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PubMed2002

Direct projections from cochlear nuclear complex to auditory thalamus in the rat.

It is known that the dorsal cochlear nucleus and medial geniculate body in the auditory system receive significant inputs from somatosensory and visual-motor sources, but the purpose of such inputs is not totally understood. Moreover, a direct connection of these structures has not been demonstrated, because it is generally accepted that the inferior colliculus is an obligatory relay for all ascending input. In the present study, we have used auditory neurophysiology, double labeling with anterograde tracers, and retrograde tracers to investigate the ascending projections of the cochlear nuclear complex. We demonstrate that the dorsal cochlear nucleus and the small cell cap of the ventral cochlear nucleus have a direct projection to the medial division of the medial geniculate body. These direct projections from the cochlear nucleus complex bypass the inferior colliculus and are widely distributed within the medial division of the medial geniculate, suggesting that the projection is not topographic. As a nonlemniscal auditory pathway that parallels the conventional auditory lemniscal pathway, its functions may be distinct from the perception of sound. Because this pathway links the parts of the auditory system with prominent nonauditory, multimodal inputs, it may form a neural network through which nonauditory sensory and visual-motor systems may modulate auditory information processing.

Animals↗
PubMed1982

Neuronal architecture in nucleus magnocellularis of the chicken auditory system with observations on nucleus laminaris: a light and electron microscope study.

This report presents the major structural features of neurons and their afferent input in nucleus magnocellularis, the avian homologue of the mammalian anteroventral cochlear nucleus. Results of light-microscope observations, as seen in Golgi, Nissl, and normal fiber preparations, as well as ultrastructural morphology are reported. In addition, cells and axons in nucleus laminaris, the presumed homologue of the mammalian medial superior olivary nucleus, are also described. In Golgi-impregnated material, the mature principal cell in nucleus magnocellularis has an ovoid soma encrusted with somatic spines. A dendrite, when present, emerges from the cell soma, travels for a short distance and breaks into a tuft of stubby terminal branches. Foremost among the afferents to nucleus magnocellularis are auditory nerve axons that terminate in large, axosomatic endings, or end-bulbs, covering a large portion of the somatic surface. Other afferents, which also end in relation to the perikaryon, are of undetermined and perhaps multiple origins. The neurons resemble the bushy cells of the mammalian anteroventral cochlear nucleus. Evidence is presented that individual axons from the nucleus magnocellularis bifurcate and send branches to the nucleus laminaris bilaterally, thus placing constraints on the binaural interactions possibly involved in lateralization functions. In electron micrographs, the end-bulbs appear as large, elongate structures which can cover a third of the cell soma. Multiple sites of synaptic specialization occur along these terminals. The synaptic membrane complexes may form directly on the cell body or on the sides or crests of somatic spines. These complexes are characterized by asymmetric membrane densities with a cluster of clear, spherical vesicles on the axonal side. Other small terminal profiles are also present on the somata receiving the end-bulbs. Dendritic profiles are scarce, in agreement with observations in Golgi impregnations. The structural findings indicate that the medial part of the nucleus magnocellularis is homologous to the anterior part of the mammalian anteroventral cochlear nucleus in that the neurons of nucleus magnocellularis are homologous to the bushy cells of the cat. On this basis, the cells in nucleus magnocellularis could faithfully preserve the acoustic response patterns generated in the auditory nerve. This should, in turn, allow a secure relay of bilateral latency differences essential for binaural interactions in the nucleus laminaris.

Animals↗
PubMedDate not supplied

Conductive hearing loss affects the growth of the cochlear nuclei over an extended period of time.

