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PubMed2003

Equivalent dipoles of the binaural interaction components and their comparison with binaurally evoked human auditory 40 Hz steady-state evoked potentials.

OBJECTIVE: The purpose of this study was to acquire the Binaural Interaction (BI) components of the auditory middle-latency steady-state 40 Hz potentials, compare them with those of the binaurally evoked 40 Hz response and with transient-evoked Auditory Middle Latency Evoked Potentials (AMEP) and suggest possible contributors and generators of the composite 40 Hz BI. METHODS: Potentials were recorded from 15 normal-hearing adults in response to 40/sec clicks. BI was derived by subtracting the binaurally evoked potentials from the algebraic sum of the evoked potentials to left and to right ear stimulation. Latencies, magnitudes and orientations of the dipole equivalents of 40 Hz components were compared with their BI counterparts, as estimated by three-channel Lissajous' trajectories. Comparison of the transient AMEP to binaural stimulation with the BI of the steady-state 40 Hz response was also conducted to elucidate the contributions of different levels along the auditory pathway to the 40 Hz BI responses. RESULTS: Each cycle of the BI of the steady-state 40 Hz AMEP included four components that corresponded in latency, amplitude, and dipole orientation to their counterparts in the binaurally evoked waveform. Amplitudes of BI components were 50 to 60% of the respective values in the binaurally evoked potentials. Orientations of BI components matched those of the cortical components in the transient-evoked AMEP. CONCLUSIONS: The results suggest that the main contribution to the 40 Hz BI is from rate resistant thalamo-cortical neurons. The results also suggest that the binaural cortical neurons contributing to the 40 Hz BI are less affected by increased rate than monaural neurons.

Acoustic Stimulation↗
PubMed1997

The central auditory system and auditory deprivation: experience with cochlear implants in the congenitally deaf.

In the present paper we briefly review the response of the central auditory system to auditory deprivation and describe recent experimental and clinical experience with cochlear implants. While the central auditory system undergoes marked changes in response to auditory deprivation, it would appear that at least a rudimentary cochleotopic organisation is maintained at the level of the brainstem and auditory cortex in animals deafened from birth. Moreover, recent studies have demonstrated the ability of the central auditory system to undergo functional reorganisation in response to changes in the pattern of afferent activity. Clinical experience has shown that deaf children with little or no prior auditory experience can obtain significant benefit from cochlear implants, provided the device is fitted at a young age. Furthermore, factors predicting successful clinical outcomes with these devices reflect the importance of auditory experience, either prior to an acquired loss or with the use of a cochlear implant. These findings suggest that functional reorganisation within the central auditory pathway can at least partially account for improvements in clinical performance over time.

Adult↗
PubMed1995

Connections of the superior olive in the chicken.

The avian superior olive (OS) is known to be a station in the auditory pathway, although its anatomic connections remain uncertain. The afferent and efferent connections of OS neurons in the chicken were identified with wheat germ agglutinin conjugated to horse radish peroxidase (WGA-HRP) injected into the OS nucleus. Projections to the OS originate bilaterally in the cochlear nuclei (nucleus angularis) and the nucleus laminaris. Anterogradely labelled axon terminals were found in the ipsilateral nucleus magnocellularis, the contralateral intermediate nucleus of the lateral lemniscus, and the shell portion of the central nucleus of the inferior colliculus. Retrograde transport of [3H]-glycine from the OS was also charted. Glycine-transporting cells were found ipsilaterally in the nucleus angularis and the nucleus laminaris. Neuronal soma in a newly identified nucleus of the trapezoid body (NTB) were found to actively concentrate glycine, although the neurons probably do not synapse within the OS. Anatomically, the avian OS would appear to be part of the interaural intensity difference pathway; however, our data and published information are insufficient to establish a homology to the human lateral superior olive.

Animals↗
PubMed1986

Brain stem auditory evoked potentials in patients with multiple system atrophy with progressive autonomic failure (Shy-Drager syndrome).

Brain stem potentials from three groups of patients, namely those with pure progressive autonomic failure, Parkinson's disease and multisystem atrophy with progressive autonomic failure (Shy-Drager syndrome) were compared with each other and a group of normal subjects. In virtually all the patients with multisystem atrophy with progressive autonomic failure the brain stem potentials were abnormal in contrast to normal findings with Parkinson's disease. The closely associated group of patients with progressive autonomic failure alone also revealed no abnormalities of the BAEP. This separation of the two groups, Parkinson's disease and progressive autonomic failure from multisystem atrophy with progressive autonomic failure is important clinically as multiple system atrophy of the Shy-Drager type has extra-pyramidal features closely resembling Parkinsonism or a late onset cerebellar degeneration. From the abnormalities of the brain stem response in multisystem atrophy with progressive autonomic failure, it is clear that some disruption of the auditory pathway occurs in the ponto-medullary region as in nearly all patients there is a significant delay or reduction in the amplitude of components of the response generated beyond this region. The most likely area involved is the superior olivary complex.

