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PubMed1994

The relationship between electrical acoustic reflex thresholds and behavioral comfort levels in children and adult cochlear implant patients.

The accuracy with which behavioral comfort levels could be predicted by the electrically elicited acoustic reflex threshold (EART) was examined in 35 Nucleus Cochlear Implant patients (16 adults and 19 children). EARTs were obtained by stimulating bipolar pairs of electrodes through the Nucleus Diagnostic Programming System and monitoring the change in middle ear admittance in the ear contralateral to the implanted ear. EARTs were successfully elicited in 24 patients. EARTs differed from behavioral comfort levels by a mean of 19.4 stimulus level units for adults and 9.6 stimulus level units for children. While EARTs were found to be acceptably close to behavioral comfort levels in four adults and eight children, EARTs significantly overestimated or underestimated comfort levels in the rest. The results of this study suggested that while the EART does not accurately predict comfort levels in all cases, it may provide valuable information regarding levels which should not be exceeded when programming the cochlear implant. Cautious use of information available from the EART may prove useful for programming the cochlear implant in children or adults who are unable to make reliable psychophysical judgments.

Acoustic Stimulation↗
PubMed1982

Aspartate aminotransferase immunoreactivity in cochlea of guinea pig.

The distribution of aspartate aminotransferase-like immunoreactivity in the cochlea of the guinea pig was studied at the light microscopy level. Indirect immunofluorescence histochemistry using antisera against cytoplasmic aspartate aminotransferase prepared from pig heart was applied to surface preparations of the organ of Corti and cryostat sections of the cochlea. In the modiolus, immunofluorescence was localized to spiral ganglion cells and myelinated fibers of the auditory nerve and intraganglionic spiral bundles. In the organ of Corti, immunofluorescence was seen in upper tunnel crossing fibers and at the base of outer hair cells, following a distribution similar to that of the efferent innervation of the outer hair cells. Weak immunofluorescence was seen in the inner spiral bundle and tunnel spiral bundle, but was not present in all preparations. Immunofluorescence was not seen in inner hair cells, nor at the base of inner hair cells, and may have been absent from outer hair cells. It is concluded that spiral ganglion cells and myelinated auditory nerve axons contain aspartate aminotransferase-like immunoreactivity such immunoreactivity has previously been determined in auditory nerve endings inthe cochlear nucleus. Olivocochlear neurons that innervate outer hair cells also contain such immunoreactivity while other cochlear efferents contain little or none.

Animals↗
PubMed1985

Afferent influences on brain stem auditory nuclei of the chicken: effects of conductive and sensorineural hearing loss on n. magnocellularis.

Nucleus magnocellularis is the avian homologue of the spherical cell region of the mammalian anteroventral cochlear nucleus. Its primary excitatory synaptic input is from large end bulbs of Held from the eighth nerve ganglion cells. We have examined the effects of three peripheral manipulations--middle ear ossicle (columella) removal (monaural and binaural), columella removal and oval window puncture (monaural), and monaural earplug--on cross-sectional cell area ("cell size") of second-order auditory neurons in n. magnocellularis of the chicken. Manipulations were performed between embryonic day 19 and posthatch day 4. Survival time was varied from 2 to 60 days. Air conduction and bone conduction thresholds were determined to assess for conductive and sensorineural hearing loss associated with each of these manipulations. Hair cell counts were made from basilar papillae of each experimental group. We found that a columella removal alone, which produced a 50-55-dB purely conductive hearing loss, was not associated with changes in cell size of n. magnocellularis neurons. Similarly, chronic monaural earplugging did not affect the cross-sectional area of these second-order auditory neurons. Conversely, a combined columella removal and oval window puncture, which produced a mixed hearing loss with a 15-40-dB sensorineural component was associated with an 18-20% reduction in n. magnocellularis cell area. Hair cell counts for experimental ears were not significantly different from control ears. These results, in conjunction with measurements of multiunit activity recorded in n. magnocellularis, suggest that manipulations which markedly attenuate extrinsic auditory stimulation, but do not result in chronic change in the average activity levels, also do not influence the size of n. magnocellularis cell bodies. On the other hand, a manipulation which influences overall activity levels, but does not result in degeneration of receptor cells, resulted in marked changes in n. magnocellularis cell size.