During normal growth in CBA/J mice, the volume of dorsal and ventral cochlear nuclei change very little between 1 and 3 days of age; then more than double between 6 and 12 days of age. After 12 days, the rate of growth declines, but growth continues through at least 90 days. The globular cells of the ventral cochlear nucleus also double their soma areas between 6 and 12 days, but then grow no more. The number of ventral cochlear nucleus neurons containing Nissl substance doubles between 6 and 12 days of age and then remains stable. This increase in neuronal numbers is probably caused by differentiation of neuroblasts into neurons, not by mitoses. Conductive losses from 4 to 45 days, and from 24 to 45 days, both result in reduced volume of the ventral cochlear nucleus, but have no effect on the volume of the dorsal cochlear nucleus. Globular cell area is affected by a conductive loss from 4 to 45 days of age, but not by a conductive loss from 24 to 45 days. Therefore, conductive losses affect neuropil growth beyond the time when soma size is no longer affected by these losses.

Age Factors↗
PubMed2005

Normative findings of electrically evoked compound action potential measurements using the neural response telemetry of the Nucleus CI24M cochlear implant system.

One hundred and forty-seven adult recipients of the Nucleus 24 cochlear implant system, from 13 different European countries, were tested using neural response telemetry to measure the electrically evoked compound action potential (ECAP), according to a standardised postoperative measurement procedure. Recordings were obtained in 96% of these subjects with this standardised procedure. The group results are presented in terms of peak amplitude and latency, slope of the amplitude growth function and ECAP threshold. The effects of aetiological factors and the duration of deafness on the ECAP were also studied. While large intersubject variability and intrasubject variability (across electrodes) were found, results fell within a consistent pattern and a normative range of peak amplitudes and latencies was established. The aetiological factors had little effect on the ECAP characteristics. However, age affected ECAP amplitude and slope of the amplitude growth function significantly; i.e., the amplitude is higher in the lowest age category (15-30 years). Principal component analysis of the ECAP thresholds shows that the thresholds across 5 electrodes can be described by two factors accounting for 92% of the total variance. The two factors represent the overall level of the threshold profiles ('shift') and their slopes across the electrode array ('tilt'). Correlation between these two factors and the same factors describing the T- and C-levels appeared to be moderate, in the range of 0.5-0.6.

Action Potentials↗
PubMed1976

Origins of axons in the cat's acoustic striae determined by injection of horseradish peroxidase into severed tracts.

Origins and terminations of fibers of the dorsal and intermediate acoustic striae were studied by surgically severing these tracts and injecting HRP into the incision. This procedure results in filling the severed axons with HRP. Filled axons were traced to cell groups of origin and to some terminations of the acoustic striae. HRP-labeled terminals were found in the cochlear nuclei as well as in periolivary cell groups. Filling of cells with HRP RANged from being complete, resulting in Golgi-like images, to being barely detectable. Labeled cells were abundant in the dorsal and posteroventral cochlear nucleus adjacent to the injection as well as scattered throughout the periolivary cell groups of both sides, being highest in concentration around the ipsilateral lateral superior olive. On the side contralateral to the injection, labeled cells were found along the medial border of the dorsal cochlear nucleus, in the interstitial nucleus of the stria of Held, and sparsely throughout the ventral cochlear nucleus. The distribution of labeled cells was similar following HRP injections of the dorsal cochlear nucleus, except that these injections revealed additional descending projections from the inferior colliculi and from the ventral nucleus of the trapezoid body of both sides. These additional projections were interpreted as entering the CN by a ventral route. Findings of this study are in accord with physiological recordings made from fibers of the acoustic striae.

Afferent Pathways↗
PubMed1999

Distribution of BDNF, NT-3 and NT-4 in the developing auditory brainstem.

