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Results for “Auditory Cortex”

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At least 19 recordsLinked to original sources
PubMed2002

Cortical spreading depression and involvement of the motor cortex, auditory cortex, and cerebellum in eyeblink classical conditioning of the rabbit.

The interrelationships of cerebellar and cerebral neural circuits in the eyeblink paradigm were explored with the controlled application of cortical spreading depression (CSD) and lidocaine in the New Zealand albino rabbit. The initial research focus was directed toward the involvement of the motor cortex in the conditioned eyeblink response. However, CSD timing and triangulation results indicate that other areas in the cerebral cortex, particularly the auditory cortex (acoustic conditioned stimulus), appear to be critical for the CSD effect on the eyeblink response. In summary: (1) CSD can be elicited, monitored, and timed and its side effects controlled in 97% of awake rabbits in the right and/or left cerebral hemisphere(s) during eyeblink conditioning. (2) The motor cortex appears to play little or no part in classical conditioning of the eyeblink in the rabbit in the delay paradigm. (3) Inactivating the auditory cortex with CSD or lidocaine temporarily impairs the conditioned response during the first 5 to 15 days of training, but has little effect past that point.

Animals↗
PubMed1997

Serial and parallel processing in rhesus monkey auditory cortex.

Auditory cortex on the exposed supratemporal plane in four anesthetized rhesus monkeys was mapped electrophysiologically with both pure-tone (PT) and broad-band complex sounds. The mapping confirmed the existence of at least three tonotopic areas. Primary auditory cortex, AI, was then aspirated, and the remainder of the cortex on the supratemporal plane was remapped. PT-responses in the caudomedial area, CM, were abolished in all animals but one, in which they were restricted to the high-frequency range. Some CM sites were still responsive to complex stimuli. In contrast to the effects on CM, no significant changes were detectable in the rostral area, R. After mapping cortex in four additional monkeys, injections were made with different tracers into matched best-frequency regions of AI, R, and CM. Injections in AI and R led to retrograde labeling of neurons in all three subdivisions of the medial geniculate (MG) nucleus (MGv, MGd, and MGm), as well as nuclei outside MG, whereas CM injections led to only sparse labeling of neurons in a restricted zone of the lateral MGd and, possibly, MGm, in addition to labeling in non-MG sites. The combined results suggest that MGv sends direct projections in parallel to areas AI and R, which drive PT-responses in both areas. PT-responses in area CM, however, appear to be driven by input relayed serially from AI. The direct input to CM from MGd and other thalamic nuclei may thus be capable of mediating responses only to broad-band sounds.

Acoustic Stimulation↗
PubMed2003

Acoustic factors govern developmental sharpening of spatial tuning in the auditory cortex.

Auditory localization relies on the detection and interpretation of acoustic cues that change in value as the head and external ears grow. Here we show that the maturation of these structures is an important determinant for the development of spatial selectivity in the ferret auditory cortex. Spatial response fields (SRFs) of high-frequency cortical neurons recorded at postnatal days (P) 33-39 were broader, and transmitted less information about stimulus direction, than in older ferrets. They also exhibited slightly broader frequency tuning than neurons recorded in adult animals. However, when infant neurons were stimulated through virtual ears of adults, SRFs sharpened significantly and the amount of transmitted information increased. This improvement was predicted by a model that generates SRF shape from the localization cue values and the neurons' binaural spectrotemporal response properties. The maturation of spatial response characteristics in auditory cortex therefore seems to be limited by peripheral rather than by central factors.

Acoustic Stimulation↗
PubMed2006

[Preliminary study on the functional localization of auditory cortex in auditory pathology patients using magnetoencephalography].

