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At least 937 records · Page 52Linked to original sources
PubMed2001

Lethal X-linked microcephaly with dysmorphic features, bilateral optic pathway aplasia and normal eyes.

We describe a family, consisting of two brothers and a maternal uncle who died of an apparently identical condition, within a few days of birth, suggestive of an X-linked mode of inheritance. The propositus (the older sibling) was investigated in detail and showed the following clinical features: microcephaly, facial dysmorphism, malformations of hands and feet, and cryptorchidism. Examination of the brain revealed arhinencephaly, a primitive gyral pattern, arrested cortical maturation, absence of corticofugal tracts and corpus callosum, agenesis of the optic pathway with preserved eyes and oculomotor system, absent auditory pathway, agenesis of the pars compacta of the substantia nigra and severe hypoplasia of the cerebellum and its connections. This family belongs to the group of X-linked microcephalies and has some features in common with the Juberg-Marsidi syndrome. The fact that the CNS abnormalities were incompatible with life and the facial dysmorphic features were quite different makes it unlikely that the affected individuals in this family had Juberg-Marsidi syndrome. However, this does not exclude the possibility that more restricted anterior induction defects may occur in some X-linked microcephalies such as Juberg-Marsidi syndrome resulting in prolonged survival.

Eye↗
PubMed2006

Brain-stem auditory function in very preterm infants with chronic lung disease: delayed neural conduction.

OBJECTIVE: To examine brain-stem auditory function at term in very preterm infants who suffered chronic lung disease (CLD). METHODS: Brain-stem auditory evoked response (BAER) was recorded at term with clicks in 25 very preterm infants with CLD and no concomitant other major perinatal problems. RESULTS: Compared to those in normal term controls, BAER wave V latency and I-V and III-V interpeak intervals in the CLD infants increased significantly (ANOVA P<0.01-0.001). III-V/I-III interval ratio also increased significantly (P<0.01). The latencies of waves I and III did not differ significantly from the controls. However, no abnormalities were found in BAER wave amplitudes. These BAER findings, obtained at 21/s clicks, were also seen at the rates 51 and 91/s, although the increase in III-V interval tended to be more significant. Click rate-dependent changes in BAER variables in the CLD infants were generally similar to the controls, with slight differences. CONCLUSIONS: BAER components, mainly reflecting central auditory function, increased significantly. The increase in wave V latency and I-V interval is due to the increase in III-V interval. SIGNIFICANCE: Neural conduction in the more central portion of the brain-stem auditory pathway is delayed and thus brain-stem auditory function is impaired in CLD infants.

Acoustic Stimulation↗
PubMed2002

Rapid development of cortical auditory evoked potentials after early cochlear implantation.

The aim of our research was to estimate the time course of development and plasticity of the human central auditory pathways following cochlear implantation. We recorded cortical auditory-evoked potentials in 3-year-old congenitally deaf children after they were fitted with cochlear implants. Immediately after implantation cortical response latencies resembled those of normal-hearing newborns. Over the next few months, the cortical evoked responses showed rapid changes in morphology and latency that resulted in age-appropriate latencies by 8 months after implantation. Overall, the development of cortical response latencies for the implanted children was more rapid than for their normal-hearing age-matched peers. Our results demonstrate a high degree of central auditory system plasticity during early human development.

Analysis of Variance↗
PubMed2004

A phenomenological model of peripheral and central neural responses to amplitude-modulated tones.

A phenomenological model with time-varying excitation and inhibition was developed to study possible neural mechanisms underlying changes in the representation of temporal envelopes along the auditory pathway. A modified version of an existing auditory-nerve model [Zhang et al., J. Acoust. Soc. Am. 109, 648-670 (2001)] was used to provide inputs to higher hypothetical processing centers. Model responses were compared directly to published physiological data at three levels: the auditory nerve, ventral cochlear nucleus, and inferior colliculus. Trends and absolute values of both average firing rate and synchrony to the modulation period were accurately predicted at each level for a wide range of stimulus modulation depths and modulation frequencies. The diversity of central physiological responses was accounted for with realistic variations of model parameters. Specifically, enhanced synchrony in the cochlear nucleus and rate-tuning to modulation frequency in the inferior colliculus were predicted by choosing appropriate relative strengths and time courses of excitatory and inhibitory inputs to postsynaptic model cells. The proposed model is fundamentally different than others that have been used to explain the representation of envelopes in the mammalian midbrain, and it provides a computational tool for testing hypothesized relationships between physiology and psychophysics.

Acoustics↗
PubMed1987

Abnormal auditory brain-stem responses in hallucinating schizophrenic patients.

