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PubMed1988

An animal model for tinnitus.

Subjective tinnitus remains obscure, widespread, and without apparent cure. In the absence of a suitable animal model, past investigations took place in humans, resulting in studies that were understandably restricted by the nature of human investigation. Within this context, the development of a valid animal model would be considered a major breakthrough in this field of investigation. Our results showed changes in the spontaneous activity of single neurons in the inferior colliculus, consistent with abnormally increased neuronal activity within the auditory pathways after manipulations known to produce tinnitus in man. A procedure based on a Pavlovian conditioned suppression paradigm was recently developed that allows us to measure tinnitus behaviorally in conscious animals. Accordingly, an animal model of tinnitus is proposed that permits tests of hypotheses relating to tinnitus generation, allowing the accommodation of interventional strategies for the treatment of this widespread auditory disorder.

Animals↗
PubMedDate not supplied

Differing non-additive alterations in different parts of the nervous system of the rat.

Synergistic loss of auditory sensitivity has been observed after combined exposure to xylene and n-hexane, and to toluene and n-hexane. After these combined exposures, antagonisms were seen in the auditory pathway, visual pathway, peripheral nerve and testes. synergistic interaction in one part of the nervous system and antagonistic interaction in another part has also been seen after combined exposure to toluene and dichloromethane. Two conclusions can be drawn from these observations: (1) an antagonism seen in one part of the nervous system after exposure to a specific combination of chemicals does not exclude the possibility of a synergism in other parts; and (2) both synergism and antagonism can occur within the same neurosensory organ after identical combined exposure. The observed, presumably cochlear, loss of auditory sensitivity after exposure to xylene and n-hexane was synergistic, while antagonism was found in the auditory pathway. These observations suggest that extrapolation of the combined effect in one part of the nervous system to another part, even within the same organ system, can be unreliable.

Animals↗
PubMed2001

Auditory brainstem evoked potentials in healthy full-term and pre-term infants.

BACKGROUND: Auditory brainstem evoked potentials (ABEP) are used to evaluate the integrity of auditory pathways. Since there are difficulties in the performance and still no reference ranges for pre-term infants in Taiwan, the purpose of this study was to evaluate the characteristics of ABEP in full-term and pre-term infants. METHODS: Forty full-term and 52 pre-term infants were enrolled between January and December 1997. ABEP study was performed at 3-7 days after birth, 3, 6 and 12 months of age in the full-term group while the pre-term infants were assessed at 34-36 weeks of gestational age, at term age, and at 3, 6, 12 months of corrected age. Acoustic stimulation of mixed frequency rarefaction clicks was presented to each ear through earphones. The clicks were presented at an intensity of 70-90 dB (hearing level) and a gradual decrement of intensity to 20-40 dB to determine the threshold. Electrical activity was picked up by surface electrodes. Latency of peaks I, III, V, inter-peak latency I-III, III-V, I-V and the threshold were assessed. RESULTS: In the full-term group, the peak and inter-peak latencies decreased with age. In the pre-term group, the responses of 70 dB stimulus intensity were 53.8%, 58%, 82.8%, 88.9%, 100% in the sequence and the threshold of response decreased with age. CONCLUSION: There are maturational changes after birth in both full-term and pre-term infants. We conclude that ABEP study is a sensitive, non-invasive tool for the evaluation of auditory pathway in infants.

Evoked Potentials, Auditory, Brain Stem↗
PubMed1995

Prolonged brainstem auditory evoked potential latencies in tropical pancreatic diabetics with normal hearing.

Twenty patients with Tropical Pancreatic Diabetes (TPD) were evaluated by Brainstem Auditory Evoked Potentials (BAEP) in order to detect any possible subclinical involvement of auditory pathways. The latencies of BAEP Wave III (p < 0.009) and V (p < 0.47) as well as the Interpeak Latencies I-III (p < 0.002), and I-V (p < 0.019) were significantly prolonged in patients with TPD when compared to age and sex matched healthy volunteers. There was correlation between the abnormalities of BAEP and duration of diabetes (p < 0.006), male sex of patients (p < 0.05), and the presence of retinopathy (p < 0.003) and nephropathy (p < 0.38). There was no significant correlation with the age of the patients, type of treatment, blood sugar levels and presence of peripheral neuropathy. These changes suggest a subclinical involvement of the auditory pathways in TDP patients.

