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Results for “Auditory Cortex”

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At least 1,621 records · Page 90Linked to original sources
PubMed1985

[Ultrastructural organization of endings of the efferent fibers of zones A1 and A4 of the auditory cortex of the cat in the superior olivary complex].

Distribution of synapses formed by straight corticofugal fibers running from the zone A1 and A4 of the acoustic cortex in the main basilar nuclei of the cat superior olive has been studied electron microscopically. These synapses are presented as axodendritic structures situating on processes of small and middle diameters, predominantly at the side of the operation (both in the medial and lateral complexes). Problems on functional influence of the acoustic cortex projections on subcortical acoustic centers depending on the form and amount of the synaptic terminals are discussed.

Animals↗
PubMed2005

Time course of top-down and bottom-up influences on syllable processing in the auditory cortex.

In speech perception, extraction of meaning from complex streams of sounds is surprisingly fast and efficient. By tracking the neural time course of syllable processing with magnetoencephalography we show that this continuous construction of meaning-based representations is aided by both top-down (context-based) expectations and bottom-up (acoustic-phonetic) cues in the speech signal. Syllables elicited a sustained response at 200-600 ms (N400m) which became most similar to that evoked by words when the expectation for meaningful speech was increased by presenting the syllables among words and sentences or using sentence-initial syllables. This word-like cortical processing of meaningless syllables emerged at the build-up of the N400m response, 200-300 ms after speech onset, during the transition from perceptual to lexical-semantic analysis. These findings show that the efficiency of meaning-based analysis of speech is subserved by a cortical system finely tuned to lexically relevant acoustic-phonetic and contextual cues.

Adult↗
PubMed1991

Reorganization of auditory cortex after neonatal high frequency cochlear hearing loss.

Cochleotopic representation in cortex (AI) is extensively reorganized in cats having neonatal, bilateral high frequency cochlear hearing loss. Anterior areas of AI, normally devoted to high frequencies, contain neurons which are almost all tuned to one lower frequency. This frequency corresponds, at the level of the cochlea, to the border between normal and damaged haircell regions.

Amikacin↗
PubMed2005

Relative sparing of primary auditory cortex in Williams Syndrome.

Williams Syndrome (WS) is a neurodevelopment disorder associated with a hemizygous deletion on chromosome 7. WS is characterized with mental retardation, severe visual-spatial deficits, relative language preservation, and excellent facial recognition. Distinctive auditory features include musical ability, heightened sound sensitivity, and specific patterns of auditory evoked potentials. These features have led to the hypothesis that the dorsal forebrain is more affected than the ventral. Previously, we reported primary visual area 17 abnormalities in rostral striate cortex, a region contributing to the dorsal visual pathway. Based on the dorsal-ventral hypothesis, and language and auditory findings, we predicted a more normal histometric picture in auditory area 41. We used an optical dissector method to measure neurons in layers II-VI of area 41 in right and left hemispheres of the same 3 WS and 3 control brains used in the area 17 study. There was a hemisphere by diagnosis interaction in cell packing density (CPD) in layer IV and in cell size in layer III between WS and control brains. Post hoc analysis disclosed in control brains, but not WS, a layer IV left > right asymmetry in CPD, and a layer III left < right asymmetry in cell size. WS brains showed more large neurons bilaterally in layer II and in left layer VI. Histometric alterations in area 41 were less widespread than rostral visual cortex. Also, there was less asymmetry in the WS brain. We interpret layers II and VI differences as reflecting increased limbic connectivity in primary auditory cortex of WS.

Adult↗
PubMed1990

The subparafascicular thalamic nucleus of the rat receives projection fibers from the inferior colliculus and auditory cortex.

The sources of afferent fibers to the subparafascicular thalamic nucleus (SPF) of the rat were investigated by the retrograde WGA-HRP and anterograde PHA-L methods. Layer V of the areas 3, 1 and 2 of the temporal cortex as well as the dorsal and external cortices of the inferior colliculus were found to send projection fibers to the whole rostrocaudal extent of the SPF bilaterally with a clear-cut ipsilateral dominance. The results indicate that the SPF of the rat may constitute a relay nucleus in the central auditory pathways.