Abnormal auditory brain-stem responses (ABRs) were recorded in 10 out of 20 schizophrenic in-patients. The response abnormalities did not show any correlation to the degree of psychopathology, sub-group of schizophrenia, age, sex, or cerebral ventricular enlargement. Nor was there any correlation to previous neuroleptic treatment: a pathological ABR was recorded in 5 of the 8 patients who had never received such medication. A statistically significant relationship was found between ABR pathology and auditory hallucinations: 9 of the 11 patients who admitted having hallucinations exhibited brain-stem response abnormality, whereas ABR abnormality was recorded in only 1 of the 9 patients who denied having hallucinations. The data imply that brain-stem dysfunction is involved in the psychopathology of schizophrenia, and that interference with the auditory pathways in the brain-stem may induce auditory hallucinations in schizophrenic patients.

Adult↗
PubMed2001

On and off pathways segregated at the auditory thalamus of the guinea pig.

ON and OFF auditory responses were examined on the medial geniculate body (MGB) of the guinea pig. Single-unit and multiunit recordings were performed on 13 anesthetized subjects while either noise-burst or pure-tone stimuli were applied to the ear contralateral to the recorded hemisphere. Of 2187 uneven-spaced samples, 1142 were ON neurons, 386 were OFF neurons, and 488 were ON-OFF neurons. Neither ON nor OFF neurons changed their response patterns when the stimulus was changed from a noise burst of 60 dB sound pressure level intensity (expressed in decibels per 20 mPa) to pure tones or noise bursts of other intensities. However, most of the ON-OFF neurons changed to either ON or OFF responses with some stimuli. OFF neurons formed clusters. With anatomical confirmation, we found that OFF neuron clusters are always segregated from ON neuron clusters and form OFF sheets in various divisions of the MGB. In the ventral division of the MGB (MGv), the neurons showed mainly ON responses in its core and OFF responses in its periphery or on its boundary with other divisions. The MGv was partially surrounded by an OFF sheet dorsolaterally at the caudal part and medioventrally at the rostral part and was almost completely surrounded by an OFF sheet at the central level rostrocaudally.

Acoustic Stimulation↗
PubMed2006

Effects of sound level on fMRI activation in human brainstem, thalamic and cortical centers.

The dependence of fMRI activation on sound level was examined throughout the auditory pathway of normal human listeners using continuous broadband noise, a stimulus widely used in neuroscientific investigations of auditory processing, but largely neglected in neuro-imaging. Several specialized techniques were combined here for the first time to enhance detection of brainstem activation, mitigate scanner noise, and recover temporal resolution lost by the mitigation technique. The main finding was increased activation with increasing level in cochlear nucleus, superior olive, inferior colliculus, medial geniculate body and auditory cortical areas. We suggest that these increases reflect monotonically increasing activity in a preponderance of individual auditory neurons responsive to broadband noise. While the time-course of activation changed with level, the change was subtle and only significant in a part of the cortex. To our knowledge, these are the first fMRI data showing the effects of sound level in subcortical centers or for a non-tonal, non-speech stimulus at any stage of the pathway. The present results add to the body of parametric data in normal human listeners and are fundamental to the design of any fMRI experiment employing continuous noise.

Acoustic Stimulation↗
PubMed1984

Identification and structure of neurons in the medial geniculate body projecting to primary auditory cortex (AI) in the cat.

The neuronal types in the ventral nucleus of the cat medial geniculate body projecting to the primary auditory cortex (AI) were investigated using the retrograde transport of horseradish peroxidase. These cells were compared with the morphology of neurons as revealed in Golgi and Nissl preparations, plastic-embedded tissue, and electron microscopic material. After large injections, more than 90% of the neurons in the ventral nucleus, the principal nucleus of the lemniscal auditory pathway, were labeled, and the population of labeled cells included both large and small neuronal somata. Since the ventral nucleus contains only two varieties of cells--large neurons with bushy dendrites and an unbranched axon, and smaller cells with thin dendrites and a locally projecting axon--it is concluded that at least some of the small cells, previously believed to be interneurons, may function both as local circuit and as projection neurons. These findings were confirmed in toluidine blue-stained, 1-2 micron thick sections, and in the electron microscope, where small cells with sparse cytoplasm and a deeply invaginated nuclear envelope often contained intracellular horseradish peroxidase granules, as well as the larger neurons. Besides the small, labeled neurons in the ventral nucleus, many labeled cells were seen in the interstitial nucleus of the brachium of the inferior colliculus. This hitherto poorly characterized group of cells is embedded among the fibers of the brachium of the inferior colliculus. Many of the morphologically distinct varieties of cells in the medial division of the medial geniculate body, including small neurons, were labeled. Thus, in addition to the route embodied by the large bushy neurons which project to primary auditory cortex, at least one other pathway--represented by certain of the small cells in the ventral nucleus, reaches the primary auditory cortex.

