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PubMed2006

A thalamo-cortico-amygdala pathway mediates auditory fear conditioning in the intact brain.

The neural substrates of fear conditioning in rats have been well characterized, with converging lines of evidence indicating that conditioned stimulus (CS) and unconditioned stimulus (US) information form a CS-US association in the amygdala. Auditory CS information can reach the amygdala via two routes: a direct thalamo-amygdala pathway, and an indirect thalamo-cortico-amygdala pathway. Although either pathway can fully support learning when the alternate pathway is disrupted, many studies to date have argued that the thalamo-amygdala pathway is the principal auditory CS pathway in intact brains. To test this hypothesis, we trained rats in auditory fear conditioning, and 24 h later lesioned either pathway, leaving the alternate pathway intact. Later, animals were tested for conditioned freezing to the auditory CS. We report that lesions of the thalamo-amygdala pathway produced severe but incomplete deficits in freezing during the tone retention test, while lesions of the thalamo-cortico-amygdala pathway completely abolished freezing during tone presentation. These results suggest that the thalamo-cortico-amygdala pathway is the principal auditory CS pathway when the brain is intact.

Acoustic Stimulation↗
PubMed2006

Reversible impairment of auditory callosal pathway in 5-fluorouracil-induced leukoencephalopathy: parallel changes in function and imaging.

OBJECTIVE: To report the course of functional and imaging recovery of the auditory callosal pathway in a patient with 5-fluorouracil-induced leukoencephalopathy. DESIGN: Case study. SETTING: University hospital. PATIENT: A 58-year-old man with hypopharyngeal cancer who developed 5-fluorouracil-induced leukoencephalopathy. MAIN OUTCOME MEASURES: Imaging (magnetic resonance imaging) and functional (dichotic listening test) evaluation on the auditory callosal pathway. RESULTS: The patient underwent systemic chemotherapy with pirarubicin, cisplatin, and 5-fluorouracil. On the last day of the regimen, the patient suddenly became restless and convulsive. On diffusion-weighted magnetic resonance images, the signal intensity at the splenium of the corpus callosum was very high. Fluid-attenuated inversion recovery images showed no abnormal findings at this time. Intravenous methylprednisolone sodium succinate and glycerin 10% was started immediately. On the ninth day after onset, the patient was free of neurologic symptoms. Although pure-tone audiograms and speech discrimination scores were normal, dichotic listening tests revealed significant left ear suppression, indicating severe injury of the auditory callosal pathway. On fluid-attenuated inversion recovery images, the signal intensity at the splenium was high, whereas the posterior trunk was normal. At 6 weeks after onset, dichotic listening test results returned to normal and hyperintensity at the splenium was much less marked on fluid-attenuated inversion recovery images. CONCLUSION: By using both functional and imaging modalities, this case study demonstrated, for the first time in a reversible manner, that the auditory callosal pathway runs through the most posterior part of the corpus callosum including the splenium. Diffusion-weighted magnetic resonance imaging was considered useful for early diagnosis of 5-fluorouracil-induced leukoencephalopathy.

Antimetabolites, Antineoplastic↗
PubMed1990

Auditory brainstem response in hyperbilirubinemic rat: Part I.

The effect of hyperbilirubinemia on the auditory brainstem response (ABR) of rats and its change by hyperosmolality were examined. The ABR wave I did not change significantly. In bilirubin-loaded rats, the latencies of wave II and IV were prolonged and the amplitudes decreased. Bilirubin injection damaged the central auditory pathway but the peripheral auditory pathway was spared. These ABR changes were reversible in the acute phase of hyperbilirubinemia. Mannitol administration hastened the appearance of the ABR peaks and the recovery of the changed ABR. This tendency was more remarkable in latency changes than in amplitude changes.

Animals↗
PubMed2000

A candidate pathway for a visual instructional signal to the barn owl's auditory system.

Many organisms use multimodal maps to generate coherent neuronal representations that allow adequate responses to stimuli that excite several sensory modalities. During ontogeny of these maps, one modality typically acts as the dominant system the other modalities are aligned to. A well studied model for the alignment of sensory maps is the calibration of the auditory space map by the visual system in the optic tectum of the barn owl. However, a projection from the optic tectum to the site of plasticity in the auditory pathway that could deliver an instructive signal has not been found so far. We have analyzed the development of the connectivity between the bimodal (visual and auditory) map of space in the barn owl's optic tectum and the auditory space map in the inferior colliculus with tracing methods and intracellular fills. Neurons in the tectal stratum griseum centrale were found to be suited to deliver an alignment signal from the visual midbrain to the auditory pathway. These neurons are presumably part of the efferent tectal projection pathway that mediates head saccades. The implications of a sensory alignment signal possibly being delivered by a (pre)motor command pathway are discussed.

