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PubMed1970

Studies on cholinergic transmission in the medial geniculate nucleus.

1. Studies were made on the effects of iontophoretically and intravenously administered cholinergic antagonists on the synaptic responses of medial geniculate (MG) neurones evoked by stimulation of the auditory cortex, inferior colliculus and mesencephalic reticular formation.2. Atropine specifically blocked a proportion of the excitatory responses evoked by stimulating the auditory cortex, inferior colliculus and reticular formation, although it was without effect on some of them.3. Neostigmine and eserine facilitated some excitatory synaptic responses evoked by inferior collicular stimulation.4. It is suggested that the feline MG nucleus receives excitatory cholinergic, as well as non-cholinergic, pathways from the auditory cortex, inferior colliculus and lower brain stem. The cholinergic pathways from the auditory cortex may be either corticofugal fibres or recurrent axon collaterals of afferent projections from the MG nucleus to the cortex. Those from the lower brain stem are possibly the cholinesterase-containing fibres described by Shute & Lewis (1967).

Animals↗
PubMed2005

Corticofugal feedback for collicular plasticity evoked by electric stimulation of the inferior colliculus.

Focal electric stimulation of the auditory cortex, 30-min repetitive acoustic stimulation, and auditory fear conditioning each evoke shifts of the frequency-tuning curves [hereafter, best frequency (BF) shifts] of cortical and collicular neurons. The short-term collicular BF shift is produced by the corticofugal system and primarily depends on the relationship in BF between a recorded collicular and a stimulated cortical neuron or between the BF of a recorded collicular neuron and the frequency of an acoustic stimulus. However, it has been unknown whether focal electric stimulation of the inferior colliculus evokes the collicular BF shift and whether the collicular BF shift, if evoked, depends on corticofugal feedback. In our present research with the awake big brown bat, we found that focal electric stimulation of collicular neurons evoked the BF shifts of collicular neurons located near the stimulated ones; that there were two types of BF shifts: centripetal and centrifugal BF shifts, i.e., shifts toward and shifts away from the BF of stimulated neurons, respectively; and that the development of these collicular BF shifts was blocked by inactivation of the auditory cortex. Our data indicate that the collicular BF shifts (plasticity) evoked by collicular electric stimulation depended on corticofugal feedback. It should be noted that collicular BF shifts also depend on acetylcholine because it has been demonstrated that atropine (an antagonist of muscarinic acetylcholine receptors) applied to the IC blocks the development of collicular BF shifts.

Acoustic Stimulation↗
PubMed2005

Hemispheric asymmetry for spectral and temporal processing in the human antero-lateral auditory belt cortex.

The present study investigates the acoustic basis of the hemispheric asymmetry for the processing of speech and music. Experiments on this question ideally involve stimuli that are perceptually unrelated to speech and music, but contain acoustic characteristics of both. Stimuli in previous studies were derived from speech samples or tonal sequences. Here we introduce a new class of noise-like sound stimuli with no resemblance of speech or music that permit independent parametric variation of spectral and temporal acoustic complexity. Using these stimuli in a functional MRI experiment, we test the hypothesis of a hemispheric asymmetry for the processing of spectral and temporal sound structure by seeking cortical areas in which the blood oxygen level dependent (BOLD) signal covaries with the number of simultaneous spectral components (spectral complexity) or the temporal modulation rate (temporal complexity) of the stimuli. BOLD-responses from the left and right Heschl's gyrus (HG) and part of the right superior temporal gyrus covaried with the spectral parameter, whereas covariation analysis for the temporal parameter highlighted an area on the left superior temporal gyrus. The portion of superior temporal gyrus in which asymmetrical responses are apparent corresponds to the antero-lateral auditory belt cortex, which has been implicated with spectral integration in animal studies. Our results support a similar function of the anterior auditory belt in humans. The findings indicate that asymmetrical processing of complex sounds in the cerebral hemispheres does not depend on semantic, but rather on acoustic stimulus characteristics.

Acoustic Stimulation↗
PubMed1999

Frequency organization and responses to complex sounds in the medial geniculate body of the mustached bat.

