Cochlear and middle ear effects on metabolism in the central auditory pathway during silence: a 2-deoxyglucose study.
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Acoustic Stimulation↗
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Auditory pathway in rheumatoid arthritis. A comparative study and surgical perspectives.
CONCLUSION: Rheumatoid arthritis (RA) patients present with both conductive and sensorineural deafness. OBJECTIVE: To evaluate the prevalence and features of hearing impairment in patients with RA. MATERIAL AND METHODS: A total of 28 RA patients underwent a rheumatological evaluation, including determination of rheumatoid factor, protein 2-glycoprotein I level and the Lee index. An audiological assessment consisting of pure-tone audiometry (PTA) and determination of auditory brainstem responses (ABRs) and transient evoked otoacoustic emissions (TEOAEs) was performed. The results were compared with those of 28 age- and sex-matched healthy subjects. Four selected RA patients underwent stapedectomy; PTA and TEOAEs were evaluated 6 months postoperatively. RESULTS: Increased air conduction thresholds at 250, 500 and 1000 Hz were found in RA subjects in comparison to controls (p<0.001). RA patients showed higher air-bone gaps in PTA (p<0.05) and an increased Wave I latency in ABRs (p=0.03). Decreased reproducibility (p<0.001) and amplitude (p<0.001) of TEOAEs were found in RA subjects in comparison to controls. A significant correlation between disease duration and echo amplitude was noticed (r=0.389). After stapedectomy, a reduction in the air-bone conduction gap (11 vs 2 dB HL) was noticed; no significant difference in TEOAEs was found.
Adult↗
The human auditory pathways. A quantitative study.
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Adolescent↗
[Brain-stem auditory pathways: effects of atropine].
The efferent pathways exert a control action on the function of the cochlear nucleus and hair cells. Acetylcholine is the neurotransmitter of the centrifugal system and its action can be blocked by Atropine. In order to give a contribution to the knowledge of the function of the efferent bundle, Auditory Brainstem Responses (ABRs) and Acoustic Reflex Latencies (ARLs) have been examined in 10 young normal subjects there was also a decrease in latency greater than or equal to 100 microseconds by at least other two waves. The only statistically significant difference was relative to the latency mean value of the wave III recorded in contralateral derivation at 11 pps. The ARLs, after the infusion of atropine, showed a statistically significant increase in 7 of the 10 cases; no change was recorded in the AR amplitude. It can be concluded that the pharmacological block of the olivo-cochlear bundle determines a delay in the neural conduction of the acoustic impulses; this finding means that the atropine can inhibit the facilitating activity of the efferent system on the brainstem afferent pathways.
Acetylcholine↗
[Electrophysiological study of auditory pathways and the vestibular system in tumor pathology of the 8th cranial nerve and of the cerebellopontile angle].
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Audiometry↗
The descending auditory pathway and acousticomotor systems: connections with the inferior colliculus.
In this review the following major points are emphasized. First, the descending auditory system includes 3 separate, but parallel pathways connecting the AC, MGB and IC. Each pathway makes a strong set of connections with a distinctive area from each of 3 auditory centers. The three sets of connections are mutually exclusive, such that the pathways describe 3 separate corticocolliculo-geniculate systems. Thus, multiple feedback loops between the AC and the IC are formed which create a great capacity for parallel processing of auditory information. Second, the IC projects to the SOC and, in particular, to the source of olivocochlear efferent neurons. The connections of the IC with the AC rostrally, and with the olivocochlear neurons caudally, imply a descending trisynaptic pathway from the cortex to the cochlea whose travel time could better that of the ascending pathway and thus provide an efficient feedback mechanism. It is probable that the IC influences cochlear signal processing. The reciprocal connectivity between any two of either the IC, SOC or the CN, again, affords to the auditory system remarkable parallel processing capabilities. Finally, the descending auditory, and 'extra-auditory' connections of the IC bestow a functional separateness to the 3 nuclei of the IC, a view that is best illustrated by description of the ICX as an acousticomotor nucleus, having connections with the SC, cerebellum and somatosensory and vocalization systems. More sophisticated questions about the descending auditory system will incorporate these present observations and test functional implications to which they allude.
Animals↗
Activity-dependent regulation of synaptic strength and neuronal excitability in central auditory pathways.
Neural activity plays an important role in regulating synaptic strength and neuronal membrane properties. Attempts to establish guiding rules for activity-dependent neuronal changes have led to such concepts as homeostasis of cellular activity and Hebbian reinforcement of synaptic strength. However, it is clear that there are diverse effects resulting from activity changes, and that these changes depend on the experimental preparation, and the developmental stage of the neural circuits under study. In addition, most experimental evidence on activity-dependent regulation comes from reduced preparations such as neuronal cultures. This review highlights recent results from studies of the intact mammalian auditory system, where changes in activity have been shown to produce alterations in synaptic and membrane properties at the level of individual neurons, and changes in network properties, including the formation of tonotopic maps.
