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Results for “Auditory Cortex”

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At least 1,531 records · Page 85Linked to original sources
PubMed1986

Neurons accumulating [3H]gamma-aminobutyric acid (GABA) in supragranular layers of cat primary auditory cortex (AI)

The classes of neurons accumulating exogenously injected, tritiated gamma-aminobutyric acid [( 3H]GABA) were studied in the supragranular layers in the primary auditory field of the adult cat. The size, laminar locus, and somatodendritic profiles of labeled neurons were studied light microscopically in frozen- or Vibratome-sectioned, 30 micron thick material, and in semithin, 1-2 micron thick, plastic-embedded high-resolution autoradiographic preparations. The chief goals of the study were to determine which types of cells could be identified as accumulating [3H]GABA in layers I, II and III, and to establish possible relationships between these cells and neurons described in Golgi studies of these layers, and the neurons found, in parallel investigations of the connections of the primary auditory field, to participate as ipsilateral corticocortical and commissural cells of origin. The principal findings are: that neurons in every layer in the primary auditory field take up tritiated gamma-aminobutyric acid; that their Nissl-counterstained somata have a smaller average area, and a smaller range of areas, than do the unlabeled cells; that more than one type of labeled neuron-as defined by somatic size and shape, height:width ratios, and nuclear membrane morphology-could be identified in each layer; that none of the labeled neurons had a soma with a pyramidal configuration; that the labeled cells are comparable in size, shape, and laminar distribution to some populations of non-pyramidal ipsilateral corticocortical cells of origin in layers II and III, and perhaps to certain classes of commissurally projecting, layer III non-pyramidal neurons; and finally, that only a rather small proportion-perhaps 10% or less, except in layer I-of the supragranular cells appear to accumulate labeled material. With regard to the identity of particular classes of neurons accumulating silver grains above background in the individual layers, in layer I, 2 of the 4 types of neurons characterized in Golgi preparations take up gamma-aminobutyric acid and the remaining 2 types may also, and the relative number of labeled cells appears to be higher than in the other layers; in layer II, 2 of the 9 varieties are labeled, and 4 other types may also be; and in layer III, 2 of the 11 types take up gamma-aminobutyric acid, and 5 other varieties may as well. Three types of non-pyramidal layer II cells that project ipsilaterally from AI to the second auditory cortical field, AII, possibly accumulate gamma-aminobutyric acid; 3 types of commissural non-pyramidal cells of origin linking AI to AI appear to be labeled by gamma-aminobutyric acid.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

Intracortical microstimulation induced changes in spectral and temporal response properties in cat auditory cortex.

Intracortical microstimulation (ICMS), consisting of a 40 ms burst (rate 300 Hz) of 10 microA pulses, repetitively administered once per second, for a total duration of 1 h, induced cortical reorganization in the primary auditory cortical field of the anesthetized cat. Multiple single-unit activity was simultaneously recorded from three to nine microelectrodes. Spiking activity was recorded from the same units prior to and following the application of ICMS in conjunction with tone pips at the characteristic frequency (CF) of the stimulus electrode. ICMS produced a significant increase in the mean firing rate, and in the occurrence of burst activity. There was an increase in the cross-correlation coefficient (R) for unit pairs recorded from sites distant from the ICMS site, and a decrease in R for unit pairs that were recorded at the stimulation site. ICMS induced a shift in the CF, dependent on the difference between the baseline CF and the ICMS-paired tone pip frequency. ICMS also resulted in broader tuning curves, increased driven peak firing rate and reduced response latency. This suggests a lasting reduction in inhibition in a small region surrounding the ICMS site that allows expansion of the frequency range normally represented in the vicinity of the stimulation electrode.

Acoustic Stimulation↗
PubMedDate not supplied

[Participation of the auditory cortex and emotionogenic subcortical systems in the formation and reproduction of conditioned reactions].

Analysis of the activity of several brain structures in conditioned neurographic response taken as an analog of conditioned motor reaction was performed on a model of short-delay defensive reflex with unavoidable reinforcement (immobilized cats). It has been shown that the conditioned electrographic signs may appear in the central nervous system both in the presence and in the absence of conditioned motor reaction. The probability of their occurance increases in the cortex, Zona incerta and in the preoptic area during achievement of conditioned effector reaction. The probability of their appearance in other formations does not change considerably neither in the absence nor in the occurance of conditioned motor reaction. Combinations of brain structures are singled out in which the appearance of conditioned electrographic signs is accompanied by conditioned effector reaction. The optimal variant for its occurance is simultaneous appearance of the conditioned electrographic signs in Zona incerta, in the cortex and in the preoptic area.