The auditory cortex of the mustached bat (Pteronotus parnellii) displays some of the most highly developed physiological and organizational features described in mammalian auditory cortex. This study examines response properties and organization in the medial geniculate body (MGB) that may contribute to these features of auditory cortex. About 25% of 427 auditory responses had simple frequency tuning with single excitatory tuning curves. The remainder displayed more complex frequency tuning using two-tone or noise stimuli. Most of these were combination-sensitive, responsive to combinations of different frequency bands within sonar or social vocalizations. They included FM-FM neurons, responsive to different harmonic elements of the frequency modulated (FM) sweep in the sonar signal, and H1-CF neurons, responsive to combinations of the bat's first sonar harmonic (H1) and a higher harmonic of the constant frequency (CF) sonar signal. Most combination-sensitive neurons (86%) showed facilitatory interactions. Neurons tuned to frequencies outside the biosonar range also displayed combination-sensitive responses, perhaps related to analyses of social vocalizations. Complex spectral responses were distributed throughout dorsal and ventral divisions of the MGB, forming a major feature of this bat's analysis of complex sounds. The auditory sector of the thalamic reticular nucleus also was dominated by complex spectral responses to sounds. The ventral division was organized tonotopically, based on best frequencies of singly tuned neurons and higher best frequencies of combination-sensitive neurons. Best frequencies were lowest ventrolaterally, increasing dorsally and then ventromedially. However, representations of frequencies associated with higher harmonics of the FM sonar signal were reduced greatly. Frequency organization in the dorsal division was not tonotopic; within the middle one-third of MGB, combination-sensitive responses to second and third harmonic CF sonar signals (60-63 and 90-94 kHz) occurred in adjacent regions. In the rostral one-third, combination-sensitive responses to second, third, and fourth harmonic FM frequency bands predominated. These FM-FM neurons, thought to be selective for delay between an emitted pulse and echo, showed some organization of delay selectivity. The organization of frequency sensitivity in the MGB suggests a major rewiring of the output of the central nucleus of the inferior colliculus, by which collicular neurons tuned to the bat's FM sonar signals mostly project to the dorsal, not the ventral, division. Because physiological differences between collicular and MGB neurons are minor, a major role of the tecto-thalamic projection in the mustached bat may be the reorganization of responses to provide for cortical representations of sonar target features.

Animals↗
PubMed1978

[Auditory response at the posterior part of the first temporal convolution (author's transl)].

Among the epileptic patients investigated by the stereotactic E. E. G. (Talairach) whose electrodes were introduced at or around the auditory cortex (Area 41, 42), the topography of the auditory responses by the electrical bipolar stimulation and that of the auditory evoked potential by the bilateral click sound stimulation were studied in relation to the ac--pc line (Talairach). The positive points of auditory responses and those of evoked potential were found in the posterior part of the first temporal convolution at or around the Hesch's transverse gyrus. The contralateral auditory responses to the stimulating electrodes situated more anterior and superior than the homolateral responses in lateral projection and more medial in frontal projection. The points of the sensation of "elevation" or "fall" elicited by the electrical stimulation which were thought to be related to the vestibular function were scattered more superior and posterior than the points of the auditory responses in lateral projection and more medial in frontal projection. This study gave the accurate topography concerning the auditory responses, the positive auditory evoked potentials and the vestibular function related sensation (sensation of "elevation" or "fall"). Further study will be required to elucidate the functional anatomy of the human auditory cortex.

Adolescent↗
PubMed1977

The effect of superior temporal lesions on the recognition of species-specific calls in the squirrel monkey.

Eleven squirrel monkeys (Saimiri sciureus) were trained to discriminate species-specific calls from non-species-specific complex sounds in a go, no-go procedure with social contact as positive reinforcement. The task required that the animals not only responded to a particular call but that this response should be generalized to any squirrel monkey call, whether or not it had been presented previously in training. After having reached a performance level of 75% correct responses in three consecutive sessions, seven animals received bilateral lesions of the auditory cortex; the other four animals served as controls. It was found that small lesions within the superior temporal gyrus did not interfere with the discrimination task. Lesions destroying about three quarters of the auditory cortex led to loss of retention; during retraining the animals did not reach criterion, but performed significantly above chance. These animals were able, however, to master a simplified version of the task where one species-specific call had to be discriminated from one non-species-specific sound. Animals with almost total ablation of the auditory cortex were capable of mastering neither the generalized task nor the simplified version. From these results, together with those of the literature, it is concluded 1) that recognition of complex sounds is not possible after complete auditory cortex ablation, probably because of interference with gestalt-formation processing, and 2) that species-specific calls are processed in the auditory system in the same way as other complex sounds.

