RESUMEN
Based on the auditory periphery and the small head size, Etruscan shrews (Suncus etruscus) approximate ancestral mammalian conditions. The auditory brainstem in this insectivore has not been investigated. Using labelling techniques, we assessed the structures of their superior olivary complex (SOC) and the nuclei of the lateral lemniscus (NLL). There, we identified the position of the major nuclei, their input pattern, transmitter content, expression of calcium binding proteins (CaBPs) and two voltage-gated ion channels. The most prominent SOC structures were the medial nucleus of the trapezoid body (MNTB), the lateral nucleus of the trapezoid body (LNTB), the lateral superior olive (LSO) and the superior paraolivary nucleus (SPN). In the NLL, the ventral (VNLL), a specific ventrolateral VNLL (VNLLvl) cell population, the intermediate (INLL) and dorsal (DNLL) nucleus, as well as the inferior colliculus's central aspect were discerned. INLL and VNLL were clearly separated by the differential distribution of various marker proteins. Most labelled proteins showed expression patterns comparable to rodents. However, SPN neurons were glycinergic and not GABAergic and the overall CaBPs expression was low. Next to the characterisation of the Etruscan shrew's auditory brainstem, our work identifies conserved nuclei and indicates variable structures in a species that approximates ancestral conditions.
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Musarañas , Complejo Olivar Superior , Animales , Musarañas/anatomía & histología , Complejo Olivar Superior/anatomía & histología , Complejo Olivar Superior/metabolismo , Vías Auditivas/anatomía & histología , Neuronas/metabolismo , Colículos Inferiores/anatomía & histología , Colículos Inferiores/metabolismo , Proteínas de Unión al Calcio/metabolismo , Proteínas de Unión al Calcio/genética , Tronco Encefálico/anatomía & histología , Tronco Encefálico/metabolismo , Masculino , Núcleo Olivar/anatomía & histología , Núcleo Olivar/metabolismoRESUMEN
Although rats and mice are among the preferred animal models for investigating many characteristics of auditory function, they are rarely used to study an essential aspect of binaural hearing: the ability of animals to localize the sources of low-frequency sounds by detecting the interaural time difference (ITD), that is the difference in the time at which the sound arrives at each ear. In mammals, ITDs are mostly encoded in the medial superior olive (MSO), one of the main nuclei of the superior olivary complex (SOC). Because of their small heads and high frequency hearing range, rats and mice are often considered unable to use ITDs for sound localization. Moreover, their MSO is frequently viewed as too small or insignificant compared to that of mammals that use ITDs to localize sounds, including cats and gerbils. However, recent research has demonstrated remarkable similarities between most morphological and physiological features of mouse MSO neurons and those of MSO neurons of mammals that use ITDs. In this context, we have analyzed the structure and neural afferent and efferent connections of the rat MSO, which had never been studied by injecting neuroanatomical tracers into the nucleus. The rat MSO spans the SOC longitudinally. It is relatively small caudally, but grows rostrally into a well-developed column of stacked bipolar neurons. By placing small, precise injections of the bidirectional tracer biotinylated dextran amine (BDA) into the MSO, we show that this nucleus is innervated mainly by the most ventral and rostral spherical bushy cells of the anteroventral cochlear nucleus of both sides, and by the most ventrolateral principal neurons of the ipsilateral medial nucleus of the trapezoid body. The same experiments reveal that the MSO densely innervates the most dorsolateral region of the central nucleus of the inferior colliculus, the central region of the dorsal nucleus of the lateral lemniscus, and the most lateral region of the intermediate nucleus of the lateral lemniscus of its own side. Therefore, the MSO is selectively innervated by, and sends projections to, neurons that process low-frequency sounds. The structural and hodological features of the rat MSO are notably similar to those of the MSO of cats and gerbils. While these similarities raise the question of what functions other than ITD coding the MSO performs, they also suggest that the rat MSO is an appropriate model for future MSO-centered research.