Aged↗
PubMed1993

[Progress in phono-audiology: the deaf child].

Functional explorations, the physiopathology of the auditory pathways and centres, morphological investigations, molecular biology, and substitute processes make up the five major themes that best illustrate the progress achieved in phono-audiology. The management of the deaf child is characterized by early and multidisciplinary treatment. Thanks to the technical progress achieved in phono-audiology, the otorhinolaryngologist can apply a humanist medicine.

Auditory Pathways↗
PubMed1989

Learning-related activation in the auditory system of the rat produced by long-term habituation: a 2-deoxyglucose study.

Autoradiography with [14C]2-deoxyglucose (2-DG) was used to examine the functional activity of the rat auditory system during long- and short-term habituation of the acoustic startle reflex. The data showed that presentation of the acoustic stimulus to long-term habituated rats resulted in a learning-related metabolic enhancement that was significantly greater than the response evoked by the same acoustic stimulus in the inexperienced rats. This enhancement was localized to brainstem and midbrain auditory nuclei and no significant changes occurred at thalamocortical levels of the auditory pathway. The largest difference in 2-DG uptake between long- and short-term habituated rats was in the lateral superior olivary nucleus (LSO). The LSO activation suggests that olivocochlear efferents may operate in a central feedback control of peripheral auditory input during long-term habituation. Findings of enhanced metabolism from the cochlear nuclei to the central nucleus of the inferior colliculus indicated that active processes of neuronal plasticity take place in the lower auditory system during long-term habituation. The results provide the first demonstration of how a nonassociative learning experience such as long-term habituation modifies the metabolic activity of the auditory system. The findings support the conclusion that auditory responses of behaving animals to acoustic stimuli are dependent not only on the physical parameters of a stimulus, but also on its learned behavioral significance.

Acoustic Stimulation↗
PubMedDate not supplied

Speech sound representation in the brain.

Biologic processes underlying speech sound perception and learning have been addressed using the mismatch negativity (MMN) evoked response. First is a consideration of how the acoustic properties of the signal affect the neural mechanisms and brain regions engaged. Because the MMN differs depending on the acoustic characteristics of the stimuli used to elicit the response, it has been used to probe mechanisms underlying the neural representation of stimuli along the auditory pathway. Second is a consideration of neurophysiologic correlates of speech sound perception and learning. Detailed is a 'behavioral-neurophysiologic, acoustic-phonetic approach', used to link perception with underlying physiologic processes in humans. The focus here is on children and what has been learned about normal maturation of speech sound perception and its disruption in certain children with learning disorders. The last topic is a consideration of central nervous system changes with perceptual learning. This includes long-term experience with one's native language and short-term auditory training in the laboratory. Limitations and future challenges are discussed.

Auditory Pathways↗
PubMed1996

gamma-Aminobutyric acid and glycine in the baboon cochlear nuclei: an immunocytochemical colocalization study with reference to interspecies differences in inhibitory systems.

Previous studies of the cochlear nuclei in cat, rat, and guinea pig have demonstrated neural structures that are enriched in the inhibitory neurotransmitter amino acids gamma-aminobutyric acid (GABA) and glycine. In these mammals, inhibitory terminals are widely distributed throughout the nuclear complex, but somata of inhibitory neurons are concentrated in the dorsal cochlear nucleus, in granule cell regions, and in the cap area. Because these are the subdivisions that undergo the most pronounced phylogenetic changes in primates, we wanted to see whether the inhibitory systems are influenced by changes in cytoarchitecture. Therefore, we applied light microscopic postembedding immunostaining and optical densitometry to the cochlear nuclei of an anthropoid primate, the Senegalese baboon (Papio anubis). Our results demonstrate that, in baboon 1) glycinergic neurons and axons in the ventral cochlear nucleus seem to form a commissural system similar to that of other mammals; 2) the tuberculoventral system appears to be unchanged in morphology but exhibits a higher level of colocalization of GABA with glycine; 3) there is a reduction of the granule/cartwheel cell system, which is reflected in lesser numbers of inhibitory cartwheel, Golgi, and molecular layer stellate cells; 4) the cap area is larger than in rodents and carnivores and contains many neurons that colocalize GABA and glycine; and 5) throughout the nuclear complex, a higher proportion of the inhibitory terminals colocalize GABA and glycine. We conclude that modulation of the ascending auditory pathway in baboon is likely to differ from that in rodents and cat.