Animals↗
PubMed2003

Functional MR imaging of the auditory cortex with electrical stimulation of the promontory in 35 deaf patients before cochlea implantation.

BACKGROUND AND PURPOSE: Promontory testing is used for preoperative assessment of the auditory pathway before cochlear implantation. This method depends on patient cooperation and cannot be used in children or disabled persons. Promontory stimulation during functional MR imaging (fMRI) provides a new and objective method to test the integrity of the auditory pathway. To evaluate the method, we performed this prospective study in deaf adult patients. METHODS: fMRI of the auditory pathway with electrical stimulation of the promontory was performed in 35 profoundly deaf patients, bilaterally in seven. For safe stimulation inside the MR environment, a specially designed nerve stimulator was used. We acquired nine sections parallel to the sylvian fissure by using an echo-planar pulse sequence (1.5 T). To evaluate the number of pixels in the auditory cortex, areas were counted and the minimum confidence level (p(st) value) was determined. The auditory pathway was called intact when the minimal p(st) value was 10(-5) or when the minimal p(st) value was 10(-4) in at least five activated pixels. RESULTS: Images in 85% of patients reporting an auditory sensation showed activation of the contralateral auditory cortex. In the group of patients reporting no hearing sensation, images in 75% did not show activation. CONCLUSION: This method can prove the intactness of the auditory pathway and help the surgeon in decision making before cochlear implantation. However, a negative finding should not be interpreted as indicating a nonfunctioning auditory pathway. Additional technical refinements and experience are needed to further improve this method.

Adult↗
PubMed2002

[Otoacoustic emissions and auditory brain stem responses in insulin dependent diabetic patients].

UNLABELLED: The relationship between diabetes mellitus and hearing impairment has been studied for more than 100 years, and is still a matter of controversy. In our study hearing in diabetic patients was studied by tonal audiometry, brain stem auditory evoked responses and evoked otoacoustic emissions. The aim of this study was to evaluate the function of peripheral and central auditory pathway in subjects with insulin dependent diabetes mellitus (IDDM). Possible correlation between auditory function and microangiopathy (retinopathy or nephropathy) also have been investigated. Cochlear activity was evaluated by means of otoacoustic emissions. The functional changes in the brain stem were evaluated by ABR. OAEs and ABR were measured in 42 normally hearing IDDM patients aged between 21 and 42 years, and 33 aged- and sex-matched non-diabetic control subjects. IDDM patients were distributed into two groups, 17 patients without microangiopathy and 25 patients with microangiopathy. RESULTS: Both of the groups (diabetic and control) had normal and undifferentiated results in tonal and impedance audiometry. The mean amplitudes of various DPOAEs were significantly reduced in the diabetic group compared with control subjects. No correlations were found between microangiopathy and DPOAE amplitudes reduced. ABR latencies were longer in diabetic patients when compared with those of control subjects. These findings indicate a central disturbance in the auditory pathway. Microvascular complications (retinopathy or nephropathy) were associated only with the prolongation wave I latency. In conclusion, the combined use of different procedures for monitoring the central and peripheral portions of the auditory pathway in diabetic patients showed the existence of the alterations in the cochlear micromechanics and in the retrocochlear auditory pathway.

Adult↗
PubMed2002

Deficits in auditory brainstem pathway encoding of speech sounds in children with learning problems.

Auditory brainstem responses were recorded in normal children (NL) and children clinically diagnosed with a learning problem (LP). These responses were recorded to both a click stimulus and the formant transition portion of a speech syllable /da/. While no latency differences between the NL and LP populations were seen in responses to the click stimuli, the syllable /da/ did elicit latency differences between these two groups. Deficits in cortical processing of signals in noise were seen for those LP subjects with delayed brainstem responses to the /da/, but not for LPs with normal brainstem measures. Preliminary findings indicate that training may be beneficial to LP subjects with brainstem processing delays.

Acoustic Stimulation↗
PubMed1998

Forebrain pathway for auditory space processing in the barn owl.

