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PubMed2004

[Treatment of severe hearing loss. Hopeful results with cochlear implants and nerve cell implantations].

Progress in techniques and strategies for tissue engineering has increased our interest in allografting and xenografting in various organ systems. Previous work has shown that peripherally implanted fetal dorsal root ganglion neurons (DRGs) can grow axons across the boundary between the central and peripheral nervous system in the dorsal root and make functional connections within the spinal cord. We have extended this experimental paradigm to the auditory system and successfully implanted fetal DRG neurons into the normal and deafened cochlea, adjacent to deafferented auditory spiral ganglion neurons. These findings demonstrate the feasibility of using fetal sensory cells in a new strategy to repair or replace the auditory nerve. Further studies will show whether the surviving DRGs can restore a functional conduit from the cochlea to the brainstem. If so, implanting neuronal tissue close to the auditory nerve could be used to regain auditory function in e.g. profoundly deaf patients.

Animals↗
PubMed1981

The acoustic reflex test in cochlear and eighth nerve pathology ears.

The clinical interpretation of acoustic reflex test results in ears with sensorineural impairment should be based on a consideration of three characteristics of the response: the reflex threshold hearing level, the reflex threshold sensation level, and the decay of the reflex. Examination of results in 152 ears with cochlear pathology and in 152 ears with acoustic tumor indicated that in some cases the combination of characteristics may be contradictory as to site of lesion. Regarding a contradictory response pattern as questionable -- neither confirming nor denying a specific site of lesion -- improves the predictive accuracy of the test through a reduction in the number of false identifications.

Adolescent↗
PubMed2005

Neuro-otologic findings in unilateral isolated narrow internal auditory meatus.

OBJECTIVE: To report neuro-otologic findings concerning the four nerves in the internal auditory meatus (IAM) in patients with isolated congenitally narrow IAM and explore the implications regarding ontogeny of the nerves in the IAM. DESIGN: Retrospective case series study. SETTING: University hospital. SUBJECTS: Five consecutive patients between 1997 and 2002 with unilateral isolated narrow IAM demonstrated by high-resolution computed tomography whose chief complaint was hearing loss (1 male and 4 females, 4 right sides and 1 left; age range 5-37 years, mean 20 years; IAM diameter at the porus: 26-33% of that on the normal side). MAIN OUTCOME MEASURES: Functional studies concerning the VIIth cranial nerve and the three branches of the VIIIth cranial nerve. RESULTS: In all ears, auditory brain stem responses were absent, the speech discrimination score was 0%, and otoacoustic emissions were absent or markedly reduced compared with those on the normal side. Caloric responses were absent in two ears, reduced in two ears, and normal in one ear. Galvanic body sway tests showed no responses in the two ears in which caloric responses were absent. Inferior vestibular nerve function was estimated as normal in all ears on the basis of vestibular evoked myogenic potential recordings. Facial nerve functions were normal in all patients. CONCLUSIONS: In isolated congenital stenosis of IAM, dysfunction of each nerve in the IAM can occur independently. In the ontogeny of the VIIIth cranial nerve, the cochlear and superior vestibular nerves tended to be involved together, whereas the cochlear and inferior vestibular nerves appeared independent of each other.

Adolescent↗
PubMed1993

The projections of intracellularly labeled auditory nerve fibers to the dorsal cochlear nucleus of cats.

