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PubMed2003

Auditory cortical neurons respond to somatosensory stimulation.

The prevailing hierarchical model of cortical sensory processing holds that early processing is specific to individual modalities and that combination of information from different modalities is deferred until higher-order stages of processing. In this paper, we present physiological evidence of multisensory convergence at an early stage of cortical auditory processing. We used multi-neuron cluster recordings, along with a limited sample of single-unit recordings, to determine whether neurons in the macaque auditory cortex respond to cutaneous stimulation. We found coextensive cutaneous and auditory responses in caudomedial auditory cortex, an area lying adjacent to A1, and at the second stage of the auditory cortical hierarchy. Somatosensory-auditory convergence in auditory cortex may underlie effects observed in human studies. Convergence of inputs from different sensory modalities at very early stages of cortical sensory processing has important implications for both our developing understanding of multisensory processing and established views of unisensory processing.

Acoustic Stimulation↗
PubMed1982

Response plasticity of single neurons in rabbit auditory association cortex during tone-signalled learning.

Single unit activity was monitored in rabbit auditory association cortex (AC) throughout the acquisition of classically conditioned, nictitating-membrane response. The CS was a tone burst at the characteristic frequency of each neuron. Rabbits which were pseudoconditioned or received conditioning trials but did not learn the response served as control groups. Significant alterations in CS-evoked firing rate were termed 'response plasticity'. Neurons in conditioned animals were more than twice as likely to show response plasticity during the 250 ms CS-US interval than neurons in control animals. Such differences were evident both in the early (0-60 ms) and late (60-250 ms) portions of the CS-US interval. Most early changes appeared at 21-40 ms after CS onset. Response plasticity was most commonly manifested as an increase or decrease in CS-evoked firing rate with little change in the response pattern (PST histogram shape). In some neurons, subcomponents of response patterns (early or late portions of the CS-US interval) were observed to change independently of each other. Spontaneous rate and UCS-evoked activity were not modified with learning. Early in training (transition trials), neural activity evoked by the tone CS in conditioned animals was not different from that in controls. Response plasticity was most pronounced after the CR was first learned (trained trials) and stabilized once the Cr was well established (overtrained trials). Recording sites of neurons showing conditioning-related response plasticity were co-extensive with those of cells that did not.

Animals↗
PubMed2004

Pyramidal cell size reduction in schizophrenia: evidence for involvement of auditory feedforward circuits.

BACKGROUND: Subjects with schizophrenia have decreased gray matter volume of auditory cortex in structural imaging studies and exhibit deficits in auditory sensory processing that might reflect impairments of feedforward and/or feedback circuits within the auditory cortex. Recently, we reported that one component of these circuits, pyramidal cells in deep layer 3 of the auditory association cortex (area 42), has reduced mean somal volume in subjects with schizophrenia. To discriminate between involvement of feedforward and feedback circuit components, we examined pyramidal cell somal volume in layer 3 of primary auditory cortex (feedforward) and layer 5 of auditory association cortex (feedback). METHODS: We estimated somal volumes of pyramidal neurons in deep layer 3 of area 41 and layer 5 of area 42 in subjects with schizophrenia (area 41, n = 16; area 42, n = 18), each of whom was matched to one normal comparison subject for gender, age, and postmortem interval. RESULTS: In deep layer 3 of area 41, mean pyramidal cell somal volume was significantly reduced, by 10.4%. No significant reduction was present in layer 5 of area 42. CONCLUSIONS: Pyramidal cell somal volume is reduced in layer 3 of area 41 and area 42, but not in layer 5 of area 42, of subjects with schizophrenia. This pattern of abnormalities is consistent with impairments of auditory feedforward projection neurons.

Adult↗
PubMed2004

Functional magnetic resonance imaging: contemporary and future use.

PURPOSE OF REVIEW: Functional magnetic resonance imaging is a relatively new neuroimaging technique that is being used in both research and clinical applications. Increasing work has been done to elucidate the auditory cortex. RECENT FINDINGS: Current studies focus on enhancing the sensitivity of functional magnetic resonance imaging in studying the auditory cortex and subcortical pathways in response to tonal stimulation, to evaluate the integrity of the auditory cortex before cochlear implantation, and as a screening tool for hearing impairment in the young child. SUMMARY: Recent work has been encouraging: silent functional magnetic resonance imaging techniques allow for better evaluation of the auditory cortex with less confounding scanner noises. Functional magnetic resonance imaging can be safely and reproducibly performed in hearing-impaired children and in the preoperative evaluation of candidates for cochlear implantation.