Animals↗
PubMed2006

[Auditory evoked potentials].

Auditory evoked potentials (AEPs) are an electrical manifestation of the brain response to an auditory stimulus. The waveform represents the passage of electrical activity provoked by auditory stimuli from the cochlea to cortex. The waves represented by I-VII are generated mainly in the brainstem. These waves are called the brain stem auditory evoked potentials (BAEPs) or the auditory brain stem response (ABR). The middle latency AEPs (MLAEP) are generated from the medial geniculate and primary auditory cortex. The long latency AEPs (LLAEP) are generated from the frontal cortex and association areas. The BAEPs appear to be an exquisitely sensitive monitor for pathological events during surgery. Anesthetics and mild hypothermia have minimum effect, if any, on the BAEPs. The BAEPs are useful during the microvascular decompression of the fifth or seventh cranial nerve, resection of acoustic neuroma and posterior fossa operations. Because the auditory pathway occupies a small area in the brainstem, combined use of other evoked potentials such as short latency sensory evoked potentials is recommended. The MLAEPs are most promising evoked responses for monitoring awareness or depth of anesthesia. When the concentration of anesthetics is increased, the amplitudes of the MLAEP's peaks are decreased and their latencies are elongated. Commercially developed A-line AEP monitor or aepEX can extract the AEPs waveform in a short period and automatically analyze the changes in the MLAEPs. These AEP based monitors may be superior to bispectral index (BIS) in detecting the transition from unconsciousness to consciousness.

Anesthesia↗
PubMed1994

Auditory early- and middle-latency evoked potentials in patients with quadrigeminal plate tumors.

Both early auditory evoked potentials (BAEPs) and middle-latency auditory evoked potentials (MLAEPs), were recorded in nine patients suffering from a quadrigeminal plate tumor. These recordings were performed before surgery in six cases and after surgery in three cases. The results of these examinations were correlated with impairments of the midbrain auditory pathways as shown by magnetic resonance imaging. BAEPs and MLAEPs were abnormal in five of nine cases and eight of nine cases, respectively. The two examinations yielded normal results in only one case. These data show that the functional evaluation of the midbrain should not be limited to the recording of BAEPs, routinely performed for brain stem functional evaluation, but should also include recording of MLAEPs, although the technique is a little more delicate. In the five patients with abnormal BAEPs, I-V conduction time was increased unilaterally (three patients) and bilaterally (two patients), and the I/V amplitude ratio was abnormal in two patients. In one of these two patients, isolated destruction of the right inferior colliculus was responsible for an abnormality affecting Wave V of the BAEP that was visible only after left ear stimulation. The most frequently observed MLAEP abnormality was a delay in the peaking of the Pa component, assumed to be of cortical origin. Therefore, a limited impairment of the midbrain may delay the peaking latency of Pa. Unilateral hypovoltage of Na-Pa was also observed. In only one case were Na and Pa components unilaterally abolished, in a patient suffering from a postoperative lesion extending from the right inferior colliculus to the right medial geniculate body.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1981

Variability of the hereditary deafness in the white cat. I. Physiology.

Electrophysiological investigations, at different levels of the auditory pathway, were performed on 54 white cats. Hearing tests generally consisted of recording electrocochleograms or making audiograms from collicular or cortical responses. Some investigations were performed with chronically implanted electrodes to detect the first appearance of a hearing defect. Results showed no evident relationship between the age of the white cat and the appearance, severity or completeness of hearing loss. A large variety of hearing remnants was encountered in partly deaf animals which is tentatively related to a similar variety of histological damage of the cochlea described in a companion paper (Rebillard, M., Pujol, R. and Rebillard, G. (1981): Hearing Res. 5, 189-200).

Age Factors↗
PubMed2004

An unusual case of X-linked adrenoleukodystrophy with auditory processing difficulties as the first and sole clinical manifestation.

X-linked adrenoleukodystrophy (X-ALD) is characterized by demyelination that is associated with a deficient beta-oxidation of very long chain fatty acids. We report the unusual case of a male adult with X-ALD who was diagnosed at the age of 26 by a brain MRI performed because his brother had been diagnosed with a rapidly deteriorating form of X-ALD. His sole symptom was hearing difficulties in the presence of a normal audiogram since childhood. He has remained stable for seven years. Central auditory testing in our patient revealed severe deficits in several auditory processes. These findings correlated with involvement of the auditory pathway at the level of the trapezoid body, and posterior corpus callosum in particular, on his brain MRI. This case highlights not only the need for thorough audiological investigation of the patient who complains of hearing difficulties in the presence of a normal audiogram, but also that audiological investigations could be of value in the phenotypic evaluation of cases with adrenoleukodystrophy.