Adult↗
PubMed1985

Behavioural studies on auditory development in mammals in relation to higher nervous system functioning.

The development of hearing measured behaviourally is compared in a quantitative way with studies on the physiological development in the auditory pathway of cats, house mice and humans. The similarity of time constants and of the beginning and end of the developments suggests that behavioural threshold sensitivity measured by unconditioned and conditioned reflexes is determined at or below the midbrain level.

Animals↗
PubMed1995

[Reliability of brain stem audiometry in specific learning disorders (disorders of sensory integration)].

Diagnostic audiological tests performed in ten children from 1985 to 1991 showed remarkable differences between the results of behavioral audiometry (free field or pure tone audiometry) and those of auditory evoked response audiometry. Auditory brainstem response (ABR) was absent in seven children with sensory neural hearing loss. Neuropsychological evaluation was performed on four children, neuropsychological observation was performed on two children, pediatric examination was performed on three children and one child showed signs of neuropediatric disorder. The results of neuropsychological evaluation showed moderate to severe learning disabilities (sensory integration disorders, learning disorders) in all four children tested. Available neuropsychological observation also indicated the presence of sensory integration disorders in two children. Two children had multiple handicaps with cerebral abnormalities, two further children were diagnosed as suffering from "minimal cerebral dysfunction," one of which was mentally retarded. The fact that ABRs were absent in seven children indicates that a response desynchronisation in the auditory pathway may exist in these disorders. Thus, ABR might not be a reliable method for audiological testing in children with learning disabilities or other cerebral dysfunctions, but serves as an adjunct to conventional testing methods.

Audiometry, Evoked Response↗
PubMed2002

Cross-modal neuroplasticity in neonatally enucleated hamsters: structure, electrophysiology and behaviour.

Potential auditory compensation in neonatally bilaterally enucleated Syrian hamsters was explored anatomically, electrophysiologically and behaviourally. Gross morphology of the visual cortex appeared normal and no obvious cytoarchitectural malformation was discerned. However, enucleation induced a significant increase in the spontaneous firing rate of visual cortex cells. Further, auditory stimuli elicited field potentials and single unit responses in the visual cortex of enucleated, but not normal, animals. About 63% of the cells isolated in the visual cortex of 16 enucleated hamsters responded to at least one type of auditory stimulus. Most of the responses were less vigorous and less time-locked than those of auditory cortex cells, and thresholds were typically higher. Projection tracing with WGA-HRP disclosed reciprocal connections between the visual cortex and the dorsal lateral geniculate nucleus in both intact and enucleated animals. However, in the enucleated animals retrogradely labelled cells were also found in the inferior colliculus, the major midbrain auditory nucleus. Behaviourally determined auditory sensitivity across the hearing range did not differ between enucleated and intact hamsters. Minimum audible angle, as determined by a conditioned suppression task, ranged from around 17 to 22 degrees, with no significant difference between normal and enucleated animals. The two groups also did not differ with regard to the direction of their unconditioned head orientating response to intermittent noise. However, the enucleated animals showed a more vigorous response and were slower to habituate to the noise. These results show that bilateral enucleation of newborn hamsters results in auditory activation of visual targets, in addition to the typical activation of the intact auditory pathway. Behaviourally it appears that enucleated hamsters, compared with their normal littermates, are slower to habituate in their response to an unexpected source of sound.

Action Potentials↗
PubMed1997

[The clinical significance of auditory evoked potentials of the brainstem in neonates].

INTRODUCTION: Brainstem auditory evoked potentials (BAEP) are an objective test that provides an early detection of hearing losses and a functional evaluation of the auditory pathway. MATERIAL AND METHODS: All neonates born between November 1989 and December 1994 presenting some factor of audiologic or neurologic failure were tested by ABR, in order to determine the prognostic significance of abnormalities on follow-up. RESULTS: Of 40 selected babies 17 did not pass the former test and were classified as follows: eleven in a peripheral hearing loss group of mild-moderate degree and 6 in groups of severe peripheral hearing loss or central disorder of the auditory pathway. CONCLUSIONS: On follow-up an ABR test was included disclosing that many of the mild-moderate peripheral abnormalities has a transitory nature. Infants included in the other two groups had a very poor outcome from the point of view of life expectancy and psychomotor development.

