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Results for “Auditory Cortex”

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At least 73 records · Page 4Linked to original sources

PubMed1992

Separate neuronal populations of the rat globus pallidus projecting to the subthalamic nucleus, auditory cortex and pedunculopontine tegmental area.

The topographic arrangement of globus pallidus neurons sending axons to the subthalamic nucleus, auditory cortex and pedunculopontine tegmental nucleus was studied in the rat using retrograde fluorescent tracers. Neurons projecting to the subthalamic nucleus were localized in the rostral part of the globus pallidus, while neurons projecting to the auditory cortex and to the pedunculopontine tegmental nucleus were located in the caudal part. The two populations of pallidocortical and pallidotegmental neurons were also distributed in a separate manner within the caudal globus pallidus. The former neurons were large and located more ventromedially, whereas the latter were medium-sized and located more dorsolaterally. Using a retrograde fluorescent tracing technique combined with choline acetyltransferase immunofluorescence histochemistry, it was found that a vast majority of pallidocortical neurons expressed choline acetyltransferase immunoreactivity, and that pallidotegmental neurons rarely exhibited choline acetyltransferase immunoreactivity. A method of retrograde tracing with wheatgerm agglutinin conjugated with horseradish peroxidase associated to immunohistochemistry for glutamate decarboxylase confirmed the GABAergic nature of the pallidotegmental pathway. The present study revealed the independent nature of the globus pallidus neurons projecting to the subthalamic nucleus, auditory cortex and pedunculopontine tegmental nucleus. Within this cellular arrangement, the presence of functionally distinct neuronal populations at the caudal pallidal level was also identified, with large cholinergic cells innervating the neocortex and medium-sized GABAergic cells "feeding" the mesencephalic tegmentum.

Animals↗

PubMedDate not supplied

Functional organization of the callosal connections of the cat auditory cortex.

In acute experiments on immobilized cats, using a method of topographical recording of homotopic and heterotopic transcallosal responses, the functional organization of the callosal connections of the auditory cortex was investigated. It was established that the homotopic potentials of the primary projection field (AI) have the greatest amplitude, minimal temporal parameters, and the maximal stability of these characteristics as compared with the associative fields of the auditory cortex (AII, AIV, Ep). The heterotropic transcallosal responses in field AI appeared during stimulation of the analogous field, while in field Ep, they were recorded both during stimulation of the analogous field, and of fields AI and AII of the opposite hemisphere. It is hypothesized that the structure of the transcallosal connections of the primary projection field s of the auditory cortex is characterizised by homotopy, whereas in the associative auditory fields the role of heterotopic transcallosal interactions increases. It is possible that such a structure of the transcallosal connections assures a significant role for interhemispheric interactins in the mechanisms of spatial audition.

Animals↗

PubMedDate not supplied

[The structural-functional organization of the auditory cortex in rats].

Using axonal transport of horseradish peroxidase and electrophysiological mapping technique, studies have been made on structural and functional organization of the auditory cortex in rats. After the injection of HRP to peripheral parts of the auditory cortex, mainly initial neurones were found in the dorsal and median parts of the geniculate body. Electrophysiological experiments revealed the localization of neurones with widespread frequency-threshold curves and high thresholds at characteristic frequency. On the basis of the data obtained, it is suggested that similar to other mammals, rats have the areas of secondary fields of the auditory cortex which surround central coniocortex.

Animals↗

PubMed1992

The auditory cortex of the mouse: connections of the ultrasonic field.

The cortical and subcortical connections of the ultrasonic field (UF) of the auditory cortex of the house mouse (Mus musculus) were studied by using retrograde and anterograde transport of horseradish peroxidase (HRP). Small amounts of HRP were locally injected into the electrophysiologically defined UF. Superficial (layer I-IV) and deep (layer IV-VI) injections were prepared. Superficial injections led to labelling of both cells (retrograde) and terminals (anterograde) in areas of the ipsilateral primary and secondary auditory cortex and in its dorsoposterior field, in an ipsilateral dorsal association area (patches of label), probably in ipsilateral secondary somatosensory cortex, in the contralateral homotopic UF, and in the ipsilateral medial geniculate body (MGBv, MGBd, and MGBm) and caudal posterior nucleus complex. Deep injections showed the same connectivities as superficial ones and, in addition, terminals in the very caudal caudatoputamen, in the nucleus limitans and the nucleus reticularis of the thalamus, in the rostral pole, the dorsomedial, and lateral nucleus of the inferior colliculus, in the stratum griseum intermediale of the superior colliculus, and in a pontine nucleus ventromedial of the lateral lemniscus. All these projections occurred only ipsilaterally. The majority of connections, except those with the nucleus limitans, superior colliculus and pontine nucleus, suggest that UF is part of the primary anditory cortex (AI) and/or of the anterior anditory field (AAF) of the auditory cortex. Since UF has no regular tonotopy, this has important implications for the functional role that AI/AAF can have in communication-sound analysis.