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Vías Auditivas , Axones , Localización de Sonidos , Complejo Olivar Superior , Animales , Complejo Olivar Superior/fisiología , Complejo Olivar Superior/anatomía & histología , Vías Auditivas/fisiología , Vías Auditivas/anatomía & histología , Axones/fisiología , Ratas , Masculino , Dextranos/metabolismo , Biotina/análogos & derivados , Estimulación Acústica , Vías Eferentes/fisiología , Vías Eferentes/anatomía & histología , Núcleo Olivar/fisiología , Núcleo Olivar/anatomía & histología , Femenino , Técnicas de Trazados de Vías Neuroanatómicas , Ratas WistarRESUMEN
The auditory cortex (AC) sends long-range projections to virtually all subcortical auditory structures. One of the largest and most complex of these-the projection between AC and inferior colliculus (IC; the corticocollicular pathway)-originates from layer 5 and deep layer 6. Though previous work has shown that these two corticocollicular projection systems have different physiological properties and network connectivities, their functional organization is poorly understood. Here, using a combination of traditional and viral tracers combined with in vivo imaging in both sexes of the mouse, we observed that layer 5 and layer 6 corticocollicular neurons differ in their areas of origin and termination patterns. Layer 5 corticocollicular neurons are concentrated in primary AC, while layer 6 corticocollicular neurons emanate from broad auditory and limbic areas in the temporal cortex. In addition, layer 5 sends dense projections of both small and large (>1 µm2 area) terminals to all regions of nonlemniscal IC, while layer 6 sends small terminals to the most superficial 50-100 µm of the IC. These findings suggest that layer 5 and 6 corticocollicular projections are optimized to play distinct roles in corticofugal modulation. Layer 5 neurons provide strong, rapid, and unimodal feedback to the nonlemniscal IC, while layer 6 neurons provide heteromodal and limbic modulation diffusely to the nonlemniscal IC. Such organizational diversity in the corticocollicular pathway may help to explain the heterogeneous effects of corticocollicular manipulations and, given similar diversity in corticothalamic pathways, may be a general principle in top-down modulation.SIGNIFICANCE STATEMENT We demonstrate that a major descending system in the brain is actually two systems. That is, the auditory corticocollicular projection, which exerts considerable influence over the midbrain, comprises two projections: one from layer 5 and the other from layer 6. The layer 6 projection is diffusely organized, receives multisensory inputs, and ends in small terminals; while the layer 5 projection is derived from a circumscribed auditory cortical area and ends in large terminals. These data suggest that the varied effects of cortical manipulations on the midbrain may be related to effects on two disparate systems. These findings have broader implications because other descending systems derive from two layers. Therefore, a duplex organization may be a common motif in descending control.
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Corteza Auditiva/anatomía & histología , Vías Auditivas/anatomía & histología , Animales , Femenino , Masculino , Ratones , Ratones Endogámicos BALB CRESUMEN
PURPOSE: The aim of the present study is to show a MR procedure for the evaluation of simultaneous left and right auditory functions with functional MRI, and high-resolution acquisition of anatomical auditory pathway using parallel-transmit (pTx) methods at 7T. METHODS: The time-efficient MR acquisition included two steps: RF weights were optimized for the regions-of-interest and high-resolution MR images of the inner-ear were acquired for the first 30 min (400 µm-iso resolution) followed by functional MRI acquisitions along the whole auditory pathway during the next 20 minutes. Data was processed with a linear cross-correlation analysis to define frequency preferences for each voxel in the auditory relays. RESULTS: Tonotopic maps revealed ordered bilateral frequency gradients in the auditory relays whereas at the level of the cochlear nuclei and superior olivary complexes the frequency gradients were less evident. A 21% increase in transmit-field efficiency was achieved over the left/right inner-ear regions and thus its main structures were clearly discernible using the pTx methods, compared to a single transmit RF coil. CONCLUSION: Using 7T pTx allows a fast (less than 60 min in total) and qualitative evaluation of the simultaneous left and right auditory response along the entire auditory pathway, together with high-resolution anatomical images of the inner-ear. This could be further used for patient examination at 7T.
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Vías Auditivas/fisiología , Oído Interno/fisiología , Adulto , Vías Auditivas/anatomía & histología , Vías Auditivas/diagnóstico por imagen , Oído Interno/anatomía & histología , Oído Interno/diagnóstico por imagen , Diseño de Equipo , Femenino , Humanos , Procesamiento de Imagen Asistido por Computador , Imagen por Resonancia Magnética/métodos , Masculino , Adulto JovenRESUMEN
In the last years, the attention to the role of gender in physiopathology and pharmacology of diseases in several medical disciplines is rising; however, the data on the relationship between gender and audio-vestibular disorders are still inconclusive and sometimes confusing. With this letter to the editor, we would like to review the role of gender in audio-vestibular disorders. Literature data show that anatomic variances of the inner ear do exist in men and women and that the different physiology and/or hormonal influence between genders could produce different clinical outcome of routine audiological and vestibular tests. Beyond the epidemiological gender-related differences, the clinical data suggest that the gender has a potential role as an etiopathogenetic factor in audio-vestibular disorders and it is probably responsible for the different clinical features observed between male and female subjects.