Evoked Potentials, Auditory, Brain Stem↗
PubMed1996

Auditory neurophysiologic responses and discrimination deficits in children with learning problems.

Children with learning problems often cannot discriminate rapid acoustic changes that occur in speech. In this study of normal children and children with learning problems, impaired behavioral discrimination of a rapid speech change (/dalpha/versus/galpha/) was correlated with diminished magnitude of an electrophysiologic measure that is not dependent on attention or a voluntary response. The ability of children with learning problems to discriminate another rapid speech change (/balpha/versus/walpha/) also was reflected in the neurophysiology. These results indicate that some children's discrimination deficits originate in the auditory pathway before conscious perception and have implications for differential diagnosis and targeted therapeutic strategies for children with learning disabilities and attention disorders.

Adolescent↗
PubMed2006

Development of synapses and expression of a voltage-gated potassium channel in chick embryonic auditory nuclei.

The potassium channel protein, Kv3.1, is abundantly expressed in the chick auditory pathway. Its b-isoform is found in nucleus magnocellularis, which receives the cochlear input, both before and after the establishment of synaptic connections. It is also present in cell cultures in the absence of any peripheral input. However, the expression of this isoform in the embryo has been shown to increase with development. Here, we address the question of the correlation between maturation of synapses in the auditory pathway and the pattern of expression of the b-isoform in a series of embryos prepared for immunohistochemistry at Hamburger-Hamilton stages equivalent to E10, E12, E14, and E17. We show here that this subunit translocates from the perinuclear cytoplasm to the cell membrane domain in nucleus magnocellularis at the time that cochlear nerve endings emerge as endbulbs of Held (E17). In nucleus laminaris, by this time, while abundant Kv3.1b occurs in the perinuclear cytoplasm, a translocation to the cell membrane domain has not yet occurred, and the mature peri-synaptic localization is delayed to a later stage. This difference suggests a hierarchy in the developmental expression of Kv3.1. An unexpected finding is the expression of the a-isoform of Kv3.1 in astrocytes, especially those which surround the developing nuclei and their connecting fibers. We also report here for the first time the presence of Kv3.1b in the initial segments of axons at the times when they begin to form. Our observations suggest that the Kv3.1 channel protein is regulated through mechanisms linked to the development of synaptic activity.

Animals↗
PubMed1983

Age-dependent changes of the compound action potential in the guinea pig.

As a measure of age-related changes in the most peripheral neural part of the auditory pathway, the compound action potential of the guinea pig was analyzed. In addition to a marked threshold elevation, there was a significantly lower potential amplitude in old animals. By contrast, the latency of the compound action potential was unchanged. In view of the fact that the relative amplitude increase in the intensity range tested was the same in old as in young animals, the implication is that the auditory-nerve neurons that are still excited do not exhibit functional deterioration with aging.

Aging↗
PubMed1999

Fos-like immunoreactivity in the auditory brainstem evoked by bipolar intracochlear electrical stimulation: effects of current level and pulse duration.