This study describes the developmental expression of three neurotrophins, brain derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3) and neurotrophin (NT-4) in the rat auditory brain-stem using immunohistochemistry. At postnatal day 0 (PND 0), neurotrophins expression was virtually absent from all auditory nuclei in the brainstem, even though some positive neurons were observed in the mesencephalic trigeminal nucleus at this age. However, BDNF, NT-3 and NT-4 positive neurons were observed in most brainstem auditory nuclei by PND 6. At the following stages, there was a general increase in the intensity of the neurotrophins immunoreactivity and BDNF labeling was particularly prominent in most cochlear nucleus neurons. A differential pattern of staining emerged in cochlear nucleus subdivisions, with more intense staining present in the ventral part. The superior olivary complex nuclei followed a similar pattern of BDNF staining compared to the cochlear nucleus. In the adult, BDNF heavily labeled most neurons of the superior olivary nuclei and moderately labeled neurons of the inferior colliculus (IC). NT-3 and NT-4 showed a similar pattern of staining in most auditory brainstem nuclei. The first staining was observed by PND 6 in some neuronal cell bodies. NT-3 and NT-4 immunoreactivity increased in the following stages and in the adult moderate labelings were observed in most neurons of the cochlear nucleus, the superior olivary nuclei and the IC. These results show that neurotrophins are expressed 1 week before the onset of hearing and the increase of their expressions correlate with the appearance of sound-evoked activity in the system. The temporal distribution of neurotrophins does not correlate with neuronal birth, axonal outgrowth or the formation of connection in the auditory structures, suggesting a role primarily in the maintenance and/ or modulation of postnatal and adult functions.

Aging↗
PubMed2006

Auditory brainstem implants: surgical aspects.

Patients with neurofibromatosis type 2 often develop bilateral life-threatening vestibular schwannoma necessitating tumor removal, which results in deafness. We developed the auditory brainstem implant (ABI) in order to be able to electrically stimulate the cochlear nucleus complex in patients with bilateral cochlear nerve injury from bilateral schwannoma. After tumor removal, the electrode array of the ABI is inserted into the lateral recess of the fourth ventricle and placed over the surface of the ventral and dorsal cochlear nuclei. The ABI is designed to stimulate auditory neural structures within the cochlear nucleus in order to convey salient cues about the frequency, amplitude, and temporal characteristics of sounds. To date, more than 200 patients have received an ABI device at our institution. Recently, penetrating ABIs were introduced, and preliminary results of penetrating ABIs are discussed in this paper. The surgical anatomy of the nucleus and surgical placement of the ABI in patients with neurofibromatosis type 2 are described, and surgical considerations in this group of challenging patients are detailed.

Auditory Brain Stem Implants↗
PubMed2001

The cytoarchitecture of the nucleus angularis of the barn owl (Tyto alba).

The cochlear nucleus angularis (NA) of the barn owl (Tyto alba) was analyzed using Golgi, Nissl, and tract tracing techniques. NA forms a column of cells in the dorsolateral brainstem that partly overlaps with, and is rostral and lateral to, the cochlear nucleus magnocellularis (NM). Highest best frequencies are mapped in lateral NA (NAl), intermediate in medial NA (NAm), and lowest in the foot region (NAf). Cell density followed the tonotopic axis and decreased with decreasing best frequency. NA contained four major cell classes: planar, radiate, vertical, and stubby. Planar and radiate classes were further subdivided into bipolar and multipolar types according to their number of primary dendrites. Planar neurons were confined to an isofrequency band, whereas radiate neurons had dendrites that could extend across an isofrequency band. Vertical cells had long dendrites oriented perpendicularly to isofrequency bands. Stubby cells were the most numerous and were confined to an isofrequency band because of their short dendrites. Neurons in each of these four classes projected to the inferior colliculus and dorsal nucleus of the lateral lemniscus.

Animals↗
PubMed1992

Evaluations of 3M/House single-channel and nucleus multichannel cochlear implants.

3M/House single-channel (n = 158) and Nucleus multichannel (n = 71) adult cochlear implant users were surveyed about their devices. In comparison to the 3M/House users, the Nucleus users reported better speech and environmental sounds perception and more hours of daily use. However, Nucleus users also were more likely to report that the expense of upkeep and frequent movement of external parts of their implants were problems. On average, users in both groups were satisfied and felt that their implants had positively affected their lifestyle, enjoyment of social events, and employability. Differences between groups regarding these variables were not found. Multiple regression indicated that the users' ratings of the effects of their implants on speech perception, environmental sounds perception, enjoyment of social events, and lifestyle were all statistically significant predictors of satisfaction. It was concluded that the majority of the users in either group thought their devices provided real-world benefits.