Animals↗
PubMed1998

Vibration-induced auditory-cortex activation in a congenitally deaf adult.

Considerable changes take place in the number of cerebral neurons, synapses and axons during development, mainly as a result of competition between different neural activities [1-4]. Studies using animals suggest that when input from one sensory modality is deprived early in development, the affected neural structures have the potential to mediate functions for the remaining modalities [5-8]. We now show that similar potential exists in the human auditory system: vibrotactile stimuli, applied on the palm and fingers of a congenitally deaf adult, activated his auditory cortices. The recorded magnetoencephalographic (MEG) signals also indicated that the auditory cortices were able to discriminate between the applied 180 Hz and 250 Hz vibration frequencies. Our findings suggest that human cortical areas, normally subserving hearing, may process vibrotactile information in the congenitally deaf.

Adult↗
PubMed2004

Attention and arousal related modulation of spontaneous gamma-activity in the auditory cortex of the cat.

Sensory information processing in neocortex is associated with rhythmic synchronized gamma frequency firing of sensory cortical units and similar frequency oscillations of the field potentials. Different aspects of the gamma activity (20-80 Hz) have been suggested as correlates of attention, arousal and sensory binding. It is clear that attention has a modality selective influence, while arousal has a more general effect on the sensory systems. We used an experimental conditioning paradigm to separate these differential effects of attention and arousal on spontaneous neocortical gamma activity. We recorded field potentials with epidural electrodes placed above the auditory cortical areas of cats. The animals performed a simple instrumental alimentary conditioning task with different modality (visual and auditory) conditioned stimuli. When they attended to the auditory conditioned stimulus, both frequency and power increase of spontaneous gamma activity were detected. However when they attended visual, we found no power increase of gamma activity recorded above auditory areas, while the frequency increase was the same as in the "attend auditory" condition. We conclude that the power modulation of gamma activity is modality specific and thus can be attributed to selective attention, whereas the frequency modulation of gamma activity shows no modality specificity, it is influenced by the arousal level.

Acoustic Stimulation↗
PubMed1997

Projections of auditory cortex onto the inferior colliculus in the rat.

The organization of the neocortical projection to the inferior colliculus (IC) was studied in 36 rats using retrograde transport of horseradish peroxidase (HRP) or horseradish peroxidase conjugated with lectin (WGA-HRP). Projection to the external and dorsal cortices originates in the temporal neocortical areas Te 1, Te 2 and Te 3 and in the parietal area Par 2. The corticocollicular projection is predominantly ipsilateral with a weak contralateral contribution. Projection to the rostromedial and rostrolateral part of the external cortex (EC) of the IC arises mainly from the areas Par 2 and Te 1. The participation of the cortical areas Te 2 and Te 3 in this projection is only small. The fibres to the caudobasal part of the external cortex descend from the caudal parts of areas Te 1, Te 2, and Te 3. The corticocollicular projections to the dorsal part of the IC are more numerous than the projections to the EC and originate in all temporal areas, i.e. in area Te 1, Te 2 and Te 3. However, the topographical organization of the corticocollicular projection is more pronounced in the part which projects to the EC. We suggest that the topographical organization of the projections to the EC corresponds with the map of auditory space in the EC. The source of corticocollicular fibres are exclusively neurones of lamina V of all cortical areas sending their fibres to the IC.

Animals↗
PubMed2002

Simultaneous sampling of event-related BOLD responses in auditory cortex and brainstem.