Adult↗
PubMed1998

[Visualization of central auditory processes with functional magnetic resonance tomography].

BACKGROUND: Central auditory processes can be visualized using functional MRI in a non-invasive manner and at high spatial resolution. Acoustic stimulation leads to an increase of blood flow of activated areas in the plane of the superior temporal gyrus. Radiologically, this may be visualized based on the long T2-relaxation time of oxyhemoglobin. PATIENTS: Ten normal-hearing subjects with ages between 28 and 38 years took part in the investigations. They received binaural, monaural right, and monaural left stimulation with pulsed sine tones of 1000 Hz at a pulse rate of 6 Hz and a sound pressure level of 100 dB SPL. Tonotopic organization of the auditory cortex was visualized using stimulation by pulsed sine tones of 500 Hz and 4000 Hz. RESULTS: Following monaural acoustic stimulation, increased activity of the contralateral auditory cortex could be demonstrated in 9 subjects. In one subject, bilateral activity was noted. Concerning the tonotopic organization of the auditory cortex, we could show that the higher frequencies were localized more medially and anteriorly; the lower frequencies were localized more laterally and posteriorly in the superior temporal gyrus. However, considerable overlap was noted. CONCLUSIONS: The overlap of the different frequencies could explain the controversial discussion of the tonotopic organization of the auditory cortex. The results of the monaural acoustic stimulation show clearly the predominant signal increase of contralateral areas in the primary auditory cortex. These results confirm the opinion of the current textbooks that the fiber of the auditory pathways mostly cross. Further investigations using functional MRI are necessary for better understanding of physiological and pathophysiological central-auditory processes.

Acoustic Stimulation↗
PubMed1986

Neuroanatomy, neurophysiology, and central auditory assessment. Part II: The cerebrum.

In this second article of a three-part series, the auditory areas of the cerebrum are defined. Anatomical descriptions of various structures within the auditory areas of the brain as well as an overview of selected electrophysiological research on auditory cortex are presented. Ablation studies involving auditory cortex and principal aspects of the vascular neuroanatomy are also reviewed. Finally, extensive clinical findings are presented from a case with damage to the cerebral auditory areas.

Animals↗
PubMed2005

A model for the mechanism of generating the auditory evoked field.

The auditory evoked potentials and fields, recorded with electro- and magneto-encephalography, respectively, have the prominent peak at the latency of about 100 ms, named N100(m). The mechanism for generating the peak is not yet fully elucidated, however. Firstly, this study reviewed empirical results on the mechanism that had been previously published by the same author. The results showed that phases of the ongoing oscillations at around 6 Hz above the auditory cortex are locked with respect to onsets of the auditory stimuli during the period of N100 m, and also that powers of the oscillations are increased during the same period. Taking into account these results as well as another evidence that the peak arises from multiple sources within the auditory cortex, a model for the mechanism of generating the auditory N100 m was proposed. The model assumed several oscillators in the auditory cortex, whose phases were locked during the period of N100 m, but not locked at other periods. Computer simulation validated the model. The model could represent a starting point for further experiment and simulation.

Acoustic Stimulation↗
PubMed2003

Corticofugal modulation on both ON and OFF responses in the nonlemniscal auditory thalamus of the guinea pig.

Corticofugal modulation on both ON and OFF responses in various nuclei in the medial geniculate body (MGB) was examined by locally activating the auditory cortex and looking for effects on the neuronal responses to acoustic stimuli. In contrast with a major corticofugal facilitatory effect on the ON neurons in the lemniscal nucleus of the MGB of the guinea pigs, of 132 ON neurons tested in three conditions with cortical activation through each of three implanted electrodes, the majority of the tested conditions (319/396) that were sampled from the nonlemniscal nuclei of the MGB received inhibitory modulation from the activated cortex. This inhibitory effect was >50% for 99 cases while the auditory cortex was activated. Most of the OFF and ON-OFF MGB neurons (44/54) showed a facilitatory effect of 111.4 +/- 99.9%, and three showed a small inhibitory effect of 25.7 +/- 5.8% on their OFF responses. Thirty neurons in the border region between the lemniscal and nonlemniscal MGB showed mainly facilitatory corticofugal effects on both ON and OFF responses. Meanwhile, cortical stimulation induced almost exclusive inhibitory effects on the ON response and facilitatory effects on the OFF response in the MGcm. It is suggested that the OFF response is produced as a disinhibition from the inhibitory input of the auditory stimulus. The present results provide a possible explanation for selective gating of the auditory information through the lemniscal MGB while switching off other unwanted sensory signals and the interference from the limbic system, leaving the other auditory cortex prepared to process only the auditory signal.