Adult↗
PubMed2004

Distribution of Fos-like immunoreactivity in the auditory pathway evoked by bipolar electrical brainstem stimulation.

OBJECTIVE: The auditory brainstem implant (ABI) represents a new modality for the treatment of patients deafened as a result of complete excision of a bilateral VIIIth nerve tumor. However, little work has been done on the effect of the ABI on the mammalian auditory pathway. The aim of this study was to demonstrate the effect of the ABI using Fos-like immunoreactivity. MATERIAL AND METHODS: A bipolar electrode was implanted in the dorsal cochlear nucleus of bilaterally deafened Sprague-Dawley rats, and electrical stimulation was presented at an intensity four times that of threshold. RESULTS: Fos-like immunoreactivity was induced in the neurons of various auditory brainstem nuclei and observed in the low-to-middle frequency area. In the ipsilateral dorsal cochlear nucleus, ipsilateral posterior ventral cochlear nucleus and bilateral inferior colliculus, Fos-like immunoreactive neurons were observed as a distinct banding pattern. CONCLUSIONS: This study showed that Fos-like immunoreactivity was observed in the restricted area of the primary brainstem auditory pathway with the appropriate tonotopicity. These results indicate that the ABI can provide auditory information suitable for speech recognition.

Animals↗
PubMed2003

Parallel auditory pathways: projection patterns of the different neuronal populations in the dorsal and ventral cochlear nuclei.

The cochlear nuclear complex gives rise to widespread projections to nuclei throughout the brainstem. The projections arise from separate, well-defined populations of cells. None of the cell populations in the cochlear nucleus projects to all brainstem targets, and none of the targets receives inputs from all cell types. The projections of nine distinguishable cell types in the cochlear nucleus-seven in the ventral cochlear nucleus and two in the dorsal cochlear nucleus-are described in this review. Globular bushy cells and two types of spherical bushy cells project to nuclei in the superior olivary complex that play roles in sound localization based on binaural cues. Octopus cells convey precisely timed information to nuclei in the superior olivary complex and lateral lemniscus that, in turn, send inhibitory input to the inferior colliculus. Cochlear root neurons send widespread projections to areas of the reticular formation involved in startle reflexes and autonomic functions. Type I multipolar cells may encode complex features of natural stimuli and send excitatory projections directly to the inferior colliculus. Type II multipolar cells send inhibitory projections to the contralateral cochlear nuclei. Fusiform cells in the dorsal cochlear nucleus appear to be important for the localization of sounds based on spectral cues and send direct excitatory projections to the inferior colliculus. Giant cells in the dorsal cochlear nucleus also project directly to the inferior colliculus; some of them may convey inhibitory inputs to the contralateral cochlear nucleus as well.

Animals↗
PubMed1996

The anatomy of the cochlear nuclei and superior olivary complex of arboreal Australian marsupials.

Cytoarchitectural and morphometric analyses were carried out on the cochlear nuclear and superior olivary complexes of nine representative possums and gliders, members of a large group of nocturnal, arboreal Australian marsupials, many of which have well developed vocalizations. The cochlear nuclear complex was displaced medial to the restiform body in all species; this has previously been reported in other marsupials. The dorsal cochlear nucleus was generally very much larger than any other nucleus in this complex. A small cochlear nerve root nucleus was present in all species, a feature shared with rodents. The anteroventral cochlear nucleus was present throughout almost the entire rostrocaudal extent of the complex. The component nuclei of the superior olivary complex had similar positional relationships to those in eutherians. The lateral superior olive was the largest nucleus, having a volume usually greater than the sum of the volumes of the medial superior olive and medial nucleus of the trapezoid body. The smaller species had a very much larger number of neurons in the superior olive relative to brain size than did the larger species. A similar disproportion was demonstrated between cochlear nucleus volume and brain weight.

Animals↗
PubMed2007

Speech understanding in background noise with the two-microphone adaptive beamformer BEAM in the Nucleus Freedom Cochlear Implant System.