Animals↗
Acetylcholinesterase staining differentiates functionally distinct auditory pathways in the barn owl.
The aim of this study was to examine how the functional specialization of the barn owl's auditory brainstem might correlate with histochemical compartmentalization. The barn owl uses interaural intensity and time differences to encode, respectively, the vertical and azimuthal positions of sound sources in space. These two auditory cues are processed in parallel ascending pathways that separate from each other at the level of the cochlear nuclei. Sections through the auditory brainstem were stained for acetylcholinesterase (AChE) to examine whether nuclei that process different auditory cues stain differentially for this enzyme. Of the two cochlear nuclei, angularis showed more intense staining than nucleus magnocellularis. Nucleus angularis projects to all of the nuclei and subdivisions of nuclei that belong to the intensity processing pathway. Acetylcholinesterase stained all regions that contain terminal fields of nucleus angularis and thus provided discrimination between the time and intensity pathways. Moreover, staining patterns with acetylcholinesterase were complementary to those previously reported with an anti-calbindin antibody, which stains terminal fields of nucleus laminaris, and thus stains all the nuclei and subdivisions of nuclei that belong to the time pathway. Some of the gross staining patterns observed with AChE were similar to those reported with antibodies to glutamate decarboxylase. However, AChE is a more convenient and definitive marker in discriminating between these pathways than is calbindin or glutamate decarboxylase. Acetylcholinesterase staining of the intensity pathway in the owl may be related to encoding of sound intensity by spike rate over large dynamic ranges.
Acetylcholinesterase↗
Visual and nonvisual auditory systems in mammals. Anatomical evidence indicates two kinds of auditory pathways and suggests two kinds of hearing in mammals.
Examination of the structural organization of the auditory system of the brain stem shows that the system is composed of a number of separate ascending pathways. This suggests that there may be at least two auditory systems, analogous to the rod and cone pathways in vision. We examined this possibility by investigating the variation in relative size of the medial and lateral superior olivary nuclei in a number of different mammalian species. The lateral superior olive is present in the hedgehog (an insectivore), cat (acarnivore), and squirrel monkey a(primate), but the medial superior olive is absent in the hedgehog. In a group of animals of the same taxonomic order (rodents) the lateral superior olive was present in all species examined, but the medial superior olive was almost wholly absent in the mouse and very prominent in the chinchilla and guinea pig. The absence of the medial superior olive in some animals is surprising because recent anatomical and physiological work has implicated the nucleus in auditory localization. Because of this implication, the medial and lateral olivary nuclei were examined in three species of bat and one dolphin, all echolocating animals. The medial superior olive was absent in these animals, and the lateral superior olive was prominent. These observations support the idea that the medial and lateral superior olives are nuclei on two different ascending auditory systems. It was also noted that the medial superior olive was always well developed in animals with well-developed eyes, and this suggested that the nucleus is in some way related to the visual system. We examined this idea by studying the relation between the numbers of cells in the medial superior olive and in the nucleus of the 6th cranial nerve (one of the motor nuclei concerned with eye movement) in a number of mammalian species. An approximately linear function was found between the sizes of the 6th nucleus and of the medial superior olive in three primates with cone-cell retinas (squirrel monkey, man, and macaque) and four rodents with rod-cell retinas (mouse, rat, guinea pig, and chinchilla). The cell numbers for the ground squirrel (a rodent with cone-cell retina) fitted an extension of the primate curve, and the cell numbers for the cat (in whose retina rods predominate) fitted an extension of the rodent curve. Thus, it is clear that the medial superior olive is related to the visual system, and that it is present in animals with cone-cell fovea and retina (diurnalanimals) and animals with rod-cell retina (that is, nocturnal animals) having good vision. In nonvisual nocturnal animals the nucleus is small or absent. The medial superior olive is probably not concerned with auditory localization in the psychophysical sense but is probably concerned with the movement of head and eyes in the direction of a sound in space. Localization in the psychophysical sense and fine auditory discrimination probably depend upon the ascending pathway which includes the lateral superior olive.
Anatomy, Comparative↗
Combined dynamics of EEG and evoked potentials. II. Studies of simultaneously recorded EEG-EPograms in the auditory pathway, reticular formation, and hippocampus of the cat brain during sleep.