OBJECTIVE: To access the pathological changes of the functional localization of the primary auditory cortex in auditory neuropathy patients using magnetoencephalography (MEG). METHODS: The M100 waves of cortical evoked magnetic fields (AEF) evoked by 0.5, 1, 2, 4, 6, 8 kHz pure tones were measured respectively in 10 auditory neuropathy patients (20 ears) and 15 healthy young subjects (30 ears) using a whole head 306 channel magnetoencephalography (MEG) system. The auditory cortex magnetic source imaging obtained by superimposing functional MEG data on structural magnetic resonance image (MRI). RESULTS: The M100 sources were obtained in all 15 healthy young subjects in all frequency except for 8 kHz in 16 ears. But in auditory neuropathy patients, the ratio of M100 from 0.5 to 6 kHz were 27.5% (11/40), 22.5% (9/40), 7.5% (3/40), 5% (2/40), 5% (2/40) respectively and no any waves in 8 kHz. The evoked ratio of M100 in low frequency was high and that decreased gradually with increasing of evoked pure tone frequency. The M100 latentencies and amplitudes were longer and lower in patient group than that in control group (P < 0.01). CONCLUSIONS: Auditory neuropathy is an audiology disease with pathological lesions from the VIII cranial nerve to auditory cortex. MEG might become an important reference in decision making for therapies.

Adolescent↗
PubMed2005

Long-term cortical plasticity evoked by electric stimulation and acetylcholine applied to the auditory cortex.

Auditory fear conditioning with tone bursts followed by electric leg stimulation activates neurons not only in the auditory and somatosensory systems but also in many other regions of the brain and elicits shifts in the best frequencies (BFs) of collicular and cortical neurons, i.e., reorganization of the frequency (co-chleotopic) maps in the inferior colliculus and auditory cortex (AC). What are the neural elements minimally necessary for evoking long-term cortical BF shifts? We found that: (i) both electric stimulation and acetylcholine applied to the AC evoke the long-term cortical BF shift as does the conditioning; (ii) both electric stimulation of the AC and acetylcholine applied to the inferior colliculus increase the short-term collicular BF shift evoked by the cortical electric stimulation but do not change it into long-term; and (iii) as this short-term collicular BF shift is blocked by atropine, the development of the long-term cortical BF shift becomes slow and small. Therefore, the most essential neural elements for evoking the long-term cortical BF shift are the AC, corticofugal feedback and the cholinergic nucleus. Our current data support the Gao-Suga model, which hypothesizes that the small short-term cortical BF shifts are evoked by tonal stimuli without the association of conditioned and unconditioned stimuli in the multisensory thalamic nuclei and that these BF shifts are augmented and changed into the large long-term BF shifts by cholinergic neurons.

Acetylcholine↗
PubMed2003

Complexity and temporal dynamics of frequency coding in the awake rat auditory cortex.

Auditory cortical neurons are elements of a neuronal network that decomposes sounds into spectral and temporal information. In particular, their frequency selectivity has been investigated in great detail. Most studies used anaesthetized preparations and found mainly simple V-shaped tuning. The few data available from awake animals indicate that more complex forms of spectral receptive fields, i.e. frequency response areas, can be found there. We investigated frequency response areas in the awake rat primary auditory cortex using statistical evaluation and found complex forms of frequency response areas with several separate subregions in many neurons, besides classical V-shaped tuning. Response areas, as determined with narrow band noise, were very similar to those measured with pure tones. Their width was well correlated to the response strength to white noise stimulation. These results suggest that the excitatory subregions of frequency response areas were the neurons' predominant characteristic, relevant also for the processing of more complex types of stimuli. Investigating the spectrotemporal dynamics of frequency response areas revealed that approximately one-third of the neurons showed long-lasting excitatory or inhibitory components in addition to the typical ON-response. Inhibition was usually of longer duration and occurred mainly in frequency ranges outside the range of initial excitatory responses. These results indicate that auditory cortical neurons in awake animals can represent spectrotemporal information of rather different complexity.

Acoustic Stimulation↗
PubMed2005

Temporal nonlinearity during recovery from sequential inhibition by neurons in the cat primary auditory cortex.

