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Auditory Pathway (auditory + pathway)
Selected AbstractsDevelopment of tinnitus-related neuronal hyperactivity through homeostatic plasticity after hearing loss: a computational modelEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2006Roland Schaette Tinnitus, the perception of a sound in the absence of acoustic stimulation, is often associated with hearing loss. Animal studies indicate that hearing loss through cochlear damage can lead to behavioral signs of tinnitus that are correlated with pathologically increased spontaneous firing rates, or hyperactivity, of neurons in the auditory pathway. Mechanisms that lead to the development of this hyperactivity, however, have remained unclear. We address this question by using a computational model of auditory nerve fibers and downstream auditory neurons. The key idea is that mean firing rates of these neurons are stabilized through a homeostatic plasticity mechanism. This homeostatic compensation can give rise to hyperactivity in the model neurons if the healthy ratio between mean and spontaneous firing rate of the auditory nerve is decreased, for example through a loss of outer hair cells or damage to hair cell stereocilia. Homeostasis can also amplify non-auditory inputs, which then contribute to hyperactivity. Our computational model predicts how appropriate additional acoustic stimulation can reverse the development of such hyperactivity, which could provide a new basis for treatment strategies. [source] A method for the direct electrical stimulation of the auditory system in deaf subjects: A functional magnetic resonance imaging studyJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2002Adnan Z. Alwatban BSc Abstract Purpose To develop a safe functional magnetic resonance imaging (fMRI) procedure for auditory assessment of deaf subjects. Materials and Methods A gold-plated tungsten electrode has been developed which has zero magnetic susceptibility. Used with carbon leads and a carbon reference pad, it enables safe, distortion-free fMRI studies of deaf subjects following direct electrical stimulation of the acoustic nerve. Minor pickup of the radio frequency (RF) pulses by the electrode assembly is difficult to eliminate, and a SPARSE acquisition sequence is used to avoid any effects of unintentional auditory nerve stimulation. Results The procedure is demonstrated in a deaf volunteer. Activation is observed in the contralateral but not the ipsilateral primary auditory cortex. This is in sharp contrast to studies of auditory processing in hearing subjects, but consistent with the small number of previous positron emission tomography (PET) and MR studies on adult deaf subjects. Conclusion The fMRI procedure is able to demonstrate whether the auditory pathway is fully intact, and may provide a useful method for preoperative assessment of candidates for cochlear implantation. J. Magn. Reson. Imaging 2002;16:6,12. © 2002 Wiley-Liss, Inc. [source] Mild carbon monoxide exposure and auditory function in the developing ratJOURNAL OF NEUROSCIENCE RESEARCH, Issue 5 2003Janet E. Stockard-Sullivan Abstract We have examined the influence of chronic mild exposure to carbon monoxide (CO) on cognitive (learning) and auditory function in the developing rat. We have demonstrated that the auditory pathway is compromised at exposures less than 50 ppm, whereas learning was not influenced at 100 ppm. Artificially reared rat pups were exposed to CO during the brain growth spurt and onset of myelination. Spatial learning was assessed using the Morris Water Maze and three tests of auditory function: (1) auditory brainstem conduction times; (2) the amplitude of the eighth nerve's action potential; and (3) otoacoustic emissions carried out on rat pups (age 22, 24 days). The pups were gastrostomy-reared on a rat milk substitute and chronically exposed to CO at discrete concentrations in the range of 12,100 ppm from 6 days of age to post-weaning at 21,23 days of age. We found no difference in auditory brainstem conduction times at all CO concentrations in comparison to non-exposed controls. There was a difference in otoacoustic emissions for test and controls at CO concentrations of 50 ppm but not at lower concentrations. There was a consistent attenuation of the amplitude of the eighth nerve's action potential, even at the lowest CO exposure examined. The attenuation of the amplitude of the action potential of the eighth nerve at 50 ppm carbon monoxide exposure did not completely recover by 73 days of age. We conclude that prolonged mild exposure to carbon monoxide during development causes measurable functional changes at the level of the eighth cranial nerve. © 2003 Wiley-Liss, Inc. [source] Neural recognition molecule NB-2 of the contactin/F3 subgroup in rat: Specificity in neurite outgrowth-promoting activity and restricted expression in the brain regionsJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2001Junko Ogawa Abstract NB-2, a neural cell recognition molecule of the contactin/F3 subgroup, promoted neurite outgrowth of the cerebral cortical neurons but not the hippocampal neurons. NB-2 in rat became apparent after birth at protein level, reaching a maximum at postnatal day 14 in the cerebrum and postnatal day 3 in the cerebellum. NB-2 in