 9 subjects were affected unilaterally. Thus, 19 ears had CN deficiency (absent CN, 16; small CN, 3). Eleven ears had normal-size IACs and deficient CNs. Of the 9 ears with small IACs, 8 had deficient CNs (absent, 7; small, 1) on the basis of both MRI and functional assessments. Two ears with small IACs had clear morphologic and/or functional evidence for the presence of a CN: one had a small-size CN on MRI, whereas another had a single nerve in a small IAC with present facial and auditory functions. CONCLUSION: The findings of this study suggest that CN deficiency is not an uncommon cause of congenital hearing loss. The findings that most ears with CN deficiency had normal IAC morphology and that two ears with small IACs had CNs present indicate that IAC morphology is an unreliable surrogate marker of CN integrity. On the basis of these findings, we think that high-resolution MRI, rather than CT imaging, should be performed in all cases of pediatric hearing loss, especially in those cases where profound hearing loss has been documented. For ears with small IACs, the resolution of MRI currently remains limiting. In these cases, the determination of CN status frequently requires a variety of anatomic (CT and MRI) and functional tests (auditory brainstem response, otoacoustic emissions, behavioral audiometry, and physical examination).

Audiometry↗
PubMed1994

Nonlinear input-output functions derived from the responses of guinea-pig cochlear nerve fibres: variations with characteristic frequency.

Rate-versus-level functions (RLFs) were recorded from individual cochlear nerve fibres in anaesthetised guinea-pigs. Variations in the shapes of these functions with frequency were used to derive input-output (IO) relationships for the mechanical preprocessing mechanisms in the cochlea. It was assumed that these preprocessing mechanisms operated linearly at frequencies well below each fibre's characteristic frequency (CF). The IO functions derived at each fibre's CF provided strong evidence of compressively nonlinear preprocessing in most regions of the cochlea. However, the apparent degree of compression depended on the fibre's CF, and hence on the presumed site of cochlear innervation. For fibres with CFs of between 1.5 and 3.6 kHz, the CF derived IO functions grew at rates of around 0.5 dB/dB. For fibres with CFs above 4 kHz, the IO functions were more compressive, with high-intensity asymptotic slopes of around 0.13 dB/dB. In the highest (> or = 10 kHz) CF fibres, the degree of compression depended on the physiological condition of the cochlea; the derived IO functions becoming more linear as the cochlea became less sensitive. The derived IO technique was not well suited to analyse responses evoked by very low frequency (e.g., < 500 Hz) tones. Nonetheless, the CF RLFs from fibres with CFs lower than approximately 1 kHz provided little evidence of mechanical nonlinearity near the apex of the cochlea. These findings imply a longitudinal variation in the mechanisms of cochlear preprocessing, and provide important new tests for functional models of the cochlea.

Acoustic Stimulation↗
PubMed1983

Response of cochlear nerve fibers to brief acoustic stimuli: role of discharge-history effects.

The probability that a cochlear nerve fiber spike discharge occurs during a time interval delta t depends on both the acoustic stimulus and on aftereffects from earlier spike discharges. We have examined the influence of discharge-history on post-stimulus time (PST) histogram responses to acoustic click and tone-burst stimuli. Discharge-history effects were found to include the modification of observed interpeak times of PST responses to clicks, a loss of distinct peaks in the click response of high characteristic frequency (CF greater than 5 kHz) fibers, and changes in the ratio of initial to steady-state response portions of tone-burst responses. The method used to separate discharge-history from stimulus-related factors is based on a model developed in Gaumond et al. [J. Neurophysiol. 48, 856-873 (1982)]. The results are in general agreement with those obtained by the method of Peter Gray [Biophys. J. 7, 759-777 (1967)], which discards from consideration those portions of the response record not preceded by a silent interval of 20 or 25 ms or more. Our method requires more assumptions about the spike train, but produces less variable results by utilizing more of the spike train data.

Acoustic Stimulation↗
PubMed1996

Cochlear nerve activity after intense sound exposure in neonatal chicks.