Agnosia↗
PubMed2003

Stimulus complexity enhances auditory discrimination in patients with extremely severe brain injuries.

There is controversy as to what extent the processing of spectrally rich sounds in the human auditory cortex is related to the processing of singular frequencies. An informative index of the function of the auditory cortex, particularly important in neurological patients, is the mismatch negativity (MMN), a component of auditory event-related potentials. In the present study the MMN was recorded in 79 patients with extremely severe diffuse brain injuries, most of them in persistent vegetative state or minimal consciousness state. Both sinusoidal ('pure') and complex musical tones were used. Different statistical approaches converged in that musical tones elicited an MMN significantly more frequently, and of a larger amplitude, than simple sine tones. This implies that using simple stimuli in clinical populations may lead to a severe underestimation of the functional state of a patient's auditory system. The findings are also in line with behavioral and physiological data indicating independent processing of complex sounds in the auditory cortex.

Acoustic Stimulation↗
PubMed2005

Perinatal anoxia degrades auditory system function in rats.

Little is known about the neural bases of the reduced auditory and cortical processing speeds that have been recorded in language-impaired, autistic, schizophrenic, and other disabled human populations. Although there is strong evidence for genetic contributions to etiologies, epigenetic factors such as perinatal anoxia (PA) have been argued to be contributors, or causal, in a significant proportion of cases. In this article, we explored the consequences of PA on this elementary aspect of auditory behavior and on auditory system function in rats that were briefly perinatally anoxic. PA rats had increased acoustic thresholds and reduced processing efficiencies recorded in an auditory behavioral task. These rats had modestly increased interpeak intervals in their auditory brainstem responses, and substantially longer latencies in poststimulus time histogram responses recorded in the primary auditory cortex. The latter were associated with degraded primary auditory cortex receptive fields and a disrupted tonotopy. These processing deficits are consistent with the parallel behavioral and physiological deficits recorded in children and adults with a history of language-learning impairment and autism.

Acoustic Stimulation↗
PubMed1987

Effects of signal probability on sensory evoked potentials in cats.

The present experiment was designed to follow the evoked potential (EP) changes recorded from the association cortex and A II area of the auditory cortex and from the vertex of the freely moving cat. The EPs elicited by clicks of different probabilities used as warning stimuli during aversive conditioning were analyzed. It was found that the EPs recorded from the auditory cortex and the vertex showed different changes during the aversive conditioning to the rare clicks of 3 and 10% probabilities. The N50 and P100 components of the auditory cortical (A II area) EPs increased significantly at both signal probabilities. On the vetex and association cortical EPs, elicited by the rare signals, a broadly distributed positivity, the P250 wave could be detected. The amplitude increase of the P250 was inversely proportional to the used probability of the signal.

Acoustic Stimulation↗
PubMed1987

Generators of middle- and long-latency auditory evoked potentials: implications from studies of patients with bitemporal lesions.