OBJECTIVE: This paper evaluates the benefit of the two-microphone adaptive beamformer BEAM in the Nucleus Freedom cochlear implant (CI) system for speech understanding in background noise by CI users. DESIGN: A double-blind evaluation of the two-microphone adaptive beamformer BEAM and a hardware directional microphone was carried out with five adult Nucleus CI users. The test procedure consisted of a pre- and post-test in the lab and a 2-wk trial period at home. In the pre- and post-test, the speech reception threshold (SRT) with sentences and the percentage correct phoneme scores for CVC words were measured in quiet and background noise at different signal-to-noise ratios. Performance was assessed for two different noise configurations (with a single noise source and with three noise sources) and two different noise materials (stationary speech-weighted noise and multitalker babble). During the 2-wk trial period at home, the CI users evaluated the noise reduction performance in different listening conditions by means of the SSQ questionnaire. In addition to the perceptual evaluation, the noise reduction performance of the beamformer was measured physically as a function of the direction of the noise source. RESULTS: Significant improvements of both the SRT in noise (average improvement of 5-16 dB) and the percentage correct phoneme scores (average improvement of 10-41%) were observed with BEAM compared to the standard hardware directional microphone. In addition, the SSQ questionnaire and subjective evaluation in controlled and real-life scenarios suggested a possible preference for the beamformer in noisy environments. CONCLUSIONS: The evaluation demonstrates that the adaptive noise reduction algorithm BEAM in the Nucleus Freedom CI-system may significantly increase the speech perception by cochlear implantees in noisy listening conditions. This is the first monolateral (adaptive) noise reduction strategy actually implemented in a mainstream commercial CI.

Adult↗
PubMed1995

Longitudinal assessment of physiological and psychophysical measures in cochlear implant users.

OBJECTIVE: The purpose of this study was to evaluate the effects of long-term electrical stimulation on human cochlear implant users. DESIGN: Repeated measures of electrically evoked auditory brain steam response (EABR) threshold, slope of the EABR growth function, and behavioral measures of threshold and dynamic range were made for a group of 22 Ineraid cochlear implant users and 19 Nucleus cochlear implant users over a 3- to 5-yr period. RESULTS: Data from both Ineraid and Nucleus cochlear implant users suggest that EABR threshold, slope of the EABR growth function, and behavioral measures of threshold and dynamic range remain reasonably stable for periods up to 5 yr postimplant. CONCLUSIONS: The results of this study show little evidence that prolonged electrical stimulation through daily use of a cochlear implant has deleterious effects on the auditory system.

Cochlear Implants↗
PubMed1997

Histological and physiological effects of the central auditory prosthesis: surface versus penetrating electrodes.

To rehabilitate profoundly deaf patients who are not suitable for cochlear implants, central auditory prostheses have been implanted. To compare two possible electrode configurations - penetrating and surface ones - electrical stimulation of the cochlear nucleus with both types of arrays was tested on guinea pigs and cats. Electrophysiological, autoradiographic and histological measures were used to study effects of the central auditory prostheses on the auditory pathway. The results showed that a successful electrically evoked auditory brainstem response could be recorded with both surface and penetrating electrodes in cats and guinea pigs. In guinea pigs the penetrating electrodes had advantages over surface arrays in the sense of lower thresholds and wider dynamic ranges. In cats penetrating electrodes showed lower thresholds than surface ones. In cats and guinea pigs stimulated with either surface or penetrating electrodes, evoked 2-deoxyglucose (2-DG) label was found in the auditory pathway from the cochlear nucleus to the inferior colliculus. No non-auditory tissues were found with evoked 2-DG label. Histological results showed that in subdivisions of the guinea pig cochlear nucleus stimulated with penetrating electrodes the neurone density was decreased, and the mean soma area was increased compared with the control side. In the cat, penetrating electrodes were associated only with increased mean soma area in parts of the stimulated cochlear nucleus. These results suggest that the physiological advantages of penetrating electrodes over surface ones were achieved with some trade-off in safety, especially in the guinea pig.

Animals↗
PubMed1990

Anatomy of the cochlear nuclear complex of guinea pig.