Animals↗
PubMed1998

Parvalbumin is expressed in a reciprocal circuit linking the medial geniculate body and auditory neocortex in the rabbit.

Recent studies of the rabbit auditory forebrain have shown that antibodies directed against the calcium-binding protein parvalbumin (PV) specifically demarcate auditory neocortex and the ventral division of the medial geniculate body (MGV). The auditory cortex is characterized by two PV- immunoreactive bands: dense terminal-like labeling within layer III/IV and a prominent band of PV+ somata in the upper half of layer VI. In some cases, there are distinct patches of PV immunoreactivity within layers III/IV of auditory cortex that appear similar to the patchy termination of thalamocortical axons labeled by the injection of anterograde tracers into MGV. The presence of PV+ patches in III/IV, PV+ somata in layer VI, and the high density of PV+ neurons and terminals in the MGV suggest the existence of a reciprocal PV+ circuit linking primary auditory cortex (AI) and the MGV. In the present study, double-labeling experiments in adult rabbits were carried out to provide evidence for this circuit. Focal injections of the tracers biocytin or biotinylated dextran amine (BDA) into the MGV labeled thalamocortical afferent patches within layer III/IV and retrogradely labeled corticothalamic neurons in layer VIa of the ipsilateral auditory cortex. Adjacent sections stained with antibodies against PV revealed terminal-like PV-immunoreactive patches in III/IV and PV+ somata in VIa that were in register with those labeled by BDA injections into the MGV. Serial section reconstruction of BDA-labeled corticothalamic neurons in VIa revealed pyramidal cells with tangentially oriented basal dendrites and sparsely branched apical dendrites that ascended to layer I. Fluorescent double-labeling studies demonstrated that a subpopulation of corticothalamic neurons also express PV. PV-negative corticothalamic neurons were also found. Discrete injections of BDA into auditory cortex labeled bands of neurons in the ipsilateral MGV, whose orientation paralleled the fibrodendritic laminae characteristic of this subdivision. Retrograde double-labeling experiments showed that most MGV relay neurons also express PV. Small numbers of PV-negative relay neurons were also found. These studies provide evidence for the existence of multiple, chemically coded pathways linking primary auditory cortex and the MGV.

Animals↗
PubMedDate not supplied

Hearing loss of a central type secondary to anoxic anoxia.

The effect of anoxic anoxia on the threshold sensitivity and amplitude of the responses from the auditory cortex, inferior colliculus and cochlea to acoustic stimuli in guinea pigs was studied. Decay of the amplitude of the responses from the auditory cortex and the inferior colliculus occurs faster and is more severe than that of the cochlea. Recovery of the amplitude of the responses is slower at the auditory cortex and the inferior colliculus than at the cochlea. Loss of auditory threshold sensitivity in anoxic anoxia is most prominent at the auditory cortex. The loss of sensitivity at the inferior colliculus is the next most severe. The loss of sensitivity at the cochlea is negligible. The relative vulnerability of the central auditory pathway to anoxic anoxia as compared to the end organ is demonstrated.

Animals↗
PubMed1996

Human middle latency auditory evoked magnetic fields.

The magnetic equivalents of SN10, Po, Na, Pa, Nb and Pb (SN10m, Pom, Nam, Pam, Nbm, and Pbm) in short and middle latency auditory evoked potentials were measured with a 7-channel DC superconducting quantum interference device (SQUID). The sources of Pom, Nam, Pam, Nbm and Pbm responses were estimated to be located in the auditory cortex, while the source of SN10m was considered to be in a deeper part of the brain. In addition, the source of Pam was estimated to be in the vicinity of the moving N100m source. The source of Pbm was considered to be in a separate area, anterior to the source of Pam and N100m, which suggested that source of Pam was located in the primary auditory cortex, while the source of Pbm was located in the secondary auditory cortex. The source of N100m was considered to spread from the primary auditory cortex to the secondary auditory cortex.

