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PubMedDate not supplied

Performance of adult Ineraid and Nucleus cochlear implant patients after 3.5 years of use.

Forty-two postlingually deafened adult patients, 21 with a formant extraction version of the Nucleus cochlear implant and 21 with the Ineraid cochlear implant (analog processing), were evaluated on a series of speech perception tests after using their implants for about 3.5 years. A wide range of performance was observed across patients for both devices. All but 4 patients showed an enhancement in their lipreading ability with the implant. Word recognition averaged about 14-19% correct, and word recognition in sentences averaged about 43-49% correct for the two implant groups. Average performance was superior with the Ineraid implant on consonant recognition in noise. An information transmission analysis suggested that vowel perception was influenced by first- and third-formant frequency for the Nucleus, and first-formant and fundamental frequency for the Ineraid patients. It appeared that the Ineraid device was more effective, on average, at conveying information about consonant nasality and frication. For consonant perception, nasality and frication contributed most to the total information transmitted for both implant types. Both devices had difficulty conveying information about vowel second-formant frequency and consonant place information. These scores at 3.5 years are substantially elevated from preoperative performance and, overall, the patients clearly benefit from their implant.

Adult↗
PubMed1994

The unipolar brush cells of the rat cerebellar cortex and cochlear nucleus are calretinin-positive: a study by light and electron microscopic immunocytochemistry.

Cell class-specific markers are powerful tools for the study of individual neuronal populations. The peculiar unipolar brush cells of the mammalian cerebellar cortex have only recently been definitively identified by means of the Golgi method, and we have explored markers of cerebellar neurons with the purpose of facilitating the analysis of this new cell population and, especially, its distribution and ultrastructural features. By light microscopic immunocytochemistry, we demonstrate that, in the rat, the unipolar brush cells are the cortical neurons that are most densely immunostained with antiserum to calretinin, a recently discovered calcium-binding protein. The unipolar brush cells are highly concentrated in the flocculo-nodular lobe, the ventral uvula and the ventral paraflocculus, occur at relatively high density in the lingula, at moderate-to-low density in other folia of the vermis and in the narrow intermediate cortex, and at low to very low density, with the exception of a few hot spots, in the lateral regions of the cerebellar hemispheres and in the dorsal paraflocculus. Unipolar brush cells are also found in the cochlear nucleus. In addition to the unipolar brush cells, calretinin antibody distinctly stains certain mossy fibers, and weakly to moderately stains other cerebellar elements, such as granule neurons and climbing fibers. In the lobules containing high densities of unipolar brush cells, the granule cell bodies and the parallel fibers are much less immunoreactive, and there are many more densely immunostained mossy fibers than in the lobules, where these cells are rare, which suggests some relationships between these elements. In the cerebellar nuclei, small neurons are densely immunostained, while large neurons are immunonegative. The unipolar brush cells reside nearly exclusively in the granular layer. They are small neurons, intermediate in size between granule cells and Golgi cells, and their features are remarkably similar across all lobules. They usually have a single, relatively thick dendrite of varying length that terminates in a brush-like tip consisting of several short branchlets. Utilizing a pre-embedding protocol, we have identified unipolar brush cells with the electron microscope. The cytoplasm of these cells is partially obscured by the electron dense product of calretinin immunoreaction in all regions of the soma and processes. The cells are often covered with non-synaptic appendages and contain a peculiar cytoplasmic inclusion consisting of ringlet subunits. Other characteristic components are numerous neurofilaments, mitochondria and large, dense-core vesicles. Individual brushes enter one or two glomeruli, where the dendritic branchlets establish an unusually extensive synapse with mossy fiber rosettes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1982

Abnormal tonotopic organization in the ventral cochlear nucleus of the hearing-impaired DBA/2 mouse.

The representation of sound frequency by auditory neurons (tonotopic organization) was evaluated in the ventral cochlear nucleus (VCN) of DBA/2 mice, a strain with impaired sensitivity to the highest and lowest frequencies heard by normal mice. Tuning curves were obtained from multiple-unit activity (MUA) and compared with those of C57 mice, which do not have severe hearing loss. Tuning curves in the C57 VCN displayed the dorsoventral progression from high- to low-frequency sensitivity that is typical of mammals. By contrast, tuning curves of DBA mice varied little as a function of dorsoventral location, and most MUA thresholds were lowest for frequencies within a narrow range (about 12-16 kHz). Thus, normal tonotopic organization is absent in the DBA mouse's VCN. In addition, because of the consistently low thresholds for 12-16 kHz tones in DBA MUA, mean thresholds for these frequencies are lower than those of C57 MUA in the dorsal and ventral portions of the VCN.

