Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Auditory Cortex”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMed1986

Evoked potentials of the auditory cortex of the porpoise, Phocoena phocoena.

Evoked potential (EP) recordings in the auditory cortex of the porpoise, Phocoena phocoena, were used to obtain data characterizing the auditory perception of this dolphin. The frequency threshold curves showed that the lowest EP thresholds were within 120-130 kHz. An additional sensitivity peak was observed between 20 and 30 kHz. The minimal EP threshold to noise burst was 3 X 10(-4) - 10(-3) Pa. The threshold for response to modulations in sound intensity was below 0.5 dB and about 0.1% for frequency modulations. Special attention was paid to the dependence of the auditory cortex EP on the temporal parameters of the acoustic stimuli: sound burst duration, rise time, and repetition rate. The data indicate that the porpoise auditory cortex is adapted to detect ultrasonic, brief, fast rising, and closely spaced sounds like echolocating clicks.

Acoustic Stimulation↗
PubMed1986

The relationship between the auditory cortex and the claustrum in the cat.

The relationship between the primary auditory cortex and the claustrum has been re-examined in the cat with axoplasmic flow and axonal degeneration methods. Labelled cells are found in a restricted part of the claustrum after injections of HRP or HRP-WGA in the primary auditory cortex, but they are relatively few in number and are palely stained. The number of labelled cells and their depth of staining are greatest at 72 h (the longest survival time used here), and this survival period an occasional labelled cell is also present in the claustrum of the contralateral hemisphere. No labelled cells are seen after 24 h. After small lesions in the primary auditory cortex, fibre and terminal degeneration are present in the part of the claustrum where labelled cells are seen with axoplasmic flow techniques. It is concluded that there are reciprocal connections between the primary auditory cortex and the claustrum, but the rate of axoplasmic flow is unusually slow.

Animals↗
PubMed1986

Representation of amplitude modulation in the auditory cortex of the cat. I. The anterior auditory field (AAF).

The ability of cortical neurons to follow amplitude modulation (AM) of tones was examined in the anterior auditory cortical field (AAF) of anesthetized cats using multiple-unit recording techniques. Sinusoidal and rectangular modulations (100%) of a monaural carrier tone at the characteristic frequency of each location were presented to study the degree of response synchronization and changes in firing rate as a function of the modulation frequency. All investigated locations were tuned to a 'best modulation frequency' (BMF) as determined by synchronization measures. Almost all locations (94%) were tuned to a BMF as determined by spike rate. Maximal binaural-interaction strength was observed for modulation frequencies close to the BMF of neurons. For sinusoidal AM, a correlation (r = 0.63, P less than 0.01) between BMF and CF of neurons in AAF could be demonstrated for the synchronization of the response.

Acoustic Stimulation↗
PubMed1998

Experience-dependent modulation of tonotopic neural responses in human auditory cortex.

Experience-dependent plasticity of receptive fields in the auditory cortex has been demonstrated by electrophysiological experiments in animals. In the present study we used PET neuroimaging to measure regional brain activity in volunteer human subjects during discriminatory classical conditioning of high (8000 Hz) or low (200 Hz) frequency tones by an aversive 100 dB white noise burst. Conditioning-related, frequency-specific modulation of tonotopic neural responses in the auditory cortex was observed. The modulated regions of the auditory cortex positively covaried with activity in the amygdala, basal forebrain and orbitofrontal cortex, and showed context-specific functional interactions with the medial geniculate nucleus. These results accord with animal single-unit data and support neurobiological models of auditory conditioning and value-dependent neural selection.

Adult↗
PubMed1989

Connections of primary auditory cortex in the New World monkey, Saguinus.

Connections of primary auditory cortex (A-I) were investigated in the tamarin (Saguinus fuscicollis), a New World monkey. In each case, A-I was defined by multiunit recordings, and best frequencies were determined for neurons at different recording sites. Microlesions were placed to mark recording sites for correlation with cortical architecture. Following mapping, separate injections of up to three different tracers (HRP-WGA and fluorescent dyes) were placed into the representations of different frequencies within A-I. The results support several conclusions: (1) high to low frequencies are represented in a dorsocaudal to ventrorostral sequence in A-I, (2) intrinsic connections in A-I are more pronounced along isofrequency contours, (3) the pattern of connections between A-I and adjoining cortex suggests that this surrounding auditory cortex contains at least two tonotopically organized fields and possibly one or more additional auditory fields, (4) callosal connections of A-I are largely between parts of A-I matched for frequency representation, (5) thalamic connections of A-I include topographic connections with the ventral division of the medial geniculate complex (MGv) and more diffuse connections with the medial (MGm) and dorsal (MGd) divisions of the medial geniculate complex and the suprageniculate nucleus (Sg), and (6) A-I projects bilaterally to the dorsal cortex of the inferior colliculus.

