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PubMed1999

Communicative ability in an audiological perspective. Theory and application to post-secondary school students.

The underlying assumption in the present study is that the individual's speech and hearing communicative ability is composed of three components, each corresponding to different functional systems of the brain: afferent functions (A) represent the auditory activity and sound perception largely corresponding to activity in the ascending auditory pathways. The central functions (C) include cortical auditory and language abilities controlled in parts of the left temporal lobe and subcortical centres. The efferent functions (E) consist of speech motor processes and articulation. A test battery of 20 tests measuring several aspects of afferent, central and efferent functions was applied to 11 hearing-impaired post-secondary school students and several control groups. All data were normalized with the normal materials as references. Individual communicative profiles were obtained from these primary data, which consisted of audiometric tests (tone and speech audiometry, impedance tests, brainstem response audiometry and phase audiometry), sound environmental tests with hearing aids (directional speech-in-noise, word localization, sound environment identification test), and language tests (reading tests, prosody, auditory memory and recall, phonology and articulation). Since the central functions cannot truly and directly be determined in hearing-imparied subjects, they were assessed under optimal listening conditions. Furthermore, central functions were estimated according to three different models: distributive, parallel model (model 1), multiplicative, serial model (model 2) and compensatory model (model 3). On the basis of these models, a three-component description of the communicative ability consisting of A,C and E functions was obtained. It was found that C and E functions were largely independent of the adult afferent functions, but C functions were negatively correctly to hearing in childhood. A preliminary comparison between the tests and a comparison between the models was performed by predicting benefit of hearing aid. Model 3 gave the best prediction. Beyond the three-component A,C, and E characterization of the students, a total communicative ability score could be calculated giving values from 37% to 79% of the normal mean. On the basis of the conceptual and statistical analyses, the test battery could be reduced to include tone 0-12 years, tone adults, word localization test (afferent); word chain, lecture test (central), articulatory test (efferent) and audiovisual test. The simple algorithm of adding the normalized loss of afferent (peripheral) function to the normalized results of the acoustic central tests seems to be promising for isolation for the central auditory capacity even in cases with peripheral impairment. It is concluded that a wider perspective is desirable in the diagnostic evaluation of the hearing-impaired individual in order to understand his communicative abilities and form a cornerstone in the planning of rehabilitation in conjunction with social and psychological factors.

Adolescent↗
PubMed1997

Intracochlear, electrical, multichannel stimulation effects on the development of auditory system in neonatally deafened kittens.

OBJECTIVE: To investigate the effect of chronic electrical stimulation in acoustically deprivated animals during maturation. MATERIALS AND METHODS: Latencies of EABR measurements from acoustically deprivated and acoustically deprivated, but electrically stimulated animals were compared with ABR from normal hearing cats. In addition, morphological analyses of the cochlear nuclei and the auditory cortex and their subdivisions were done. RESULTS AND DISCUSSION: EABR latencies demonstrated that the most peripheral auditory pathway is more independent from the normal auditory or external electrical stimulation than the more central regions. Morphological analysis also demonstrated the reverse of the acoustically deprivation effect during maturation in the auditory cortex via intracochlear electrical stimulation.

Animals↗
PubMed1995

[Tinnitus models for use in tinnitus counselling therapy of chronic tinnitus patients].

Tinnitus models are an integral part of tinnitus counselling. In cases with compensated tinnitus, counselling represents the only therapeutic measure necessary. In contrast, patients with uncompensated tinnitus require further therapy in the form of medication, tinnitus-maskers or psychotherapy. Sound processing along the peripheral and central auditory pathways is achieved by functional loops that direct mechanical, electrical or chemical information to various points in the pathway. Minor damage to a loop can cause destabilization of this finely balanced system and can induce tinnitus. Current peripheral tinnitus models are reviewed and discussed with respect to in vitro data from isolated outer hair cells of the guinea pig cochlea. Audiological findings of a patient with central tinnitus after brainstem surgery are discussed in view of central tinnitus models. Specific models for common hearing disorders, such as tinnitus with normal hearing, noise trauma, sudden hearing loss, toxic cochlear lesions, presbyacusis, acoustic neurinoma and Menière's disease are presented for the ENT-surgeon involved with tinnitus-counselling.

Adult↗
PubMed2003

Pathophysiology of tinnitus.