The cyto- and fibre-architecture of the cochlear nuclear complex of the guinea-pig has been studied in serial sections using Nissl, Golgi and combined cell-myelin staining of normal material, and a silver degeneration method after cochlear ablation. The nuclear subdivisions and major cell types can be recognised on the basis of those found in the cat, but there are some differences between the two species in the precise distribution and morphology of the neurons. The rostrodorsal part of the anteroventral cochlear nucleus (AVCN) contains predominantly spherical bushy cells, but these cannot be readily divided into large and small types as in the cat. Globular bushy cells are seen in the caudal region of the AVCN, but the majority occur in the posteroventral cochlear nucleus (PVCN), in an area extending from the nerve root right up to the boundary of the dorsal cochlear nucleus (DCN). The octopus cells constitute a distinct region in the most dorsomedial part of the PVCN underneath the DCN. Giant cells are seen scattered around the nerve root region. Multipolar and small cells are seen throughout the non-granular regions of the ventral cochlear nucleus (VCN) except for the octopus cell area, but occur mainly in the more rostral regions of the PVCN. Small cells occur in greatest abundance in the thin cap area at the dorsal edge of the VCN below a superficial granule cell layer. The latter covers the dorsolateral surface of the VCN, and a lamina of granule cells partially separates the PVCN from the DCN. The DCN can be divided into four layers. The outermost molecular layer (layer 1) is separated from the deeper regions by a prominent layer of granule cells (layer 2) which also contains the pyramidal cells. Molecular layer stellate cells are seen in layer 1 and a staggered row of cartwheel neurons is found at the boundary between layers 1 and 2. Layer 3 contains the basal dendrites of the pyramidal cells and some small (vertical) cells, and is innervated by the descending branches of the cochlear nerve. The deepest layer 4, which contains multipolar cells and giant cells, does not appear to receive this direct cochlear input.

Animals↗
PubMed1984

The central projections of intracellularly labeled auditory nerve fibers in cats.

The central projections of physiologically characterized auditory nerve fibers were studied in the cochlear nuclei of adult cats after intracellular staining with horseradish peroxidase (HRP). This technique consistently labels only the type I spiral ganglion neurons which contact inner hair cells in the cochlea (Liberman and Oliver, '84). The central axon of each type I neuron bifurcates in the cochlear nucleus to form an ascending branch and a descending branch. The characteristic frequency (CF) of a fiber corresponds to the dorsoventral position of these major branches and their collateral ramifications within the nucleus. Fibers of low CFs are distributed ventrally, and fibers of increasing CF are distributed progressively more dorsally. In some cases, the collateral branches deviate from this tonotopic arrangement, particularly in (1) the octopus cell region of the posteroventral cochlear nucleus, (2) the zone of bifurcations of the auditory nerve fibers, and (3) the anterior, dorsal, and lateral margins of the ventral cochlear nucleus. Spontaneous discharge rate (SR) is related to the complexity of the axon arbor, especially along the ascending branch. Fibers of low and medium SR exhibit more axonal branch points and longer collateral lengths than do those with high SR. Six of 37 labeled fibers fail to innervate the dorsal cochlear nucleus, a feature apparently unrelated to CF or SR.

Afferent Pathways↗
PubMed1994

Surgical treatment and rehabilitation of prelingually and perilingually deafened children and adults with the nucleus multichannel cochlear implant.

We began our program in September 1992, using the Nucleus 22 Channel Cochlear Implant. To date, we have operated on four patients, one child with congenital hearing loss, two prelinguistically deaf adults and one perilingually deaf adult. Our results have shown a significant increase in auditory and speech reception and perception skills in the child. The perilingually deaf adult is able to understand speech in open set speech discrimination testing and, although we do not expect open set speech discrimination in the prelinguistically deaf adults, to date their results have been satisfactory. The two prelingually deaf adults are in an audiological rehabilitation program. Their response in prosodic aspects of speech and lipreading ability with sound have improved significantly. The only surgical complication was an infection of the flap in the child, but it was treated satisfactorily with i.v. penicillin.

Adult↗