Auditory stimuli occur most often in sequences rather than in isolation. It is therefore necessary to understand how responses to sounds occurring in sequences differ from responses to isolated sounds. Cells in primary auditory cortex (AI) respond to a large set of binaural stimuli when presented in isolation. The set of responses to such stimuli presented at one frequency comprises a level response area. A preceding binaural stimulus can reduce the size and magnitude of level response areas of AI cells. The present study focuses on the effects of the time interval between a preceding stimulus and the stimuli of a level response area in pentobarbital-anesthetized cats. After the offset of a preceding stimulus, the ability of AI cells to respond to succeeding stimuli varies dynamically in time. At short interstimulus intervals (ISI), a preceding stimulus can completely inhibit responses to succeeding stimuli. With increasing ISIs, AI cells respond first to binaural stimuli that evoke the largest responses in the control condition, i.e., not preceded by a stimulus. Recovery rate is nonlinear across the level response area; responses to these most-effective stimuli recover to 70% of control on average 187 ms before responses to other stimuli recover to 70% of their control sizes. During the tens to hundreds of milliseconds that a level response area is reduced in size and magnitude, the selectivity of AI cells is increased for stimuli that evoke the largest responses. This increased selectivity results from a temporal nonlinearity in the recovery of the level response area which protects responses to the most effective binaural stimuli. Thus in a sequence of effective stimuli, a given cell will respond selectively to only those stimuli that evoke a strong response when presented alone.

Acoustic Stimulation↗
PubMed1998

Bi-hemispheric study of single trial MEG signals of the human auditory cortex.

Auditory evoked magnetic fields were recorded from 5 human subjects, simultaneously over each hemisphere, using the BTi twin MAGNES system (2 x 37 channel). Accurate placing of each probe and the use of optimally designed linear sums of signals allow the estimation of the millisecond by millisecond history of activation of the complex of generators responsible for the M100 response in each single trial. Thus it can be shown in much greater detail than any study so far, how the average signal around the M100 period is built up by events in single trials. We found consistent features across subjects, defining a dynamic baseline from which the stimulus related activity can be differentiated. Our analysis indicates that prior to the stimulus onset the activity in each auditory cortex proceeds more or less independently. The onset of the stimulus establishes a binding of activity in the two hemispheres, probably through a common input. The coordinated activity is well described by an exponentially saturating function with a characteristic time constant in the 'magic' 15-30 ms range.

Acoustic Stimulation↗
PubMed1993

Modulation of early sensory processing in human auditory cortex during auditory selective attention.

Neuromagnetic fields were recorded from human subjects as they listened selectively to sequences of rapidly presented tones in one ear while ignoring tones of a different pitch in the opposite ear. Tones in the attended ear evoked larger magnetic brain responses than did unattended tones in the latency ranges 20-50 msec and 80-130 msec poststimulus. Source localization techniques in conjunction with magnetic resonance imaging placed the neural generators of these early attention-sensitive brain responses in auditory cortex on the supratemporal plane. These data demonstrate that focused auditory attention in humans can selectively modulate sensory processing in auditory cortex beginning as early as 20 msec poststimulus, thereby providing strong evidence for an "early selection" mechanism of auditory attention that can regulate auditory input at or before the initial stages of cortical analysis.

Acoustic Stimulation↗
PubMed1998

Role of the primary auditory cortex in auditory selective attention studied by whole-head neuromagnetometer.

In order to identify the human cortical areas involved in the auditory attention, neuromagnetic fields were recorded from 12 healthy adults with a 122-channel whole-head magnetometer while the subjects performed the auditory selective attention task. Randomized sequence of 900 Hz (P=0.9) and 950 Hz (P=0.1) tones was presented to each ear with random interstimulus intervals across ears ranging from 300 to 500 ms. Subjects were asked to pay attention to the designated ear (attended ear) and to count the number of the 950 Hz tones presented to the attended ear. Twelve sessions were performed for each subject, among which the attended ear was changed alternately in a counterbalanced order among subjects. In seven out of twelve subjects, averaged neuromagnetic fields in response to frequent tones presented to the attended ear showed attention-related deflection over the bilateral temporal areas starting at around 100 ms after the stimulus presentation. Although the dipole moment for N100m in the attended condition showed significant increase compared to that in the non-attended condition, locations of the two equivalent current dipoles in the auditory cortex were not significantly different from each other. Moreover, a simulation study supported the enhancement of N100m rather than participation of additional dipoles in the auditory selective attention task. These results suggest that the primary auditory cortex plays a main role in the auditory selective attention starting as early as 100 ms after the stimulus presentation.