This study is carried out on single (not averaged) recordings combining the spontaneous activity preceding the stimulus onset and the EP recorded upon acoustical stimulation. These recordings, which we call EEG-EPograms, are measured simultaneously from different subdural structures, such as the auditory cortex, medial geniculate nucleus, inferior colliculus, reticular formation and the hippocampus of the cat brain during the slow wave sleep stage. Using a combined analysis procedure (C.A.P.), the relevant frequency components of spontaneous EEG and EPs, recorded simultaneously from these brain nuclei, are analyzed according to the consistent selectivity bands depicted by the determined amplitude-frequency characteristics for the SWS-stage. In parallel with the results which we obtained for the waking stage, these analyses provide also the following information: (1) there is an important congruency in the time courses of simultaneous response components in common frequency bands, especially in the alpha and beta frequency ranges; (2) there exist significant coupling and synchrony between the evoked amplitude enhancements in the simultaneously recorded single response components; (3) the inter-nuclei coherency in the brain's electrical activity is enormously increased upon stimulation;(4) the evoked response magnitude can be predicted, with reasonable accuracy, from the spontaneous activity preceding the stimulus. All these findings are discussed with reference to those obtained for the waking stage.
Animals↗
Combined dynamics of EEG and evoked potentials. I. Studies of simultaneously recorded EEG-EPograms in the auditory pathway, reticular formation, and hippocampus of the cat brain during the waking stage.
This study is carried out on single (not averaged) recordings combining the spontaneous activity preceding the stimulus onset and the EP recorded upon acoustical stimulation. These recordings, which we call EEG-EPograms, are measured simultaneously from different subdural brain structures, such as the auditory cortex, medial geniculate nucleus, inferior colliculus, reticular formation and the hippocampus of awake cats. Using a combined analysis procedure (C.A.P.), the relevant frequency components of spontaneous EEG and EPs, recorded simultaneously from these brain nuclei, are analyzed according to the consistent selectivity bands depicted by the determined amplitude-frequency characteristics. These analyses provide us the following information: (1) there is an important congruency in the time courses of simultaneous response components in common frequency bands, especially in the alpha and beta frequency ranges; (2) there exist significant coupling and synchrony between the evoked amplitude enhancements in the simultaneously recorded single response components; (3) the inter-nuclei coherency in the brain's electrical activity is enormously increased upon stimulation; (4) the evoked response magnitude can be predicted, with reasonable accuracy, from the spontaneous activity preceding the stimulation. The strong dependence of the response magnitude on the stimulus-preceding EEG is explained by means of a model network consisting of a population of relaxation oscillators, which can be brought to different states of synchrony and asynchrony. Some suggestions and comments are also made for investigators working toward theories of signal transmission in the brain.
Animals↗
AMPA receptors with high Ca2+ permeability mediate synaptic transmission in the avian auditory pathway.
1. The permeability of AMPA (alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionate) receptors in the chick cochlear nucleus, the nucleus magnocellularis (nMAG), was examined by measuring the shift in reversal potential (Erev) of current through glutamate or neurotransmitter-gated channels in solutions of different ionic composition. 2. Outwardly rectifying glutamate-activated currents in outside-out membrane patches showed rapid activation and desensitization. The Erev of glutamate-evoked current in zero sodium solutions was dependent on the extracellular Ca2+ concentration. The relation between Erev and Ca2+ ionic activities could be described by the Goldman-Hodgkin-Katz equation with a permeability ratio, PCa/PCs, of 3.3. The PNa/PCs was estimated as 0.66, indicating a PCa/PNa of 5. 3. Evoked excitatory postsynaptic currents (EPSCs) could be recorded during local perfusion of the auditory nerve-nMAG synapse with isotonic Ca2+. The Erev of the EPSC shifted in the positive direction in high-Ca2+ solution as predicted from the preceding analysis. The fraction of current carried by Ca2+ during the AMPA receptor EPSC was estimated as 18%.
Animals↗
Decreased expression of the c-Fos, but not Jun B, transcription factor in the auditory pathway of the rat after repetitive acoustic stimulation.
Between the 21st and 34th postnatal days, male rats received an acoustic stimulus every second day, and the expression of c-Fos and Jun B proteins was compared with rats that received only a single acoustic stimulus at postnatal day 34. For acoustic stimulation, 8-kHz pure-tone bursts (100 ms duration at a rate of 6.3 Hz) were applied for 5 min. The numbers of neurons immunoreactive to c-Fos and Jun B were studied 2 h after the last or acute stimulus, respectively, in the ventral cochlear nucleus (VCN), dorsal cochlear nucleus (DCN) and inferior colliculus (IC). Compared with the single stimulus, repetitive stimulation significantly reduced the number of c-Fos labeled neurons in the VCN by 51%, in the DCN by 75% and in the IC by 48%. In contrast to c-Fos, repetitive stimulation did not significantly lower the number of Jun-B-expressing neurons. These findings indicate that independent intraneuronal pathways terminate on the induction of c-Fos- and Jun-B-expressing genes during the juvenile maturation of the acoustic pathway and that chronic exposure of acoustic events alters the program of intraneuronal gene expression by reducing transcriptional activities with subsequent stabilization at the genetic level.