Animals↗
PubMed1982

The maturation of the end bulb of Held in the rat anteroventral cochlear nucleus.

The maturation of the end bulb of Held was studied in serial thin sections through the rostral pole of the rat anteroventral cochlear nucleus (AVCN) at 2-day intervals from birth through 16 days of age. In the neuropil of newborn rats primary auditory terminals occasionally synapse with large dendritic processes of spherical cells. Between 6 and 10 days of age, the spherical cell has numerous, long, fingerlike appendages at the base and proximal part of its primary dendrite which extend into the neuropil and envelope a single primary terminal. Small processes from the terminal extend along the appendages toward the cell body. At 10 days, these processes reach the dendritic pole of the soma and fill the interstices between the appendages. Synaptic contacts are present between the end bulb processes and the cell body. At 12 days, the end bulb covers most of the dendritic pole of the spherical cell. The remaining somatic appendages are small and are clustered beneath the end bulb. Synapses between the end bulb and soma are frequent. At 16 days, the end bulb resembles that seen in the mature rat. Nonprimary terminals appear on the soma at 10 days. These terminals are randomly distributed, with fine processes which extend from the end bulb over the remaining regions of the cell body.

Aging↗
PubMedDate not supplied

Ultrastructural features of neurons in the C57BL/6J mouse anteroventral cochlear nucleus: young mice versus old mice with chronic presbycusis.

Transmission electron microscopy was used to examine "bushy" and "multipolar" neurons in the anteroventral cochlear nucleus (AVCN) of young (2-month-old) and old (2-year-old) C57BL/6J mice, a strain that develops profound peripheral sensorineural auditory impairment during the second year of life. Two features differed with age irrespective of cell type or location within the AVCN: there was an increase in the incidence of neurons with heterochromatic nuclei and an increase in the percent of the neuron occupied by lipofuscin. Two features differed with age in multipolar cells only: there was a decrease in the roundness of nuclei and an increase in the number of nuclear invaginations. Some features differed with age to a greater extent in the dorsal portion of the AVCN: there were decreases in the length of terminals on bushy cells, and in the percentage of soma surface apposed by terminals, and increases in the incidence of neurons contacted by myelinated axons, in mean synaptic vesicle density, and in the amount of lipofuscin in bushy cells. Some features did not differ with age: the mean area of mitochondria, percentage of cytoplasm occupied by mitochondria, size of dense synaptic junctions, and for bushy cells only, nuclear shape and invaginations and width of perinuclear cisternae. Aging per se, chronic presbycusis, and neuronal type play roles in determining age-related changes in AVCN neurons.

Age Factors↗
PubMed2001

Tonotopic projections of the auditory nerve to the cochlear nucleus angularis in the barn owl.

The nucleus angularis (NA), one of the two cochlear nuclei of birds, plays an important role in the processing of sound intensity. To begin investigating the NA in detail in the barn owl, which is a popular animal model for neural mechanisms of sound localization, a frequency map for this nucleus is presented here. Focal injections of horseradish peroxidase or neurobiotin were placed either in the NA or in the cochlear nucleus magnocellularis, labeling small groups of auditory nerve fibers of known characteristic frequency (CF) from 0.25 to 9.6 kHz. The courses of their axonal branches were used to construct a composite average map of the tonotopic frequency representation in the nucleus angularis. Nucleus angularis in the barn owl, as seen in frontal sections, resembles a sheet of cells bent approximately into an S shape. The lowest frequencies were found represented at the ventromedial extreme. The representation of increasingly higher frequencies then followed the S shape, with the highest frequencies located at the ventrolateral tip. Auditory nerve fibers of a given CF always entered the nucleus angularis within a well-restricted area and then traveled along their isofrequency band within the NA while branching off terminals. The isofrequency bands were typically slanted from caudo-ventro-medial to rostro-dorso-lateral. The basic tonotopic organization is comparable to that found in other birds, the major differences being the large size and unusual shape of the barn owl's nucleus angularis.

Animals↗
PubMed1991

Simulations of cochlear nucleus neural circuitry: excitatory-inhibitory response-area types I-IV.