Afferent Pathways↗
PubMed1979

Projections to the ventral surface of the cat brainstem demonstrated by horseradish peroxidase.

Topical application of horseradish peroxidase (HRP) to the ventral surface of the medulla oblongata revealed various cells with axons terminating near this region. Fibers traced from the ventral surface originated in the nucleus of the tractus solitarius and the dorsal nucleus of the vagus, both near the dorsal surface of the medulla. Projections from the cochlear nucleus were also observed. Using short HRP contact time, fibers were shown which terminate at, or near, the ventral surface. The possible involvement of these projections in various responses mediated from the ventral surface is discussed.

Animals↗
PubMed1970

Auditory frequency-following response: neural or artifact?

An electrical response which reproduces the waveform and frequency of the sound stimulus can be recorded from the central neural pathway for audition. Controversy has existed for some years over whether this frequency-following response (FFR) is neural or an artifact such as remote pickup of the cochlear microphonic or cross talk in the recording system. Two experiments resolve this issue by demonstrating that the frequency-following response depends upon functionally intact neural pathways. The frequency-following response, as well as auditory evoked potentials, is abolished by section of the eighth nerve; it is reversibly abolished by cooling of the cochlear nucleus.

Cochlear Nerve↗
PubMed1978

Peripheral auditory processing in normal and abnormal ears: physiological considerations for attempts to compensate for auditory deficits by acoustic and electrical prostheses.

The processing of complex acoustic signals, such as speech, by the normal peripheral auditory system is described in terms of the properties of individual cochlear nerve fibres and the effects of lateral inhibition in the cochlear nucleus. The implications of the peripheral filtering of signals is indicated in psychophysical terms. In cochlear pathology, these filtering characteristics deteriorate, and the implications arising from the consequent deterioration in auditory frequency selectivity are outlined for the coding of loudness and for the analysis of speech. These considerations suggest theoretically ideal methods of compensation for recruitment by multichannel instantaneous compression, and for deterioration in format analysis by dichotic frequency partition. Finally, the implications for a minimal design for artificial electrical multi-electrode array stimulation of the cochlea in order to impart speech information to the profoundly deaf, are explored. Single wire stimulation, on the other hand, should be able to impart useful prosodic and minimal speech feature information to aid in lip reading and in the acquisition of speech.

Animals↗
PubMed1986

Brain stem auditory nuclei and their connections in a carnivorous marsupial, the northern native cat (Dasyurus hallucatus).

The cytoarchitecture and connections of the brain stem auditory nuclei in the marsupial native cat (Dasyurus hallucatus) were studied using Nissl material in conjunction with the retrograde transport of horseradish peroxidase injected into the inferior colliculus. Some features different from those of Eutheria include the disposition of the cochlear nuclear complex medial to the restiform body, a lack of large spherical cells in the anteroventral cochlear nucleus, a small medial superior olive, and a large superior paraolivary nucleus.

Animals↗
PubMed1991

Functional use of the Nucleus 22-channel cochlear implant in the elderly.

A questionnaire was sent to 101 Nucleus 22-channel cochlear implant recipients aged 65 years and older to investigate the perceived impact of cochlear implantation on their quality of life. The questionnaire was designed to gain insight into the patient's daily use of the Nucleus implant. Sixty-seven questionnaires were returned over a 3-month period. The results of the survey showed that elderly cochlear implant patients obtained similar benefits to younger adult patients who were implanted with the same device. We believe that the results of this study will aid other centers when counseling elderly patients on the expected daily functional benefits of this device.

Aged↗
PubMed1996

Initial independent results with the Clarion cochlear implant.