Acoustic Stimulation↗
PubMed1998

Distribution of response types across entire hemispheres of the mustached bat's auditory cortex.

AILDD1 AC'1 The responses of neurons in the mustached bat's auditory cortex are specialized to extract particular information from biosonar signals. For this study, we mapped response properties across entire hemispheres in several animals. These experiments enabled us to construct a standard map that aided in determining the connections among the areas, as described subsequently. The mapping also yielded quantitative data regarding the relative sizes of areas and the proportion of cortex devoted to different response types. We identified six response types that were distributed in 11 areas. Eight areas, comprising two-thirds of the auditory cortex, contained neurons sensitive to particular components in biosonar signals. Most were facilitated by combinations of frequency modulated and constant frequency biosonar signal components (FMs and CFs, respectively). There were three major types of combination-sensitive neurons: FM-FM, CF/CF, and FM-CF. Each type of combination sensitivity occurred in multiple areas. The largest proportion were FM-FM neurons (approximately 30% of all neurons in auditory cortex), followed by FM1-CF2 (approximately 23%) and CF/CF (approximately 11%). In the other three areas comprising approximately one-third of the auditory cortex, most neurons responded well to frequencies not contained in biosonar signals.

Animals↗
PubMed1996

Pyramidal cells in primary auditory cortex project to cochlear nucleus in rat.

Recent work has demonstrated that the auditory cortex in rat sends direct projections to the auditory nuclei of the brainstem, including the cochlear nucleus and superior olive. To determine the cortical origin of the projections to cochlear nucleus, Fast Blue, a retrograde fluorescent tracer, was injected into the cochlear nucleus. Labeled cells in the forebrain were then studied with light microscopy and mapped. The projection was found to originate from large pyramidal neurons in layer V of primary auditory cortex. The projection was predominantly ipsilateral, and no labeled neurons were found in other cortical areas. These data imply that primary auditory cortex exerts influence over ascending auditory information at the earliest stages of the central auditory system.

Amidines↗
PubMed1984

A type of apparently axonless granule cell in the cat auditory cortex.

In the auditory areas (A I, A II and the posterior ectosylvian gyrus) of the cat, unusually small granule cells apparently lacking an axon are described. They are exclusively located in layer 2/3 and sometimes impregnate in groups of 4 or 5, being probably quite frequent. Some morphological differences between granule cells of young and adult cats are noted.

Aging↗
PubMed2000

Topographic and temporal indices of vowel spectral envelope extraction in the human auditory cortex.

The auditory-evoked neuromagnetic field elicited by single vowel formants and two-formant vowels was recorded under active listening conditions using a 37-channel magnetometer. There were three single formants with formant frequencies of 200, 400, and 800 Hz, another single formant with a formant frequency of 2600 Hz, and three vowels that were constructed by linear superimposition of the high- onto one of the low-frequency formants. P50 m and N100 m latency values were inversely correlated with the formant frequency of single formants. A strong effect of formant frequency on source location was obtained along the postero-anterior axis, which is orthogonal to the well-established latero-medial tonotopic gradient. Regardless of whether single formants or first formants of vowels were considered, N100 m sources were more anterior and sustained field sources were more posterior for higher-frequency than for lower-frequency formants. The velocity of the apparent posterior-to-anterior movement across cortical surface of N100 m sources first reported by Rogers et al. [Rogers, R. L., Papanicolaou, A. C., Baumann, S. B., Saydjari, C., & Eisenberg, H. M. (1990). Neuromagnetic evidence of a dynamic excitation pattern generating the N100 auditory response. Electroencephalography and Clinical Neurophysiology,77, 237-240] decreased as a function of latency. The amount of deceleration was positively correlated with formant frequency. Responses to the vowels were superadditive, indicating that the processes elicited by the constituents of composite stimuli interact at one or more stages of the afferent auditory pathway. Such interaction may account for the absence of a lateral-to-medial tonotopic mapping of first formant frequency. The source topography found may reflect activity in auditory fields adjacent to AI with the strength of the contribution varying with formant frequency. Alternatively, it may reflect sharpness-of-tuning and inhibitory response-area asymmetry gradients along isofrequency stripes within AI. Either alternative may be interpreted in terms of a spectral blurring mechanism that abstracts spectral envelope information from the details of spectral composition, an important step towards the formation of invariant phonetic percepts.