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Trastornos de la Audición/patología , Caracteres Sexuales , Enfermedades Vestibulares/patología , Vías Auditivas/anatomía & histología , Vías Auditivas/patología , Oído Interno/anatomía & histología , Oído Interno/patología , Femenino , Trastornos de la Audición/epidemiología , Pérdida Auditiva Sensorineural/epidemiología , Pérdida Auditiva Sensorineural/patología , Hormonas/fisiología , Humanos , Masculino , Factores Sexuales , Enfermedades Vestibulares/epidemiologíaRESUMEN
OBJECTIVES: Although hearing has been shown to interact with sleep, the underlying mechanisms for the interaction remain largely unclear. In the absence of knowledge about the neural pathways that are associated with hearing-sleep interaction, this study aimed to examine whether the auditory radiation, the final portion of the auditory pathway from the cochlea to the cerebral cortex, shows association with sleep duration. METHODS: Using Diffusion Tensor Imaging (DTI) data from enhanced Nathan Kline Institute-Rockland Sample (NKI-RS), we isolated the white matter tracts between the medial geniculate nucleus of the thalamus and Heschl's gyrus in each individual subject (N = 465) using probabilistic tractography. As a measure of the white matter microstructure integrity, the mean fractional anisotropy (FA) of the whole auditory radiation was examined and tested for an association with sleep length in the Pittsburgh Sleep Assessment Index. RESULTS: A significant inverse-U shaped association was found between the auditory radiation FA and sleep duration. DISCUSSION: It is suggested that the auditory radiations are a part of the pathway mediating the sleep-hearing interaction. Although the current study does not resolve the causal relationship between hearing and sleep, it would be the first evidence that the auditory radiation is associated with sleep duration.
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Corteza Auditiva/anatomía & histología , Cuerpos Geniculados/anatomía & histología , Sueño , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Vías Auditivas/anatomía & histología , Niño , Imagen de Difusión Tensora , Femenino , Humanos , Masculino , Persona de Mediana Edad , Sustancia Blanca/anatomía & histología , Adulto JovenRESUMEN
Music and language engage the dorsal auditory pathway, linked by the arcuate fasciculus (AF). Sustained practice in these activities can modify brain structure, depending on length of experience but also age of onset (AoO). To study the impact of early experience on brain structure we manually dissected the AF in bilinguals with and without music training (MT) who differed in the AoO of their second language (L2), or MT. We found the usual left-greater-than-right asymmetry in the volume of the long segment (LS) of the AF across all groups. However, simultaneous exposure to two languages from birth enhanced this leftward asymmetry, while early start of MT (≤7) enhanced the right LS macrostructure, reducing the normative asymmetry. Thus, immersive exposure to an L2 in the first year of life can produce long-term plastic effects on the left LS, which is considered to be largely under genetic control, while deliberate music training in early childhood alters the right LS, whose structure appears more open to experience. These findings show that AoO of specific experience plays a key role in a complex gene-environment interaction model where normative brain maturation is differentially impacted by diverse intensive auditory-motor experiences at different points during development.
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Vías Auditivas/anatomía & histología , Encéfalo/anatomía & histología , Vías Eferentes/anatomía & histología , Multilingüismo , Música , Adolescente , Adulto , Vías Auditivas/fisiología , Encéfalo/fisiología , Niño , Preescolar , Imagen de Difusión Tensora , Vías Eferentes/fisiología , Femenino , Humanos , Aprendizaje/fisiología , Masculino , Plasticidad Neuronal/fisiología , Adulto JovenRESUMEN
Infant brain development incorporates several intermingled mechanisms leading to intense and asynchronous maturation across cerebral networks and functional modalities. Combining electroencephalography (EEG) and diffusion magnetic resonance imaging (MRI), previous studies in the visual modality showed that the functional maturation of the event-related potentials (ERP) during the first postnatal semester relates to structural changes in the corresponding white matter pathways. Here investigated similar issues in the auditory modality. We measured ERPs to syllables in 1- to 6-month-old infants and related them to the maturational properties of underlying neural substrates measured with diffusion tensor imaging (DTI). We first observed a decrease in the latency of the auditory P2, and in the diffusivities in the auditory tracts and perisylvian regions with age. Secondly, we highlighted some of the early functional and structural substrates of lateralization. Contralateral responses to monoaural syllables were stronger and faster than ipsilateral responses, particularly in the left hemisphere. Besides, the acoustic radiations, arcuate fasciculus, middle temporal and angular gyri showed DTI asymmetries with a more complex and advanced microstructure in the left hemisphere, whereas the reverse was observed for the inferior frontal and superior temporal gyri. Finally, after accounting for the age-related variance, we correlated the inter-individual variability in P2 responses and in the microstructural properties of callosal fibers and inferior frontal regions. This study combining dedicated EEG and MRI approaches in infants highlights the complex relation between the functional responses to auditory stimuli and the maturational properties of the corresponding neural network.