The cochlear nucleus receives incoming auditory nerve discharges, preserves or transforms the signals, and distributes outgoing activity to higher centers. The organization of auditory nerve input to the cochlear nucleus will heavily influence the mechanisms by which acoustic information is processed. In order to study structure-function relationships between auditory nerve and cochlear nucleus, the axonal arborizations of type I spiral ganglion cells were labeled with intracellular injections of horseradish peroxidase after first being electrophysiologically characterized by recording with a micropipette inserted into the axon. For each auditory nerve fiber, spontaneous discharge rate (SR) and a frequency tuning curve were determined. The tuning curve yielded the characteristic frequency (CF, that frequency to which the fiber is most sensitive) and CF threshold in dB SPL. Individual axonal arborizations including all terminal swellings were reconstructed through serial sections with the aid of a light microscope and drawing tube. On average, 13.4 +/- 8.1% of the terminal swellings were found in the dorsal cochlear nucleus (DCN) and the remaining terminal swellings were located in the ventral cochlear nucleus. In the DCN, the terminal fields of auditory nerve fibers were restricted to layer III, contributed to cytoarchitectonic striations, and exhibited a systematic relationship between fiber CF and position along the strial (or long) axis of the nucleus. Computer-aided rotations revealed that the terminal fields were anisotropic, being flattened within the trans-strial axis. The maximal width of the terminal fields along the strial axis ranged from 31-321 microns and was inversely related to fiber CF and SR. Variation in the number of terminals or depth of the terminal field within layer III was not related to SR grouping or CF of the fiber.

Animals↗
PubMed1975

Acoustic reflex and reflex decay. Occurrence in patients with cochlear and eighth nerve lesions.

Acoustic reflex and reflex decay tests were administered to 50 normal ears, 50 ears with hearing loss due to noise trauma, 50 ears that had Meniere disease, and 28 ears that had involvement of the eighth nerve. In one normal ear, ten noise trauma ears, 11 Meniere disease ears, and 24 eighth nerve lesion ears to reflexes or reflex decay that were suggestive or retrocochlear lesions were observed. Acoustic reflex and reflex decay results are also compared to tone decay results for these patients.

Acoustic Stimulation↗
PubMed1985

Electrophysiologic studies in neonatal adrenoleukodystrophy.

Recent electrophysiologic studies have focussed attention on the X-linked adrenoleukodystrophy (ALD) and its myeloneuropathic variant. No organized studies are, however, yet available on its relatively recently described neonatal variant. We conducted electroencephalographic, electroretinographic and evoked response studies in 2 patients with neonatal ALD. In one patient, an infant, initial EEG, hypsarrhythmic in waking and somewhat periodic in sleep, showed dramatic improvement on ACTH therapy accompanied with a seizure-free status. The EEG and clinical improvement, however, were temporary. No improvement occurred following pyridoxine therapy. Her electroretinogram (ERG), visual evoked responses (VERs) and far-field short latency brain-stem auditory evoked responses were also abnormal. The latter studies probably reflected photoreceptor degeneration, optic nerve involvement, cochlear and/or auditory nerve involvement respectively in neonatal ALD. The other patient, a 3.5-year-old girl, also had an EEG characterized by a moderate- to high-amplitude slow background activity and high-amplitude multifocal, generalized or periodic paroxysmal discharges, but presence of some better formed theta frequencies in background activity precluded a hypsarrhythmic label on her EEG. Her ERGs and VERs were totally extinct but in contrast to the first patient, she had clear-cut optic atrophy and retinitis pigmentosa on ophthalmological examination.

Adrenoleukodystrophy↗
PubMed1978

Auditory responses in cats produced by pulsed ultrasound.

Auditory-nerve responses and cochlear microphonics are produced in cats by pulsed 5-MHz ultrasonic energy from a transducer placed against the dura mater. The pulses must be relatively intense (approximately 30 W/cm2) to produce a response, but can be sufficiently brief (less than 70 microsecond) that the brain tissue is not observably heated. The cats apparently respond to radiation pressure transients accompanying the absorption of the ultrasound in the brain tissue. Both the amplitude and latency of the N1 neural responses to the ultrasound can be matched to those produced by relatively weak tone pips or clicks from an external source. The cochlear microphonic (CM) produced by a pulse shows a prominent ringing at 5-10 kHz in different cats; the amplitued of the N1 response exhibits broad maximum, for constant amplitude pulses, a pulse widths of 20-60 microsecond. This variation of N1 response amplitude with pulse width is similar to that of a high-pass filter with a cutoff frequency at the dominent frequency of the CM, which is tentatively identified with a ringing frequency of the skull.

