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Journal of Comparative Physiology. A,... Jan 2023The mammalian inferior colliculus (IC) is massively innervated by multiple descending projection systems. In addition to a large projection from the auditory cortex (AC)... (Review)
Review
The mammalian inferior colliculus (IC) is massively innervated by multiple descending projection systems. In addition to a large projection from the auditory cortex (AC) primarily targeting the non-lemniscal portions of the IC, there are less well-characterized projections from non-auditory regions of the cortex, amygdala, posterior thalamus and the brachium of the IC. By comparison, the frog auditory midbrain, known as the torus semicircularis, is a large auditory integration center that also receives descending input, but primarily from the posterior thalamus and without a projection from a putative cortical homolog: the dorsal pallium. Although descending projections have been implicated in many types of behaviors, a unified understanding of their function has not yet emerged. Here, we take a comparative approach to understanding the various top-down modulators of the IC to gain insights into their functions. One key question that we identify is whether thalamotectal projections in mammals and amphibians are homologous and whether they interact with evolutionarily more newly derived projections from the cerebral cortex. We also consider the behavioral significance of these descending pathways, given anurans' ability to navigate complex acoustic landscapes without the benefit of a corticocollicular projection. Finally, we suggest experimental approaches to answer these questions.
Topics: Animals; Auditory Pathways; Inferior Colliculi; Auditory Cortex; Mesencephalon; Amygdala; Mammals
PubMed: 36323876
DOI: 10.1007/s00359-022-01588-5 -
Arquivos de Neuro-psiquiatria Oct 2023Multiple sclerosis (MS) is an inflammatory demyelinating disease. Auditory evoked potential studies have demonstrated conduction and neural processing deficits in adults...
BACKGROUND
Multiple sclerosis (MS) is an inflammatory demyelinating disease. Auditory evoked potential studies have demonstrated conduction and neural processing deficits in adults with MS, but little is known about the electrophysiological responses in children and adolescents.
OBJECTIVE
to evaluate the central auditory pathway with brainstem auditory evoked potentials (BAEP) and long-latency auditory evoked potentials (LLAEP) in children and adolescents with MS.
METHODS
The study comprised 17 individuals with MS, of both sexes, aged 9 to 18 years, and 17 healthy volunteers, matched for age and sex. All individuals had normal hearing and no middle ear impairments. They were assessed with click-BAEP and LLAEP through oddball paradigm and tone-burst stimuli.
RESULTS
Abnormal responses were observed in 60% of electrophysiologic assessments of individuals with MS. In BAEP, 58.82% of MS patients had abnormal responses, with longer wave V latency and therefore longer III-V and I-V interpeak latencies than healthy volunteers. In LLAEP, 52.94% of MS patients had abnormal responses. Although statistical differences were found only in P2-N2 amplitude, MS patients had longer latencies and smaller amplitudes than healthy volunteers in all components.
CONCLUSION
Children and adolescents with MS had abnormal BAEP responses, with delayed neural conduction between the cochlear nucleus and the lateral lemniscus. Also, abnormal LLAEP results suggest a decrease in neural processing speed and auditory sensory discrimination response.
Topics: Male; Adult; Female; Humans; Child; Adolescent; Auditory Pathways; Multiple Sclerosis; Evoked Potentials, Auditory; Evoked Potentials, Auditory, Brain Stem; Hearing Tests
PubMed: 37852288
DOI: 10.1055/s-0043-1775985 -
Hearing Research Jun 2017
Topics: Auditory Pathways; Auditory Perception; Hearing; Hearing Loss, Noise-Induced; Humans; Military Medicine; Military Personnel; Noise, Occupational; Occupational Exposure; Occupational Injuries; Tinnitus
PubMed: 28526261
DOI: 10.1016/j.heares.2017.04.010 -
Hearing Research Apr 2019Neurons in various sensory systems show some level of spontaneous firing in the absence of sensory stimuli. In the auditory system spontaneous firing has been shown at... (Review)
Review
Neurons in various sensory systems show some level of spontaneous firing in the absence of sensory stimuli. In the auditory system spontaneous firing has been shown at all levels of the auditory pathway from spiral ganglion neurons in the cochlea to neurons of the auditory cortex. This internal "noise" is normal for the system and it does not interfere with our ability to perceive silence or analyze sound. However, this internal noise can be elevated under pathological conditions, leading to the perception of a phantom sound known as tinnitus. The efforts of many research groups, including our own, led to the development of a mechanistic understanding of this process: After cochlear insult the input to the central auditory system becomes markedly reduced. As a result, the neural activity in the central auditory system is enhanced to compensate for this reduced input. Such hyperactivity is hypothesized to be interpreted by the brain as a presence of sound. This implies that suppression of hyperactivity should reduce/eliminate tinnitus. This review explores research from our laboratory devoted to identifying the mechanism underlying residual inhibition of tinnitus, a brief suppression of tinnitus following a sound stimulus. The key mechanisms that govern neural suppression of spontaneous activity in animals closely resemble clinical psychoacoustic findings of residual inhibition (RI) observed in tinnitus patients. This suppression is mediated by metabotropic glutamate receptors (mGluRs). Lastly, drugs targeting mGluRs suppress spontaneous activity in auditory neurons and reduce/eliminate behavioral signs of tinnitus in mice. Thus, these drugs are therapeutically relevant for tinnitus suppression in humans.
