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At least 181 records · Page 10Linked to original sources
PubMed1994

Changes in directly recorded cochlear nerve compound action potentials during acoustic tumor surgery.

Damage to labyrinthine, neural, and vascular structures may possibly account for failure to achieve hearing preservation after removal of small acoustic neuromas. The pathogenesis of auditory impairment is, however, sometimes unclear. Intraoperative monitoring of auditory evoked potentials enables us to study possible correlations between surgical maneuvers and the function of auditory structures and pathways. To this end, simultaneous recording of brainstern auditory evoked potentials and direct cochlear nerve action potentials (CNAPs) was utilized in 14 patients with small (12 to 18 mm) unilateral acoustic neuromas. The latency of the first negative component (N(1)) of the CNAPs proved extremely sensitive in detecting intraoperative auditory damage and was a good predictive index of postoperative auditory outcome. Evaluation of temporal and morphologic CNAP patterns allowed identification of coagulation close to the cochlear nerve, drilling of the internal auditory canal, and removal of the intrameatal portion of the tumor, the most critical steps in hearing preservation. The mechanisms of damage are analyzed and discussed.

Journal Article↗
PubMed1982

Cochlear nerve fiber populations in 25 patients with profound deafness due to Menière's disease or sudden deafness.

Surgical biopsy specimens of the cochlear nerve from 19 patients with Menière's disease and six patients with sudden deafness were studied. The total number of myelinated nerve fibres in the transverse fascicular area of each nerve were counted and the results were correlated with the clinical and preoperative audiological data. The total number of cochlear neurons in patients with Menière's disease ranged from 5,760 to 27,722 and in patients with sudden deafness from 8,500 to 22,714. The long duration of the disease or absent speech discrimination appeared not to be connected with lower numbers of neurons than preserved speech discrimination or short history of the disease.

Adult↗
PubMed1978

Derived cochlear nerve and brainstem evoked responses of the human auditory system. The effect of masking in the derived band.

Derived cochlear nerve and brainstem evoked responses (CBER) were obtained for various frequency bands and were masked using special maskers. These maskers were designed to match exactly the intensity/frequency profile characteristics of the bands from which derived CBERs were obtained. Derived responses were markedly affected whenever the masker frequency limits coincided with the corresponding derived band. Other derived responses from adjacent bands were not affected. Since adjacent derived bands overlap, these overlapping regions were not considered to be represented in the derived responses. Therefore the actual frequency regions which the derived responses represented were considered to be smaller than the derived bands calculated from the physical parameters of the high-pass masking noises.

Brain Stem↗
PubMed1991

Factors that influence rate-versus-intensity relations in single cochlear nerve fibers of the gerbil.

The relationship between characteristic frequency (CF) and rate-intensity curve shape was examined in 144 cochlear nerve fibers obtained from 39 Mongolian gerbils. Quasi-steady-state firing rates were measured in response to tone bursts at the CF. From each intensity curve, estimates of slope, firing rate at saturation, and dynamic range were derived using nonlinear curve fitting. Saturation firing rate was depressed for stimuli with a high duty cycle, especially for units with low rates of spontaneous discharge. The distributions of slope and saturation firing rate differed for fibers with CFs above and below 3 to 4 kHz. The interrelation of slope, dynamic range, maximum driven rate, and spontaneous firing rate was also different for fibers with CFs above and below this band. This mid-CF transition is discussed in terms of possible longitudinal changes in the function of the gerbil cochlea.

Animals↗
PubMed1978

Frequency specific components of the cochlear nerve and brainstem evoked responses of the human auditory system.

A technique of high-pass (HP) masking was used to obtain masked cochlear nerve and brainstem evoked responses (CBER) of the human auditory system. The masking noise was extended progressively into the lower frequency regions of the cochlea for consecutively recorded responses, and the effect upon the response waveform was observed. Masked response waveforms were then subtracted to produce derived CBER waveforms representing activity initiated at specific frequency locations along the cochlear partition. Derived response components from various frequency bands were characterized and related to changes in the complex CBER during the process of frequency selective high-pass masking.

Adult↗
PubMed1982

The effects of intracochlear and systemic furosemide on the properties of single cochlear nerve fibres in the cat.