Several circuitry schemes have been explored among model stellate and fusiform cochlear nucleus neurons in an effort to reproduce excitatory-inhibitory response-area (EIRA scheme) types I-IV. Single cell models incorporated known nonlinear membrane properties and spike-discharge characteristics, as described in previous modeling and intracellular recording. In addition, a unique method of implementing dendritic electrotonic distance processing was developed that provides greater computational efficiency, but with results similar to compartmental models. As an initial simple case, results were examined for a kHz pure tone. Auditory nerve (AN) population responses across characteristic frequencies from 200 Hz to 50 kHz based on actual single unit recordings were incorporated into the model as input. The findings and conclusions are (1) relatively simple inhibitory connections among stellate and fusiform cells, all of which receive AN excitatory inputs, can account for the salient features of EIRA-scheme types I-IV; (2) both types III and IV may be obtained using fusiform cells with small adjustments in the anatomical connections; (3) if stellate cells laterally inhibit their own neighbors, they can create inhibitory sidebands, but may have difficulty avoiding multiple sidebands; (4) in the model, type II cells are not responsive to broadband noise but rather to pure tones, and the reason for this was partly because the type II cells were inhibited by other CN units, and partly because the simulated AN fiber response to broadband noise was near their threshold; and (5) the type IV complex response areas may actually arise not necessarily because of elaborate circuitry, but as a result of a complex AN fiber population profile at high stimulus levels in conjunction with the type II inhibitory input to the type IV cells.

Acoustic Stimulation↗
PubMed1981

Postnatal development of frequency and intensity sensitivity of neurons in the anteroventral cochlear nucleus of kittens.

Tuning curves and spike count-vs.-intensity functions were derived form tone-burst responses of single neurons of the anteroventral cochlear nucleus of kittens 4-45 days of age. During the first postnatal week tuning curves are relatively shallow and thresholds are high. With advancing age there is a progressive reduction in threshold and sharpness of tuning. Sharpening of tuning during the first several weeks postpartum seems to be due to a differential reduction in threshold between CF and frequencies below CF. Spike count-vs.-intensity functions are steep in young kittens as compared to adults. During the first few postnatal weeks the dynamic range and shapes of the functions take on the characteristics of adult AVCN neurons.

Action Potentials↗
PubMed1987

Efferent projections from posteroventral cochlear nucleus to lateral superior olive in guinea pig.

Phaseolus vulgaris leucoagglutinin (PHA-L), a kidney bean lectin used as an anterograde tracer, was iontophoretically injected into the posteroventral cochlear nucleus (PVCN) of guinea pigs. PHA-L-labeled fiber segments and their terminal specializations were observed within the ipsilateral lateral superior olive (LSO) thereby establishing the existence of an efferent neural pathway from PVCN to this nucleus. Furthermore, the pathway is topographically organized with dorsal regions of PVCN projecting to the medial limb and ventral regions projecting to the lateral limb of LSO.

Animals↗
PubMed1991

A search for a mesencephalic periaqueductal gray-cochlear nucleus connection.

Horseradish peroxidase placed into the ventral mesencephalic periaqueductal gray (PAG) and in the lateral superior olivary complex region demonstrated indirect paths towards the cochlear nucleus (CN). Because no direct connections could be observed, a pathway throughout the auditory efferent system was proposed. The results suggest three possibilities: 1) The PAG is connected to the lateral superior peri-olivary complex synapsing with known efferent fibers that reach the CN; 2) Neurons located at the dorsal PAG were demonstrated to be connected to the inferior colliculus (IC). The possibility of synapses with known neurons that run from IC to the CN is postulated; 3) Neurons in the trapezoid body, which are partially associated with a system that communicates with the CN, are also connected to and from the PAG. The present results anatomically support an extracellular study (1) describing PAG actions on CN units.

Animals↗
PubMed1976

Intracellular study of synaptic events related to phase-locking responses of cat cochlear nucleus cells to low frequency tones.

In this study intracellular recording techniques were used to study the synaptic events related to phase-locking of cochlear nucleus cells to low frequency stimuli. A variable degree of phase-locking was noted even with units of the same low characteristic frequency. With low frequency phase-locking units an excitatory postsynaptic potential (EPSP) occurred in response to each period of the frequency stimulus, but the probability of an action potential occurring decreased as the frequency of the stimulus was raised. Complex units were described which phase-locked at lower frequencies of stimulation but did not at higher frequencies where the temporal pattern of firing to tone burst stimulation changed as well. Results are discussed as they relate to the frequency following response recorded with gross electrodes in the lower auditory pathway and the relationship to frequency coding in the auditory pathway.

Animals↗
PubMed1993

Development of GAD-immunoreactivity in the dorsal cochlear nucleus of the hamster and cat: light and electron microscopic observations.