Topics: Acoustic Stimulation; Animals; Auditory Cortex; Auditory Pathways; Bridged Bicyclo Compounds; Cochlea; Evoked Potentials, Auditory, Brain Stem; Excitatory Amino Acid Agonists; Humans; Inhibitory Postsynaptic Potentials; Mice; Prepulse Inhibition; Psychoacoustics; Receptors, Metabotropic Glutamate; Reflex, Startle; Tinnitus
PubMed: 30822633
DOI: 10.1016/j.heares.2019.01.022 -
Frontiers in Neural Circuits 2015The acoustic signal is crucial for animals to obtain information from the surrounding environment. Like other sensory modalities, the central auditory system undergoes... (Review)
Review
The acoustic signal is crucial for animals to obtain information from the surrounding environment. Like other sensory modalities, the central auditory system undergoes adaptive changes (i.e., plasticity) during the developmental stage as well as other stages of life. Owing to its plasticity, auditory centers may be susceptible to various factors, such as medical intervention, variation in ambient acoustic signals and lesion of the peripheral hearing organ. There are critical periods during which auditory centers are vulnerable to abnormal experiences. Particularly in the early postnatal development period, aural inputs are essential for functional maturity of auditory centers. An aural deprivation model, which can be achieved by attenuating or blocking the peripheral acoustic afferent input to the auditory center, is ideal for investigating plastic changes of auditory centers. Generally, auditory plasticity includes structural and functional changes, some of which can be irreversible. Aural deprivation can distort tonotopic maps, disrupt the binaural integration, reorganize the neural network and change the synaptic transmission in the primary auditory cortex or at lower levels of the auditory system. The regulation of specific gene expression and the modified signal pathway may be the deep molecular mechanism of these plastic changes. By studying this model, researchers may explore the pathogenesis of hearing loss and reveal plastic changes of the auditory cortex, facilitating the therapeutic advancement in patients with severe hearing loss. After summarizing developmental features of auditory centers in auditory deprived animals and discussing changes of central auditory remodeling in hearing loss patients, we aim at stressing the significant of an early and well-designed auditory training program for the hearing rehabilitation.
Topics: Animals; Auditory Pathways; Central Nervous System; Hearing Disorders; Humans; Neuronal Plasticity; Sensory Deprivation; Time Factors
PubMed: 26082685
DOI: 10.3389/fncir.2015.00026 -
Hearing Research Aug 2014We live in a world imbued with a rich mixture of complex sounds. Successful acoustic communication requires the ability to extract meaning from those sounds, even when... (Review)
Review
We live in a world imbued with a rich mixture of complex sounds. Successful acoustic communication requires the ability to extract meaning from those sounds, even when degraded. One strategy used by the auditory system is to harness high-level contextual cues to modulate the perception of incoming sounds. An ideal substrate for this process is the massive set of top-down projections emanating from virtually every level of the auditory system. In this review, we provide a molecular and circuit-level description of one of the largest of these pathways: the auditory corticocollicular pathway. While its functional role remains to be fully elucidated, activation of this projection system can rapidly and profoundly change the tuning of neurons in the inferior colliculus. Several specific issues are reviewed. First, we describe the complex heterogeneous anatomical organization of the corticocollicular pathway, with particular emphasis on the topography of the pathway. We also review the laminar origin of the corticocollicular projection and discuss known physiological and morphological differences between subsets of corticocollicular cells. Finally, we discuss recent findings about the molecular micro-organization of the inferior colliculus and how it interfaces with corticocollicular termination patterns. Given the assortment of molecular tools now available to the investigator, it is hoped that his review will help guide future research on the role of this pathway in normal hearing.
Topics: Acoustic Stimulation; Animals; Auditory Cortex; Auditory Pathways; Cues; Humans; Inferior Colliculi; Neural Pathways; Neuronal Plasticity; Neurons; Perception; Sound
PubMed: 24911237
DOI: 10.1016/j.heares.2014.05.004 -
Noise & Health 2022To assess the effects of noise and chemical exposure on peripheral and central auditory pathways in normal-hearing workers exposed to chemicals or high noise levels and...
OBJECTIVES
To assess the effects of noise and chemical exposure on peripheral and central auditory pathways in normal-hearing workers exposed to chemicals or high noise levels and compare the groups with each other and with workers not exposed to either of these agents.
METHODS
A total of 54 normal-hearing workers were divided into three groups (chemical, noise, control) and submitted to the following assessments: conventional and extended high-frequency pure-tone audiometry; transient and distortion-product otoacoustic emissions, the inhibitory effect of the efferent auditory pathway; and Staggered Spondaic Word (SSW) and Pitch Pattern Sequence (PPS) test.