Tinnitus is not a single entity but a rather diverse group of disorders. Despite symptoms that indicate the ear is the site of the pathology, there is strong evidence that most forms of severe tinnitus are caused by functional changes in the central nervous system. The changes are induced through expression of neural plasticity, some of which may have been caused initially by abnormalities in the ear or the auditory nerve. The involvement of the nonclassical ascending auditory pathway with its subcortical connections to limbic structures (the amygdala) may explain some of the symptoms of some forms of tinnitus including hyperacusis and affective disorders, such as phonophobia and depression, which often accompany severe tinnitus.

Auditory Pathways↗
PubMed1999

[Modern hearing-aids at the cutting edge of microelectronics. Increased possibilities for individual customization].

The development of modern hearing aids has been so great that they now represent the cutting edge of micro-electronics. Flexibility has been enhanced by computer-aided programming of the devices, and particularly by digital signal processing, developments which enable improved customization. Increased knowledge of the pathophysiology of the auditory system, fundamental processes in central auditory pathways, and cognitive function enable technological developments to be exploited, thus enhancing our ability to cope with an increasingly broad spectrum of hearing impairment, ranging from mild high-frequency loss to severe loss across the entire frequency range.

Auditory Pathways↗
PubMed2000

Modification of delayed rectifier potassium currents by the Kv9.1 potassium channel subunit.

Within auditory pathways, the intrinsic electrical properties of neurons, and in particular their complement of potassium channels, play a key role in shaping the timing and pattern of action potentials produced by sound stimuli. The Kv9.1 gene encodes a potassium channel alpha subunit that is expressed in a variety of neurons, including those of the inferior colliculus. When cRNA encoding this subunit is injected into Xenopus oocytes, no functional channels are expressed. When, however, Kv9.1 is co-expressed with certain other alpha potassium channel subunits, it changes the characteristics of the currents produced by these functional channel proteins. We have found that Kv9.1 isolated from a rat brain cDNA library alters the kinetics and the voltage-dependence of activation and inactivation of Kv2.1, a channel subunit that generates slowly inactivating delayed rectifier potassium currents. The rate of activation of Kv2.1 is slowed by co-expression with Kv9.1. With Kv2.1 alone, the amplitude of evoked currents increases monotonically with increasing command potentials. In contrast, when Kv2.1 is co-expressed with Kv9.1, the amplitude of currents increases with increasing depolarization up to potentials of only approximately +60 mV, after which increasing depolarization results in a decrease in current amplitude. Currents produced by Kv2. 1 alone and by Kv2.1/Kv9.1 are both sensitive to the potassium channel blocker tetraethyl ammonium ions (TEA), but higher concentrations of TEA (20 mM) eliminate the biphasic voltage-dependence of the Kv2.1/Kv9.1 currents. Co-expression with Kv9.1 also produces an apparent negative shift in the voltage-dependence of inactivation and activation. Computer simulations of model neurons suggest that co-expression of Kv9.1 with Kv2.1 may have different effects in neurons depending on whether their firing pattern is limited by the inactivation of inward currents. In excitable cells in which the inward currents do not inactivate, co-expression with Kv9.1 could produce an inhibition of firing during sustained depolarization. In contrast, in model neurons with rapidly inactivating inward current, the change in the voltage-dependence of activation produced by Kv9.1 may allow the cells to follow high frequency stimulation more effectively.

Animals↗
PubMed2003

The lateral superior olive: a functional role in sound source localization.

Sound location in azimuth is signaled by differences in the times of arrival (interaural time difference, ITDs) and the amplitudes (interaural level differences, ILDs) of the stimuli at the ears. Psychophysical studies have shown that low- and high-frequency sounds are localized based on ITDs and ILDs, respectively, suggesting that dual mechanisms mediate localization. The anatomical and physiological bases for this "duplex theory" of localization are found in the medial (MSO) and lateral (LSO) superior olives, two of the most peripheral sites in the ascending auditory pathway receiving inputs from both ears. The MSO and LSO are believed to be responsible for the initial encoding of ITDs and ILDs, respectively. Here the author focuses on ILDs as a cue to location and the role of the LSO in encoding ILDs. Evidence from disparate fields of study supports the hypothesis that the LSO is the initial ILD processor in the mammalian auditory system.

Animals↗
PubMed1996

Acoustically activated c-fos expression in auditory nuclei of the anaesthetised guinea pig.

