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PubMedDate not supplied

[Properties of nuclear and dispersed elements of the cortical end of the auditory analyzer according to total evoked potentials to sound].

In chronic experiments on cats short-latency evoked potentials (EPs) to clicks were recorded simultaneously in three cortical areas--auditory (nuclear elements of the cortical end of the auditory analyser) sensorimotor and visual ones (scattered auditory elements). EPs to above threshold clicks in the auditory area differed from EPs of non-auditory areas by a greater amplitude and relatively stable configuration. The EP threshold in the auditory area was lower and the increase in its amplitude throughout a rise in clicks' intensity far greater than in the non-auditory areas. The above difference in responses of nuclear elements in the primary auditory cortex and of scattered elements in non-auditory areas are considered as the sign of specificity of their functional organization, i. e. as the manifestation of the participation of auditory nuclear elements in a relatively delicate analysis of auditory stimuli and that of scattered ones--in a more simple and limited analysis.

Animals↗

PubMed1993

Effects of bilateral lesions of auditory cortex in mice on the acoustic startle response.

The acoustic startle response (ASR) was used to investigate the effects of auditory cortical lesions on a brain stem-mediated auditory behavior. The ASRs were obtained longitudinally from young adult C57BL/6J mice before bilateral ablation of auditory cortex, 1 day after ablation, and 1 month later. Control mice received lesions of nonauditory cortex. For some mice, averaged brain stem-evoked responses (ABR) were obtained, and these indicated no effects of lesions on auditory sensitivity. One month after surgery, mice with auditory cortex ablations were statistically indistinguishable from controls on all suprathreshold measures of ASR. However, 1 day after ablation of auditory cortex, experimental animals (but not controls) exhibited a change in ASR amplitude (but not threshold or latency). When a noise burst of 80 dB SPL was used to elicit the ASR, the amplitude was diminished, but with a 110 dB stimulus, amplitude was enhanced. The findings can be interpreted in one of two ways: temporary interference with modulation of the ASR normally performed by auditory cortex; or a general effect of auditory cortex ablation on brain stem auditory circuits not specific to the ASR. In any event, if auditory cortex plays a modulatory role with regard to the ASR, it is apparently nonessential and/or readily compensated for after ablation.

Acoustic Stimulation↗

PubMed1990

Psychophysical measures of central auditory dysfunction in multiple sclerosis: neurophysiological and neuroanatomical correlates.

Central auditory function was assessed in 15 patients with multiple sclerosis (MS) to determine whether the demyelinating lesions resulted in disruption of temporal processing. Auditory evoked potential (AEP) recordings included all three latency regions: Auditory brain stem responses (ABRs), midlatency responses (MLRs), and long-latency responses (LLRs). Two psychophysical tasks thought to involve temporal processing were used: a monaural-processing task (gap-detection) and a binaural-processing task (masking level difference; MLD). Further, AEP abnormalities and psychophysical performance deficits were related to lesion location, based on magnetic resonance imaging (MRI) scans. Reduced MLDs were seen in six MS subjects. Abnormal MLDs were always accompanied by abnormal ABRs and MLRs, and compared to subjects with normal MLDs, the subjects with abnormal MLDs were more likely to have bilateral abnormalities in the AEPs. Further, MLR indices of abnormal binaural interaction appeared to be specifically related to the psychophysical measure of binaural processing. The MRI data of these patients indicated widespread involvement of the auditory pathway. MS subjects with abnormal MRI signals restricted to levels caudal to the lateral lemniscus did not have abnormal MLDs. Gap-detection thresholds were more resistant to the effects of the demyelinating lesions; only two subjects had abnormal gap-detection thresholds. These subjects had extensive AEP abnormalities (bilaterally, in all three latency regions). The gap-detection thresholds were most specifically related to abnormalities of the LLRs. In addition, the subjects with elevated gap-detection thresholds were the only ones with a prolonged interval between the ABRs and MLRs. Thus, efficient neural conduction between the upper brain stem and auditory cortex appears to be crucial for normal monaural temporal processing. The results indicate that demyelinating lesions can cause deficits in temporal processing in the central auditory pathway. However, auditory temporal processing is not a unitary phenomenon since abnormalities at different levels of the auditory system disrupt different types of temporal processing. Finally, abnormal psychophysical performance was not seen in all subjects with AEP and MRI evidence of involvement of the auditory pathway; rather, these psychophysical measures appeared to be sensitive to disruption only in specific portions of the auditory system.