the cerebellum declined abruptly thereafter. In situ hybridization demonstrated that NB-2 mRNA was highly expressed in regions implicated in the central auditory pathway, including the cochlear nuclei, superior olive, inferior colliculi, medial geniculate nuclei, and auditory cortex. In addition, a high level of NB-2 expression was observed in the accessory olfactory bulb, thalamic nuclei, facial nucleus, and inferior olive. By immunohistochemistry, intense immunoreactivity against NB-2 was also detected in the auditory pathway. Thus, NB-2 is expressed in highly restricted brain regions, including the auditory system, suggesting that it plays specific roles in the development and/or maturation of the regions. J. Neurosci. Res. 65:100,110, 2001. © 2001 Wiley-Liss, Inc. [source] Manganese-enhanced MRI of the mouse auditory pathwayMAGNETIC RESONANCE IN MEDICINE, Issue 1 2008Takashi Watanabe Abstract Functional mapping of the lateral lemniscus and the superior olivary complex as part of the auditory pathway was accomplished for the first time in mice in vivo using manganese-enhanced MRI (2.35T, 3D FLASH, 117 ,m isotropic resolution). These and other auditory centers in the brainstem presented with pronounced signal enhancements after systemic administration of manganese chloride when animals were exposed to acoustic stimuli for 48 hr, but not when kept in a quiet environment. The results indicate an activation-dependent accumulation of manganese in the neural circuit composed of the cochlear nucleus, the superior olivary complex, the lateral lemniscus, and the inferior colliculus. The marked enhancement of the lateral lemniscus suggests that the stimulus-related accumulation of manganese reflects not only a regional uptake from extracellular fluid but also a concurrent delivery by axonal transport within the auditory system. Magn Reson Med 60:210,212, 2008. © 2008 Wiley-Liss, Inc. [source] Frequency processing at consecutive levels in the auditory system of bush crickets (tettigoniidae)THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 15 2010Tim Daniel Ostrowski Abstract We asked how processing of male signals in the auditory pathway of the bush cricket Ancistrura nigrovittata (Phaneropterinae, Tettigoniidae) changes from the ear to the brain. From 37 sensory neurons in the crista acustica single elements (cells 8 or 9) have frequency tuning corresponding closely to the behavioral tuning of the females. Nevertheless, one-quarter of sensory neurons (approximately cells 9 to 18) excite the ascending neuron 1 (AN1), which is best tuned to the male's song carrier frequency. AN1 receives frequency-dependent inhibition, reducing sensitivity especially in the ultrasound. When recorded in the brain, AN1 shows slightly lower overall activity than when recorded in the prothoracic ganglion close to the spike-generating zone. This difference is significant in the ultrasonic range. The first identified local brain neuron in a bush cricket (LBN1) is described. Its dendrites overlap with some of AN1-terminations in the brain. Its frequency tuning and intensity dependence strongly suggest a direct postsynaptic connection to AN1. Spiking in LBN1 is only elicited after summation of excitatory postsynaptic potentials evoked by individual AN1-action potentials. This serves a filtering mechanism that reduces the sensitivity of LBN1 and also its responsiveness to ultrasound as compared to AN1. Consequently, spike latencies of LBN1 are long (>30 ms) despite its being a second-order interneuron. Additionally, LBN1 receives frequency-specific inhibition, most likely further reducing its responses to ultrasound. This demonstrates that frequency-specific inhibition is redundant in two directly connected interneurons on subsequent levels in the auditory system. J. Comp. Neurol. 518:3101,3116, 2010. © 2010 Wiley-Liss, Inc. [source] Interactions between multiple sources of short-term plasticity during evoked and spontaneous activity at the rat calyx of HeldTHE JOURNAL OF PHYSIOLOGY, Issue 13 2008Matthias H. Hennig Sustained activity at most central synapses is accompanied by a number of short-term changes in synaptic strength which act over a range of time scales. Here we examine experimental data and develop a model of synaptic depression at the calyx of Held synaptic terminal that combines many of these mechanisms (acting at differing sites and across a range of time scales). This new model incorporates vesicle recycling, facilitation, activity-dependent vesicle retrieval and multiple mechanisms affecting calcium channel activity and release probability. It can accurately reproduce the time course of experimentally measured short-term depression across different stimulus frequencies and exhibits a slow decay in EPSC amplitude during sustained stimulation. We show that the slow decay is a consequence of vesicle release inhibition by multiple mechanisms and is accompanied by a partial recovery of the releasable vesicle pool. This prediction is supported by patch-clamp data, using long duration repetitive EPSC stimulation at up to 400 Hz. The model also explains the recovery from depression in terms of interaction between these multiple processes, which together generate a stimulus-history-dependent recovery after repetitive stimulation. Given the high rates of spontaneous