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Vías Auditivas/anatomía & histología , Encéfalo/anatomía & histología , Electroencefalografía/métodos , Imagen por Resonancia Magnética/métodos , Femenino , Humanos , Lactante , MasculinoRESUMEN
OBJECTIVE: The functional importance of the superior temporal lobe at the level of Heschl's gyrus is well known. However, the organization and function of these cortical areas and the underlying fiber tracts connecting them remain unclear. The goal of this study was to analyze the area formed by the organization of the intersection of Heschl's gyrus-related fiber tracts, which the authors have termed the "Heschl's gyrus fiber intersection area" (HGFIA). METHODS: The subcortical connectivity of Heschl's gyrus tracts was analyzed by white matter fiber dissection and by diffusion tensor imaging tractography. The white matter tracts organized in relation to Heschl's gyrus were isolated in 8 human hemispheres from cadaveric specimens and in 8 MRI studies in 4 healthy volunteers. In addition, these tracts and their functions were described in the surgical cases of left temporal gliomas next to the HGFIA in 6 patients who were awake during surgery and underwent intraoperative electrical stimulation mapping. RESULTS: Five tracts were observed to pass through the HGFIA: the anterior segment of the arcuate fasciculus, the middle longitudinal fasciculus, the acoustic radiation, the inferior fronto-occipital fasciculus, and the optic radiation. In addition, U fibers originating at the level of Heschl's gyrus and heading toward the middle temporal gyrus were identified. CONCLUSIONS: This investigation of the HGFIA, a region where 5 fiber tracts intersect in a relationship with the primary auditory area, provides new insights into the subcortical organization of Wernicke's area. This information is valuable when a temporal surgical approach is planned, in order to assess the surgical risk related to language disturbances.
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Corteza Auditiva/diagnóstico por imagen , Corteza Auditiva/fisiología , Vías Auditivas/diagnóstico por imagen , Vías Auditivas/fisiología , Percepción Auditiva/fisiología , Lenguaje , Adulto , Anciano , Anciano de 80 o más Años , Corteza Auditiva/anatomía & histología , Vías Auditivas/anatomía & histología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Fibras Nerviosas/fisiología , Vías Nerviosas/diagnóstico por imagen , Vías Nerviosas/fisiologíaRESUMEN
There has been a spurt in structural neuroimaging studies of the effect of hearing loss on the brain. Specifically, magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) technologies provide an opportunity to quantify changes in gray and white matter structures at the macroscopic scale. To date, there have been 32 MRI and 23 DTI studies that have analyzed structural differences accruing from pre- or peri-lingual pediatric hearing loss with congenital or early onset etiology and postlingual hearing loss in pre-to-late adolescence. Additionally, there have been 15 prospective clinical structural neuroimaging studies of children and adolescents being evaluated for cochlear implants. The results of the 70 studies are summarized in two figures and three tables. Plastic changes in the brain are seen to be multifocal rather than diffuse, that is, differences are consistent across regions implicated in the hearing, speech and language networks regardless of modes of communication and amplification. Structures in that play an important role in cognition are affected to a lesser extent. A limitation of these studies is the emphasis on volumetric measures and on homogeneous groups of subjects with hearing loss. It is suggested that additional measures of morphometry and connectivity could contribute to a greater understanding of the effect of hearing loss on the brain. Then an interpretation of the observed macroscopic structural differences is given. This is followed by discussion of how structural imaging can be combined with functional imaging to provide biomarkers for longitudinal tracking of amplification. This article is categorized under: Developmental Biology > Developmental Processes in Health and Disease Translational, Genomic, and Systems Medicine > Translational Medicine Laboratory Methods and Technologies > Imaging.