RESULTS
There were no significant differences between the groups in extended high-frequency hearing thresholds. Significantly lower amplitudes were observed in the noise group for otoacoustic emissions. There were significantly more absences of the inhibitory effect of the efferent system in the noise group. There was no difference between the groups in the SSW test, while in PPS, the noise group performed worse than the control group.
CONCLUSION
These findings suggest that noise exposure produced deleterious effects on the workers' peripheral and central auditory systems, despite their normal hearing thresholds. The chemical group did not have significantly different results from those of the control group. It is important that individuals exposed to noise or chemicals have their auditory pathways monitored with complementary assessments.
Topics: Auditory Pathways; Hearing; Hearing Loss, Noise-Induced; Humans; Noise; Occupational Exposure
PubMed: 36124528
DOI: 10.4103/nah.nah_10_22 -
Hearing Research Nov 2022The cochlear efferent system comprises multiple populations of brainstem neurons whose axons project to the cochlea, and whose responses to acoustic stimuli lead to... (Review)
Review
The cochlear efferent system comprises multiple populations of brainstem neurons whose axons project to the cochlea, and whose responses to acoustic stimuli lead to regulation of auditory sensitivity. The major groups of efferent neurons are found in the superior olivary complex and are likely activated by neurons of the cochlear nucleus, thus forming a simple reflex pathway back to the cochlea. The peripheral actions of only one of these efferent cell types has been well described. Moreover, the efferent neurons are not well understood at the cellular- and circuit-levels. For example, ample demonstration of descending projections to efferent neurons raises the question of whether these additional inputs constitute a mechanism for modulation of relay function or instead play a more prominent role in driving the efferent response. Related to this is the question of synaptic plasticity at these synapses, which has the potential to differentially scale the degree of efferent activation across time, depending on the input pathway. This review will explore central nervous system aspects of the efferent system, the physiological properties of the neurons, their synaptic inputs, their modulation, and the effects of efferent axon collaterals within the brainstem.
Topics: Acoustic Stimulation; Auditory Pathways; Brain Stem; Cochlea; Cochlear Nucleus; Efferent Pathways; Neurons, Efferent; Olivary Nucleus
PubMed: 35606211
DOI: 10.1016/j.heares.2022.108516 -
The World Journal of Biological... Jan 2015The interhemispheric auditory pathway has been shown to play a crucial role in the processing of acoustic stimuli, and alterations of structural and functional...
OBJECTIVES
The interhemispheric auditory pathway has been shown to play a crucial role in the processing of acoustic stimuli, and alterations of structural and functional connectivity between bilateral auditory areas are likely relevant to the pathogenesis of auditory verbal hallucinations (AVHs). The aim of this study was to examine this pathway in patients with chronic schizophrenia regarding their lifetime history of AVHs.
METHODS
DTI scans were acquired from 33 healthy controls (HC), 24 schizophrenia patients with a history of AVHs (LT-AVH) and nine schizophrenia patients without any lifetime hallucinations (N-LT-AVH). The interhemispheric auditory fibre bundles were extracted using streamline tractography. Subsequently, diffusivity indices, namely Fractional Anisotropy (FA), Trace, Mode, Axial and Radial diffusivity, were calculated.
RESULTS
FA was decreased over the entire pathway in LT-AVH compared with N-LT-AVH. Moreover, LT-AVH displayed decreased FA and Mode as well as increased radial diffusivity in the midsagittal section of the fibre tract.
CONCLUSIONS
These findings indicate complex microstructural changes in the interhemispheric auditory pathway of schizophrenia patients with a history of AVHs. Alterations appear to be absent in patients who have never hallucinated.
Topics: Acoustic Stimulation; Adult; Anisotropy; Auditory Cortex; Auditory Pathways; Brain Mapping; Case-Control Studies; Chronic Disease; Diffusion Tensor Imaging; Female; Hallucinations; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Schizophrenia
PubMed: 25224883
DOI: 10.3109/15622975.2014.948063 -
Frontiers in Neural Circuits 2017During development, the organization of the auditory system into distinct functional subcircuits depends on the spatially and temporally ordered sequence of neuronal... (Review)
Review
During development, the organization of the auditory system into distinct functional subcircuits depends on the spatially and temporally ordered sequence of neuronal specification, differentiation, migration and connectivity. Regional patterning along the antero-posterior axis and neuronal subtype specification along the dorso-ventral axis intersect to determine proper neuronal fate and assembly of rhombomere-specific auditory subcircuits. By taking advantage of the increasing number of transgenic mouse lines, recent studies have expanded the knowledge of developmental mechanisms involved in the formation and refinement of the auditory system. Here, we summarize several findings dealing with the molecular and cellular mechanisms that underlie the assembly of central auditory subcircuits during mouse development, focusing primarily on the rhombomeric and dorso-ventral origin of auditory nuclei and their associated molecular genetic pathways.
Topics: Animals; Auditory Pathways; Cell Differentiation; Cell Movement; Gene Expression Regulation, Developmental; Mice; Neurons
PubMed: 28469562
DOI: 10.3389/fncir.2017.00018