Animals↗
PubMed2000

Identification of a pathway for intelligible speech in the left temporal lobe.

It has been proposed that the identification of sounds, including species-specific vocalizations, by primates depends on anterior projections from the primary auditory cortex, an auditory pathway analogous to the ventral route proposed for the visual identification of objects. We have identified a similar route in the human for understanding intelligible speech. Using PET imaging to identify separable neural subsystems within the human auditory cortex, we used a variety of speech and speech-like stimuli with equivalent acoustic complexity but varying intelligibility. We have demonstrated that the left superior temporal sulcus responds to the presence of phonetic information, but its anterior part only responds if the stimulus is also intelligible. This novel observation demonstrates a left anterior temporal pathway for speech comprehension.

Acoustic Stimulation↗
PubMed2004

Auditory brainstem evoked responses in insulin-dependent (ID) and non-insulin-dependent (NID) diabetic subjects with normal hearing.

Hearing impairment has been reported to be one of the late complications of diabetes mellitus (DM), and the frequency varies. Previous data suggest that auditory brainstem potentials deteriorate long before the hearing impairment appears in patients with DM. Delay in neural conductance along the auditory pathway due to DM was assessed by means of auditory brainstem response (ABR) in 43 patients with normal hearing in a controlled study. Patients were classified according to age, presence of neuropathy. metabolic control, and duration and type of DM. ABR recordings revealed that absolute latencies of waves I, III and V were prolonged significantly in the diabetic group when compared to the control group (p < 0.05). When two diabetic groups (insulin-dependent and non-insulin-dependent) were compared with each other, the difference between the latency of wave I and the inter-peak latencies of I-III, III-V and I-V was not significant (p > 0.05). However, the difference between the latencies of waves III and V in the two diabetic groups was statistically significant. The duration of diabetes, blood glucose level and age were not associated with prolonged ABR latencies (p > 0.05). Prolongation of latency of ABR in patients with DM should alert us to possible damage to the auditory nerve, and close follow-up is needed in these patients.

Adolescent↗
PubMed2002

Mechanisms of tinnitus.

The generation of tinnitus is a topic of much scientific enquiry. This chapter reviews possible mechanisms of tinnitus, whilst noting that the heterogeneity observed within the human population with distressing tinnitus means that there may be many different mechanisms by which tinnitus can occur. Indeed, multiple mechanisms may be at work within one individual. The role of the cochlea in tinnitus is considered, and in particular the concept of discordant damage between inner and outer hair cells is described. Biochemical models of tinnitus pertaining to the cochlea and the central auditory pathway are considered. Potential mechanisms for tinnitus within the auditory brain are reviewed, including important work on synchronised spontaneous activity in the cochlear nerve. Whilst the number of possible mechanisms of tinnitus within the auditory system is considerable, the identification of the physiological substrates underlying tinnitus is a crucial element in the design of novel and effective therapies.

Aminoglycosides↗
PubMed2002

Increased vulnerability of auditory system to noise exposure in mdx mice.

OBJECTIVES: Dystrophin is a cytoskeletal protein mainly found just beneath the sarcolemma. Lack of dystrophin is known to be the cause of Duchenne muscular dystrophy (DMD). Other tissues, including the brain, retina, and cochlear hair cells, also express dystrophin. Recently, a gene (Xp21.2) associated with sensorineural hearing impairment has been mapped within the localization site for dystrophin in two families. Thus, it is reasonable to assume that dystrophin may play a role in auditory function. However, animal studies have produced conflicting results. STUDY DESIGN: An attempt was made to clarify the differences between the auditory systems of dystrophin-deficient mdx mice and control B-10 mice by exposure to noise. METHODS: In the present study, mdx mice and B-10 mice were used. Animals were exposed daily to noise for 1 month, and their auditory functions were evaluated by recording the brainstem auditory evoked potentials (BAEPs). RESULTS: Before noise exposure, the mdx mouse demonstrated normal BAEP threshold when compared with the B-10 mouse. After 1 month of noise exposure, the B-10 mouse showed no apparent change in hearing threshold and BAEP latencies. In contrast, significantly increased hearing threshold and prolonged BAEP peak and interpeak latencies were observed in the mdx mouse after noise exposure. CONCLUSIONS: These results indicate that the mdx mice are more vulnerable to noise damage. This involves not only the peripheral auditory system, but also the brainstem central auditory pathway. Therefore, a significant role for dystrophin in the auditory system, especially under noise stress, is suggested.