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Encéfalo/anatomía & histología , Pérdida Auditiva/patología , Neuroimagen , Vías Auditivas/anatomía & histología , Vías Auditivas/fisiología , Encéfalo/diagnóstico por imagen , Mapeo Encefálico , Imagen de Difusión Tensora , Sustancia Gris/anatomía & histología , Sustancia Gris/diagnóstico por imagen , Sustancia Gris/fisiología , Humanos , Imagen por Resonancia Magnética , Sustancia Blanca/anatomía & histología , Sustancia Blanca/diagnóstico por imagen , Sustancia Blanca/fisiologíaRESUMEN
The dorsal (DCIC) and lateral cortices (LCIC) of the inferior colliculus are major targets of the auditory and non-auditory cortical areas, suggesting a role in complex multimodal information processing. However, relatively little is known about their functional organization. We utilized in vivo two-photon Ca2+ imaging in awake mice expressing GCaMP6s in GABAergic or non-GABAergic neurons in the IC to investigate their spatial organization. We found different classes of temporal responses, which we confirmed with simultaneous juxtacellular electrophysiology. Both GABAergic and non-GABAergic neurons showed spatial microheterogeneity in their temporal responses. In contrast, a robust, double rostromedial-caudolateral gradient of frequency tuning was conserved between the two groups, and even among the subclasses. This, together with the existence of a subset of neurons sensitive to spontaneous movements, provides functional evidence for redefining the border between DCIC and LCIC.
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Vías Auditivas/anatomía & histología , Mapeo Encefálico , Colículos Inferiores/anatomía & histología , Neuronas/fisiología , Estimulación Acústica , Potenciales de Acción , Animales , Vías Auditivas/fisiología , Colículos Inferiores/fisiología , Ratones Endogámicos C57BL , Imagen Óptica , VigiliaRESUMEN
Studying the human subcortical auditory system non-invasively is challenging due to its small, densely packed structures deep within the brain. Additionally, the elaborate three-dimensional (3-D) structure of the system can be difficult to understand based on currently available 2-D schematics and animal models. Wfe addressed these issues using a combination of histological data, post mortem magnetic resonance imaging (MRI), and in vivo MRI at 7 Tesla. We created anatomical atlases based on state-of-the-art human histology (BigBrain) and postmortem MRI (50 µm). We measured functional MRI (fMRI) responses to natural sounds and demonstrate that the functional localization of subcortical structures is reliable within individual participants who were scanned in two different experiments. Further, a group functional atlas derived from the functional data locates these structures with a median distance below 2 mm. Using diffusion MRI tractography, we revealed structural connectivity maps of the human subcortical auditory pathway both in vivo (1050 µm isotropic resolution) and post mortem (200 µm isotropic resolution). This work captures current MRI capabilities for investigating the human subcortical auditory system, describes challenges that remain, and contributes novel, openly available data, atlases, and tools for researching the human auditory system.
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Vías Auditivas/anatomía & histología , Mapeo Encefálico , Adulto , Femenino , Histocitoquímica , Humanos , Imagen por Resonancia Magnética , MasculinoRESUMEN
BACKGROUND: Diffusion tensor imaging is currently the only noninvasive way to map subcortical white matter tractography. Radiologists and neurologists often fail to reconstruct the complex auditory pathways when applying the most commonly used approach, deterministic fiber tracking, as this method is limited in spatial and angular resolution. A different fiber-tracking method involving a probabilistic approach could partly compensate for these limitations. We investigated efficiency and potential usefulness of probabilistic fiber tracking in depicting human auditory pathways in healthy individuals and patients with unilateral vestibular schwannoma (VS). METHODS: Eight healthy volunteers and 14 patients with unilateral VS underwent diffusion tensor imaging. Probabilistic fiber tracking of the auditory pathways for each subject was carried out using FSL software. Tracking rate, reliability of results, fiber volume, fiber length, and fractional anisotropy values were considered in assessing reliability and sensitivity of this method. Fiber length and fiber volume were analyzed separately for the healthy group and VS group. RESULTS: Good tracking sensitivity and consistency were shown in healthy subjects and patients with VS. For fiber length, the 8 healthy subjects exhibited significant between-sides differences, whereas the 14 patients with VS showed no such difference. For fiber volume, there was a statistically significant difference between groups, as the patients with VS displayed a smaller fiber volume on the nontumor side. Fractional anisotropy values revealed no significant autologous or between-group differences. These results match results of previous anatomic and neurologic studies. CONCLUSIONS: The auditory pathway can be depicted well by probabilistic fiber tracking. This method can compensate in part for weaknesses of the widely used deterministic tractography approach in depicting fine and complicated subcortical fibers.