Adult↗
PubMed2004

Representation of concurrent acoustic objects in primary auditory cortex.

Auditory scene analysis involves the simultaneous grouping and parsing of acoustic data into separate mental representations (i.e., objects). Over two experiments, we examined the sequence of neural processes underlying concurrent sound segregation by means of recording of human middle latency auditory evoked responses. Participants were presented with complex sounds comprising several harmonics, one of which could be mistuned such that it was not an integer multiple of the fundamental frequency. In both experiments, Na (approximately 22 ms) and Pa (approximately 32 ms) waves were reliably generated for all classes of stimuli. For stimuli with a fundamental frequency of 200 Hz, the mean Pa amplitude was significantly larger when the third harmonic was mistuned by 16% of its original value, relative to when it was tuned. The enhanced Pa amplitude was related to an increased likelihood in reporting the presence of concurrent auditory objects. Our results are consistent with a low-level stage of auditory scene analysis in which acoustic properties such as mistuning act as preattentive segregation cues that can subsequently lead to the perception of multiple auditory objects.

Adult↗
PubMed1992

Modified activity of the human auditory cortex during auditory hallucinations.

Previous reports have shown abnormalities in brain metabolism and evoked responses of schizophrenic patients with hallucinations. The authors recorded electric and magnetic auditory responses during transitory auditory hallucinations in two patients. Small but replicable response delays occurred during hallucinations. The results suggest that the effect of hallucinations on auditory cortex activity is similar to the effect of real sounds.

Acoustic Stimulation↗
PubMed1998

Observation of quantization effects in human auditory cortex.

Auditory evoked magnetic fields were recorded from five human subjects using the BTi whole head system (148 channels). The stimuli were simple tone bursts with different inter-stimulus intervals (ISI). The magnetic field was also recorded from the same subjects in place without stimulation to provide baseline 'noise' measurements. Magnetic field tomography (MFT) was applied to the average data and activation curves were computed from well circumscribed regions of interest (ROI). Objective statistical measures (Kolmogorov-Smirnov test) were then used to identify latency segments with distribution significantly different from the baseline distribution. For latency segments with significant activations the dependence of the activation strength on ISI was modeled by an exponentially saturating function. In earlier studies, the characteristic time (tau) in this function was interpreted as a measure of a memory trace for auditory tones. Our analysis identified distinct levels for tau: all subjects had the same lower two levels (0.50 s and 0.69 s). Attention modulation introduced considerably higher tau values in most subjects but it did not change the two 'ground state' tau levels. To our knowledge, this is the first demonstration of quantization effects in the macro-properties of brain activity, which were universal amongst the subjects we studied.

Acoustic Stimulation↗
PubMed1989

Auditory evoked potentials and magnetic fields in patients with lesions of the auditory cortex.

Auditory evoked potentials and magnetic fields of 40-200 ms latencies were measured from 4 patients with temporal lobe infarcts and compared with results from healthy subjects. Magnetic fields over the diseased hemisphere were abnormal in all 4; the responses were missing in 2. In one patient the responses were of abnormally high amplitude, and in one parts of the response sequence were missing. Evoked potentials were also abnormal in all 4 patients and the results were in accordance with the findings in the magnetic field measurements.

Adult↗
PubMed2005

Musical imagery: sound of silence activates auditory cortex.

Auditory imagery occurs when one mentally rehearses telephone numbers or has a song 'on the brain'--it is the subjective experience of hearing in the absence of auditory stimulation, and is useful for investigating aspects of human cognition. Here we use functional magnetic resonance imaging to identify and characterize the neural substrates that support unprompted auditory imagery and find that auditory and visual imagery seem to obey similar basic neural principles.

Acoustic Stimulation↗
PubMed2002

Disruption of primary auditory cortex by synchronous auditory inputs during a critical period.