Adolescent↗

PubMed2003

Auditory evoked potentials from the cortex: audiology applications.

PURPOSE OF REVIEW: The audiological applications of cortical auditory evoked potentials are reviewed. Cortical auditory evoked potentials have some advantages compared with more commonly used techniques such as the auditory brainstem response, because they are more closely tied to perception and can be evoked by complex sounds such as speech. These response characteristics suggest that these potentials could be used clinically in the estimation of threshold and also to assess speech discrimination and perception. RECENT FINDINGS: Clinical uses of auditory evoked potentials include threshold estimation and their use as an electrophysiological index of auditory system development, auditory discrimination and speech perception, and the benefits from cochlear implantation, auditory training, or amplification. SUMMARY: Cortical auditory evoked potentials obtained in passively alert adults have a remarkably high correspondence with perceptual threshold. Acoustic features of complex sounds may be reflected in the waveform and latency of these potentials and so might be used to determine the integrity of neural encoding for such features and thus contribute to speech perception assessment. MMN and P3 have been used to discern discrimination abilities among groups of normal-hearing and hearing-impaired individuals; however, their sensitivity and specificity for testing an individual's abilities has not yet been established. Cortical auditory potentials are affected by listening experience and attention and so could be used to gauge the effects of aural habilitation. The presence of cortical potentials in children with auditory neuropathy appears to indicate residual hearing abilities. Parametric and developmental research is needed to further establish these applications in audiology.

Audiology↗

PubMed1996

Effects of prenatal alcohol exposure and aging on auditory function in the rat: preliminary results.

This study investigated select aspects of peripheral and central auditory dysfunction, as well as the pathological effects of aging, In an animal model of fetal alcohol syndrome (FAS). Pregnant rats consumed liquid alcohol diets containing 0, 17.5, or 35% ethanol-derived calories, from gestation day 7 to parturition. A fourth group was untreated. Offspring of these mothers were tested for auditory and neurological function, using the auditory brainstem response at 6, 12, and 18 months of age. Some animals in the alcohol-exposed groups showed a peripheral auditory disorder in the form of congenital sensorineural hearing loss. This was correlated with punctate lesions and malformed stereocilia on the auditory sensory receptor cells of the inner ear. Alcohol-exposed animals also showed a central auditory processing disorder characterized by prolonged transmission of neural potentials along the brainstem portion of the auditory pathway. Animals in the highest dose group also showed an augmentation in the age-related deterioration of auditory acuity. Thus, increased peripheral and central auditory dysfunctions and pathological deterioration of auditory function in old age may be sequelae of FAS. Such morbidities have important implications for the long-term clinical assessment and management of FAS patients.

Age Factors↗

PubMed1991

Topography of projections from the auditory cortex to the inferior colliculus in the rat.