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Vías Auditivas/diagnóstico por imagen , Imagen de Difusión Tensora/métodos , Procesamiento de Imagen Asistido por Computador/métodos , Neuroma Acústico/diagnóstico por imagen , Sustancia Blanca/diagnóstico por imagen , Adulto , Vías Auditivas/anatomía & histología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Neuroma Acústico/patología , Reproducibilidad de los Resultados , Sustancia Blanca/anatomía & histología , Sustancia Blanca/patologíaRESUMEN
The medial division of the medial geniculate (MGM) and the posterior intralaminar nucleus (PIN) are association nuclei of the auditory thalamus. We made tracer injections in these nuclei to evaluate/compare their presynaptic terminal and postsynaptic target features in auditory cortex, amygdala and striatum, at the light and electron microscopic levels. Cortical labeling was concentrated in Layer 1 but in other layers distribution was location-dependent. In cortical areas designated dorsal, primary and ventral (AuD, Au1, AuV) terminals deep to Layer 1 were concentrated in infragranular layers and sparser in the supragranular and middle layers. In ectorhinal cortex (Ect), distributions below Layer 1 changed with concentrations in supragranular and middle layers. In temporal association cortex (TeA) terminal distributions below Layer 1 was intermediate between AuV/1/D and Ect. In amygdala and striatum, terminal concentrations were higher in striatum but not as dense as in cortical Layer 1. Ultrastructurally, presynaptic terminal size was similar in amygdala, striatum or cortex and in all cortical layers. Postsynaptically MGM/PIN terminals everywhere synapsed on spines or small distal dendrites but as a population the postsynaptic structures in cortex were larger than those in the striatum. In addition, primary cortical targets of terminals were larger in primary cortex than in area Ect. Thus, although postsynaptic size may play some role in changes in synaptic influence between areas it appears that terminal size is not a variable used for that purpose. In auditory cortex, cortical subdivision-dependent changes in the terminal distribution between cortical layers may also play a role.
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Amígdala del Cerebelo/anatomía & histología , Corteza Auditiva/anatomía & histología , Vías Auditivas/anatomía & histología , Cuerpo Estriado/anatomía & histología , Cuerpos Geniculados/anatomía & histología , Animales , Axones/ultraestructura , Mapeo Encefálico , Núcleos Talámicos Intralaminares , Masculino , Microscopía Electrónica , Ratas , Ratas Long-Evans , Sinapsis/ultraestructuraRESUMEN
Systematic examination of the inputs and outputs of the nonlemniscal auditory thalamus will facilitate the functional elucidation of this complex structure in the central auditory system. In mice, comprehensive tracing studies that reveal the long-range connectivity of the nonlemniscal auditory thalamus are lacking. To this end, we used Cre-inducible anterograde and monosynaptic retrograde viruses in Calbindin-2A-dgCre-D and Calretinin-IRES-Cre mice, focusing on the differences across subdivisions of the nonlemniscal auditory thalamus. We found that, 1) the dorsal and medial parts of the auditory thalamus were predominantly connected to sensory processing centers, whereas the posterior intralaminar (PIN) and peripeduncular nucleus (PP) were additionally connected to emotion and motivation modulation centers; 2) ventral auditory cortical areas were the major source of cortical inputs for all subdivisions, and the PIN/PP received more inputs from cortical layer 5 than other subdivisions did; 3) deep layers of the superior colliculus and rostral part of the nonlemniscal inferior colliculus preferentially projected to the PIN/PP; and 4) compared with the dorsal auditory thalamus, the PIN/PP mainly innervated association cortices. In addition, new brain areas connected to the nonlemniscal auditory thalamus, mostly the PIN/PP, were identified. Our results suggested subdivision-specific function of the nonlemniscal auditory thalamus in sound processing.