Adult↗
PubMed2001

Hierarchical organization of the human auditory cortex revealed by functional magnetic resonance imaging.

The concept of hierarchical processing--that the sensory world is broken down into basic features later integrated into more complex stimulus preferences--originated from investigations of the visual cortex. Recent studies of the auditory cortex in nonhuman primates revealed a comparable architecture, in which core areas, receiving direct input from the thalamus, in turn, provide input to a surrounding belt. Here functional magnetic resonance imaging (fMRI) shows that the human auditory cortex displays a similar hierarchical organization: pure tones (PTs) activate primarily the core, whereas belt areas prefer complex sounds, such as narrow-band noise bursts.

Adult↗
PubMed2001

Arterial blood supply to the auditory cortex of the chinchilla.

Utilizing optical imaging we identified and named the arteries that supply the primary auditory cortex in the chinchilla (Chinchilla laniger). The primary auditory cortex is located 2-3 mm caudal to the medial cerebral artery and is supplied by it. Using corrosion casts and scanning electron microscopy we visualized the capillary networks in the auditory cortex and found regional variations in the densities of the capillary bed. We hypothesize that the uneven capillary densities observed in the auditory cortex correspond to neurologically more active areas.

Animals↗
PubMed2002

Maturation of human auditory cortex: implications for speech perception.

This project traced the maturation of the human auditory cortex from midgestation to young adulthood, using immunostaining of axonal neurofilaments to determine the time of onset of rapid conduction. The study identified 3 developmental periods, each characterized by maturation of a different axonal system. During the perinatal period (3rd trimester to 4th postnatal month), neurofilament expression occurs only in axons of the marginal layer. These axons drive the structural and functional development of cells in the deeper cortical layers, but do not relay external stimuli. In early childhood (6 months to 5 years), maturing thalamocortical afferents to the deeper cortical layers are the first source of input to the auditory cortex from lower levels of the auditory system. During later childhood (5 to 12 years), maturation of commissural and association axons in the superficial cortical layers allows communication between different subdivisions of the auditory cortex, thus forming a basis for more complex cortical processing of auditory stimuli.

Adult↗
PubMed1997

Effects of noradrenaline on frequency tuning of rat auditory cortex neurons.

The selectivity of rat auditory cortex neurons for pure tone frequency was studied during and after ionophoretic application (5-40 nA) of noradrenaline in urethane-anaesthetized rats. The dominant effect induced by noradrenaline was a significant decrease in spontaneous (93/268 cells) and evoked activity (133/268 cells) which outlasted the application. In the whole population of cells (n = 268) the signal-to-noise ratio, computed using as the signal either the mean evoked response or the response at the best frequency, was unchanged during noradrenaline application. It was significantly increased only for cells showing significantly decreased spontaneous activity, and was significantly decreased for cells showing increased spontaneous activity. Frequency selectivity was significantly increased for the whole population during and after noradrenaline application. It was also significantly increased for cells showing significantly decreased evoked activity, and was significantly decreased for cells showing increased evoked activity. The noradrenaline-induced inhibition was not blocked by propranolol (beta antagonist); it was blocked by prazosin (alpha1 antagonist) and partly mimicked by phenylephrine (alpha1 agonist). GABA, which also inhibited spontaneous and evoked activity, slightly increased the signal-to-noise ratio and significant increased frequency selectivity. However, when noradrenaline was ejected in the presence of bicuculline at doses that were able to block GABAergic inhibition, the inhibitory effects of noradrenaline on spontaneous and evoked activity were still observed. The possible function of noradrenaline-induced inhibitions in sensory cortices is briefly discussed.

Animals↗
PubMed1987

[Functional organization of the callosal connections in the auditory cortex of the cat].