The spatial expression of the immediate-early gene c-fos in central auditory nuclei of the anaesthetised guinea pig was investigated following exposure of the animal to acoustic stimulation. Accurate control of both the spectra and the level of the stimulus was designed so that the presumed excitation of central auditory nuclei was similar across animals. For unstimulated anaesthetised control animals levels of labelling were significantly higher when compared with unanaesthetised controls. This appeared to a result of the combination of the experimental manipulations and also the use of the anaesthetic. A surprising finding was that unstimulated control animals placed in an anechoic chamber demonstrated the highest levels of fos-like immunoreactivity (Fos-LIR). When anaesthetised animals were exposed to acoustic stimuli the total number of cells showing Fos-LIR was elevated when compared to anaesthetised, but unstimulated animals. There was no evidence at any level of the auditory pathway that these animals demonstrated spatially restricted Fos-LIR which may have suggested place-frequency mapping. In contrast, spatially restricted labelling was found in awake animals exposed to an identical stimulus.

Acoustic Stimulation↗
PubMed1991

Issues in neural plasticity as related to cochlear implants in children.

There is compelling evidence across species for a changing place code during development. This change in frequency organization may provide a mechanism for all elements within the central auditory pathways to receive the necessary stimulation to promote normal growth and development. We must take these normal developmental processes into consideration when deciding on the appropriate stimulation, training, and success procedures in cochlear implants in children.

Animals↗
PubMed1985

Brainstem auditory-evoked potentials.

Brainstem auditory-evoked potentials (BAEPs) are generated in the ear and brainstem nuclei of the ascending auditory pathways following a transient acoustic stimulus. Because they can be recorded noninvasively in humans, BAEPs have a number of clinical and research applications. This paper reviews the properties of BAEPs, with particular emphasis on those characteristics that are relevant to the acquisition and analysis of the responses. Theories of the neural origins of the responses are reviewed. The dependence of the responses on the stimulus waveform and the problem of stimulus artifact are considered. Then, origins of the background noise are discussed, and the use of linear filtering and methods of artifact detection to improve the signal-to-noise ratio are reviewed. Finally, the problem of identifying parameters to quantify the responses is considered. The definition of response components in terms of response peaks and data on intra- and intersubject variability are reviewed, and the use of algorithms to measure parameters is discussed.

Acoustic Stimulation↗
PubMed1998

Role of acoustic striae in hearing: reflexive responses to elevated sound-sources.

This report is the fourth in a series describing the results of ablation-behavior experiments directed to the ascending output of the cochlear nuclei as it is conducted centrally within the acoustic striae. This fourth report focuses on the unique physiology of the fusiform or 'output' cells of the dorsal cochlear nucleus whose axons course through the dorsal acoustic stria (DAS). Because electrophysiological studies have shown that the cues for sensing the elevation of a sound source would seem to be best analyzed by the dorsal cochlear nucleus and projected centrally via its DAS, we tested normal cats and cats deprived of DAS for their ability to orient to elevated sources of broad-band noise. For behavioral testing, we made use of reflexive or unconditioned orienting responses to elevated sound sources using a similar method to one we have used previously for azimuth testing (Thompson GC, Masterton RB. Brainstem auditory pathways involved in reflexive head orientation to sound. J Neurophysiol 1978;41:1183-1202). The results show that cats deprived of their DAS do indeed have a marked deficit in their ability to orient to an elevated sound source. Further behavioral testing indicated that this deficit is not the secondary result of an attentional or peripheral motor deficit. Although the present results do not prove that the reflexive deficit is strictly auditory in nature, the deficit is notable in that it is the only one yet known to result from a lesion of the dorsal cochlear nucleus or its central projections.

Acoustic Stimulation↗
PubMed2001

Encoding of the temporal regularity of sound in the human brainstem.

We measured the neural activity associated with the temporal structure of sound in the human auditory pathway from cochlear nucleus to cortex. The temporal structure includes regularities at the millisecond level and pitch sequences at the hundreds-of-milliseconds level. Functional magnetic resonance imaging (fMRI) of the whole brain with cardiac triggering allowed simultaneous observation of activity in the brainstem, thalamus and cerebrum. This work shows that the process of recoding temporal patterns into a more stable form begins as early as the cochlear nucleus and continues up to auditory cortex.

Acoustic Stimulation↗
PubMed1981

The connections of the inferior colliculus and the organization of the brainstem auditory system in the greater horseshoe bat (Rhinolophus ferrumequinum).