1. Single-neuron behavior in the cochlear nerve of neonatal (3-day-old) chicks was examined after exposure to a 120-dB SPL pure tone (0.9 kHz) for 48 h. Exposed animals were tested after 0 days or 12 days of recovery. Nonexposed chicks, age-matched to the exposed animals, formed two control groups. 2. Spectral response plots were obtained from each cell. These plots described the neuron discharge rates in response to 1,767 tone burst stimuli, each with a unique frequency-intensity combination. The tone bursts were presented at frequencies between 0.1 and 4.5 kHz and for intensities between 0 and 100 dB SPL. From these plots the characteristic frequency (CF), CF threshold, and sharpness of tuning (Q10 dB) were derived for each cell. Frequency response-area functions at selected stimulus levels and rate-intensity functions at the CF were also constructed from the spectral response plots. In addition, spontaneous activity was determined. Data were obtained from 903 cells. 3. Neuron activity in the control cells revealed no differences between CF thresholds, Q10 dB, or spontaneous activity in the two age groups. However, age differences at all frequencies were noted in the rate-intensity functions. 4. A frequency-dependent loss in CF threshold was observed in the 0-day recovered cells. The threshold shift (relative to age-matched control cells) was 55-65 dB between 0.8 and 1.5 kHz, but only 10-15 dB between 0.1-0.4 kHz and 2.5-3.5 kHz. The exposed cells showed no loss in frequency selectivity (Q10 dB) at < 0.5 kHz, whereas above this frequency an increasing deterioration in tuning was noted. Spontaneous activity in the 0-day cells was suppressed across the entire range of CFs. The rate-intensity function of exposed cells had a steeper growth rate than that of control cells. 5. At 12 days of recovery, CF threshold, Q10 dB, and spontaneous activity all recovered to the levels exhibited by age-matched control cells. However, the rate-intensity function for cells with CFs between 0.8 and 1.0 kHz showed abnormal growth and higher discharge rates at saturation than the control cells. Outside of this frequency range the rate-intensity functions of control and exposed cells were similar to each other. 6. Recovery of function in the sound-damaged chick ear is accompanied by almost complete repair of the basilar papilla. The tectorial membrane, however, retains a major defect and only the lower layer of this membrane regenerates. An important observation in this presentation was the abnormal rate-intensity functions (in the 12-day recovered cells) reported for frequencies served by that region of the sensory epithelium where the tectorial membrane defect was found. This observation may be related to sustained structural damage to the short hair cell region of the papilla and/or alterations in the efferent control of papilla function mediated by the short hair cells.

Aging↗
PubMed1982

The neuronal architecture of the anteroventral cochlear nucleus of the cat in the region of the cochlear nerve root: horseradish peroxidase labelling of identified cell types.

Golgi impregnations of the posterior part of the cat's anteroventral cochlear nucleus have revealed two types of neurons, bushy cells with short bush-like dendrites and stellate cells with long, tapered processes; Nissl stains have revealed globular and multipolar cell bodies with dispersed and clumped ribosomal patterns, respectively. In the present study, we injected horseradish peroxidase into the trapezoid body. Ipsilaterally, retrograde, diffuse labelling of neurons, presumably through damaged fibers, yielded Golgi-like profiles of numerous bushy cells with typical dendrites and with thick axons projecting toward the trapezoid body. Stellate cells were almost never labelled in this way. Anterograde diffuse labelling of thick axons demonstrated calyx endings in the contralateral medial nucleus of the trapezoid body. In the electron-microscope, the perikarya of diffusely-filled bushy neurons were found to have the dispersed ribosomal pattern and the kinds of synaptic endings typical of globular cells, including large profiles of end-bulbs from cochlear nerve axons. After injections restricted to the medial trapezoid nucleus, granularly-labelled cells in the cochlear nucleus were almost completely confined to the contralateral side; Nissl counterstaining showed them to be globular cells in the posterior part of the anteroventral cochlear nucleus. After larger injections, involving surrounding regions of the superior olivary complex, granular labelling occurred throughout the ventral cochlear nucleus on both sides. There is also evidence that stellate cells in Golgi impregnations correspond to multipolar cell bodies in Nissl stains. We conclude that bushy cells typically correspond to globular cells, which receive end-bulbs from the cochlea and send thick axons to the contralateral medial trapezoid nucleus, where they form calyces on principal cells. Principal cells, in turn, are known to project to the lateral superior olive and to one of the nuclei of origin of the crossed olivo-cochlear bundle, which feeds back to the cochlea. In this circuit, correlations between synaptic patterns and particular physiological signal transfer characteristics can be suggested. These could be related to binaural intensity interactions in the lateral superior olive and to a regulatory loop involving the olivo-cochlear bundles.

Animals↗
PubMed2002

Coding of sound intensity in the chick cochlear nerve.

Tuning curves, spontaneous activity, and rate-intensity (RI) functions were obtained from units in the chick cochlear nerve. The characteristic frequency (CF) was determined from each tuning curve. The shape of each RI function was subjectively evaluated and assigned to one of four RI types. The breakpoint, discharge rate at the highest SPLs, and slopes of the primary and secondary segments were quantified for each function. The CF and RI type were then related to these variables. A new RI function was observed in which the discharge activity in the secondary segment diminished as stimulus level increased above the breakpoint. This function was called a "sloping-down" type. In 959 units, saturating, sloping-up, sloping-down, and straight RI types were identified in 39.2, 35.5, 12.6, and 12.7% of the sample, respectively. The slope of the primary segment was nearly the same in each of the four types and averaged 5.48 S. s(-1). dB(-1) across all units. The slopes of the secondary segments formed four groupings when segregated by RI type based on the subjective assignments and averaged 0.03, 1.22, -0.90, and 3.95 S. s(-1). dB(-1) in the saturating, sloping-up, sloping-down, and straight types, respectively. The data describing the secondary segments of all units were fit with a multi-compartment polynomial and showed a continuous distribution that segregated, with some overlap, into the different RI categories. The proportion of RI types, as well as the secondary and primary slopes were approximately constant across CFs. In addition, it would appear that the other parameters that define the four types were, for the most part, homogeneously distributed across the frequency axis of the chick inner ear. Finally, a comparison of RI functions having a common CF suggested that the compressive nonlinearity that determines RI type may be a phenomenon localized to individual hair cells in the bird ear.

Animals↗