Physiologic and pharmacologic evidence suggests that inhibitory influences are active in the mammalian dorsal cochlear nucleus (DCN) by the onset of hearing, while anatomical evidence suggests that inhibitory synapses are not present until days or weeks later. One inhibitory neurotransmitter in the DCN is gamma aminobutyric acid (GABA) and its presence can be indexed by immunohistochemical localization of its synthetic enzyme glutamic acid decarboxylase (GAD). The present study investigated the ingrowth and synapse formation of GAD-immunoreactive inputs in the DCN of cat and hamster. GAD-immunoreactive puncta are present in the DCN of the cat at birth and of the hamster on postnatal day (PND) 3. Thus, the present data correlate well with the physiologic and pharmacologic evidence. In both species the first labelled puncta are near the dorsal acoustic stria and may originate from efferent axons in the stria. Several days later a band of labelled puncta is found in the fusiform cell layer. This location is equivalent to the termination zone of cartwheel cells, GAD-immunoreactive interneurons in the DCN. Based on this spatiotemporal sequence in the appearance of GAD-immunoreactive puncta, we suggest that sources of GABA extrinsic to the DCN mature first, followed by intrinsic sources.

Animals↗
PubMed1994

Intraoperative and postoperative electrically evoked auditory brain stem responses in nucleus cochlear implant users: implications for the fitting process.

Electrically evoked auditory brain stem responses (EABR) were measured in 12 adults and 14 children with the Nucleus cochlear implant. Measures were made both intraoperatively and several months following surgery. EABR thresholds were consistently greater than clinically determined measures of behavioral threshold (T-level) but less than maximum comfort levels (C-level). When the data were pooled across subjects and different stimulating electrodes, EABR thresholds were strongly correlated with both T- and C-levels. In subjects where both intraoperative and postimplant EABR measures were obtained, intraoperative EABR thresholds were consistently higher than postimplant thresholds. The electrophysiologic data have been incorporated into a practical procedure for programming the implant in young children.

Acoustic Stimulation↗
PubMed2004

Optimizing dynamic range in children using the nucleus cochlear implant.

OBJECTIVE: The aim of this study was to investigate the benefits of the preprocessing scheme "Adaptive Dynamic Range Optimization" (ADRO) in children using Nucleus cochlear implants. Previous research with adults indicates improved speech perception in quiet and improved sound quality in everyday listening environments with the ADRO scheme. DESIGN: Children were given 4 wk of take-home experience with ADRO, with a minimum of 2 wk in which ADRO was "locked-in." After 1 wk of ADRO use and again after 4 wk of ADRO use, Bench-Kowal-Bamford (BKB) sentence perception in quiet at a low input level of 50 dB SPL (unweighted root mean square) and sentence perception in noise were compared with the child's everyday (Standard) program and the ADRO program. Children also rated the loudness of a variety of environmental sounds and indicated which program provided the best hearing in a variety of everyday listening situations. RESULTS: On average, BKB sentence perception in quiet at 50 dB SPL was significantly better with the ADRO program compared with the Standard program. The group mean improvement was 8.60%. Similarly, group mean scores for BKB sentences presented at 65 dB SPL in multitalker babble were significantly higher with the ADRO program (an improvement of 6.87%). The ADRO program was the preferred program in 46% of the listening situations, whereas the Standard program was preferred in 26% of situations. Everyday sounds were not unacceptably loud with ADRO. CONCLUSIONS: There was an ADRO benefit for this group of children in quiet and in noise. These findings suggest that young children would benefit from the ADRO programming option being locked in along with other processor settings in the SPrint processor once their MAP levels have stabilized. Some older children and teenagers may choose to use ADRO selectively for specific listening situations.

Acoustic Stimulation↗
PubMed1991

Organization of dorsal cochlear nucleus type IV unit response maps and their relationship to activation by bandlimited noise.

1. Response maps of 49 type IV neurons in cat dorsal cochlear nucleus (DCN) were studied by moving a tone in small steps along the frequency dimension and along the intensity dimension. Type IV responses are recorded from DCN principal cells. Data were collected from 38 units with best frequencies (BFs) from 2.16 to 50.3 kHz with the use of electrode penetrations along the long (strial) axis of the DCN; an additional 11 units from a previous study were analyzed. A stereotypical type IV response map is defined as consisting of two excitatory and two inhibitory regions. Type IV units from both the pyramidal cell layer (probably pyramidal cells) and the deep layer (probably giant cells) show the same types of response maps. 2. Two of the regions, one excitatory and one inhibitory, are seen in all type IV units. These regions are a low-threshold excitatory region at best frequency (BFER) and an inhibitory area at higher levels, usually centered below BF but extending upward in frequency to include BF (central inhibitory area, or CIA). The high resolution of the response maps in this paper allows us to show that type IV units fall into two groups on the basis of whether their CIAs are narrow with well-defined borders (35 units) or broad with poorly defined borders (14 units). 3. Two additional features of type IV response maps can be defined, most consistently in units with well-defined CIAs. These features are an excitatory region along the high-frequency edge of the CIA (upper excitatory region, UER) and an upper inhibitory sideband (UIS). The BFER and UER are continuous in many units, but in some cases their continuity is broken by the CIA. It seems likely that the BFER and UER represent a single excitatory input to type IV units and are revealed because the tuning curve of the stronger inhibitory inputs that produce the CIA has thresholds greater than and BFs lower than the excitatory inputs. 4. The CIA is probably produced by inhibitory inputs from DCN type II neurons. The bandwidths of type IV CIAs are about 1-3 times larger (at 40 dB above threshold) than the excitatory bandwidths of DCN type II units, suggesting a convergence of the equivalent in tuning of about two type II units onto each type IV unit. The BF of the CIA is below the excitatory BF of the type IV unit in most cases.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1976