OBJECTIVE: This paper reports some preliminary findings from patients, implanted at the University of Iowa, using the Advanced Bionics Clarion cochlear implant (version 1.0). We compared the performance of patients using both simultaneous analog and nonsimultaneous pulsatile processing strategies. The performance of Clarion patients was also compared with a group of patients who were using either the feature-extraction Nucleus cochlear implant or the compressed-analog Ineraid cochlear implant. DESIGN: One aim was to compare the analog and pulsatile stimulation in 19 patients using the Clarion implant. This aim could be accomplished only partially because of difficulties encountered in adequately fitting patients with the analog strategy. A second aim was to compare the Clarion users' performance with feature-extraction Nucleus and compressed-analog Ineraid patients. Comparisons were made with all patients having 9 mo experience postimplantation. RESULTS: Subjects performed better using the pulsatile mode compared with the analog mode. All subjects chose to use the pulsatile strategy after the first 3 mo of the study. Results comparing performance at 9 mo with our compressed-analog Ineraid and feature-extraction Nucleus patients indicated, in general, better average performance for the Clarion users. CONCLUSIONS: We conclude that the pulsatile version of the Clarion cochlear implant typically produces superior performance to the analog version of that device at this stage in its development. After 9 mo of experience, users of the Clarion implant are performing better than are users of the feature-extraction Nucleus and compressed-analog Ineraid cochlear implants with comparable amounts of experience.

Adult↗
PubMed1995

Fibroblast growth factor-2-like immunoreactivity in auditory brainstem nuclei of the developing and adult rat: correlation with onset and loss of hearing.

Fibroblast growth factor-2 (FGF-2; basic FGF) is widely distributed in the developing and adult brain and has numerous effects on cultured and lesioned neural cells. The physiological role of FGF-2 in the unlesioned nervous system, however, is still not understood. We have studied the distribution of FGF-2 in the developing, adult, and functionally impaired central auditory system of the rat using specific antibodies and peroxidase-antiperoxidase immunocytochemistry. FGF-2-like immunoreactivity (FGF-2-IR) occurred in neuronal cell bodies and/or nerve fibers but was very rarely observed in glial cells. Several auditory brainstem nuclei, including the superior paraolivary nucleus, the medial superior olive, the lateral and ventral trapezoid nuclei, and the central nucleus, as well as the external cortex of the inferior colliculus, were entirely devoid of FGF-2-IR. In the dorsal cochlear nucleus, the lateral superior olive, and the nuclei of the lateral lemniscus, FGF-2-IR was not detectable in nerve cell bodies prior to adult age. Neurons in the medial geniculate body exhibited FGF-2-IR only transiently, from postnatal day (P) 5 until P16. Neurons in the medial nucleus of the trapezoid body were immunoreactive from P8 onwards. FGF-2-IR in anteroventral and posteroventral cochlear neurons disappeared at P14, i.e., at the onset of hearing, but immunoreactivity returned after P21. A transient expression of FGF-2 around the time when hearing function commences was observed in the dorsal cortex of the inferior colliculus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Longitudinal evaluation of communication skills of children with single- or multichannel cochlear implants.

Performance on speech perception, speech production, and language tests was measured over time in children who used the 3M/House or the Nucleus cochlear implant. The speech perception and production results demonstrated higher performance levels and faster rates of learning for the multichannel than for the single-channel users. The performance of the children with the single-channel implant on the speech perception and production measures reached a plateau by 1.5 years post implant, whereas the children using the multichannel device continued to show improvement after 2 or more years of implant use. Changes in language were limited over time with no obvious difference in performance as a function of type of implant.

Acoustic Stimulation↗
PubMed1984

Is the inferior colliculus an obligatory relay in the cat auditory system?

The status of the inferior colliculus of the cat as an obligatory relay in the ascending auditory pathway was examined by attempting to infiltrate totally the fibres of the brachium of the inferior colliculus on one side with horseradish peroxidase. Following a transport time of 24 h, alternate sections from thalamus to caudal brainstem were reacted with a sensitive histochemical method to reveal tracer reaction product. Results for three cats revealed that the inferior colliculus is an obligatory relay for the overwhelming majority of axons comprising the lateral lemniscus and originating in the cochlear nucleus and superior olive.