Adult↗
PubMed2004

Phase shift detection in thalamocortical oscillations using magnetoencephalography in humans.

Magnetoencephalography was used to investigate exogenously stimulated oscillatory activity between cortex and thalamus resulting from clicks presented binaurally at the rate of 40 Hz. Analysis of the responses demonstrated activation of left and right auditory cortex, medial parietal cortex, thalamus, and cerebellum. Cross-correlations of the source waveforms revealed synchronicity between the auditory cortex sources (r > 0.9), auditory cortex and thalamic sources (r > 0.7), and thalamic and parietal sources (r > 0.7). The 40 Hz response in auditory cortex occurred 6 ms after thalamic activation. Supporting earlier findings, the results demonstrate the networks involved in the maintenance of 40 Hz auditory steady-state response and will prove useful for the interrogation of dysfunction in disorders demonstrating thalamocortical dysrhythmia, such as schizophrenia, Parkinson's disease, and depression.

Acoustic Stimulation↗
PubMed1975

Role of neocortex in binsural hearing in the cat. I. Contralateral masking.

Cats with earphones were trained with a shock avoidance procedure to detect the occurrence of 1 kHz tone pulses at one ear while continuous noise pulses were simultaneously presented to the opposite ear. For normal cats the presence of the noise produced a mean increase of 5.4 dB in the thresholds for detection of tones at the opposite ears. After large unilateral auditory cortex ablations the same cats exhibited an asymmetry between the ears in the size of the contralateral masking effect. There was a mean increase of 10.9 dB in the detection thresholds for tones at the ear contralateral to the damaged hemisphere when noise was presented to the ear opposite the intact hemisphere. Noise of the same physical intensity when presented to the ear contralateral to the damaged cortex produced no significant changes from the preoperative masking levels. Subsequent ablation of the auditory cortex of the opposite hemisphere resulted in a cancellation of the unilateral lesion effect; the cats exhibited interaurally symmetrical masking levels of the same magnitude as those observed prior to the first operation. Additional control tests indicate that the unilateral lesion effect is a central nervous system phenomenon and is specific to lesions of auditory cortex.

Animals↗
PubMedDate not supplied

Relationships between human auditory cortical structure and function.

The human auditory cortex comprises multiple areas, largely distributed across the supratemporal plane, but the precise number and configuration of auditory areas and their functional significance have not yet been clearly established. In this paper, we discuss recent research concerning architectonic and functional organisation within the human auditory cortex, as well as architectonic and neurophysiological studies in non-human species, which can provide a broad conceptual framework for interpreting functional specialisation in humans. We review the pattern in human auditory cortex of the functional responses to various acoustic cues, such as frequency, pitch, sound level, temporal variation, motion and spatial location, and we discuss their correspondence to what is known about the organisation of the auditory cortex in other primates. There is some neuroimaging evidence of multiple tonotopically organised fields in humans and of functional specialisations of the fields in the processing of different sound features. It is thought that the primary area, on Heschl's gyrus, may have a larger involvement in processing basic sound features, such as frequency and level, and that posterior non-primary areas on the planum temporale may play a larger role in processing more spectrotemporally complex sounds. Ways in which current knowledge of auditory cortical organisation and different data analysis approaches may benefit future functional neuroimaging studies which seek to link auditory cortical structure and function are discussed.

Animals↗
PubMed2004

Enhancement of steady-state auditory evoked magnetic fields in tinnitus.