Animals↗

PubMed1987

The personalized auditory cortex of the mustached bat: adaptation for echolocation.

1. In the mustached bat, Pteronotus parnellii, the "resting" frequency of the constant-frequency component of the second harmonic (CF2) of the orientation sound (biosonar signal) is different among individuals within a range from 59.69 to 63.33 kHz. The standard deviation of CF2 resting frequency is 0.091 kHz on the average for individual bats. The male's CF2 resting frequency (61.250 +/- 0.534 kHz, n = 58) is 1.040 kHz lower than the female's (62.290 +/- 0.539 kHz, n = 58) on the average. Females' resting frequencies measured in December are not different from those measured in April when almost all of them are pregnant. Therefore, the orientation sound is sexually dimorphic. 2. In the DSCF (Doppler-shifted CF processing) area of the auditory cortex, tonotopic representation differs among individual bats. The higher the CF2 resting frequency of the bat's own sound, the higher the frequencies represented in the DSCF area of that bat. There is a unique match between the tonotopic representation and the CF2 resting frequency. This match indicates that the auditory cortex is "personalized" for echolocation and that the CF2 resting frequency is like a signature of the orientation sound. 3. If a bat's resting frequency is normalized to 61.00 kHz, the DSCF area overrepresents 60.6-62.3 kHz. The central region of this overrepresented band is 61.1-61.2 kHz. This focal band matches the "reference" frequency to which the CF2 frequency of a Doppler-shifted echo is stabilized by Doppler-shift compensation. 4. Since DSCF neurons are extraordinarily sharply tuned in frequency, the personalization of the auditory cortex or system is not only suited for the detection of wing beats of insects, but also for the reduction of the masking effect on echolocation of consepecific's biosonar signals. 5. Because the orientation sound is sexually dimorphic and the auditory cortex is personalized, the tonotopic representation of the auditory cortex is also sexually dimorphic.

Acoustic Stimulation↗

PubMed1991

Basal forebrain stimulation modifies auditory cortex responsiveness by an action at muscarinic receptors.

We have hypothesized that auditory cortex plasticity involves modification of thalamocortical transmission by basal forebrain (BF) cholinergic neurons, and that this action may involve muscarinic receptors. In a first test of this hypothesis, we report that BF stimulation can suppress or facilitate, depending on the intensity of stimulation, auditory cortical responses elicited by thalamic stimulation. BF-mediated facilitation is antagonized by atropine, implicating muscarinic receptors. These data suggest that BF cholinergic neurons functionally modify auditory cortex by regulating thalamocortical transmission.

Animals↗

PubMed1977

Effects of unilateral ablation of auditory cortex on monaural cat's ability to localize sound.

1. Cats with one cochlea destroyed were trained to localize sound. After behavioral measures of the animal's accuracy of localization were made, cortical auditory areas were ablated unilaterally. 2. The results showed: a) like binaural localization, monaural localization of sound in space, as measured by the ability of an animal to move toward a sound source, depends on integrity of auditory cortex; b) it is only ablation of cortex contralateral to the functional ear that seriously affects localizing behavior; ablation of cortex ipsilateral to the intact cochlea has little or no effect on localizing behavior. 3. To explain the results, we suggest that auditory cortex is essential for an organized perception of space including the relation of the animal's position to other objects in space. We also suggest that auditory cortex contralateral to a given ear is necessary in order for the animal to recognize that a stimulus is presented to that ear of, when both ears are intact, to recognize that the stimulus to the given ear differs in some way (intensity, time of arrival, sequential arrangement of sounds) from the stimulus to the opposite ear.

Animals↗

PubMed1986

Effect of unilateral and bilateral auditory cortex lesions on the discrimination of vocalizations by Japanese macaques.

Ten Japanese macaques were trained to discriminate between two types of Japanese macaque coo vocalizations before and after auditory cortex ablation. Five of the animals were tested following left unilateral ablation, whereas the other five were tested following right unilateral ablation. After postoperative testing, symmetrical lesions were made in the remaining hemisphere in two animals from each group and the effect of bilateral lesions was assessed. The animals were tested using a shock avoidance procedure. Unilateral ablation of left auditory cortex consistently resulted in an initial impairment in the ability to discriminate between the vocalizations with the animals regaining normal performance in 5-15 sessions. In contrast, right unilateral ablation had no detectable effect on the discrimination. Bilateral auditory cortex ablation rendered the animals permanently unable to discriminate between the coos. Although the monkeys could learn to discriminate the coos from noise and from 2- and 4-kHz tones, they had great difficulty in discriminating between the coos and tones in the same frequency range as the coos (i.e., 500 Hz and 1 kHz). The initial impairment following left unilateral lesions indicates that the ability to perceive species-specific vocalizations is lateralized to the left hemisphere. The observation that bilateral lesions abolish the discrimination indicates that the recovery in the left lesion cases was the result of the right hemisphere mediating the discrimination.