1. Tuning properties and spontaneous discharge rate of single cochlear fibres in the anaesthetized cat were determined during short- and long-term poisoning of the cochlea by locally and systemically applied furosemide.2. With intra-arterial administration of furosemide, short-term reversible elevation occurred of the low threshold sharply tuned ;tip' segment of the frequency threshold (;tuning') curve (f.t.c.) by up to 40 db, without substantial changes in the threshold of the low frequency ;tail' segment of the f.t.c. These changes could occur in part without changes in the spontaneous activity and entirely without changes in the maximal evoked activity. These effects were observed in all fibres examined, the characteristic frequencies of which ranged from 3.5 to 31 kHz.3. Intracochlear administration of furosemide in 0.9 mM concentrations produced similar changes, but these were not reversible.4. The changes correlated with the depression of the amplitude of the gross cochlear action potential. The cochlear microphonic potential, however, was either unchanged, or only slightly reduced.5. In long-term furosemide poisoning of the cochlea, fibres with anomalous response properties were found alongside fibres having normal tuning. The former exhibited either reduced excitability of the low threshold tip segment, or a tip segment attenuated in both excitability and threshold.6. It is concluded that the selective effects of furosemide on the tip segment of cochlear fibre f.t.c.s offer further evidence for a physiologically vulnerable ;second filter' in the cochlea. The selective influence of the furosemide on the low threshold tip segment provides support for the hypothesis that the normal f.t.c. is generated by two largely independent processes: one vulnerable, low threshold and sharply tuned, and the other less vulnerable, but high threshold and more broadly tuned.7. The findings, obtained with an agent known to produce reversible impairment of hearing in man, provide direct physiological evidence in support of the hypothesis that in sensorineural hearing loss of cochlear origin the frequency selectivity of cochlear nerve fibres is impaired.

Action Potentials↗
PubMedDate not supplied

Cochlear nerve projections following organ of corti destruction.

Experimental organ of Corti destruction results in (1) secondary loss of all type I spiral ganglion neurons, (2) development of type III spiral ganglion neurons, (3) degeneration of most cochlear nerve myelinated fibers, and (4) terminal degeneration in the ventral and dorsal cochlear nuclei. The first signs of degenerative changes occur by eight days after organ of Corti destruction and degeneration debris remains until 28 weeks after destruction.

Animals↗
PubMed1996

[Neurinomas of the cochlear nerve].

Usually, schwannomas of the eight nerve arise from the vestibular nerve. Yet, the authors have operated from September 1993 to September 1995 three neuromas whose origin is certainly the cochlear nerve. Surgery was performed by retro-sigmoid approach magnified by endoscopic procedure of the cerebello-pontine angle before and after removing the tumor. We report here the cases and the literature is documented. Similar cases of observing cochlear neuromas at the moment of the procedure are exceptional. Because of more and more early diagnosis of these tumors, advances of microsurgery in ponto-cerebellar angle and endoscopic improvements in this area, observation of this kind of pathology could be more and more frequent.

Adult↗
PubMed2004

Ensemble spontaneous activity in the guinea-pig cochlear nerve.

Spectral analysis of electrical noise recorded from the round window (RW) of the cochlea is referred to as the ensemble spontaneous activity (ESA) of the cochlear nerve. The ESA is considered to represent the summed spontaneous activity of single fibers of the auditory nerve and changes in the spectral characteristics of the ESA have been observed in humans with tinnitus. Experiments were undertaken to determine the relationship of the ESA to auditory neurotransmission. The ESA consisted of energy centered at approximately 900 Hz, similar to the spectral peak of single auditory neuron discharges. The amplitude of the ESA was correlated with good auditory sensitivity in the 12-30 kHz region of the cochlea. Constant pure tones of 12-22 kHz suppressed the ESA reducing its amplitude in a frequency and intensity dependent manner implying that the ESA recorded at the RW is generated or dominated by neurons in the basal region of the cochlea. The ESA was significantly suppressed by round window perfusion of the P2X receptor agonist adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS) (10 mM) the glutamate receptor antagonist 6-7-dinitroquinoxaline-2,3-dione (DNQX) (1 mM), and the sodium channel antagonist tetrodotoxin (TTX) (20 microM). Following intravenous furosemide injection (40 mg/kg) reduction and recovery of the ESA correlated with similar changes in the endocochlear potential (EP). Following DNQX and ATPgammaS an additional spectral peak at 200 Hz was often observed. This peak has been postulated to be a correlate of tinnitus in humans but had not previously been observed in a guinea-pig model of tinnitus. These data confirm the spectral characteristics of the ESA in guinea-pigs and show it is dependent on the sensitivity of the auditory nerve and intact auditory neurotransmission. In addition these experiments support the view that the ESA represents summed spontaneous neural activity in the cochlea and provide a platform for studies of the influence of ototoxic compounds on the spontaneous neural outflow of the cochlea as a model of tinnitus.

Acoustic Stimulation↗
PubMedDate not supplied

Noninvasive direct stimulation of the cochlear nerve for functional MR imaging of the auditory cortex.

We herein present our preliminary experience with functional MR imaging of the direct electrical stimulation of the cochlear nerve using an MR imaging-compatible electrode placed in the external auditory meatus of five patients with binaural sensorineural hearing loss. The stimulator was placed outside the imager's bore, and the electrode produced virtually no susceptibility artifacts. In three of five patients, it was possible to activate the superior temporal gyrus during functional MR imaging. No side effects were observed.

Auditory Cortex↗
PubMed1998

Recurrence of vestibular (acoustic) schwannomas in surgical patients where preservation of facial and cochlear nerve is the priority.