The steady-state auditory evoked magnetic field and the Pbm, the magnetic counterpart of the second frontocentrally positive middle latency component of the transitory auditory evoked potential, were measured in ten tinnitus patients using a 122-channel gradiometer system. The patients had varying degrees of hearing loss. In all patients, the tinnitus frequency was located above the frequency of the audiometric edge, i.e. the location on the frequency axis above which hearing loss increases more rapidly. Stimuli were amplitude-modulated sinusoids with carrier frequencies at the tinnitus frequency, the audiometric edge, two frequencies below the audiometric edge, and two frequencies between the audiometric edge and the tinnitus frequency. Below the audiometric edge, the root-mean-square field amplitude of the steady-state response computed across the whole head as well as the contralateral and the ipsilateral dipole moment decreased as a function of carrier frequency. With carrier frequency above the audiometric edge, the steady-state response increased again. The amplitudes of the transitory Pbm component were patterned in a qualitatively similar way, but without the differences being significant. For the steady-state response, both whole-head root-mean-square field amplitude and the dipole moment of the sources at the tinnitus frequency showed significant positive correlations with subjective ratings of tinnitus intensity and intrusiveness. These correlations remained significant when the influence of hearing loss was partialled out. The observed steady-state response amplitude pattern likely reflects an enhanced state of excitability of the frequency region in primary auditory cortex above the audiometric edge. The relationship of tinnitus to auditory cortex hyperexcitability and its independence of hearing loss is discussed with reference to loss of surround inhibition in and map reorganization of primary auditory cortex.

Acoustic Stimulation↗
PubMed2005

Scanning silence: mental imagery of complex sounds.

In this functional magnetic resonance imaging (fMRI) study, we investigated the neural basis of mental auditory imagery of familiar complex sounds that did not contain language or music. In the first condition (perception), the subjects watched familiar scenes and listened to the corresponding sounds that were presented simultaneously. In the second condition (imagery), the same scenes were presented silently and the subjects had to mentally imagine the appropriate sounds. During the third condition (control), the participants watched a scrambled version of the scenes without sound. To overcome the disadvantages of the stray acoustic scanner noise in auditory fMRI experiments, we applied sparse temporal sampling technique with five functional clusters that were acquired at the end of each movie presentation. Compared to the control condition, we found bilateral activations in the primary and secondary auditory cortices (including Heschl's gyrus and planum temporale) during perception of complex sounds. In contrast, the imagery condition elicited bilateral hemodynamic responses only in the secondary auditory cortex (including the planum temporale). No significant activity was observed in the primary auditory cortex. The results show that imagery and perception of complex sounds that do not contain language or music rely on overlapping neural correlates of the secondary but not primary auditory cortex.

Acoustic Stimulation↗
PubMed2004

Adaptation of neuromagnetic N1 responses to phonetic stimuli by visual speech in humans.

The technique of 306-channel magnetoencephalogaphy (MEG) was used in eight healthy volunteers to test whether silent lip-reading modulates auditory-cortex processing of phonetic sounds. Auditory test stimuli (either Finnish vowel /ae/ or /ø/) were preceded by a 500 ms lag by either another auditory stimulus (/ae/, /ø/ or the second-formant midpoint between /ae/ and /ø/), or silent movie of a person articulating /ae/ or /ø/. Compared with N1 responses to auditory /ae/ and /ø/ when presented without a preceding stimulus, the amplitudes of left-hemisphere N1 responses to the test stimuli were significantly suppressed both when preceded by auditory and visual stimuli, this effect being significantly stronger with preceding auditory stimuli. This suggests that seeing articulatory gestures of a speaker influences auditory speech perception by modulating the responsiveness of auditory-cortex neurons.

Acoustic Stimulation↗
PubMed1976

Effect of auditory neocortex ablation on identification of click rates in cats.

Six experimental and 3 unoperated cats were trained with a go, no-go shock avoidance procedure to discriminate increases from decreases in the rate of presentation of all auditory cortex between the suprasylvian sulcus and rhinal fissure while 3 cats had bilateral auditory cortex lesions plus ablation of the cortex of the anterior lateral and anterior and middle suprasylvian gyri. A sixth 'naive' experimental cat received the present tests only after recovery from a bilateral auditory cortex ablation. After bilateral lesions, 5 of the experimental cats unexpectedly made no errors on no-go trials during retraining. This contrasts with their preoperative performance, as well as the performance of the 3 unoperated and the 'naive' operated cat, in which training was required for the successful discrimination of the two types of trials. This suggests that the neocortex may be more critical for mediating active 'go' responses to auditory stimuli than in preserving a memory for the difference between go and no-go stimuli. Further testing revealed that the thresholds of the operated cats did not differ from normal cats. All cats discriminated rates of 4/sec versus 6/sec clicks both with and without a neutral 5/sec background at levels significantly above chance.

Acoustic Stimulation↗