The connections of the inferior colliculus, the mammalian mid-brain auditory center, were determined in the greater horseshoe bat (Rhinolophus ferrumequinum), using the horseradish peroxidase method. In order to localize the auditory centers of this bat, brains were investigated with the aid of cell and fiber-stained material. The results show that most auditory centers are highly developed in this echolocating bat. However, the organization of the central auditory system does not generally differ from the mammalian scheme. This holds also for the organization of the superior olivary complex where a well-developed medial superior olivary nucleus was found. In addition to the ventral and dorsal nuclei of the lateral lemniscus a third well-developed nucleus has been defined which projects ipsilaterally to the inferior colliculus and which was called the intermediate nucleus of the lateral leminiscus. All nuclei of the central auditory pathway project ipsi-, contra-, or bilaterally to the central nucleus of the inferior colliculus with the exception of the medial nucleus of the trapezoid body and the medial geniculate body. The tonotopic organization of these projections and their possible functions are discussed in context with neurophysiological investigations.

Animals↗
PubMed1976

Intensity and rate functions of cochlear and brainstem evoked responses to click stimuli in man.

The complex of five waves, which are the responses to click stimuli of the auditory nerve and the brainstem auditory nuclei, were recorded in ten human subjects by means of earlobe and scalp electrodes. The rate of the stimuli was varied from 5/s to 80/s and their intensity was varied over a 70 dB intensity range in order to study the rate and intensity functions of each of the response components. With increasing click intensity, the amplitude of the first wave (generated by the auditory nerve) increased proportionally while the amplitudes of the later waves (generated by the brainstem auditory nuclei) reached their maximum amplitudes at intermediate click levels (saturation), and at high intensities occasionally even decreased in amplitude. The latency of each of the waves decreased by similar amounts as the intensity was increased. With increasing click rates, the amplitude of the first wave decreased the most, while there were smaller effects on the amplitude of the later waves. There was no effect of click rate on the latency of the first wave, but the latency of the later waves increased with click rate, the effect being greater on the later waves. In the rate functions, the latency change of a wave was greater than that of the waves preceding it (accumulative effect). These results are explained by overlapping convergence and divergence in the ascending auditory pathway. These results support the notion that the principal component of each wave is activated by the principal component of the previous wave. These results may explain the relative ease with which several workers record the fourth wave of the complex, and their preference for this response.

Auditory Pathways↗
PubMed1989

Batch-fabricated thin-film electrodes for stimulation of the central auditory system.

Silicon micromachining and thin-film technology have been employed to fabricate iridium stimulating arrays which can be used to excite discrete volumes of the central nervous system. Silicon multichannel probes with thicknesses ranging from 1 to 40 microns and arbitrary two-dimensional shapes can be fabricated using a high-yield, circuit-compatible process. Iridium stimulating sites are shown to have similar characteristics to iridium wire electrodes. Accelerated pulse testing with over 8 million 100 microA biphasic current pulses on 8000 microns 2 sites has demonstrated the long-term stability of iridium and activated iridium sites. In vivo tests have been performed in the central auditory pathways to demonstrate neural activation using the devices. These tests show a selective activation both as a function of site separation and site size.

Animals↗
PubMed1989

Effect of high-intensity sound on local cerebral glucose utilization in fetal sheep.

The effects of external noise on fetal sheep cerebral glucose utilization were determined with the [14C]deoxyglucose method. Seventeen animals were prepared at 130 days gestation with catheters and electrodes for assessing fetal behavioral state. Five to 7 days later, 7 animals were studied under normal laboratory sound conditions (65-70 dB), 5 animals were exposed to 105-120 dB broadband noise levels produced by two earphones applied to the abdomen of the ewe, and 5 fetuses were stimulated with an electronic artificial larynx (EAL), positioned on the abdomen directly over the fetal head. There were no significant differences between local cerebral glucose utilization in controls and earphone ewes, and no obvious alteration in behavioral states. However, there were marked, significant differences in glucose utilization along the central auditory pathway during EAL stimulation. These autoradiographs revealed isofrequency-like bands in medial geniculate body and irregular darkening of cortex of the temporal lobe. Total time spent in clearly defined high and low voltage electrocortical activity did not change during EAL stimulation.

Animals↗
PubMed1985

[Etiological evaluation of deafness in children].

In relation to cochlear implants, the authors review the various etiologies of deafness in infancy and childhood, either genetic or acquired in order to determine the criteria for advising implantation. They put forward the necessity of complete evaluation of all the auditory pathways involved to determine if a premature who has sustained hypoxicischemic encephalopathy and a full term baby have the same chance to benefit from cochlear implants after meningitis. Defined criteria are urgent needs for patients and parents.

Auditory Pathways↗