activity in the auditory pathway, the model also demonstrates how these multiple interactions cause chronic synaptic depression under in vivo conditions. While the magnitude of the depression converges to the same steady state for a given frequency, the time courses of onset and recovery are faster in the presence of spontaneous activity. We conclude that interactions between multiple sources of short-term plasticity can account for the complex kinetics during high frequency stimulation and cause stimulus-history-dependent recovery at this relay synapse. [source] Central Effects of Residual Hearing: Implications for Choice of Ear for Cochlear Implantation,THE LARYNGOSCOPE, Issue 10 2004Howard W. Francis MD Abstract Objectives/Hypothesis: The study tested the hypothesis that among patients with similar levels of residual hearing in the nonimplanted ear, speech perception outcome is the same whether or not the implanted ear has profound or severe levels of hearing loss. Study Design: Retrospective. Methods: Levels of hearing loss in postlingually deafened adults who had cochlear implantation at Johns Hopkins University (Baltimore, MD) between 1991 and 2002 were classified according to pure-tone averages as bilateral severe (n = 20), severe-profound (severe in one ear and profound in the other) (n = 23), and bilateral profound (n = 43). There was no significant difference in the age at onset and duration of deafness among the three patient groups. Individuals in the bilateral severe and severe-profound groups had comparable levels of severe hearing loss in their nonimplanted ears, whereas those in severe-profound and bilateral profound groups had comparable levels of profound hearing loss in their implanted ears. Speech perception performance was evaluated using words from the Consonant Nucleus Consonant word list, Hearing in Noise Test sentences in quiet, and Central Institute for the Deaf sentences through recorded presentation at 70 dB sound pressure level (SPL). Results: Despite the profound hearing loss of the implanted ear in the asymmetrical group, there was no significant difference in mean speech perception scores compared with the bilateral severe group within the first year after implant surgery. By comparison, the bilateral profound group had lower speech perception results compared with patients with residual hearing in one or both ears. Conclusion: The study results suggest that implantation of the profoundly deafened ear does not diminish the functional advantage conferred by residual hearing in a patient with asymmetrical hearing loss. Therefore, the central auditory pathway may be the site at which persistent auditory function has its most beneficial effects. [source] Estrogen-dependent selectivity of genomic responses to birdsongEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2006Donna L. Maney Abstract Behavioral responses to sociosexual signals often depend on gonadal steroid hormones, which are thought to modulate behavior by acting on motivational systems in the brain. There is mounting evidence that sex steroids may also modulate perception of sociosexual signals by affecting sensory processing. In seasonally breeding songbirds such as the white-throated sparrow (Zonotrichia albicollis), the female's behavioral response to hearing male song depends on her plasma levels of estradiol (E2). Here, we examined whether plasma E2 also affects the selectivity of the song-induced zenk (egr-1) response in the auditory forebrain, which is known to vary according to the behavioral relevance of song stimuli. Non-breeding females were held on a winter-like photoperiod and implanted with silastic capsules containing either no hormone or E2. E2-treated birds hearing 42 min of conspecific song had more cells immunoreactive for the protein product of zenk in the auditory forebrain than did those hearing frequency-matched synthetic tones. In birds not treated with E2, however, the zenk response to song did not differ from that to tones. We found similar effects in the avian homolog of the inferior colliculus, indicating that E2 may affect the processing of auditory information upstream of the forebrain. Our data suggest that in females, zenk induction in the auditory system is selective for song only when plasma E2 exceeds non-breeding levels. E2-dependent plasticity of auditory pathways and processing centres may promote recognition of and attention to conspecific song during the breeding season. [source] Aberrant responses to acoustic stimuli in mice deficient for neural recognition molecule NB-2EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2003Hong Li Abstract NB-2, a member of the contactin subgroup in the immunoglobulin superfamily, is expressed specifically in the postnatal nervous system, reaching a maximum level at 3 weeks postnatal. NB-2 displays neurite outgrowth-promoting activity in vitro. To assess its function in the nervous system, we generated mutant mice in which a part of the NB-2 gene was ablated and replaced with the tau-LacZ gene. The general appearance of NB-2-deficient mice and their gross anatomical features were normal. The LacZ expression patterns in heterozygous mice revealed that NB-2 is preferentially expressed in the central auditory pathways. In the audiogenic seizure test, NB-2-deficient mice