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Vías Auditivas/anatomía & histología , Tálamo/anatomía & histología , Animales , Femenino , Masculino , Ratones , Ratones Endogámicos C57BLRESUMEN
The human auditory brainstem, especially the cochlear nucleus (CN) and the superior olivary complex (SOC) are characterized by a high density of neurons associated with perineuronal nets (PNs). PNs build a specific form of extracellular matrix surrounding the neuronal somata, proximal dendrites and axon initial segments. They restrict synaptic plasticity and control high-frequency synaptic activity, a prominent characteristic of neurons of the auditory brainstem. The distribution of PNs within the auditory brainstem has been investigated in a number of mammalian species. However, much less is known regarding PNs in the human auditory brainstem. The present study aimed at the immunohistochemical identification of PNs in the cochlear nucleus (CN) and superior olivary complex (SOC) in the human brainstem. We focused on the complex nature and molecular variability of PNs in the CN and SOC by using specific antibodies against the main PN components (aggrecan, brevican, neurocan and hyaluronan and proteoglycan link protein 1). Virtually all subnuclei within the ventral CN and SOC were found to be associated with PNs. Direct comparison between gerbil and human yielded similar fine structure of PNs and confirmed the typical tight interdigitation of PNs with synaptic terminals in both species. Noticeably, an elaborate combination of immunohistochemical labelings clearly supports the still debated existence of the medial nucleus of trapezoid body (MNTB) in the human brain. In conclusion, the present study demonstrates that PNs form a prominent extracellular structure on CN and SOC neurons in the human brain, potentially stabilizing synaptic contacts, which is in agreement with many other mammalian species.
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Vías Auditivas/anatomía & histología , Núcleo Coclear/anatomía & histología , Red Nerviosa/anatomía & histología , Terminales Presinápticos , Complejo Olivar Superior/anatomía & histología , Anciano de 80 o más Años , Agrecanos/análisis , Animales , Vías Auditivas/química , Biomarcadores/análisis , Brevicano/análisis , Cadáver , Proteoglicanos Tipo Condroitín Sulfato/análisis , Núcleo Coclear/química , Femenino , Gerbillinae , Humanos , Ácido Hialurónico/análisis , Inmunohistoquímica , Lectinas Tipo C/análisis , Masculino , Persona de Mediana Edad , Red Nerviosa/química , Proteínas del Tejido Nervioso/análisis , Técnicas de Trazados de Vías Neuroanatómicas , Neurocano , Terminales Presinápticos/química , Complejo Olivar Superior/química , Cuerpo Trapezoide/anatomía & histología , Cuerpo Trapezoide/químicaRESUMEN
A major challenge in neuroscience is to longitudinally monitor whole brain activity across multiple spatial scales in the same animal. Functional UltraSound (fUS) is an emerging technology that offers images of cerebral blood volume over large brain portions. Here we show for the first time its capability to resolve the functional organization of sensory systems at multiple scales in awake animals, both within small structures by precisely mapping and differentiating sensory responses, and between structures by elucidating the connectivity scheme of top-down projections. We demonstrate that fUS provides stable (over days), yet rapid, highly-resolved 3D tonotopic maps in the auditory pathway of awake ferrets, thus revealing its unprecedented functional resolution (100/300µm). This was performed in four different brain regions, including very small (1-2 mm3 size), deeply situated subcortical (8 mm deep) and previously undescribed structures in the ferret. Furthermore, we used fUS to map long-distance projections from frontal cortex, a key source of sensory response modulation, to auditory cortex.
Asunto(s)
Corteza Auditiva/diagnóstico por imagen , Vías Auditivas/diagnóstico por imagen , Mapeo Encefálico/métodos , Lóbulo Frontal/diagnóstico por imagen , Ultrasonografía/métodos , Estimulación Acústica , Animales , Corteza Auditiva/anatomía & histología , Corteza Auditiva/fisiología , Vías Auditivas/anatomía & histología , Vías Auditivas/fisiología , Mapeo Encefálico/instrumentación , Circulación Cerebrovascular/fisiología , Electrodos Implantados , Femenino , Hurones , Lóbulo Frontal/anatomía & histología , Lóbulo Frontal/fisiología , Técnicas Estereotáxicas , Ultrasonografía/instrumentación , Vigilia/fisiologíaRESUMEN
Music learning has received increasing attention in the last decades due to the variety of functions and brain plasticity effects involved during its practice. Most previous reports interpreted the differences between music experts and laymen as the result of training. However, recent investigations suggest that these differences are due to a combination of genetic predispositions with the effect of music training. Here, we tested the relationship of the dorsal auditory-motor pathway with individual behavioural differences in short-term music learning. We gathered structural neuroimaging data from 44 healthy non-musicians (28 females) before they performed a rhythm- and a melody-learning task during a single behavioural session, and manually dissected the arcuate fasciculus (AF) in both hemispheres. The macro- and microstructural organization of the AF (i.e., volume and FA) predicted the learning rate and learning speed in the musical tasks, but only in the right hemisphere. Specifically, the volume of the right anterior segment predicted the synchronization improvement during the rhythm task, the FA in the right long segment was correlated with the learning rate in the melody task, and the volume and FA of the right whole AF predicted the learning speed during the melody task. This is the first study finding a specific relation between different branches within the AF and rhythmic and melodic materials. Our results support the relevant function of the AF as the structural correlate of both auditory-motor transformations and the feedback-feedforward loop, and suggest a crucial involvement of the anterior segment in error-monitoring processes related to auditory-motor learning. These findings have implications for both the neuroscience of music field and second-language learning investigations.