We examined the organization of descending projections from auditory and adjacent cortical areas to the inferior colliculus (IC) in the rat by using the retrograde and anterograde transport of wheat germ agglutinin-horseradish peroxidase. Small tracer injections were placed into cytologically defined subnuclei of the IC. On the basis of the resulting pattern of retrogradely labeled neurons in the cortex, different cortical areas and fields were defined. Two secondary areas located ventrocaudally (Te2) and ventrally (Te3) to the primary auditory area (Te1) were delineated. The primary auditory area was subdivided into a posterior (Te1.p), a medial (Te1.m), and an anterior (Te1.a) auditory field. In addition, we outlined an area located rostrally to the auditory areas comprising a part of the secondary somatosensory cortex, as well as a dorsal belt surrounding dorsally the auditory areas. The following basic patterns of corticocollicular projections are revealed: 1) layers 2 and 3 of the dorsal cortex of the IC (DC2, DC3) are differentially innervated by the primary auditory fields (Te1.p and Te1.a project bilaterally to DC2, while Te1.m projects bilaterally and in topographical order to DC3); cells in Te1.m, arranged in caudal to rostral sequence, project to corresponding loci in DC3 arranged from dorsolateral to ventromedial; 2) the fibrocellular capsule of the IC, comprising layer 1 of the dorsal and external cortex of the IC, receives input from the secondary auditory area Te2; 3) layers 2 and 3 of the external cortex of the IC are only weakly innervated by the primary and secondary auditory cortex; 4) the intercollicular zone receives its major input from the secondary auditory area Te3, the secondary somatosensory cortex, and the dorsal belt; and 5) finally, the central nucleus of the IC receives no input from the temporal cortex at all. Our results demonstrate that the corticocollicular projections are highly organized. These pathways may modulate auditory processing in different functional circuits of the inferior colliculus.

Animals↗

PubMed2005

Auditory steady-state responses in infants with perinatal brain injury.

Infants with perinatal brain injury present impairments in motor, visual, auditory, and cognitive functions. The most useful methods for detecting auditory alterations are auditory brainstem responses and otoacoustic emissions. Auditory steady-state responses have been reported as a reliable and objective technique for evaluating the hearing threshold. Auditory brainstem responses and auditory steady-state responses were carried out in 53 infants with perinatal brain injury and abnormal neurologic findings. With auditory brainstem responses, 33 (62.26%) infants presented normal and 20 abnormal results; 8 (15.09%) exhibited mild alterations, 8 (15.09%) moderate, and 4 (7.54%) severe alterations. With auditory steady-state responses, 17 (32.0%) infants were normal and 36 (67.9%) had abnormal results. When auditory steady-state responses were compared with auditory brainstem responses gold standard, the assessment gave 100% sensitivity, 51.51% specificity, 55.55% positive predictive value, and 100% negative predictive value. Abnormalities were mild in 21 (39.6%) infants, moderate in 10 (18.9%), and 5 (9.4%) exhibited severe hearing loss. We conclude that hearing loss is a frequent abnormality in infants with perinatal brain injury, and auditory steady-state responses have a high sensitivity for detecting hearing impairment, which is more evident in mild hearing loss for specific frequencies.

Brain Diseases↗

PubMed2002

Modification of sudden onset auditory ERP by involuntary attention to visual stimuli.

To investigate the cross-modal nature of the exogenous attention system, we studied how involuntary attention in the visual modality affects ERPs elicited by sudden onset of events in the auditory modality. Relatively loud auditory white noise bursts were presented to subjects with random and long inter-trial intervals. The noise bursts were either presented alone, or paired with a visual stimulus with a visual to auditory onset asynchrony of 120 ms. In a third condition, the visual stimuli were shown alone. All three conditions, auditory alone, visual alone, and paired visual/auditory, were randomly inter-mixed and presented with equal probabilities. Subjects were instructed to fixate on a point in front of them without task instructions concerning either the auditory or visual stimuli. ERPs were recorded from 28 scalp sites throughout every experimental session. Compared to ERPs in the auditory alone condition, pairing the auditory noise bursts with the visual stimulus reduced the amplitude of the auditory N100 component at Cz by 40% and the auditory P200/P300 component at Cz by 25%. No significant topographical change was observed in the scalp distributions of the N100 and P200/P300. Our results suggest that involuntary attention to visual stimuli suppresses early sensory (N100) as well as late cognitive (P200/P300) processing of sudden auditory events. The activation of the exogenous attention system by sudden auditory onset can be modified by involuntary visual attention in a cross-model, passive prepulse inhibition paradigm.

Acoustic Stimulation↗

PubMed1994

Supramodal and modality-specific mechanisms for stimulus-driven shifts of auditory and visual attention.