In the primary auditory cortex (AI), the development of tone frequency selectivity and tonotopic organization is influenced by patterns of neural activity. Introduction of synchronous inputs into the auditory pathway achieved by exposing rat pups to pulsed white noise at a moderate intensity during P9-P28 resulted in a disrupted tonotopicity and degraded frequency-response selectivity for neurons in the adult AI. The latter was manifested by broader-than-normal tuning curves, multipeaks, and discontinuous, tone-evoked responses within AI-receptive fields. These effects correlated with the severe impairment of normal, developmental sharpening, and refinement of receptive fields and tonotopicity. In addition, paradoxically weaker than normal temporal correlations between the discharges of nearby AI neurons were recorded in exposed rats. In contrast, noise exposure of rats older than P30 did not cause significant change of auditory cortical maps. Thus, patterned auditory inputs appear to play a crucial role in shaping neuronal processing/decoding circuits in the primary auditory cortex during a critical period.

Age Factors↗
PubMed2006

Touch activates human auditory cortex.

Vibrotactile stimuli can facilitate hearing, both in hearing-impaired and in normally hearing people. Accordingly, the sounds of hands exploring a surface contribute to the explorer's haptic percepts. As a possible brain basis of such phenomena, functional brain imaging has identified activations specific to audiotactile interaction in secondary somatosensory cortex, auditory belt area, and posterior parietal cortex, depending on the quality and relative salience of the stimuli. We studied 13 subjects with non-invasive functional magnetic resonance imaging (fMRI) to search for auditory brain areas that would be activated by touch. Vibration bursts of 200 Hz were delivered to the subjects' fingers and palm and tactile pressure pulses to their fingertips. Noise bursts served to identify auditory cortex. Vibrotactile-auditory co-activation, addressed with minimal smoothing to obtain a conservative estimate, was found in an 85-mm3 region in the posterior auditory belt area. This co-activation could be related to facilitated hearing at the behavioral level, reflecting the analysis of sound-like temporal patterns in vibration. However, even tactile pulses (without any vibration) activated parts of the posterior auditory belt area, which therefore might subserve processing of audiotactile events that arise during dynamic contact between hands and environment.

Adult↗
PubMed1998

Subdivisions of auditory cortex and ipsilateral cortical connections of the parabelt auditory cortex in macaque monkeys.

Auditory cortex of macaque monkeys can be divided into a core of primary or primary-like areas located on the lower bank of the lateral sulcus, a surrounding narrow belt of associated fields, and a parabelt region just lateral to the belt on the superior temporal gyrus. We determined patterns of ipsilateral cortical connections of the parabelt region by placing injections of four to seven distinguishable tracers in each of five monkeys. Results were related to architectonic subdivisions of auditory cortex in brain sections cut parallel to the surface of artificially flattened cortex (four cases) or cut in the coronal plane (one case). An auditory core was clearly apparent in these sections as a 16- to 20-mm rostrocaudally elongated oval, several millimeters from the lip of the sulcus, that stained darkly for parvalbumin, myelin, and acetylcholinesterase. These features were most pronounced caudally in the cortex assigned to auditory area I, only slightly reduced in the rostral area, and most reduced in the narrower rostral extension we define as the rostrotemporal area. A narrow band of cortex surrounding the core stained more moderately for parvalbumin, acetylcholinesterase, and myelin. Two regions of the caudal belt, the caudomedial area, and the mediolateral area, stained more darkly, especially for parvalbumin. Rostromedial and medial rostrotemporal, regions of the medial belt stained more lightly for parvalbumin than the caudomedial area or the lateral belt. The parabelt region stained less darkly than the core and belt fields. Injections confined to the parabelt region labeled few neurons in the core, but large numbers in parts of the belt, the parabelt, and adjacent portions of the temporal lobe. Injections that encroached on the belt labeled large numbers of neurons in the core and helped define the width of the belt. Caudal injections in the parabelt labeled caudal portions of the belt, rostral injections labeled rostral portions, and both caudal and rostral injections labeled neurons in the rostromedial area of the medial belt. These observations support the concept of dividing the auditory cortex into core, belt, and parabelt; provide evidence for including the rostral area in the core; suggest the existence of as many as seven or eight belt fields; provide evidence for at least two subdivisions of the parabelt; and identify regions of the temporal lobe involved in auditory processing.

Animals↗