Animals↗

PubMedDate not supplied

The laminar organization of the prospective auditory cortex in the human fetus (11--13.5 weeks of gestation).

The prospective auditory cortex was analysed in human fetuses at 11--13,5 post-ovulatory weeks with Nissl, Golgi and E.M. techniques. At 11--12 weeks, marginal, cortical plate, intermediate, subventricular and ventricular layers were recognized. Post-migratory neurons with developing dendrites were seen in marginal layer, cortical plate and superficial part of the intermediate zone only. At 12--13,5 weeks the superficial part of the intermediate zone is transformed into the true cortical layer--"subplate layer"--characterized by maturing neurons with growing dendrites, fine axonal arborization and low cell density. The neuronal circuitry elements are thus present very early in the prospective auditory cortex and distributed throughout the deep cortical plate of the "subplate layer" corresponding to the synaptic territory of other areas of the human fetal cortex.

Auditory Cortex↗

PubMed1988

Magnetic responses of the human auditory cortex to noise/square wave transitions.

We recorded evoked magnetic fields from the human auditory cortex to noise/square wave sequences. Two prominent deflections were observed: one 100 msec after the noise onset (N100m) and another 100 msec after the noise/square wave transition (N100m'). The amplitude of N100m' increased with decrease in square wave frequency from 2 kHz to 0.125 kHz and with increase in square wave duration from 4 msec to 200 msec. The latency of N100m' was on the average 23 msec longer for noise durations of 60 msec than 310 msec, whereas the amplitude of N100m' did not change. Increase in interstimulus interval from 1.1 to 8.8 sec enhanced the amplitude of N100m significantly more than that of N100m'. The small interaction between N100m and N100m' and their different recovery cycles suggest that different activation patterns underlie these two 100 msec responses at the auditory cortex.

Adult↗

PubMed1976

[A histochemical study of acetylcholinesterase in intact and deafferented cat auditory cortex].

The peculiarities of the AChE distribution were investigated in the intact cat auditory cortex and during early period of its neuronal isolation. It is shown that in the isolated cortex slab the staining of the AChE containing fibre disappeared from the neuropile, while in the intact cortex it was well pronounced. AChE accumulation was observed in the proximal parts of the transsected thalamo-cortical fibres. It is supposed that the AChE-containing fibres in the auditory cortex belong to nonspecific thalamic inputs.

Acetylcholinesterase↗

PubMed1989

Reactions of human auditory cortex to a change in tone duration.

Auditory evoked magnetic fields were measured using a stimulation sequence where repetitive identical tone bursts were randomly and infrequently replaced by shorter tones. The deviation in the stimulus duration evoked a specific response, the mismatch field, peaking about 130 ms after the end of the shorter stimulus. The response can be explained by neural activity at the supratemporal auditory cortex. The results suggest the existence of a neural mechanism specific to changes in sound duration.

Acoustic Stimulation↗

PubMedDate not supplied

[Comparative study of interneuronal relations in the auditory cortex of awake and anesthetized cats].

The character of interneuronal relations in the auditory cortex of alert and anaesthetized cats (nembutal) with chronicly inplanted electrodes was studied with the method of statistic analysis of cross-intervals of the two impulse series. The analysis of the histograms, obtained by means of processing a neuronal activity, showed that nembutal did not eliminate the dependent relations between neurones and that in the majority of cases the types of these relations are either retained or supplemented with new components. Experiments with a reduced dose of nembutal permitted to trace in time the changes in the amount of the inhibitory and excitatory interrelations in the anaesthetized state, and to compare these changes to the changes in the frequency of spike activity. It was found that nembutal predominantly suppresses the activity of the neurones, generating small spikes. The number of inhibitory connections is reduced simultaneously. Such synchroneity permits to assume the participation of the neurones generating small spikes in the establishment of inhibitory interrelations in the cat auditory cortex.

Anesthesia, General↗

PubMed1987

Ferrier and the study of auditory cortex.

David Ferrier was a British physician who studied the localization of function in the cerebral hemispheres during the latter half of the 19th century. Using stimulation and ablation techniques, Ferrier demonstrated that auditory cortex was located in the superior temporal gyrus of the monkey and that ablation of auditory cortex resulted in deafness. Although he was substantially correct, Ferrier's location of auditory cortex was not accepted by his contemporaries, and his observations of cortical deafness were, until recently, discounted by modern researchers. Just why his findings were rejected is of interest to the study of cortical function.