Fos-like immunoreactivity was used to compare the auditory brain stem excitation elicited by bipolar electrical stimulation of the cochlea at various current levels relative to the electrically evoked auditory brain stem response threshold for a 50-micros/phase monophasic pulse. Fos-like immunoreactive cells were labeled in primary auditory brain stem regions. The distribution of labeled cells was restricted to regions known to be cochleotopically related to the stimulated region of the scala tympani. Some labeled cells were observed at 2x electrically evoked auditory brain stem response threshold. The number, density and spatial distribution of labeled cells were quantified in the dorsal cochlear nucleus and inferior colliculus, and found to increase with increasing level of stimulation. For 50-micros pulses, the location of labeled neurons remained reasonably restricted to narrow bands within each region until the 1Ox level of stimulation (20 dB above electrically evoked auditory brain stem response threshold) was reached. While a monotonic increase in Fos-like immunoreactivity with increasing stimulus level was observed in most nuclei, for cells of the superficial layer of the dorsal cochlear nucleus, a non-monotonic change with increasing stimulus level was seen. This dorsal cochlear nucleus non-monotonicity may indicate that, at higher levels of stimulation, a secondary indirect inhibitory input, probably associated with activation of deep layer dorsal cochlear nucleus cells, reduces excitatory responses at the superficial layer of the dorsal cochlear nucleus. Electrically evoked auditory brain stem response and Fos expression showed parallel changes as a function of stimulus level and pulse duration. The data indicate that discrete activation of cell populations within the central auditory pathways can occur with bipolar electrical stimulation to the highest levels of stimulation typically useful in humans. The data also indicate a close, but not identical, quantitative relationship between Fos-like immunoreactivity and electrophysiological response amplitude. These findings support the view that a study of Fos-like immunoreactivity can provide a powerful and quantitative tool for study of the dynamic response characteristics of cells of the central auditory system to electrical stimulation at suprathreshold levels. The data suggest that there is a monotonic increase in the number of neurons responsive to intracochlear electrical stimulation as a function of stimulus level, at least through the upper half of the dynamic range, but that this increase does not result in a complete loss of spatial selectivity. Coupled with previous psychophysical studies, these results suggest that the increase in the number of activated neurons is functionally beneficial, resulting in improved discrimination of changes in the electrical signals.

Animals↗
PubMed1983

Integrated development and maturation of the hearing system. A critical review article.

The understanding of development and maturation of the auditory system is essential for many reasons, including the practical aspects of auditory behaviour, testing, and teaching a hearing-impaired child to communicate effectively. The study of maturation of the auditory system is gaining increasing importance also because it should help us to interpret correctly certain aspects of auditory behaviour in infants. When studying the auditory system we should not be concerned solely with development of function in isolation; the emphasis is on integrated development. Understanding a process of integrated development enables us to understand the peculiarities of auditory behaviour in infants. Sound became the raw material of human language for good reasons. It is the only medium which made it possible to transmit efficiently complex information encoded in human language. Phylogenetically, hearing in vertebrates is a late development, and because of this, in certain unfavourable circumstances the hearing system is more vulnerable than other phylogenetically older systems. Within the auditory system, high-frequency hearing is also phylogenetically a late development, and therefore more vulnerable to certain unfavourable metabolic influences. In all species there is a 'best frequency' range, usually the one which is most vital for communication. In humans the best frequency range is the one which is most important for transmitting speech sounds. This is already noticeable in newborn and very young infants, that is, we can obtain the best reactions in the frequencies which are important for speech. Higher sensitivity for perception of patterns is already developed in newborn and young infants (and acquires a special significance). Direction detection and localisation of sound source develops gradually. It is fully developed only when the auditory pathway matures and when the function is well integrated with the maturing motor system. The ears of the young are more vulnerable to noise damage and therefore a variety of protective mechanisms exist. The quality of the sound environment of the infant is important and can be decisive for further development. It is highly desirable to detect hearing impairment as soon as possible after birth. Lack of stimulation of the auditory system, even when it functions only partially, or along a very narrow channel of communication, may lead to permanent complete loss of function of the auditory centre. But this could be prevented by early stimulation, even when it is possible only via the narrow channel of communication which fortunately is present in the great majority of cases of even severely hearing-impaired children.

Acoustic Impedance Tests↗
PubMed1990

Normal and abnormal visual field maps in albinos. Central effects of non-matching maps.

The abnormal chiasmatic crossing characteristic of all albino mammals brings two discordant representations of the visual field to the central visual relays. The representation from the nasal retina is normal whereas the one from the temporal retina is disrupted, a part representing the contralateral visual field as is normal and a part coming from the ipsilateral visual field as a mirror image of a part of the normal representation. Experiments that were designed to define the rules on the basis of which the abnormal representations can be established in the lateral geniculate nucleus and visual cortex are described. These experiments are related to more recent studies of albino cats, and the observations of the visual pathways are related speculatively to abnormalities seen in the auditory pathways of albinos. The possibility is raised that the auditory abnormalities are secondary to the visual abnormalities, produced by a failure of the two systems to establish normally matching maps of sensory space.