The risk of tumour recurrence was measured in a series of surgically treated vestibular (acoustic) schwannoma patients where preservation of facial and cochlear nerve function was a routine objective. This report describes the influence of this surgical philosophy on the hazards of tumour recurrence or continued growth from residual tumour cells left in situ. A series of 116 consecutive vestibular schwannoma patients underwent primary surgical resection in a general community hospital by a single neurosurgeon. Recurrence of a tumour was assessed radiologically. Eighteen patients experienced a recurrence. No relationship was found between recurrence and age, residual coagulated morsels of tumour, preoperative tumour size, or opening of the internal auditory canal. Time to recurrence ranged from six to one hundred and forty-eight months and all but two recurrent lesions were non symptomatic. Lifelong follow-up of these patients is therefore, suggested.

Adult↗
PubMed1978

The validity of the derived cochlear nerve and brainstem evoked responses of the human auditory system.

It was considered that for a number of reasons, the derived response concept might not necessarily be valid when applied to the cochlear nerve and brainstem evoked responses (CBER). A statistical comparison of response measures of amplitude and latency was made between derived and non-derived responses, each representing response contributions initiated by the same locations along the cochlear partition. Relatively few statistical differences were detected. Therefore the technique of waveform summation and the production of derived response waveforms from complex responses, recorded under appropriate masking conditions, was considered to be a valid operation.

Brain Stem↗
PubMed2006

The effects of intense sound exposure on phase locking in the chick (Gallus domesticus) cochlear nerve.

Little is known about changes that occur to phase locking in the auditory nerve following exposure to intense and damaging levels of sound. The present study evaluated synchronization in the discharge patterns of cochlear nerve units collected from two groups of young chicks (Gallus domesticus), one shortly after removal from an exposure to a 120-dB, 900-Hz pure tone for 48 h and the other from a group of non-exposed control animals. Spontaneous activity, the characteristic frequency (CF), CF threshold and a phase-locked peri-stimulus time histogram were obtained for every unit in each group. Vector strength and temporal dispersion were calculated from these peri-stimulus time histograms, and plotted against the unit's CF. All parameters of unit responses were then compared between control and exposed units. The results in exposed units revealed that CF thresholds were elevated by 30-35 dB whereas spontaneous activity declined by 24%. In both control and exposed units a high degree of synchronization was observed in the low frequencies. The level of synchronization above approximately 0.5 kHz then systematically declined. The vector strengths in units recorded shortly after removal from the exposure were identical to those seen in control chicks. The deterioration in discharge activity of exposed units, seen in CF threshold and spontaneous activity, contrasted with the total absence of any overstimulation effect on synchronization. This suggested that synchronization arises from mechanisms unscathed by the acoustic trauma induced by the exposure.

Acoustic Stimulation↗
PubMed1976

[Transtympanic neurectomy of the vestibular and cochlear nerves (author's transl)].

Tympanotomy and a transvestibular approach to the fundus of the internal auditory meatus is described. The surgical technique is modified from that proposed by Alvarez de Cozar and Antoli-Candela in 1970. The surgical anatomy of the operative sites is detailed. The surgical procedure is found indicated in patients in whom preservation of hearing is not considered and vestibular neurectomy required. The described technique provides a simple but efficient and safe alternative to the translabyrinthine approach to the internal auditory meatus for division of the vestibular and cochlear nerves.

Cochlear Nerve↗
PubMed1990

The representation of the spectra and fundamental frequencies of steady-state single- and double-vowel sounds in the temporal discharge patterns of guinea pig cochlear-nerve fibers.

Psychophysical results using double vowels imply that subjects are able to use the temporal aspects of neural discharge patterns. To investigate the possible temporal cues available, the responses of fibers in the cochlear nerve of the anesthetized guinea pig to synthetic vowels were recorded at a range of sound levels up to 95 dB SPL. The stimuli were the single vowels /i/ [fundamental frequency (f0) 125 Hz], /a/ (f0, 100 Hz), and /c/ (f0, 100 Hz) and the double vowels were /a(100),i(125)/ and /c(100),i(125)/. Histograms synchronized to the period of the double vowels were constructed, and locking of the discharge to individual harmonics was estimated from them by Fourier transformation. One possible cue for identifying the f0's of the constituents of a double vowel is modulation of the neural discharge with a period of 1/f0. Such modulation was found at frequencies between the formant peaks of the double vowel, with modulation at the periods of 100 and 125 Hz occurring at different places in the fiber array. Generation of a population response based on synchronized responses [average localized synchronized rate (ALSR): see Young and Sachs [J. Acoust. Soc. Am. 66, 1381-1403 (1979)] allowed estimation of the f0's by a variety of methods and subsampling the population response at the harmonics of the f0 of the constituent vowel achieved a good reconstruction of its spectrum. Other analyses using interval histograms and autocorrelation, which overcome some problems associated with the ALSR approach, also allowed f0 identification and vowel segregation. The present study has demonstrated unequivocally that the timing of the impulses in auditory-nerve fibers provides copious possible cues for the identification of the fundamental frequencies and spectra associated with each of the constituents of double vowels.

Animals↗