Auditory Cortex↗

PubMed1989

Role of context in the expression of learning-induced plasticity of single neurons in auditory cortex.

Classical conditioning produces frequency-specific plasticity of receptive fields (RFs) of single neurons in cat auditory cortex (Diamond & Weinberger, 1986). In this article we show that although plasticity may be observed during both training trials and determination of RFs, it is usually expressed in a qualitatively different form (e.g., decreased response during conditioning vs. increased response to this same conditioned stimulus in the postconditioning RF). This differential expression of learning-induced plasticity provides evidence for a role of context in neurophysiological mechanisms of learning in auditory cortex. A model of cortical neurons functioning within a mosaic of influences is presented. The Functional Mosaic model views the induction and expression of plasticity as separate processes.

Animals↗

PubMed1989

Extrathalamic ascending projections to physiologically identified fields of the cat auditory cortex.

The neurons of origin of ascending extrathalamic projections to the auditory cortex were labeled retrogradely with WGA-HRP injected in physiologically identified auditory cortical fields of the cat (anterior (AAF), primary (AI), posterior (PAF) and secondary (AII) fields). After injection in the tonotopically organized auditory cortical fields (AAF, AI and PAF), labeled neurons were distributed in 7 extrathalamic subcortical regions included in one or the other of 2 distinct systems of ascending projections to the neocortex. In the 'diffuse' system of projection, labeled neurons were observed bilaterally in the locus coeruleus, the nuclei of the raphe, the lateral hypothalamus, ipsilaterally in the ventromedial mesencephalic tegmentum and the basal forebrain; in the 'accessory sensory' system of projection, labeled neurons were found ipsilaterally in the nucleus of the brachium of the inferior colliculus and bilaterally in the claustrum. After injection in AII, labeled neurons were seen only in the 'diffuse' system of projection. For AAF and AI, the major contribution to the total extrathalamic ascending input originated from the lateral hypothalamus, whereas for AII it was the locus coeruleus. In contrast, PAF received extrathalamic ascending inputs mainly from the claustrum. Anterogradely labeled corticofugal terminal fields were found only in the nucleus of the brachium of the inferior colliculus and, after injection in PAF, in the claustrum.

Acetylcholine↗

PubMed1976

Foetal and neonatal development of evoked responses in guinea-pig auditory cortex.

Development of the response of the auditory cortex to unilateral acoustic stimulation by a chick was studied in guinea-pig foetuses from the 50th day to the end of gestation and in newborn animals. The first cortical response appeared on the 52nd to 53rd day of gestation. The maximum responses were concentrated in the temporal cortex, between the somatosensory (parietal) and optic (occipital) area. The progressive development of the latent period of the cortical response and of its various components distinctly slowed down on the last days of gestation. At the same time, the amplitude of the cortical response was temporarily augmented. The cortical response developed from a simple negative wave in the youngest embryos into an intricate complex with an initial positive component in newborn guinea-pigs. The basic components of this complex were already discernible on the 64th to 65th day of gestation. The ability to react to repeated peripheral stimulation of 0.1-2 c/s frequency increased with foetal age, with temporary deterioration on the last days of gestation. Resistance of the cortical auditory response to cerebral anoxia rose up to term, with a temporary drop from the 64th day of gestation. After the initiation of independent respiration, cerebral hypoxia and bilateral vagotomy chiefly influenced the stability of the more recent components of the cortical auditory response in mature foetuses.

Acoustic Stimulation↗

PubMed1988

Modification of neuromagnetic responses of the human auditory cortex by masking sounds.

We have studied the effects of masking sounds on auditory evoked magnetic fields (AEFs) of healthy humans. The AEFs were elicited by 25-ms tones presented randomly to the left or to the right ear, and the responses were recorded over the right auditory cortex. Without masking, the 100-ms deflection (N100m) was of somewhat higher amplitude and of shorter latency for contra- than ipsilateral stimuli. Continuous speech, music, or intermittent noise, delivered to the left ear, dampened N100m to stimulation of both ears without correlated changes in sensation. Intermittent noise had a weaker effect on N100m than speech or music. Continuous noise fed to the left ear dampened both the sensation of and the responses to the left-ear stimuli, with no significant effect on the responses to the right-ear stimuli. The results suggest that the masking effects of continuous noise, seen at the auditory cortex, derive mainly from the periphery whereas the effects of sounds with intensity and frequency modulations take place at more central auditory pathways.

Acoustic Stimulation↗