Asunto(s)
Vías Auditivas/anatomía & histología , Percepción Auditiva/fisiología , Imagen de Difusión Tensora/métodos , Vías Eferentes/anatomía & histología , Aprendizaje/fisiología , Música , Sustancia Blanca/anatomía & histología , Adulto , Vías Auditivas/diagnóstico por imagen , Vías Eferentes/diagnóstico por imagen , Función Ejecutiva/fisiología , Retroalimentación , Femenino , Lateralidad Funcional/fisiología , Humanos , Masculino , Percepción del Tiempo/fisiología , Sustancia Blanca/diagnóstico por imagen , Adulto JovenRESUMEN
The influential dual-stream model of auditory processing stipulates that information pertaining to the meaning and to the position of a given sound object is processed in parallel along two distinct pathways, the ventral and dorsal auditory streams. Functional independence of the two processing pathways is well documented by conscious experience of patients with focal hemispheric lesions. On the other hand there is growing evidence that the meaning and the position of a sound are combined early in the processing pathway, possibly already at the level of early-stage auditory areas. Here, we investigated how early auditory areas integrate sound object meaning and space (simulated by interaural time differences) using a repetition suppression fMRI paradigm at 7â¯T. Subjects listen passively to environmental sounds presented in blocks of repetitions of the same sound object (same category) or different sounds objects (different categories), perceived either in the left or right space (no change within block) or shifted left-to-right or right-to-left halfway in the block (change within block). Environmental sounds activated bilaterally the superior temporal gyrus, middle temporal gyrus, inferior frontal gyrus, and right precentral cortex. Repetitions suppression effects were measured within bilateral early-stage auditory areas in the lateral portion of the Heschl's gyrus and posterior superior temporal plane. Left lateral early-stages areas showed significant effects for position and change, interactions Category x Initial Position and Category x Change in Position, while right lateral areas showed main effect of category and interaction Category x Change in Position. The combined evidence from our study and from previous studies speaks in favour of a position-linked representation of sound objects, which is independent from semantic encoding within the ventral stream and from spatial encoding within the dorsal stream. We argue for a third auditory stream, which has its origin in lateral belt areas and tracks sound objects across space.
Asunto(s)
Corteza Auditiva/fisiología , Vías Auditivas/fisiología , Localización de Sonidos/fisiología , Estimulación Acústica , Adulto , Corteza Auditiva/anatomía & histología , Corteza Auditiva/diagnóstico por imagen , Vías Auditivas/anatomía & histología , Vías Auditivas/diagnóstico por imagen , Percepción Auditiva/fisiología , Mapeo Encefálico , Femenino , Lateralidad Funcional/fisiología , Neuroimagen Funcional , Humanos , Imagen por Resonancia Magnética , Masculino , Modelos Anatómicos , Modelos Neurológicos , Modelos Psicológicos , Psicoacústica , Adulto JovenRESUMEN
The motion along the basilar membrane in the cochlea is due to the interaction between the micromechanical behaviour of the organ of Corti and the fluid movement in the scalae. By dividing the length of the cochlea into a finite number of elements and assuming a given radial distribution of the basilar membrane motion for each element, a set of equations can be separately derived for the micromechanics and for the fluid coupling. These equations can then be combined, using matrix methods, to give the fully coupled response. This elemental approach reduces to the classical transmission line model if the micromechanics are assumed to be locally-reacting and the fluid coupling is assumed to be entirely one-dimensional, but is also valid without these assumptions. The elemental model is most easily formulated in the frequency domain, assuming quasi-linear behaviour, but a time domain formulation, using state space method, can readily incorporate local nonlinearities in the micromechanics. Examples of programs are included for the elemental model of a human cochlea that can be readily modified for other species.