Analysis of Variance↗
PubMed1990

The Maturation of the Superior Collicular Map of Auditory Space in the Guinea Pig is Disrupted by Developmental Auditory Deprivation.

Guinea pigs, reared from birth in an environment of omnidirectional white noise, fail to develop a map of auditory space in the deeper layers of the superior colliculus. Collicular responses from such noise-reared animals reveal large auditory spatial receptive fields. The representation of auditory space in the colliculus shows no topographic order. Exposing developing animals to the noise environment only for restricted time periods showed that animals reared normally up to 26 days after birth (DAB) and then placed in the noise chamber could not construct spatial maps, whereas animals reared normally to 30 DAB and then placed in the noise chamber until the terminal mapping experiment could construct topographically organized spatial maps with local receptive fields. Limiting the noise exposure to the period between 26 and 30 DAB was sufficient to prevent spatial map formation. The failure to form a map of auditory space did not reflect environmental damage to the cochlea or the functional organization of the primary auditory pathway. The response thresholds of cochlear microphonics and of auditory responses in both the inferior and superior colliculus were normal in noise-reared animals. Similarly normal were the tonotopic organization and frequency tuning characteristics of inferior collicular neurons. The rearing environment thus appears to exert a selective effect upon the maturation of the superior collicular map of auditory space. We attribute this effect to the masking, by the omnidirectional broad-band noise, of discrete localized auditory stimuli. Cues deriving from these latter stimuli would appear to be necessary for the elaboration of the map of auditory space. This auditory experience operates during a 4 day crucial developmental period from 26 to 30 DAB. This is the same developmental time window as that during which visual experience is required for the construction of the map.

Journal Article↗
PubMed1993

Cortical specification: microcircuits, perceptual identity, and an overall perspective.

The microcircuitry within a cortical area and its perceptual identity are both specified relatively late in development. We have asked whether and how the pattern of input activity during development influences these features of cortex. Routing visual projections to the auditory pathway in ferrets leads to visual activation of the developing auditory cortex, causing auditory cortex to receive patterns of input activity very different from normal. Visual inputs respecify, in instructive fashion, the microcircuitry within primary auditory cortex and alter the perceptual identity of the area so that its activation is identified with visual stimuli. Several other features of primary auditory cortex remain unaltered, however, by the change in input modality. In general, the pattern of input activity is one of several environmental cues that influence the developing cortex and interact with its intrinsic developmental program. It is clear from our (as well as other) experiments that appropriate environmental signals must be present at the appropriate time in development in order to influence cortical specification.

Acoustic Stimulation↗
PubMed2005

Auditory cortical projections to the cochlear nucleus in guinea pigs.

We used anterograde tracing techniques to examine projections from auditory cortex to the cochlear nucleus in guinea pigs. Following injection of dextrans into the temporal cortex, labeled axons were present bilaterally in the cochlear nucleus. The distribution of boutons within the cochlear nucleus was similar on the two sides. The majority of boutons was usually located on the ipsilateral side. Most of the boutons were located in the granule cell areas, where many small boutons and a few larger, mossy-type endings were labeled. Additional small, labeled boutons were found in all layers of the dorsal cochlear nucleus, with the majority located in the fusiform cell layer. Labeled boutons were also present in the ventral cochlear nucleus, where they were located in the small cell cap as well as magnocellular parts of both posteroventral and anteroventral cochlear nucleus. Similar results were obtained with injections restricted to primary auditory cortex or to the dorsocaudal auditory field. The results illustrate direct cortical projections to the cochlear nucleus that are likely to modulate the activity in a number of ascending auditory pathways.

Animals↗
PubMed2003

Screening methods: current status.

Two technologies are currently used to screen newborn infants for hearing, auditory brainstem response (ABR), and otoacoustic emissions (OAEs). Each technology is based on detecting the infant's physiologic response to auditory stimulation. ABR is a short-latency auditory evoked response originating from eighth nerve and brainstem auditory pathway structures and detected by scalp surface electrodes. OAEs are auditory signals generated by cochlear outer hair cells in response to acoustic stimulation and detected by a miniature microphone coupled to the infant's ear. Although each technique requires specific sound generation and response recording technologies, advances in computerized stimulus delivery and response detection algorithms allow these tests to be performed by trained technicians or volunteers under the supervision of an audiologist. Results of test performance, and the advantages and disadvantages of each technique are described.

Evoked Potentials, Auditory↗