Animals↗
PubMed1991

Classification of the principal cells of the medial nucleus of the trapezoid body.

Cells in the medial nucleus of the trapezoid body were intracellularly labeled in brainstem tissue slices of two bat and two rodent species. The main cell type found in this nucleus, the principal cell, is an important link in the relay of ascending projections from the contralateral cochlear nucleus to the lateral superior olive, completing an essential pathway for sound localization. Principal cells are often viewed as a highly homogeneous group with a consistent morphology as well as a common function. Intracellular labeling has revealed a number of new axonal and dendritic features of principal cells. Some of these features vary widely from cell to cell, suggesting that the population of principal cells contains several morphologically distinct subgroups. Similar subsets of principal cells were recognized in all species examined. Five subgroups were distinguished on the basis of the position of dendritic fields. Although the dendrites of most labeled cells were confined to the medial nucleus of the trapezoid body, some principal cells had dendrites that spread outside the nucleus to one of several adjacent periolivary cell groups. Cells were also found that had dendrites that spread medially across the midline and into the contralateral medial nucleus of the trapezoid body. Axonal projections were used to distinguish two additional subgroups of principal cells. All principal cells project to the lateral superior olive and virtually all have one or more secondary projections. There are two subgroups with unusual collateral projections: one with collaterals that extended to the lateral lemniscus and one with recurrent collateral axons.

Animals↗
PubMed2000

Is the cerebellum like cerebellar-like structures?

The cerebellum and cerebellar-like structures (including the dorsal and medial octavolateral nucleus of fishes and amphibians, the electrosensory lateral line lobe of electroreceptive teleost fishes and the dorsal cochlear nucleus of mammals) have similar anatomy, common developmental origins and common cellular markers. Transplanted embryonic Purkinje cells integrate into cerebellar-like structures but not neighboring brain parenchyma, and mutations that cause cerebellar degeneration cause similar defects in cerebellar-like structures. This review advances the idea that these neuroanatomical and molecular similarities have functional equivalents. The main structural difference between the cerebellum and cerebellar-like structures, the inferior olivary nucleus, can be viewed as a relay station that evolution has interposed along the path of flow of primary sensory information to the cerebellum. Gating of sensory information to the cerebellum occurs at the level of inferior olivary nucleus depending on whether arriving information is expected. Activation of inferior olivary neurons leads to plasticity, and finely tuned inhibitory inputs suppress olivary excitation when the plasticity is not needed. Functionally, the olivo-cerebellar system performs the same kind of computation as cerebellar-like structures: the subtraction of sensory expectations.

Amphibians↗
PubMed1989

Differential ascending projections to aural regions in the 60 kHz contour of the mustache bat's inferior colliculus.

The inferior colliculus of the mustache bat is similar in many respects to the inferior colliculus of more commonly studied mammals. However, the isofrequency contour devoted to processing 60 kHz, the dorsoposterior division (DPD) is greatly expanded, encompassing an area approximately equal to one-third of the central nucleus. Of particular significance is that monaural and binaural neurons are segregated in the DPD into 4 spatially distinct aural regions. In this study we exploit the great enlargement of the 60 kHz region in the central nucleus of the inferior colliculus (ICc) of the mustache bat to determine the source of ascending projections to the 4 different aural regions of the DPD. Small iontophoretic deposits of HRP were made within each of the physiologically defined aural regions, and the locations and numbers of retrogradely labeled cells in the auditory brainstem nuclei were determined. Two major features of collicular organization were found. The first is that each aural region receives a unique set of projections from a subset of lower auditory nuclei and thus is distinguished both by its neural response properties and by the pattern of ascending projections it receives. The dorsomedial EE region receives inputs primarily from the ipsilateral intermediate nucleus of the lateral lemniscus (INLL) and ventral nucleus of the lateral lemniscus (VNLL), and the contralateral ICc. In contrast, the ventrolateral EE region receives projections from the ipsilateral medial superior olivary nucleus (MSO), VNLL, and INLL. The inputs to the EI region originate primarily from the dorsal nucleus of the lateral lemniscus (DNLL) and lateral superior olivary nucleus (LSO) bilaterally and from the ipsilateral INLL. The afferents to the EO region include the contralateral cochlear nucleus, the ipsilateral VNLL and INLL and MSO. The second major organizational feature is that the binaural nuclei of the brain-stem project upon the DPD in a more restricted manner than do some of the lower monaural nuclei, such as the VNLL and INLL, which project in a more widespread manner. The unique set of projections terminating in each aural region of the DPD suggests that the neurons should have substantially different properties, even when neurons in different regions are of the same general aural type. Moreover, the elucidation of the micro-organization of the DPD provides insights into the different ways that binaural properties of DPD neurons are created by the convergence of inputs from particular subsets of lower auditory nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1996