Albinism↗
PubMed1980

Auditory brain stem responses in the cat. I. Intracranial and extracranial recordings.

A spatial and temporal analysis of auditory evoked potentials within the brain stem were performed in cats to determine the areas of the brain stem having large amplitude voltage fields, corresponding in latency to each of the components of the scalp-recorded auditory brain stem response (ABR). On the basis of this criterion, the first few components (occurring within 2 msec post-stimulus) were attributed to activity in a single structure, the eighth nerve. In contrast, each of the other components was correlated with large amplitude fields in at least two sites within the brain stem auditory pathways. The findings demonstrate a complex spatial and temporal distribution of electrical events within the auditory brain stem pathways, which preclude any simple one-to-one relationship between a given anatomical site and a particular component of the ABR. The possibility that the determination of the generators might be influenced by filtering of the evoked potentials was also examined. High-pass filtering of the evoked potentials resulted in a modification of the defined generators for only one of the components studied (P4). Filtering had little effect on the components of the scalp-recorded ABR.

Animals↗
PubMed2004

[The cochlear implant--evolution of hearing and language with an artificial inner ear].

One of the most spectacular progresses in modern medicine is the possibility to replace a deaf ear, a sensory organ in total by an implantable electronic prosthesis, a so-called cochlear implant (CI). The CI stimulates the auditory nerve by electrical pulses and thus generates the sensation of hearing along the auditory pathway. One of the most impressive aspects of cochlear implantation is the fact that small children with profound deafness who were able a few years ago to learn spoken language only to very limited extent may achieve nowadays an almost normal language development. Duration and intensity of the training of listening and spoken language vary considerably as a function of etiology and time of deafness. Most important for the development of language is sufficient stimulation of the auditory pathway during early childhood. Early diagnosis of a severe to profound deafness is most important in order to fit hearing aids or a cochlear implant without a time delay. Affected children need intensive training by professionals specialized in education and speech therapy. Adults and adolescents who lost their hearing when language acquisition was established may understand spoken language only a few weeks after receiving a cochlear implant. Several individuals are able to use the telephone. Preliminary results after bilateral cochlear implantation of children and adults show advantages. Not only do these subjects report "better hearing with two CI as compared to hearing with one CI," but some of them developed directional hearing in a rather short time lag after fitting the second implant. And in addition they achieve better speech discrimination in environmental noise.

Adolescent↗
PubMed1991

[Phase spectral analysis of auditory brainstem response in cats].

In order to apply the phase spectral analysis of auditory brainstem response (ABR) to the clinical diagnostic test, the following studies in cats were performed. At first, the phase spectra of normal ABRs were investigated under adequate stimulus intensities. In addition the component synchrony measures (CSM) of ABRs were calculated at each stimulus level. Moreover the waveforms and phase spectra of ABRs were investigated before and after the destructions of cochlear nerve and brainstem auditory pathways in cats. The results were as follows; (1) In normal ABRs, the phase spectra were mainly composed of three frequency components at 0-300Hz (component A), 300-900Hz (component B) and 900-1500Hz (component C). The CSMs of component A represented the degree of synchrony for a slow component of the ABR and the CSMs of components B and C represented the degree of synchrony for a fast component. (2) A decrease in stimulus intensity resulted in a decrease in each average of the CSMs of the three components. (3) A greater decrease of the CSM occurred if ipsilateral destruction was performed in a peripheral lesion. Lesions of the auditory pathway were followed by a decrease of the CSM of component C to contralateral stimulation. These results suggest that the phase spectral analysis of ABRs has significant clinical value in the detection of brainstem lesions.

Animals↗
PubMed1986

[Acute unilateral deafness caused by mumps--a case description].

Reports of the aetiology of mumps induced deafness in the auditory pathway have not appeared in the literature in recent years. It is now possible to distinguish between sensory deafness and other types of profound hearing loss by combining the results of promontory testing (PT) and electrocochleography (ECochG). A very extensive examination of a case of profound sudden hearing loss due to mumps is described. It was impossible to prove a relation between the mumps virus and sudden hearing loss in this case but the site of the lesion in the auditory pathway could be localised. The hearing loss in this case was of sensory type, profound, irreversible and resistant to treatment.

Audiometry, Evoked Response↗