Event-related functional magnetic resonance imaging (fMRI) was applied to investigate blood oxygen level dependent (BOLD) responses in the human auditory system. Auditory fMRI is hindered by the disturbing acoustical noise of echo planar imaging (EPI). A sparse acquisition technique was used in which the delayed hemodynamic response was imaged at discrete sampling time-points after a brief auditory stimulus. Long repetition times (10 heartbeats (HBs)) were used to avoid interactions between the activation due to the sound stimulation and scanner noise. In addition, only a single slice was acquired, to ensure that the scanner noise was minimal in duration and intensity. The image acquisition was triggered by the HB to prevent artifacts from cardiac-related brainstem motion. An image was acquired every 10th HB. Significant hemodynamic BOLD time-course responses were measured from the primary and secondary auditory cortices, as well as the inferior colliculi in the brainstem. No systematic differences were found between the cerebral cortex and the brainstem in terms of activation amplitude or in onset time of the hemodynamic response. Apparently, the slow dynamic nature of the BOLD response signal is similar across spatially separated auditory brain regions, suggesting a corresponding design of vessels and capillaries.

Acoustic Stimulation↗
PubMed1989

Semiquantitative analyses of dynamic single photon emission computed tomography (SPECT) of the primary auditory cortex.

To date it has not been possible to work out a standard quantification for single photon emission computed tomography (SPECT). Only one mathematical model has received general recognition, but the theoretical preconditions for this model are not fulfilled by iodine-amphetamine kinetics. A practical solution is offered by semiquantitative analysis. We have developed three computer programs for this analysis for perfusion and cerebral function studies of the symmetrically arranged brain.

Adult↗
PubMed2006

A new planar multielectrode array: recording from a rat auditory cortex.

In the study of the spatiotemporal properties of the cortex, a demand often arises for recording local field evoked potentials (LFEP) and neural spikes from a quantity of points at close range from each other. In such a situation a device composed of a lot of electrodes assembled in a single bunch would be suitable. Such circumstances gave us the impetus to create the device described in this paper, namely a new planar electrode array for in vivo multisite extracellular recording. The device is made of plastic and includes platinum electrodes 50 microm in diameter. The array of 64 incorporated microelectrodes is placed on the surface of the cortex of anesthetized rats. Recordings could be made through all electrodes for more than 1 h without damage to the cortex. The inter-polar distance is approximately 100 microm so that each individual electrode can record activity from a separate population of neurons near the cortical surface. The recording system described here is highly useful for visualizing spatiotemporal structure of the cortical activities and for imaging dynamic neuronal assemblies.

Acoustic Stimulation↗
PubMed1989

Magnetic fields from the auditory cortex of a deaf human individual occurring spontaneously or evoked by stimulation through a cochlear prosthesis.

In a postlingually deaf individual, the magnetic field evoked by stimulation through a cochlear prosthesis (extracochlear electrodes) as well as of the spontaneous magnetoencephalogram was measured over the hemisphere contralateral to the prosthesis (CP), and the results were compared with those obtained from normal-hearing subjects. The latency of the 2 best developed waves M100 and M200 turned out to be prolonged in the CP patient by approximately 40 ms. The amplitude of wave M100 was significantly diminished, while wave M200 was only poorly developed. Location and direction of the equivalent current dipole (ECD) calculated for wave M100 was in good agreement with normal data, whereas the dipole moment was only about one third of the average dipole moment found in normals. Furthermore, evidence was obtained for another magnetic field wave, preceding the delayed auditory wave M100, which exhibits the same latency, ECD location and direction as reported in the literature for the somatosensory evoked magnetic field. This wave probably results from stimulation, through the intratympanic electrodes, of somatosensory nerves innervating the tympanic cavity. A potential clinical application of neuromagnetic measurements is discussed: The calculation of the ECD moment from the auditory cortical magnetic field evoked by electrical stimulation at the promontory would allow to estimate, prior to CP implantation, the number of persisting, excitable nerve fibres.

Acoustic Stimulation↗
PubMed1972

Auditory cortex of squirrel monkey: response patterns of single cells to species-specific vocalizations.

Most of the neurons tested in the superior temporal cortex of awake squirrel monkeys responded to recorded species-specific vocalizations. Some cells responded with temporally complex patterns to many vocalizations. Other cells responded with simpler patterns to only one call. Most cells lay between these two extremes. On-line deletion of parts of a vocalization revealed the role of temporal interactions in determining the nature of some responses.

Action Potentials↗