Connections of the torus semicircularis and oliva superior in the frog, Rana esculenta: a Phaseolus vulgaris leucoagglutinin labeling study.

The afferent and efferent connections of the frog principal nucleus (TP) of torus semicircularis (TOS) and superior olive (SO) were examined by employing the anterograde and retrograde transport patterns of Phaseolus vulgaris leucoagglutinin (PHA-L). After injecting the tracer into these nuclei it was found that the TP projected to the ipsilateral posterior and central thalamic nuclei, all subdivisions of the bilateral TDS and the ipsilateral nucleus isthmi (NI). In the rhombencephalon the projection was restricted mainly to the contralateral SO and the cochlear nucleus (CN). Retrogradely labeled cells were found in most of the areas that contained anterogradely labeled terminals. The termination areas of the SO fibers were similar to the projections of fibers of TP origin in the diencephalic and in the mesencephalic auditory centers. A strong projection was followed into the contralateral SO; the CNs received fibers at both sides. Caudally to the SO the reticular formation, the spinal nucleus of the trigeminal nerve, the solitary nucleus and the dorsal column nuclei were supplied by the fibers of the SO origin. Retrogradely labeled cells were found in the TOS, tegmental nuclei, solitary nucleus, dorsal column nuclei and in the spinal nucleus of the trigeminal nerve. Our results indicate that the frog auditory pathway is more complex at the level of the secondary and tertiary fiber projections than has been previously recognized.

Afferent Pathways↗
PubMed1997

Cochlear implant reimplantation.

The objective of this study was to determine whether insertion length and number of active channels remained the same after reimplantation of a cochlear implant. A retrospective case review of 170 consecutively implanted multichannedl cochlear implants was conducted. Seventeen of these devices had to be replaced. Data were analyzed for the Nucleus cochlear implant users who were reimplanted in the same ear. For most subjects, insertion length and number of channels remained unchanged, but a few subjects experienced substantial decreases. When the whole group was considered, a small but statistically significant drop was noted for both parameters. In conclusion, although reimplantation is technically possible, the first procedure provides the optimal surgical environment.

Adult↗
PubMed1992

Performance over time with a nucleus or Ineraid cochlear implant.

This investigation determined whether the audiological performance of cochlear implant users varied with experience. Thirteen Nucleus and 14 Ineraid subjects were evaluated at 1, 9, and 18 mo after cochlear implant connection. Ten Nucleus and five Ineraid subjects were tested at 30 mo. On average, the ability of the subjects to recognize words and phonemes in an audition-only condition improved during the first 9 mo, as did their ability to recognize spondees in noise. The phoneme scores continued to improve during the next 9 mo. Environmental sound recognition improved gradually; significant improvement from the 1 mo scores was not noted until 18 mo. About half of the subjects who demonstrated poor word recognition at 1 mo showed significantly improved percent word correct scores by 18 mo. The Nucleus and Ineraid subjects did not differ in their patterns of change over time. An information transmission analysis performed on the subjects' consonant confusion matrices showed relatively little change for the nasality and place features during the first 18 mo, and relatively large change for the voice, duration, and frication features. Most improvement in the feature scores occurred during the first 9 mo.

Cochlear Implants↗