Two experiments are described in which visual and/or auditory location precues preceded visual or auditory targets. Observers were required to judge the location of the targets. Conditions were such that involuntary, stimulus-driven attention shifts were the only ones likely to occur and give rise to cueing effects. It was found that visual precues affected response time to localize both visual targets and auditory targets but auditory precues affected only the time to localize auditory targets. Moreover, when visual and auditory cues conflicted, visual cues dominated in the visual task but were dominated by auditory cues in the auditory task. These results imply that involuntary stimulus-driven attention shifts might be controlled by a modality-specific mechanism for visual tasks, whereas stimulus-driven shifts of auditory attention are controlled by a supramodal mechanism. This asymmetry in attention control is consistent with the idea that attentional dominance in a multimodal experimental task depends on the relative performance possible in the modalities involved; in this case visual localization is more precise than auditory and so auditory cues may be ineffective in cueing visual location, while visual cues are effective in both modalities.

Attention↗

PubMedDate not supplied

[Are specific developmental language disorders caused by deficits in auditory perception?].

BACKGROUND: Specific language impairment is assumed to be caused by deficits in auditory perception and therefore the training of auditory abilities is recommended as a treatment. Our study focussed on the question of whether a correlation between language disorders and auditory perception abilities can be proven empirically. PATIENTS: 23 language impaired children and 52 controls aged 7 to 11 years were examined. METHOD: Auditory abilities were measured by means of a battery of nonverbal and verbal tests. The children had to identify tones of different frequencies, loudness, duration or patterns as well as every day sounds and mixtures of such sounds. Noise-overlaid, time-compressed and frequency-limited speech tasks, and binaural summation tasks were also used. In addition, phoneme discrimination ability and auditory memory were assessed. RESULTS: Language impaired children scored low on phoneme discrimination and auditory memory tests but not on nonverbal or verbal auditory perception tasks. There are significant correlations between their expressive language ability and their scores on phoneme discrimination, auditory memory and sound duration identification tests. CONCLUSIONS: The results do not support the assumption that developmental language disorders are associated with auditory perception deficits. However, there are indications that auditory memory and time processing are deficient. Thus, training of auditory perception does not appear to be a suitable treatment for language impaired children.

Audiometry, Pure-Tone↗

PubMed2004

Development of auditory processing in 6-12-year-old children: a longitudinal study.

The development of auditory processing in children was investigated in a longitudinal study. A group of 20 children with normal cognitive and language development underwent several auditory tests at the ages of 6, 7, 8, 10 and 12 years. At the age of 10 years, three subjects were lost to follow-up, as was one more subject at the age of 12 years. The auditory performance of the children was compared to the performance of a group of 20 adults. The auditory test battery consisted of a speech-in-noise test, a filtered speech test, a binaural fusion test and two auditory sequencing tests. At the ages of 6, 7 and 8 years, data on the performance on an auditory word discrimination test, an auditory synthesis test, an auditory closure test and a number recall test were also obtained. All auditory tests except the speech-in-noise test showed a clear effect of age on the performance of children. Our data suggest that maturational effects play an important role in auditory processing (at least) up to an age of 12-13 years. Correlations between the tests are in general not indicative of large amounts of overlap between the different tests. Factor analysis shows that three factors account for 68-70% of explained variance, with the three factors contributing equally. A composite score obtained by averaging all (sub)test scores can be used next to the individual test scores to describe the development of auditory processing abilities in children.

Adult↗

PubMed2003

Familial auditory neuropathy.