Acoustic Impedance Tests↗
PubMed1985

Transneuronal transport in the vestibular and auditory systems of the squirrel monkey and the arctic ground squirrel. II. Auditory system.

Transneuronal transport in the auditory system of the squirrel monkey and the arctic ground squirrel was studied after implantation of tritiated protein or glycoprotein precursors into the ampulla of a single semicircular duct. In both species, essentially the same pattern of transneuronal transport extended beyond the cochlear nuclei to the central nucleus of the inferior colliculus (CNIC), after survival periods ranging from 9 to 33 days. Animals displayed dense labeling over nearly all auditory receptors, nearly all portions of the spiral ganglion and throughout the cochlear nuclei (CN). Labeled fibers, mainly in the ventral acoustic stria, terminated over the ipsilateral lateral superior olive (LSO) and the lateral aspect of medial superior olive (MSO). Fibers continuing medially, decussated in an orderly manner, and terminated over the opposite medial nucleus of the trapezoid body (MNTB) and medial aspect of MSO. Labeled fibers projecting into the opposite lateral lemniscus (LL) terminated in the ventral nucleus of the lateral lemniscus (VNLL) and the CNIC. Fibers, but few terminals, were noted over the dorsal nucleus of the LL. The ipsilateral LL contained comparatively few labeled fibers, but sparse terminations occurred over portions of VNLL and CNIC. No transport of [3H]precursors was noted in the peripheral nuclei of the inferior colliculus or in the medial geneculate body on either side. Massive transport via the contralateral LL and the profuse terminals in the opposite CNIC suggested transneuronal transport via secondary and higher order auditory fibers. Although the largest number of fibers in the contralateral LL probably arose from the cochlear nuclei, higher order fibers also may have arisen from the ipsilateral LSO and the contralateral MSO and VNLL. Small numbers of fibers in both species descended from the region of the superior olivary complex (SOC) ventral to the facial motor nucleus. In the ground squirrel, scant auditory projections were traced into the opposite cochlear nuclei. Tritiated precursors in the endolymph passed most readily from labyrinth to cochlea, and transneuronal transport was more extensive in the auditory pathways than in the vestibular system at comparable times. Centrally transported [3H]fucose was cleared more promptly than [3H]proline in monkeys.

Animals↗
PubMed1998

Anatomical evidence for binaural processing in the descending octaval nucleus of the toadfish (Opsanus tau).

The connections of a potential auditory circuit were determined in the medulla of the toadfish (Opsanus tau). Fluorescent dextran amines placed in the medial torus semicircularis (mTS) retrogradely filled cells primarily in the dorsal region of the descending octaval nuclei (DON) with contralateral predominance. Fluorescent dextran amines placed in the DON revealed commissural fibers that cross the midline with the internal arcuate tract. The interconnections are consistent with a dorsal-ventral organization of the DON: reciprocal innervation is present for the left and right dorsal zones of the DON and for the left and right ventral zones of the DON. Based on projections to the medial (auditory) TS and the reciprocal connections, the dorsal region of the DON appears to be the major auditory processing site in the medulla and also may be a site for directional, binaural comparisons. The ventral region of the DON may be a site for bilateral vestibular processing. Double-labelling experiments revealed that some of the descending octaval cells projecting to the contralateral DON also project to the mTS. Based on the auditory pathway indicated by this study, future neurophysiological investigations of sensitivity to directional sound stimuli should begin in the dorsal DON of the toadfish.

Animals↗
PubMed1998

Auditory connections and neurochemistry of the sagulum.