[Animal experiments concerning the neurotoxicity of aminoglycosid antibiotics. Electron microscopic findings regarding dose--depending mitochondrial damage in the cochlear nucleus of the guinea pig (author's transl)].

In 34 guinea pigs (plus 8 healthy animals for control) Gentamicin, Tobramycin and Amikacin show a characteristic pattern of mitochondrial damage in the cochlear nucleus of the guinea pig after a 10-day-administration of 4/40 mg/kg body weight Gentamicin, 4/50 mg/kg Tobramycin, respectively 15/75/150 mg/kg Amikacin. Amikacin causes the most pronounced physiological damage observed by the early loss of Preyer reflex and general toxic signs--these observations correspond with the morphological findings. By the evaluation of morphological findings we are convinced that there is indication for a direct neurotoxic effect on mitochondria in the cochlea nucleus regarding the dose and time of administration.

Amikacin↗
PubMed1982

A freeze-fracture study of the maturation of synapses in the anteroventral cochlear nucleus of the developing rat.

The freeze-fracture technique was used to study the maturation of the postsynaptic membrane of spherical cells of the anteroventral cochlear nucleus (AVCN) of the developing rat brain. Observations were made at 2-day intervals from birth to 16 days of age. At all ages, the external leaflet (E-face) of the spherical cell membrane has aggregates of particles opposite presynaptic active zones. From birth to 6 days of age, these particle aggregates were found only on dendritic processes, not on the cell body. At 8 days of age, the aggregates were found on small somatic appendages and on the cell body adjacent to somatic appendages. In animals from 10 to 12 days of age, particle aggregates became increasingly common on the cell body. Morphometric analysis demonstrated a decrease in size but not packing density of the particles in the aggregates. These changes in the location and size of the aggregates correspond to the location of asymmetrical synapses seen in thin section material at these same time intervals (Neises et al., 1982). At 14 days the fracture plane no longer followed the postsynaptic membrane at the active zone; instead it shifted to the presynaptic membrane and the postsynaptic specializations were rarely seen. This fracture pattern is typical of adult animals.

Aging↗
PubMed1984

A developmental gradient of dendritic loss in the avian cochlear nucleus occurring independently of primary afferents.

Cochlear nerve axons and their target neurons in nucleus magnocellularis (NM) of the chicken undergo extensive parallel structural transformations during development. Between embryonic days 12 and 17 (E12-E17), each immature highly branched axon condenses into a mature calyxlike ending applied to a single NM neuron. Simultaneously, NM neurons are transformed from multipolar cells with many long dendrites into spherical unipolar neurons with only an axon. We tested the hypothesis that cochlear nerve input is necessary for the transformation of NM cells by surgically destroying one otocyst on E3, thereby preventing formation of the nerve. Nucleus magnocellularis neurons from embryos at E11-E12, E13-14, and E17-18 were stained by horseradish peroxidase injected into their axons or by a Golgi-Hortega method. In camera lucida drawings, the number of dendrites on each cell was counted and the cell's position along the posterior-to-anterior and lateral-to-medial axes of the nucleus quantified. At E11-12, neurons throughout NM on both the deafferented and normally innervated sides of the brain have about ten dendrites. At E13-14, there is a steep spatial gradient in dendritic number bilaterally; cells at anteromedial positions have about two dendrites, while cells in posterolateral positions have an average of nine dendrites. By E17-18, only 14% of the neurons on either side have a dendrite, and these cells are evenly distributed throughout the nucleus. We conclude that cochlear nerve axons are not required for normal spatio-temporal gradients of dendritic loss, even though the absence of these axons causes severe atrophic changes in NM.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