OBJECTIVES/HYPOTHESIS: Auditory neuropathy is a sensorineural hearing disorder characterized by absent or abnormal auditory brainstem responses and normal cochlear outer hair cell function as measured by otoacoustic emission recordings. Many risk factors are thought to be involved in its etiology and pathophysiology. Four Chinese pedigrees with familial auditory neuropathy were presented to demonstrate involvement of genetic factors in the etiology of auditory neuropathy. STUDY DESIGN: Probands of the above-mentioned pedigrees, who had been diagnosed with auditory neuropathy, were evaluated and followed in the Department of Otolaryngology-Head and Neck Surgery, China People Liberation Army General Hospital (Beijing, China). Their family members were studied, and the pedigree maps established. METHODS: History of illness, physical examination, pure-tone audiometry, acoustic reflex, auditory brainstem responses, and transient evoked and distortion-product otoacoustic emissions were obtained from members of these families. Some subjects received vestibular caloric testing, computed tomography scan of the temporal bone, and electrocardiography to exclude other possible neuropathic disorders. RESULTS: In most affected patients, hearing loss of various degrees and speech discrimination difficulties started at 10 to 16 years of age. Their audiological evaluation showed absence of acoustic reflex and auditory brainstem responses. As expected in auditory neuropathy, these patients exhibited near-normal cochlear outer hair cell function as shown in distortion product otoacoustic emission recordings. Pure-tone audiometry revealed hearing loss ranging from mild to profound in these patients. Different inheritance patterns were observed in the four families. In Pedigree I, 7 male patients were identified among 43 family members, exhibiting an X-linked recessive pattern. Affected brothers were found in Pedigrees II and III, whereas in pedigree IV, two sisters were affected. All the patients were otherwise normal without evidence of peripheral neuropathy at the time of writing. CONCLUSION: Patients with characteristics of nonsyndromic hereditary auditory neuropathy were identified in one large and three smaller Chinese families. Pedigree analysis suggested an X-linked, recessive hereditary pattern in one pedigree and autosomal recessive inheritances in the other three pedigrees. The phenotypes in the study were typical of auditory neuropathy; they were transmitted in different inheritance patterns, indicating clinical and genetic heterogeneity of this disorder. The observed inheritance and clinical audiological findings are different from those previously described for nonsyndromic low-frequency sensorineural hearing loss. This information should facilitate future molecular linkage analyses and positional cloning for the relative genes contributing to auditory neuropathy.

Adolescent↗

PubMed2006

Distributed and selective auditory representation of song repertoires in the avian song system.

For many songbirds, the vocal repertoire constitutes acoustically distinct songs that are flexibly used in various behavioral contexts. To investigate how these different vocalizations are represented in the song neural system, we presented multiple song stimuli while performing extracellular recording in nucleus HVC in adult male song sparrows Melospiza melodia, a species known for its complex vocal repertoire and territorial use of song. We observed robust auditory responses to natural song stimuli in both awake and anesthetized animals. Auditory responses were selective for multiple songs of the bird's own repertoire (BOR) over acoustically modified versions of these stimuli. Selectivity was evident in both awake and anesthetized HVC, in contrast to auditory selectivity in zebra finch HVC, which is apparent only under anesthesia. Presentation of multiple song stimuli at different recording locations demonstrated that stimulus acoustic features and local neuronal tuning both contribute to auditory responsiveness. HVC auditory responsiveness was broadly distributed and nontopographic. Variance in auditory responsiveness was greater among than within HVC recording locations in both anesthetized and awake birds, in contrast to the global nature of auditory representation within zebra finch HVC. To assess the spatial consistency of auditory representation within HVC, we measured the repeatability with which ensembles of BOR songs were represented across the nucleus. Auditory response ranks to different songs were more consistent across recording locations in awake than in anesthetized animals. This spatial reliability of auditory responsiveness suggests that sound stimulus acoustic features contribute relatively more to auditory responsiveness in awake than in anesthetized animals.

Acoustic Stimulation↗

PubMed2002

Plastic changes in the central auditory system after hearing loss, restoration of function, and during learning.

Traditionally the auditory system was considered a hard-wired sensory system; this view has been challenged in recent years in light of the plasticity of other sensory systems, particularly the visual and somatosensory systems. Practical experience in clinical audiology together with the use of prosthetic devices, such as cochlear implants, contributed significantly to the present view on the plasticity of the central auditory system, which was originally based on data obtained in animal experiments. The loss of auditory receptors, the hair cells, results in profound changes in the structure and function of the central auditory system, typically demonstrated by a reorganization of the projection maps in the auditory cortex. These plastic changes occur not only as a consequence of mechanical lesions of the cochlea or biochemical lesions of the hair cells by ototoxic drugs, but also as a consequence of the loss of hair cells in connection with aging or noise exposure. In light of the aging world population and the increasing amount of noise in the modern world, understanding the plasticity of the central auditory system has its practical consequences and urgency. In most of these situations, a common denominator of central plastic changes is a deterioration of inhibition in the subcortical auditory nuclei and the auditory cortex. In addition to the processes that are elicited by decreased or lost receptor function, the function of nerve cells in the adult central auditory system may dynamically change in the process of learning. A better understanding of the plastic changes in the central auditory system after sensory deafferentation, sensory stimulation, and learning may contribute significantly to improvement in the rehabilitation of damaged or lost auditory function and consequently to improved speech processing and production.