exhibited a lower incidence of wild running, but a higher mortality rate than the wild-type littermates. c-Fos immunohistochemistry demonstrated that neural excitability induced by the audiogenic seizure test in the NB-2-deficient mice was prominently attenuated in both the dorsal and external cortices of the inferior colliculus, where enhanced neural excitability was observed in the wild-type mice. In response to pure-tone stimulation after priming, NB-2-deficient mice exhibited a diffuse and low level of c-Fos expression in the central nucleus of the inferior colliculus, which was distinctly different from the band-like c-Fos expression corresponding to the tonotopic map in the wild-type littermates. Taken together, these results suggest that a lack of NB-2 causes impairment of the neuronal activity in the auditory system. [source] Neuroanatomy of the Subadult and Fetal Brain of the Atlantic White-sided Dolphin (Lagenorhynchus acutus) from in Situ Magnetic Resonance ImagesTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 12 2007Eric W. Montie Abstract This article provides the first anatomically labeled, magnetic resonance imaging (MRI) -based atlas of the subadult and fetal Atlantic white-sided dolphin (Lagenorhynchus acutus) brain. It differs from previous MRI-based atlases of cetaceans in that it was created from images of fresh, postmortem brains in situ rather than extracted, formalin-fixed brains. The in situ images displayed the classic hallmarks of odontocete brains: fore-shortened orbital lobes and pronounced temporal width. Olfactory structures were absent and auditory regions (e.g., temporal lobes and inferior colliculi) were enlarged. In the subadult and fetal postmortem MRI scans, the hippocampus was identifiable, despite the relatively small size of this structure in cetaceans. The white matter tracts of the fetal hindbrain and cerebellum were pronounced, but in the telencephalon, the white matter tracts were much less distinct, consistent with less myelin. The white matter tracts of the auditory pathways in the fetal brains were myelinated, as shown by the T2 hypointensity signals for the inferior colliculus, cochlear nuclei, and trapezoid bodies. This finding is consistent with hearing and auditory processing regions maturing in utero in L. acutus, as has been observed for most mammals. In situ MRI scanning of fresh, postmortem specimens can be used not only to study the evolution and developmental patterns of cetacean brains but also to investigate the impacts of natural toxins (such as domoic acid), anthropogenic chemicals (such as polychlorinated biphenyls, polybrominated diphenyl ethers, and their hydroxylated metabolites), biological agents (parasites), and noise on the central nervous system of marine mammal species. Anat Rec, 2007. © 2007 Wiley-Liss, Inc. [source] Acoustic communication in crocodilians: from behaviour to brainBIOLOGICAL REVIEWS, Issue 3 2009A. L. Vergne ABSTRACT Crocodilians and birds are the modern representatives of Phylum Archosauria. Although there have been recent advances in our understanding of the phylogeny and ecology of ancient archosaurs like dinosaurs, it still remains a challenge to obtain reliable information about their behaviour. The comparative study of birds and crocodiles represents one approach to this interesting problem. One of their shared behavioural features is the use of acoustic communication, especially in the context of parental care. Although considerable data are available for birds, information concerning crocodilians is limited. The aim of this review is to summarize current knowledge about acoustic communication in crocodilians, from sound production to hearing processes, and to stimulate research in this field. Juvenile crocodilians utter a variety of communication sounds that can be classified into various functional categories: (1) "hatching calls", solicit the parents at hatching and fine-tune hatching synchrony among siblings; (2) "contact calls", thought to maintain cohesion among juveniles; (3) "distress calls", induce parental protection; and (4) "threat and disturbance calls", which perhaps function in defence. Adult calls can likewise be classified as follows: (1) "bellows", emitted by both sexes and believed to function during courtship and territorial defence; (2) "maternal growls", might maintain cohesion among offspring; and (3) "hisses", may function in defence. However, further experiments are needed to identify the role of each call more accurately as well as systematic studies concerning the acoustic structure of vocalizations. The mechanism of sound production and its control are also poorly understood. No specialized vocal apparatus has been described in detail and the motor neural circuitry remains to be elucidated. The hearing capabilities of crocodilians appear to be adapted to sound detection in both air and water. The ear functional anatomy and the auditory sensitivity of these reptiles are similar in many respects to those of birds. The crocodilian nervous system likewise shares many features with that of birds, especially regarding the neuroanatomy of the auditory pathways. However, the functional anatomy of the telencephalic auditory areas is less well understood in crocodilians compared to birds. [source] | |||||||||||||||||||||||||