Amygdala↗
PubMed1991

Topography of projections from the auditory cortex to the inferior colliculus in the rat.

We examined the organization of descending projections from auditory and adjacent cortical areas to the inferior colliculus (IC) in the rat by using the retrograde and anterograde transport of wheat germ agglutinin-horseradish peroxidase. Small tracer injections were placed into cytologically defined subnuclei of the IC. On the basis of the resulting pattern of retrogradely labeled neurons in the cortex, different cortical areas and fields were defined. Two secondary areas located ventrocaudally (Te2) and ventrally (Te3) to the primary auditory area (Te1) were delineated. The primary auditory area was subdivided into a posterior (Te1.p), a medial (Te1.m), and an anterior (Te1.a) auditory field. In addition, we outlined an area located rostrally to the auditory areas comprising a part of the secondary somatosensory cortex, as well as a dorsal belt surrounding dorsally the auditory areas. The following basic patterns of corticocollicular projections are revealed: 1) layers 2 and 3 of the dorsal cortex of the IC (DC2, DC3) are differentially innervated by the primary auditory fields (Te1.p and Te1.a project bilaterally to DC2, while Te1.m projects bilaterally and in topographical order to DC3); cells in Te1.m, arranged in caudal to rostral sequence, project to corresponding loci in DC3 arranged from dorsolateral to ventromedial; 2) the fibrocellular capsule of the IC, comprising layer 1 of the dorsal and external cortex of the IC, receives input from the secondary auditory area Te2; 3) layers 2 and 3 of the external cortex of the IC are only weakly innervated by the primary and secondary auditory cortex; 4) the intercollicular zone receives its major input from the secondary auditory area Te3, the secondary somatosensory cortex, and the dorsal belt; and 5) finally, the central nucleus of the IC receives no input from the temporal cortex at all. Our results demonstrate that the corticocollicular projections are highly organized. These pathways may modulate auditory processing in different functional circuits of the inferior colliculus.

Animals↗
PubMed2004

Activation in the anterior left auditory cortex associated with phonological analysis of speech input: localization of the phonological mismatch negativity response with MEG.

The spatio-temporal dynamics of cortical activation underlying auditory word recognition, particularly its phonological stage, was studied with whole-head magnetoencephalography (MEG). Subjects performed a visuo-auditory priming task known to evoke the phonological mismatch negativity (PMN) response that is elicited by violations of phonological expectancies. Words and non-words were presented in separate conditions. In each of the 318 trials, the subjects first saw a word/non-word (e.g., 'cat') that was soon followed by a prime letter (e.g., 'h'). Their task was to replace mentally the sound of the first letter of the word/non-word with the prime letter, thus resulting in a new word/non-word (e.g., 'hat'). Finally, an auditory word/non-word either matching or mismatching with the anticipated item was presented. In most subjects, a PMNm followed by a later, N400m-like negativity was obtained in the left hemisphere to the mismatching auditory stimuli. A similar response pattern was obtained in the right hemisphere only in a few subjects. Source localization of the N1m, an index of acoustic analysis, and the PMNm and N400m-like responses was performed using L1 minimum-norm estimation. In the left hemisphere, the PMNm source for the words was significantly more anterior than the source of the N400m-like response; for the non-words, the PMNm source was significantly more anterior than the sources of the N1m and the N400m-like response. These results suggest that the left-hemisphere neuronal networks involved in sub-lexical phonological analysis are at least partly different from those responsible for the earlier (acoustic) and later (whole item) processing of speech input.

Acoustic Stimulation↗
PubMedDate not supplied

Multiplicity of inputs in the afferent path to cat auditory cortex neurons revealed by tone-on-tone masking.

This report presents preliminary evidence on the effect of continuous tonal maskers on the responses of single primary auditory cortical neurons in anesthetized cats to tonal signals across their effective frequency ranges 10 dB above characteristic frequency threshold. Tonal maskers had three kinds of effects. In many cells, the masker produced a generalized suppression of responses to tones across the response area. In some neurons, typically those with monotonic intensity profiles, tonal maskers on one side of the response area produced a selective suppression of responses to tone signals on the same side as the masker. This differential sensitivity to the masker is evidence of independent inputs to those neurons on the high- and low-frequency sides of their excitatory response areas. Finally, in non-monotonic neurons, tonal maskers at the high-frequency edge of the excitatory response area produced enhanced responses to tonal signals on the same side of the response area as the masker. We interpret this as a release from the effect of an inhibitory input located at the high-frequency edge of the response area.

Acoustic Stimulation↗