We recorded middle- and long-latency auditory evoked potentials (AEPs) in 5 patients (ages 39-72 years) with bilateral lesions of the superior temporal plane. Reconstructions of CT sections revealed that primary auditory cortex had been damaged bilaterally in four of the patients, while in the fifth an extensive left hemisphere lesion included primary auditory cortex while a right hemisphere lesion had damaged anterior auditory association areas but spared primary auditory cortex. Normal middle-latency AEPs (MAEPs) were recorded at the vertex electrode in all of the patients. In 3 of the 5 patients, MAEPs also showed normal coronal scalp distributions and were comparable in amplitude following stimulation of either ear. Two patients showed abnormalities. In one case, Na (latency 17 msec)-Pa (latency 30 msec) amplitudes were reduced over both hemispheres following stimulation of the ear contralateral to the more extensive lesion. In another, with both subcortical and cortical involvement, the Pa was abolished over the hemisphere with the more extensive lesion. Long-latency AEPs were normal in 2 patients whose lesions were largely confined to the superior temporal plane. In 2 patients with lesions extending into the inferior parietal lobe, N1s were abolished bilaterally. In the fifth patient, the N1 showed a slight reduction over the hemisphere with the more extensive lesion. Middle- and long-latency AEPs were differentially affected by some lesions. For example, patients with absent N1s could produce normal Pas. A review of these results and those of previous studies of bitemporal patients suggests that abnormalities in middle- and long-latency AEPs do not necessarily reflect damage to primary auditory cortex per se, but rather the degree of damage to adjacent areas. Abnormalities in MAEPs are associated with subcortical lesions, or cortical lesions extensive enough to denervate thalamic projection nuclei. Abnormalities in the long-latency N1 reflect lesion extension into the multi-modal areas of the inferior parietal lobule. This area appears to exert a critical modulatory influence over N1 generators outside of the superior temporal plane.

Adult↗
PubMed1987

Ectosylvian visual area of the cat: location, retinotopic organization, and connections.

We have mapped out the ectosylvian visual area (EVA) of the cat in a series of single- and multiunit recording studies. EVA occupies 10-20 mm2 of cortex at the posterior end of the horizontal limb of the anterior ectosylvian sulcus. EVA borders on somatosensory cortex anteriorly, auditory cortex posteriorly, and nonresponsive cortex laterally. EVA exhibits limited retinotopic organization, as indicated by the fact that receptive fields shift gradually with tangential travel of the microelectrode through cortex. However, a point-to-point representation of the complete visual hemifield is not present. We have characterized the afferent and efferent connections of EVA by placing retrograde and anterograde tracer deposits in EVA and in other cortical visual areas. The strongest transcortical fiber projection to EVA arises in the lateral suprasylvian visual areas. Area 20, the granular insula, and perirhinal cortex provide additional sparse afferents. The projection from lateral suprasylvian cortex to EVA arises predominantly in layer 3 and terminates in layer 4. EVA projects reciprocally to all cortical areas from which it receives input. The projection from EVA to the lateral suprasylvian areas arises predominantly in layers 5 and 6 and terminates in layer 1. EVA is linked reciprocally to a thalamic zone encompassing the lateromedial-suprageniculate complex and the adjacent medial subdivision of the latero-posterior nucleus. We conclude that EVA is an exclusively visual area confined to the anterior ectosylvian sulcus and bounded by nonvisual cortex. EVA is distinguished from other visual areas by its physical isolation from those areas, by its lack of consistent global retinotopic organization, and by its placement at the end of a chain of areas through which information flows outward from the primary visual cortex.

Animals↗
PubMed1990

Convergence of cortical and cerebellar projections on single basilar pontine neurons: a light and electron microscopic study in the rat.

A protocol that involved a combination of two orthogradely transported tracer substances, wheat agglutinin-horseradish peroxidase and Phaseolus vulgaris leucoagglutinin injected at separate locations in the same animal was utilized to investigate the possible congruence of axonal projection fields formed by the cerebral cortical and cerebellar afferents to the basilar pontine nuclei. When large placements of tracer material were made in the cerebellar nuclei to label the cerebellopontine projections and a second tracer was injected in one of several cerebral cortical areas to visualize certain corticopontine projections, it was noted that axon terminal zones of the cortical and cerebellar systems occupied greater or lesser amounts of the same basilar pontine territory depending on the location of the cerebral cortical injection. Cerebellopontine terminal fields exhibited their greatest congruency with projections from the motor cortex containing the representation for facial musculature and with projections from the forelimb sensorimotor cortex. A lesser degree of overlap was observed when cerebellar projection zones were visualized in combination with basilar pontine projections from sensory face cortex, hindlimb sensorimotor cortex, visual cortex and auditory cortex. In addition, it was apparent that portions of the cerebellopontine and corticopontine terminal fields did not overlap at all. A related series of electron microscopic experiments was undertaken to establish that within the zones of overlapping cerebellar and cortical projections, there was in fact a convergence of the two afferent systems on single basilar pontine neurons. Boutons of the corticopontine system were labeled by the orthograde transport of wheat germ agglutinin horseradish peroxidase injected into the sensorimotor cortex while cerebellopontine terminals were marked for electron microscopic identification in the same animal by transecting the brachium conjunctivum and allowing sufficient time for boutons in the pontine nuclei to exhibit degeneration. Although the number of definitive examples of convergence was small, nonetheless it was possible to observe single basilar pontine neuron dendrites receiving synaptic contacts from both the cortical and cerebellar afferents systems. Taken together these observations indicate that some basilar pontine neurons receive a dual or convergent input from the cerebral cortex and cerebellar nuclei. It is difficult to estimate the prevalence of such convergence since cortical and cerebellar inputs typically contact distal and proximal pontine neuron dendrites, respectively, thus limiting the chances that both types of boutons can be observed in contact with a single basilar pontine neuron dendrite.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1999