Animals↗

PubMed1982

[A case of pure word deafness and auditory agnosia associated with bilateral temporo-parietal lesions].

A-49-year-old right-handed female was reported. She showed pure word deafness and auditory agnosia because of bilateral temporo-parietal lesions. The left lesion resulted from angiospasm of the left anterior and middle cerebral arteries after subarachnoid hemorrhage due to a ruptured aneurysm of the left carotid artery, and the right one resulted from subcortical hematoma after the V-P shunt operation. CT scan revealed the abnormal low density area on the bilateral temporo-parietal regions seven months after onset. Neurophychological findings were as follows: there were no aphasic symptoms such as paraphasia, word finding difficulties, or disturbances of spontaneous writing, reading and calculation. But her auditory comprehension was severely disturbed, and she could neither repeat words after the tester nor write from dictation. She also could not recognize meaningful sounds and music in spite of normal hearing sensitivity for pure tone, BSR and AER. We discussed the neuropsychological mechanisms of auditory recognition, and assumed that each hemisphere might process both verbal and non-verbal auditory stimuli in the secondary auditory area. The auditory input may be recognized at the left association area, the final level of this mechanism. Pure word deafness and auditory agnosia of this case might be caused by the disruption of the right secondary auditory area, the pathway between the left primary auditory area and the left secondary auditory area, and between the left and right secondary auditory areas.

Agnosia↗

PubMedDate not supplied

Anatomy of the auditory cortex.

Cortical auditory areas located in the superior temporal region (STR) in monkey and human. The primary auditory area (AI) occupies the cortex of the supratemporal plane (STP) and is surrounded by auditory association areas in circular sulcus and superior temporal gyrus (STG). Architectonic studies have parcellated auditory areas into a number of subregions. Beginning from the temporal polar proisocortex up to the parietal cortex, these areas shows progressive laminar differentiation, and are arranged into three parallel lines. The most medial line occupies the cortex of the circular sulcus. The regions of this line maintains limbic features and is termed as root line. Another line is located in STG. The regions of this line show progressive emphasis in the third and fourth layer neurons and is termed as belt line. Interposed between root and belt line is a core line located in STP. In this line there is greater accumulation of fourth layer neurons. Recent physiological studies have outlined several auditory representations surrounding AI. These auditory representations correspond to above mentioned architectonic subregions of STR. The subregions within each line have bidirectional connectional laminar specificity. The feedforward connections originate from the supragranular layer III and terminate in the around layer IV of the rostrally adjacent region. Feedback projections in contrast stem from the infragranular layers and terminate in layer I. The long association connections of auditory areas are with the prefrontal cortex (PFC), the multimodal areas and the limbic regions, and are derived from belt and root line areas of STR. These projections follow the rostro-caudal architectonic differentiation of STR. Thus the rostral STG areas are mainly connected with orbital and medial PFC areas whereas the caudal STG areas are connected with caudal PFC. The intermediate STG areas are preferentially related to the lateral PFC regions. It seems that STG-PFC connections are between the areas with similar level of architectonic differentiation. The thalamic connections of the subregions of STR also follow the architectonic organizations. The core line areas are preferentially related to ventral nucleus (MGv) of medial geniculate nucleus (MGN) whereas the root and belt line areas are connected respectively to magnocellular (MGmc) and dorsal (MGd) subdivisions of MGN. The root and belt areas share some connections and are also related to pulvinar, suprageniculate, dorsomedial and intralaminar nuclei. It seems therefore that progressive laminar and tripartrate organization of auditory regions of STR is reflected in intrinsic, association and thalamic connections. The feedforward connections may be engaged in analysis of external environmental cues whereas feedback connections may have a role in matching learned or stored information with incoming auditory signals. The preferential core line connectivity with MGv may be involved in spectral analysis of sound whereas the connections of the belt and root areas with MGmc, MGd, and pulvinar may have role in sound pattern recognition, auditory memory, the localization of sound in space as well as matching auditory information with other modalities.