Homotopic transcallosal potentials of the cat auditory cortex primary projection area (AI) had the greatest amplitude, the minimal temporal parameters and the maximal stability of characteristics as compared with the responses of the auditory cortex associative fields AII, AIV, Ep. Heterotopic transcallosal responses in the AI field occurred in stimulation of the field under the same name whereas in the Ep field the responses occurred both in stimulation of the same and the AI and AII fields of the opposite hemisphere. The structure of transcallosal connections of the auditory cortex primary projection field seems to be characterized by homotopy whereas in associative fields the role of heterotopic transcallosal interactions seems to increase. Such a structure of transcallosal connections seems to maintain the important role of interhemispheric interaction in mechanisms of spatial hearing.

Animals↗
PubMed1986

Frequency representation in auditory cortex of the common marmoset (Callithrix jacchus jacchus).

The location and characteristics of the primary auditory cortex of the common marmoset, Callithrix jacchus jacchus, were determined in five anesthetized male adult animals by mapping the responses of cortical units and unit clusters to pure tone stimuli presented to the contralateral ear. The primary auditory cortex lies largely ventral to the lateral sulcus, the only major fissure on the lateral cortex of this smooth-brained primate, but in some animals it may extend significantly down the ventral bank of this sulcus. Responses are distributed such that low best frequencies are found rostroventrally whereas high best frequencies occur caudally. The disposition of frequency-band contours is fan-shaped, with contours separating low-frequency octaves nearly parallel to the lateral sulcus and high-frequency (greater than 8 kHz) contours perpendicular to that sulcus. Best frequencies range from 0.6 to 30 kHz across the primary field, but there is a disproportionate representation of the three octaves between 2 and 16 kHz. The most sensitive thresholds (as low as -2 dB SPL) are found between 7 and 9 kHz. The primary auditory cortex is similar in cytoarchitecture to that reported for the cat, showing a blurring of lamination in the middle layers (II-IV) and a preponderance of small cells in these merged layers, giving a highly granular appearance. The accessibility of the cochlear representation on the gyral surface makes the marmoset an attractive animal for studies of primate auditory cortex.

Animals↗
PubMed1983

The termination of callosal fibres in the auditory cortex of the rat. A combined Golgi--electron microscope and degeneration study.

When the corpus callosum of the rat is sectioned, the callosal fibres in the cerebral cortex undergo degeneration. In the auditory cortex (area 41) the degenerating axon terminals form asymmetric synapses, and the vast majority of them synapse with dendritic spines. Some other synapse with the shafts of both spiny and smooth dendrites, and a few with the perikarya of non-pyramidal cells. The degenerating axon terminals are contained principally within layer II/III, in which they aggregate in patches. Using a technique in which neurons within the cortex are Golgi-impregnated, then gold-toned and examined in the electron microscope, it has been shown that the dendritic spines of pyramidal neurons with cell bodies in different layers receive the degenerating callosal afferents. The spines arise from the main apical dendritic shafts and their branches, from the dendrites of the apical tufts, and in some cases from the basal dendrites of the pyramidal neurons. The shafts of some pyramidal cell apical dendrites also form asymmetric synapses with callosal afferents. Since we have encountered no spiny non-pyramidal neurons in Golgi preparations of rat auditory cortex, and because other types of non-pyramidal cells have few dendritic spines, it is concluded that practically all of the dendritic spines synapsing with callosal afferents originate from pyramidal neurons.

Animals↗
PubMed1981

Effects of changes in cortical arousal and of auditory cortex cooling on neuronal activity in the medial geniculate body.

The activity of cells in the medial geniculate body (MGB) of adult cats was recorded during different states of cortical arousal with and without cooling of the auditory cortex. In the absence of auditory cortex cooling, the overall mean unit spontaneous discharge rate was 49% higher during desynchroized Electrocorticogram (ECoG) periods (high cortical arousal). Responses to sound were somewhat more prominent vis-à-vis the spontaneous activity during periods of high arousal. Changes in spontaneous discharge rate associated with arousal shifts were significantly reduced during auditory cortex cooling. When the ECoG changed from desynchronized to synchronized activity, MGB cells showed a change in discharge pattern, typically characterized by an increase in both high-rate bursts and long-interval pauses. These changes were duplicated for most cells by cooling of the auditory cortex. Corticofugal fiber discharge thus has an effect on MGB neuronal activity which is dependent on the level of cortical arousal. This effect is most likely a result of direct corticogeniculate activity, though indirect auditory cortex - brainstem - MGB routes may also be involved.

Animals↗