Thalamocortical development of parvalbumin neurons in normal and periventricular leukomalacia brains.

To clarify disturbances in higher brain functions including cognition and learning disorders in preterm-born children, we investigated the functional development of the cerebral hemisphere, using parvalbumin (PA) immunohistochemistry in human subjects aged from 21 GW to 11 years of age. PA-immunoreactive neurons first appeared in the RNT at 24 GW, spread to the globus pallidus, and then to the VPoL and VPoM. At 38 GW, PA-immunoreactive neurons first appeared in layer 4 of the primary somatosensory cortex and auditory cortex, and comprised a dense band in layers 4 to 5 at 1 month of age. The developmental changes and course of PA expression in the early developmental stage corresponded to development of the thalamocortical connection and then to the functional development of cortical neurons. In preterm cases, PA expression was decreased in the cerebral cortices that corresponded to widespread or diffuse type PVL, but was increased in those with focal type PVL. These results indicate that accelerated expression of PA was induced by extra-uterine stimuli and a reduction of PA reflects the impairment of thalamocortical neurons.

Brain↗
PubMed2000

[Contribution of cochlear nucleus to 80Hz amplitude-modulation following response].

The steady-state response (SSR) evoked by a sinusoidally amplitude-modulated (SAM) tone is known as an amplitude-modulation following response (AMFR). The amplitude of the SSR which is elicited using clicks or tone bursts at a stimulus rate of 40 Hz, decreases during sleep. The same trend is also observed for AMFR at a modulation rate of 40 Hz. Thus it was difficult to analyzing SSR and AMFR is therefore difficult in young children, since objective audiometry just be performed while the child is asleep. Recent reports, however, have announced that the AMFR can be clearly detected at higher MFs (modulation frequencies), especially at frequencies between 80 and 100 Hz. This finding has proven useful in objective audiometry for young children. Recent reports have also suggested that AMFRs arise from multiple sources, including the auditory cortex and auditory nuclei in the brainstem. However, the exact sources of AMFRs have not been clarified. The purpose of this study is to clarify the contribution of the cochlear nucleus in evoking AMFRs at a modulation frequency of 80 Hz. The near-field potentials elicited with a SAM tone were recorded from the ipsilateral cochlear nucleus and its vicinity in cats. The near-field potential recorded by bipolar electrodes consisted of two different components: a low frequency component similar to the stimulus envelope (modulation), and a high frequency component similar to the actual stimulus tone. A sequence of field potentials was recorded using monopolar electrodes located at different sites within the cochlear nucleus and in its vicinity and on the surface of the cerebellum to confirm that near-field potentials elicited by SAM tones at a MF of 80 Hz in the cochlear nucleus can be recorded at the surface of the cerebellum or at other brain sites. The phase of the 80 Hz frequency component of the potentials elicited by a SAM tone at a MF of 80 Hz was then analyzed using a fast Fourier transformation. A contour map was produced using the means of the Fourier component phases corresponding to the 80 Hz response. The contour lines showed a rapid change in the phases recorded near the cochlear nucleus. These findings suggest that the cochlear nucleus contributes to the generation of scalp recorded AMFR at a MF of 80 Hz.