The forebrain plays an important role in many aspects of sound localization behavior. Yet, the forebrain pathway that processes auditory spatial information is not known for any species. Using standard anatomic labeling techniques, we used a "top-down" approach to trace the flow of auditory spatial information from an output area of the forebrain sound localization pathway (the auditory archistriatum, AAr), back through the forebrain, and into the auditory midbrain. Previous work has demonstrated that AAr units are specialized for auditory space processing. The results presented here show that the AAr receives afferent input from Field L both directly and indirectly via the caudolateral neostriatum. Afferent input to Field L originates mainly in the auditory thalamus, nucleus ovoidalis, which, in turn, receives input from the central nucleus of the inferior colliculus. In addition, we confirmed previously reported projections of the AAr to the basal ganglia, the external nucleus of the inferior colliculus (ICX), the deep layers of the optic tectum, and various brain stem nuclei. A series of inactivation experiments demonstrated that the sharp tuning of AAr sites for binaural spatial cues depends on Field L input but not on input from the auditory space map in the midbrain ICX: pharmacological inactivation of Field L eliminated completely auditory responses in the AAr, whereas bilateral ablation of the midbrain ICX had no appreciable effect on AAr responses. We conclude, therefore, that the forebrain sound localization pathway can process auditory spatial information independently of the midbrain localization pathway.

Animals↗
PubMed1988

Binaural acoustic stimulation exercises protective effects at the cochlea that mimic the effects of electrical stimulation of an auditory efferent pathway.

Low-level acoustic stimulation of one (contralateral) ear reduced the neural desensitization caused by a simultaneous loud sound exposure in the other (ipsilateral) ear in a loss-related manner. Greatest reductions in the temporary threshold shifts (TTS) in the exposed ear were obtained when the exposure would have caused large amounts of TTS. Low-level exposures (reduced intensity or duration of exposure) which caused low levels of TTS, from which the cochlea could recover relatively quickly, were not affected by the contralateral stimulus. Intermediate levels of TTS showed intermediate levels of reduction for the same contralateral acoustic stimulus. These effects were similar to effects previously demonstrated with electrical stimulation of an efferent pathway to the cochlea, the crossed olivocochlear bundle (COCB); lesioning the COCB prevented the contralateral stimulus from having any effect on TTS due to an ipsilateral exposure. Like COCB stimulation, the contralateral acoustic stimulus had tonic effects, so that reductions in ipsilateral TTS could be obtained even when the contralateral stimulus was presented 5 min before the ipsilateral exposure. With 10 min delay no effect on TTS occurred. The contralateral stimulus did not appear to cause any changes in responses in the ipsilateral cochlea prior to the loud sound exposure. These results are discussed as indicating an interaction between the two inputs at a central locus, leading to activation of the COCB fibres to the cochlea exposed to the loud sound.

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↗
PubMed1990

Effects of high dietary sulfur on brain functions using evoked potentials technique.

Brain stem auditory-evoked response (BAER) is a noninvasive technique used for detecting neurophysiological abnormalities of the brain stem along the auditory pathway. Brain stem auditory-evoked response recordings were obtained from subcutaneous skin electrodes from two control sheep and 22 other sheep fed high sulfur (S) diets with low or high concentration of thiamine (B1), copper (Cu), and molybdenum (Mo). At least four peaks (I,II,III,IV) of varied amplitude were observed in all animals. Neurophysiological abnormalities due to decreased conductivity and/or excitability of nerve fibers along the auditory pathway were found on the BAER recordings of sheep fed high S diet. Abnormalities of peaks and interpeak latencies within BAER recordings were related to histopathological observations of brain stem lesions. Lesions in the areas of the cochlear nuclei and lateral lemniscus were seen in conjunction with altered BAER components. However, abnormalities in BAER recordings and lesions in the brain stem also occurred in the absence of overt clinical signs. Analysis of interpeak latencies between peaks I and IV revealed significant differences among dietary groups. Sheep given diets low in Cu, Mo, and B1 were affected most. Factorial analysis indicated B1 and interactions among Cu, Mo, and B1 as significant factors influencing interpeak latencies.

Animals↗
PubMed1991

Hemispheric asymmetry of late auditory evoked response induced by pitch changes in infants: influence of sleep stages.