Acoustic Stimulation↗
Maturational aspects of the human auditory pathway: anatomical and electrophysiological findings.
Anatomical investigations were carried out on 39 human brains ranging in age from the 29th week of development to the 70th year of life. It was demonstrated that myelination, as a prerequisite for functional maturation, takes place during the 1st year of life. Functional maturation was analyzed with electrophysiological techniques. Normal development depends on adequate stimulation during certain sensitive periods in the 1st year of life as well as the continuous use of the central auditory and speech-hearing systems.
Adolescent↗
Song-induced ZENK gene expression in auditory pathways of songbird brain and its relation to the song control system.
The ZENK gene encodes a zinc-finger-containing transcriptional regulator and can be rapidly activated in songbird brain by presentation of birdsong (Mello et al., 1992). Here we map the areas of the songbird forebrain that show this genomic response to birdsong, using in situ hybridization. After 30 min of song presentation ZENK mRNA levels reach a peak in the caudomedial telencephalon, in areas adjacent to or closely related with primary auditory structures. These areas include subfields of field L (L1 and L3), the caudomedial neostriatum (NCM), the caudomedial hyperstriatum ventrale (CMHV) anterior to field L, the caudal paleostriatum, and two field L targets, HVC shelf and RA cup. In contrast, ZENK induction is absent in some areas that show a response to song by other measures and where ZENK induction might have been expected. These include the direct thalamo-recipient field L subfield L2, and the nuclei of the circuit involved in the acquisition and production of learned song. These results demonstrate that ZENK induction following song presentation occurs only in a subset of areas physiologically activated by song, and draw attention to areas previously unsuspected as related to processing of complex auditory stimuli. Based on what is known about ZENK function in mammalian systems (Christy et al., 1989; Cole et al., 1989; Wisden et al., 1990), we speculate that areas revealed by ZENK induction might correspond to sites where critical neuronal modifications occur in response to birdsong presentation, possibly leading to the formation of song-related memories.
Animals↗
[Regeneration of the auditory pathway].
In order to investigate the possibility of the treatment of sensorineural hearing disturbance, experiments were performed using animals. First, the central cochlear pathway in the brain stem to pons was transected in adult rats. Tissue from embryos was transplanted to the lesion site. In 20% of the rats examined, the axons regrew beyond the transected site and regenerated into the denervated side and terminated at the normal targets. The hearing function of animals was also recovered. Those findings contradict the widely held view that the adult mammalian central auditory system cannot be restored following damage. Then, adult rat hippocampus-derived neural stem cells(NSC) were grafted into newborn rat cochlea. Within two to four weeks of grafting to the cochlea, some NSC survived in the cochlear cavity. Some of them had adopted the morphologies and positions of hair cells. This suggests that NSC can adapt to the environment of the cochlea and gives hope for treatment of the damaged cochlea and sensorineural hearing loss.
Animals↗
[Shielding effects of an aleatory temporal series on a regular rhythm in the auditory pathways].
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Animals↗
Magnetic resonance imaging findings in the auditory pathway of patients with sudden deafness.
OBJECTIVES: The objectives of this study were to evaluate magnetic resonance imaging (MRI) findings of patients with sudden sensorineural hearing loss (SSNHL) and to grade the findings based on their clinical importance. STUDY DESIGN: A prospective clinical study. SETTING: A tertiary referral center (university hospital). PATIENTS: MRI findings of 82 consecutive patients with SSNHL fulfilling the inclusion criteria. MAIN OUTCOME MEASURES: We studied 1.0-T MR images that were analyzed by one experienced neuroradiologist. RESULTS: Of the six cases (7%) in which clearly hearing loss was obviously associated with the observed pathology, four patients had an acoustic neuroma in the internal auditory canal or cerebellopontine angle, one patient had changes at the level of pons, and one patient had an obliterated internal carotid artery. Of the six other patients (7%) in which MRI revealed changes that suggest a possible etiology to hearing loss, two patients showed a demyelinating process and four patients showed blood vessel abnormalities such as caroticocavernous fistula, abnormally locating vertebral or basilar artery, and a venous angioma. CONCLUSIONS: Enhanced MR imaging seems to be a useful examination in patients with SSNHL. The aim should not be only to exclude specific retrocochlear etiologies, but by appropriate techniques, MRI could reveal both peripheral and central abnormalities.
Adult↗