Acoustic Stimulation↗
PubMed1983

Synaptic organization of eighth nerve afferents to cat dorsal cochlear nucleus.

The synaptic organization of eighth nerve afferents to the dorsal cochlear nucleus (DCN) of cats was studied using extracellular field potential analyses. The eighth nerve was electrically stimulated and potentials produced in the DCN characterized using single shocks, paired shocks, repetitive stimulation, and one-dimensional current source-density (CSD) analysis. Field potentials and CSD profiles were correlated with the laminated cytoarchitecture of the DCN. At least four major temporally discrete components can be identified in field potentials evoked by a single shock to the eighth nerve. The amplitude and polarity of these events depends on the layers in which they are recorded. A brief positive-negative deflection (the P1-N1) is present in all layers but is maximal in the deeper layers 3 and 4. The N1 has a peak latency of approximately 0.8 ms in these layers. The N1 in the deep layers is followed by a large negative potential, termed the N2, with a peak latency of about 1.6 ms. In the superficial layers (1 and 2), the N1 is followed by a small positive potential (the P2) occurring nearly simultaneously with the N2, Immediately following the N2 is another negative potential that is most clearly observed in layer 2. The layer 2 negative wave is termed N3 and is also identifiable on the repolarizing phase of the N2 in layers 3 and 4. The N3 in layer 2 can be followed by a positive potential, the P4. Simultaneous with the P4 is a small negative wave ion layer 1, termed the N4. The P4-N4 complex is observed in about half the recordings. Frequency-following tests indicate that both the N1 and N2 waves can follow shock trains up to 333 Hz. The N1 remains nearly constant in amplitude up to about 300 Hz and decreases as the stimulus frequency is raised to 500 Hz. The N2 decrements more rapidly than the N1 at frequencies above about 250 Hz and is considerably reduced at 500 Hz. The N2 sometimes shows an increased amplitude (by about 20-40%) between 100 and 250 Hz. A paired-shock paradigm was used to characterize further potentials. The N1 was little affected by prior stimulation for intervals greater than 5 ms. The N2 and N3 generally showed a small facilitation for shock intervals from about 7 to 30 ms, with a return to base line at longer intervals. The N4 and P4 (when present) were profoundly depressed for intervals from 7 to about 30 ms, with recovery to control values by 50 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

Favorable outcome of cochlear implant in VIIIth nerve deficiency.

OBJECTIVE: To report on the outcomes of cochlear implantation (CI) in a child with cochleovestibular nerves (CVN) hypoplasia. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center, University hospital. PATIENTS: An 18-month-old child with profound bilateral congenital hearing loss and bilateral hypoplasia of the CVN at imaging. INTERVENTION: Left CI at age 29 months with a Nucleus Contour device (Cochlear Ltd., Lane Cove, New South Wales, Australia) after unsatisfactory results of hearing aid use for 10 months. MAIN OUTCOME MEASURES: Speech perception tests, behavioral observation, electrophysiologic tests, and cognitive evaluation. RESULTS: Although the child scores poorly in every perceptive category with the CI alone, the device greatly enhances his speech understanding with the hearing aid in the opposite ear. In the bimodal condition, his words and sentences identification, recognition, and comprehension far exceed the monaural figures. The Meaningful Auditory Integration Scale (MAIS) tests reaches a score of 26/40, and the MacArthur's questionnaires confirm the improvement of language production and comprehension. These results became noticeable after 5 to 6 months and continued to improve up to the 10th month. The child's cognitive scores and overall performance competences greatly benefit from the CI, with the mental age overcoming the chronological age. CONCLUSION: We can confirm the chance of achieving satisfactory results by CI even when the imaging of CVN is doubtful and the electrophysiological tests are disappointing. In our experience, a CI in Type IIb dysplasia of the CVN is a feasible option, provided that the candidate shows some responses at aided audiogram and at least minimal signs of language development. Adequate counseling is necessary for these children because the expected outcome is somewhat lower than that of their deaf peers with normal appearance of the nerves.

Audiometry, Pure-Tone↗