We studied the cytoarchitecture, neurochemical organization, and connections of the sagulum. The goal was to clarify its role in midbrain, lateral tegmental, and thalamic auditory processing. On cytoarchitectonic grounds, ventrolateral (parvocellular) and dorsomedial (magnocellular) subdivisions were recognized. The patterns of immunostaining for gamma-aminobutyric acid (GABA) and glycine were distinct. Approximately 5-10% of the neurons were GABAergic, and more than one type was identified; GABAergic axon terminals were abundant in number and varied in form. Glycinergic neurons were much rarer, < 1% of the population, and glycinergic axon terminals were correspondingly sparse. Wheat germ agglutinin conjugated to horseradish peroxidase was used for purposes of connectional mapping, and biotinylated dextran amines revealed the structure of corticosagular axons. All nine cortical areas injected project to the ipsilateral sagulum. Five (areas AI, AII, SF, EPD, and Te) had heavier projections than the others. Areas AI and AII projected throughout the rostrocaudal sagulum. Labeling from AI was moderate in density and concentrated in the central sagulum, whereas the input from AII was heavier and ended more laterally. Suprasylvian fringe input was light, especially caudally, and was chiefly in the central sagulum. The projection from the dorsal region of the posterior ectosylvian gyrus was comparatively stronger and was in the dorsolateral sagulum. Finally, the temporal cortex sent axons to the most lateral sagulum, spanning the dorsoventral extent, whereas insular cortex axons ended diffusely in the dorsolateral sagulum. Corticofugal axons ranged from fine boutons en passant to larger globular terminals. The sagulum may represent the earliest significant opportunity in the ascending auditory pathway for corticofugal modulation. The most extensive input arises from the polymodal association areas. The sagulum then projects divergently to the dorsal cortex of the inferior colliculus and the dorsal division of the medial geniculate body. The projection from the dorsal division of the auditory thalamus to nonprimary auditory cortex completes this circuit between the forebrain and the midbrain and represents a nexus in the ascending and descending auditory systems. Such circuits could play a critical role in auditory-motor adjustments to sound.

Anatomy, Artistic↗
PubMed2005

Auditory brainstem responses in young males with Fragile X syndrome.

Fragile X syndrome (FXS) is the most common inherited cause of mental retardation resulting in developmental delays in males. Atypical outer ear morphology is characteristic of FXS and may serve as a marker for abnormal auditory function. Despite this abnormality, studies of the hearing of young males with FXS are generally lacking. A few studies have suggested that a significant proportion of individuals with FXS demonstrate prolonged auditory brainstem response (ABR) latencies. The purpose of this study was to determine whether young males with FXS display atypical auditory brainstem function compared to typically developing males when conductive and sensorineural hearing loss are ruled out as possible contributors to atypical findings. Participants were 23 males with FXS, 21 typically developing males who were matched for developmental age, and 17 typically developing males who were matched for chronological age. A battery of tests to assess peripheral hearing, cochlear function, and auditory pathway integrity through the level of the brainstem was completed. Males with FXS were similar to typically developing males who were matched for developmental age level or chronological age level on all measures. They had normal hearing sensitivity and middle ear function and scored similar to the typically developing children on the measures of auditory brainstem pathway integrity. In summary, ABRs in young males with FXS were within normal limits.

Acoustic Impedance Tests↗
PubMed2004

Variability of spike trains and the processing of temporal patterns of acoustic signals-problems, constraints, and solutions.

Object recognition and classification by sensory pathways is rooted in spike trains provided by sensory neurons. Nervous systems had to evolve mechanisms to extract information about relevant object properties, and to separate these from spurious features. In this review, problems caused by spike train variability and counterstrategies are exemplified for the processing of acoustic signals in orthopteran insects. Due to size limitations of their nervous system we expect to find solutions that are stripped to the computational basics. A key feature of auditory systems is temporal resolution, which is likely limited by spike train variability. Basic strategies to reduce such variability are to integrate over time, or to average across several neurons. The first strategy is constrained by its possible interference with temporal resolution. Grasshoppers do not seem to explore temporal integration much, in spite of the repetitive structure of their songs, which invites for 'multiple looks' at the signal. The benefits of averaging across neurons depend on uncorrelated responses, a factor that may be crucial for the performance and evolution of small nervous systems. In spite of spike train variability the temporal information necessary for the recognition of conspecifics is preserved to a remarkable degree in the auditory pathway.

Acoustic Stimulation↗
PubMed1998

Imaging subcortical auditory activity in humans.

There is a lack of physiological data pertaining to how listening humans process auditory information. Functional magnetic resonance imaging (fMRI) has provided some data for the auditory cortex in awake humans, but there is still a paucity of comparable data for subcortical auditory areas where the early stages of processing take place, as amply demonstrated by single-unit studies in animals. It is unclear why fMRI has been unsuccessful in imaging auditory brain-stem activity, but one problem may be cardiac-related, pulsatile brain-stem motion. To examine this, a method eliminating such motion (using cardiac gating) was applied to map sound-related activity in the auditory cortices and inferior colliculi in the brain stem. Activation in both the colliculi and cortex became more discernible when gating was used. In contrast with the cortex, the improvement in the colliculi resulted from a reduction in signal variability, rather than from an increase in percent signal change. This reduction is consistent with the hypothesis that motion or pulsatile flow is a major factor in brain-stem imaging. The way now seems clear to studying activity throughout the human auditory pathway in listening humans.

Auditory Cortex↗