Late auditory evoked potentials (LAEPs) have been recorded in response to a 1000 Hz standard (occurrence 80%) or a 2000 Hz deviant (occurrence 20%) tone on the left (T3) and right (T4) temporal scalp in 6-week-old full-term newborns during pure quiet or active sleep states. Sleep states were premanently controlled by polygraphic recording including EEG, EOG, EMG, EKG and respiratory movements. During quiet sleep LAEPs consisted of a clear polygraphic response: N1-P2-N2-P3. Mean latencies ranges on T3 and T4 were: N1 = 28-70 ms; P2 = 343-407 ms; N2 = 966-1178 ms; and P3 = 1461-1492 ms. During active sleep LAEPs consisted of a N1-P2-N2 response. Mean latency ranges on T3 and T4 were: N1 = 36-79 ms; P2 = 278-304 ms; N2 = 555-620 ms. N2 latency was significantly shorter in AS than in QS. Amplitude of the N1-P2-N2 complex was significantly lower during active sleep. In response to standard stimuli, mean amplitudes and latencies of the LAEP were similar on T3 and T4 during active or quiet sleep states. In response to deviant stimuli mean amplitude of the N1-P2-N2 complex was significantly higher and mean latencies of N1 and N2 were significantly shorter on T3 during quiet sleep. No significant difference was observed during active sleep. These results confirm that sleep stages have a considerable influence on cortical auditory pathways. The auditory message is amplified during quiet sleep and inhibited during active sleep. Therefore sleep states need to be controlled to analyze LAEPs in young children.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1993

Brainstem auditory evoked potential interwave intervals are prolonged in vitamin B-6-deficient cats.

Vitamin B-6 deficiency has been reported to produce behavioral, neurophysiological and neuropathological abnormalities in a variety of species. In this investigation we used brainstem auditory evoked potentials (BAEP) to determine if vitamin B-6 deficiency in cats affected peripheral and brainstem auditory pathways. Brainstem auditory evoked potentials were recorded from growing cats as they developed vitamin B-6 deficiency, which was confirmed using clinical, hematological and urinary criteria. The BAEP interwave intervals measured from early (wave 1 or 1N) to late waves (5N) or from middle (wave 3) to late waves increased significantly, whereas interwave intervals from early to middle waves did not differ significantly. These results indicate that vitamin B-6 deficiency affects one or more structures of the brainstem that generate the later parts of the BAEP. The finding of prolonged interwave intervals in vitamin B-6-deficient animals is consistent with slowed axonal conduction velocity secondary to defective myelination. Recording BAEP provided a noninvasive means of detecting effects of vitamin B-6 deficiency on specific parts of the central nervous system.

Acoustic Stimulation↗
PubMedDate not supplied

Postnatal development of the auditory evoked brainstem potentials in the guinea pig.

The postnatal development of lower stations in the auditory pathway was studied in the guinea pig by recording auditory brainstem potentials. At birth, the brainstem responses of young guinea pigs already have thresholds corresponding to those of adult animals. However, the latencies of the individual potentials are significantly longer than those in the control group. Within the 4 weeks of the study, the latency of each of the five potentials reached the adult value. Both the rate of latency normalization and the characteristic changes in potential amplitude indicate that maturation of the auditory pathway proceeds centripetally.

Animals↗
PubMed2004

Lateralization of ventral and dorsal auditory-language pathways in the human brain.

Recent electrophysiological investigations of the auditory system in primates along with functional neuroimaging studies of auditory perception in humans have suggested there are two pathways arising from the primary auditory cortex. In the primate brain, a 'ventral' pathway is thought to project anteriorly from the primary auditory cortex to prefrontal areas along the superior temporal gyrus while a separate 'dorsal' route connects these areas posteriorly via the inferior parietal lobe. We use diffusion MRI tractography, a noninvasive technique based on diffusion-weighted MRI, to investigate the possibility of a similar pattern of connectivity in the human brain for the first time. The dorsal pathway from Wernicke's area to Broca's area is shown to include the arcuate fasciculus and connectivity to Brodmann area 40, lateral superior temporal gyrus (LSTG), and lateral middle temporal gyrus. A ventral route between Wernicke's area and Broca's area is demonstrated that connects via the external capsule/uncinate fasciculus and the medial superior temporal gyrus. Ventral connections are also observed in the lateral superior and middle temporal gyri. The connections are stronger in the dominant hemisphere, in agreement with previous studies of functional lateralization of auditory-language processing.

Adult↗
PubMedDate not supplied

[Objective audiometry by recording of early and middle-latency auditory evoked potentials using an external method].

The bio-electric potentials induced by a stimulus in the cochlea and the various structures of the auditory pathways of the brain stem and the primary auditory cortex may be collected using an external method. The authors frequently emply in clinical practice early components, which correspond to the cochlea response in the cochlear nucleus of the medulla, in the olive of the pons and the posterior quadrigeminal tubercle, and middle latency components, sub-cortico-cortical potentials generated in the thalamus and the primary auditory cortex. Combined use of early and middle latency components makes it possible, without preparation and with simple sedation in the child, to obtain an objective determination of threshold. In oto-neurology, this examination provides appraciable information concerning lesions in the auditory pathways: acoustic neuroma, brain stem tumour, multiple sclerosis, central deafness in patients with cerebral motor insufficiency.