Animals↗

PubMed1997

Functional MR of the primary auditory cortex: an analysis of pure tone activation and tone discrimination.

PURPOSE: To use functional MR imaging to measure the effect of frequency (pitch), intensity (loudness), and complexity of auditory stimuli on activation in the primary and secondary auditory cortexes. METHODS: Multiplanar echo-planar images were acquired in healthy subjects with normal hearing to whom auditory stimuli were presented intermittently. Functional images were processed from the echo-planar images with conventional postprocessing methods. The stimuli included pure tones with a single frequency and intensity, pure tones with the frequency stepped between 1,000, 2,000, 3,000, or 4,000 Hz, and spoken text. The pixels activated by each task in the transverse temporal gyrus (TTG) and the auditory association areas were tabulated. RESULTS: The pure tone task activated the TTG. The 1,000-Hz tone activated significantly more pixels in the TTG than did the 4,000-Hz tone. The 4,000-Hz tone activated pixels primarily in the medial TTG, whereas the 1,000-Hz tone activated more pixels in the lateral TTG. Higher intensity tones activated significantly more pixels than did lower intensity tones at the same frequency. The stepped tones activated more pixels than the pure tones, but the difference was not significant. The text task produced significantly more activation than did the pure tones in the TTG and in the auditory association areas. The more complex tasks (stepped tones and listening to text) tended to activate more pixels in the left hemisphere than in the right, whereas the simpler tasks activated similar numbers of pixels in each hemisphere. CONCLUSION: Auditory stimuli activate the TTG and the association areas. Activation in the primary auditory cortex depends on frequency, intensity, and complexity of the auditory stimulus. Activation of the auditory association areas requires more complex auditory stimuli, such as the stepped tone task or text reading.

Acoustic Stimulation↗

PubMed1996

Distribution of calcium-binding protein immunoreactivities in the guinea pig auditory brainstem.

This study was intended to provide an overview of the distribution of calcium-binding proteins in the rodent auditory brainstem. We based our observations on immunohistochemical material obtained in the guinea pig, a species widely used in auditory research in which a mapping of calcium-binding proteins in the auditory brainstem is still missing. Differences in the amounts of these proteins throughout the auditory brainstem were further analyzed semiquantitatively. Parvalbumin was present in most neurons and their axon terminals throughout the ascending auditory brainstem. Nuclei that surround the main relay nuclei of the ascending auditory pathway lacked labeling. Calretinin staining was prominent in spherical and globular cells of the cochlear nucleus, in their axon terminals in the superior olivary complex, and in principal cells of the medial superior olive. Measures of optical densities showed that auditory neurons involved in sound localization had the highest calretinin labeling levels. Calbindin D-28k was present in cartwheel cells of the dorsal cochlear nucleus, in almost all neurons of the medial nucleus of the trapezoid body, and in globular cells in the ventral nucleus of the lateral lemniscus. The labeling patterns for calretinin and calbindin D-28k were non-overlapping throughout the auditory brainstem. This was also evident in the ventral nucleus of the lateral lemniscus where calbindin D-28k-immunoreactive terminals were found in the medial portion, while the calretinin-immunoreactive terminals were observed in the lateral portion. This study presents the first direct and comprehensive comparison of these three calcium-binding proteins in the auditory brainstem of a rodent. Each antibody yields a unique staining pattern that provides a basis for further defining neuronal populations. In addition, since their axons are also selectively stained, auditory nuclei can further be compartmentalized based on different terminal fields. These immunoreactivities have provided clues to the complex structure of the auditory brainstem.

Animals↗