Acoustic Stimulation↗
PubMed1976

[Study of various morphological structures of human cerebral cortex by application on the information theory].

The investigation was undertaken to determine the quantitative estimation of the degree of vertical organization of the III layer pyramidal neurons of areas 41, 22, 17 and 18 of the human cortex auditory and visual analyzers by information methods. A brief description of the used methods of getting the evaluation (the index of organization -- Org) has been given. It has been shown that the suggested estimation in invariant with regard to the individual changes of the human brain parameters. It has been established that the projection-associative areas of the analyzers have a higher index of organization than projection areas. In making the interanalyzor comparison the index of organization of the visual areas has been found to be higher than that of the auditory areas.

Adult↗
PubMed2005

Cross-modal plasticity in deaf subjects dependent on the extent of hearing loss.

Cross-modal plasticity in deaf subjects is still discussed controversial. We tried to figure out whether the plasticity is dependent on the extent of hearing loss. Three groups of volunteers, comprising twelve individuals each, were investigated. They were characterized by three distinctive features, one had normal hearing, the other one lost hearing and the third had only minimal residual hearing ability. All participants, except those of group one, were capable of using German Sign Language (GSL). The groups were studied with functional MRI in a standard block design during individuals' watching sign language videos alternating with black frame. During sign language conditions, deaf subjects revealed a significant activation of the auditory cortex in both hemispheres comprising Brodmann areas (BA) 42 and 22 corresponding to the secondary associative auditory areas. Additionally, activation of the angular and supramarginal gyrus was seen. Activation of the primary auditory cortex was revealed in deaf subjects with total hearing loss during sign language tasks but not in subjects with residual hearing ability. In conclusion our results indicate a cortical reorganization of the auditory cortex comprising primary auditory fields only present in subjects with total hearing loss.

Adolescent↗
PubMed2000

Functional differentiation in the human auditory and language areas revealed by a dichotic listening task.

The human auditory cortex plays a special role in speech recognition. It is therefore necessary to clarify the functional roles of individual auditory areas. We applied functional magnetic resonance imaging (fMRI) to examine cortical responses to speech sounds, which were presented under the dichotic and diotic (binaural) listening conditions. We found two different response patterns in multiple auditory areas and language-related areas. In the auditory cortex, the medial portion of the secondary auditory area (A2), as well as a part of the planum temporale (PT) and the superior temporal gyrus and sulcus (ST), showed greater responses under the dichotic condition than under the diotic condition. This dichotic selectivity may reflect acoustic differences and attention-related factors such as spatial attention and selective attention to targets. In contrast, other parts of the auditory cortex showed comparable responses to the dichotic and diotic conditions. We found similar functional differentiation in the inferior frontal (IF) cortex. These results suggest that multiple auditory and language areas may play a pivotal role in integrating the functional differentiation for speech recognition.

Acoustic Stimulation↗
PubMed1998

Magnetic field tomography analysis of continuous speech.

In this article we investigate MEG correlates of syntactic violations in continuous speech. An early left anterior negativity (ELAN) has been reported in previous EEG studies and has been related to syntactic processing. We used Magnetic Field Tomography (MFT) to extract a 3D estimate of the current density distribution J, from MEG data recorded while subjects listened to continuous speech. Separate estimates were obtained from the activity associated with the first word of the sentence, and the last words of the sentence which signified syntactic violation, semantic violation or correct sentences. In each case independent 3D MFT estimates of activity were obtained 2 ms apart. After converting the solutions into a PET-like format we perform a statistical analysis on a voxel-by-voxel basis. Visual inspection of the power of J at the time of the ELAN component and the statistical maps overlaid on the individual anatomical MRI suggests generators in the vicinity of the auditory cortex and in left frontal regions. Directional activation curves are computed to show the variation of activity as a function of time, from well circumscribed areas. The activation curve for the auditory cortex has a characteristic pattern consisting of three peaks, seen in the average time-locked to the onset of the first word, and the critical word of the syntactic violation. The left auditory cortex shows a delay of about 30 ms in the syntactic violation condition compared to the first word condition. No such delay is seen in the right auditory cortex.

Adult↗