Acoustic Stimulation↗
PubMed2003

"Auditory neuropathy": physiologic and pathologic evidence calls for more diagnostic specificity.

The term "auditory neuropathy" is being used in a rapidly increasing number of papers in the audiology/otolaryngology literature for a variety of individuals (mostly children) who fulfill the following criteria: (1) understanding of speech worse than predicted from the degree of hearing loss on their behavioral audiograms; (2) recordable otoacoustic emissions and/or cochlear microphonic; together with (3) absent or atypical auditory brain stem responses. Because of the general lack of anatomic foundation for the label "auditory neuropathy" as currently used, we review the anatomy of the auditory pathway, the definition of neuropathy and its demyelinating, axonal, and mixed variants. We submit that the diagnostic term "auditory neuropathy" is anatomically inappropriate unless patients have documented evidence for selective involvement of either the spiral ganglion cells or their axons, or of the 8th nerve as a whole. In view of biologic differences between peripheral nerves and white matter tracts in the brain, the term "auditory neuropathy" is inappropriate for pathologies affecting the central auditory pathway in the brainstem and brain selectively. Published reports of patients with "auditory neuropathy" indicate that they are extremely heterogeneous in underlying medical diagnosis, age, severity, test results, and that only a small number have undergone the detailed investigations that would enable a more precise diagnosis of the locus of their pathologies. The electrophysiology of peripheral neuropathies and the deficits expected with pathologies affecting the hair cells, spiral ganglion cells and their axons (auditory neuropathy sensu stricto), and brain stem relays are reviewed. In order to serve patients adequately, including potential candidates for cochlear implants, and to increase knowledge of auditory pathologies, we make a plea for more comprehensive evaluation of patients who fulfill the currently used audiologic criteria for "auditory neuropathy" in an effort to pinpoint the site of their pathologies. We suggest that the term auditory neuropathy be limited to cases in which the locus of pathology is limited to the spiral ganglion cells, their processes, or the 8th nerve, and that the term neural hearing loss be considered for pathologies that affect all higher levels of the auditory pathway, from the brainstem to the auditory cortex.

Audiology↗
PubMed1993

Binaural auditory processing in multiple sclerosis subjects.

In order to relate human auditory processing to physiological and anatomical experimental animal data, we have examined the interrelationships between behavioral, electrophysiological and anatomical data obtained from human subjects with focal brainstem lesions. Thirty-eight subjects with multiple sclerosis were studied with tests of interaural time and level discrimination (just noticeable differences or jnds), brainstem auditory evoked potentials and magnetic resonance (MR) imaging. Interaural testing used two types of stimuli, high-pass (> 4000 Hz) and low-pass (< 1000 Hz) noise bursts. Abnormal time jnds (Tjnd) were far more common than abnormal level jnds (70% vs 11%); especially for the high-pass (Hp) noise (70% abnormal vs 40% abnormal for low-pass (Lp) noise). The HpTjnd could be abnormal with no other abnormalities; however, whenever the BAEPs, LpTjnd and/or level jnds were abnormal HpTjnd was always abnormal. Abnormal wave III amplitude was associated with abnormalities in both time jnds, but abnormal wave III latency with only abnormal HpTjnds. Abnormal wave V amplitude, when unilateral, was associated with a major HpTjnd abnormality, and, when bilateral, with both HpTjnd and LpTjnd major abnormalities. Sixteen of the subjects had their MR scans obtained with a uniform protocol and could be analyzed with objective criteria. In all four subjects with lesions involving the pontine auditory pathway, the BAEPs and both time jnds were abnormal. Of the twelve subjects with no lesions involving the pontine auditory pathway, all had normal BAEPs and level jnds, ten had normal LpTjnds, but only five had normal HpTjnds. We conclude that interaural time discrimination is closely related to the BAEPs and is dependent upon the stimulus spectrum. Redundant encoding of low-frequency sounds in the discharge patterns of auditory neurons, may explain why the HpTjnd is a better indicator of neural desynchrony than the LpTjnd. Encroachment of MS lesions upon the pontine auditory pathway always is associated with abnormal BAEPs and abnormal interaural time discrimination but may have normal interaural level discrimination. Our data provide one of the most direct demonstrations in humans of relationships among auditory performance, evoked potentials and anatomy. We present a model showing that many of these interrelationships can be readily interpreted using ideas developed from work on animals, even though these relationships could not have been predicted with confidence beforehand. This work provides a clear advance in our understanding of human auditory processing and should serve as a basis for future studies.

Acoustic Stimulation↗