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At least 145 records · Page 8Linked to original sources

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↗

PubMed1994

Binaural organization of primary auditory cortex in the ferret (Mustela putorius).

1. The distribution of binaural responses within the ferret's primary auditory cortex was determined by standard microelectrode mapping techniques. Single and multiple unit responses were recorded from the middle ectosylvian gyrus of barbiturate-anesthetized animals with tungsten microelectrodes (1.2-1.8 M omega) inserted into the brain perpendicular to the cortical surface. The characteristic frequency (CF) and binaural response characteristics were determined for each point sampled. 2. Gated pure tones were delivered independently to the two ears through a sealed sound system, and binaural response types were determined by comparison of evoked activity for monaural and binaural stimulation. Most binaural responses fell into one of three major groups: binaural summation (EE/F), binaural suppression (EO/I), or mixed binaural summation and suppression. 3. The neurons tended to be grouped together on the basis of their binaural response properties. Zones of binaural summation and suppression extended across the surface of the middle ectosylvian gyrus and intersected with regions of sound frequency representation. 4. Particular attention was paid to the distribution of binaural responses within isofrequency contours in the ferret's primary auditory cortex (AI). Along the length of each isofrequency contour, areas of EE/F alternated with areas of EO/I. The summation areas were typically between 0.5 and 0.7 mm wide. Single neurons with mixed binaural response properties were frequently found between groups of EE/F and EO/I cells. The mixed responses appeared to mark a transition in location between zones of summation and suppression responses. 5. The distribution of interaural intensity difference (IID) thresholds was also examined along the length of isofrequency contours. No systematic relation was found between IID threshold and the distance along an isofrequency contour.

Animals↗

PubMed1977

Age-related deterioration of pyramidal cell basal dendrites in rat auditory cortex.

The basal dendritic trees of layer V pyramidal cells in the rat auditory cortex were examined quantitatively in a group of 3-month-old and a group of 34- and 36-month-old rats. Two forms of analysis were used on the Golgi preparations: (1) the number of intersections between the basal dendrites and a series of concentric circles whose common center lies over the perikaryon center, and (2) the number of dendritic branches, by order, per neuron. The data indicate that in the old animals the density of the dendritic tree has decreased significantly within a radius of about 150mu of the perikaryon, yet the extent of the dendritic domain has not changed appreciably. Analysis of the dendritic branching suggests that there has been a deterioration not only in the peripheral branches of the dendritic tree, but also that entire dendrites have been lost. This loss of primary branches was confirmed through the reconstruction of layer V neuronal perikarya and their proximal dendrites from 1-mu plastic serial sections of auditory cortex. Concomitant with the loss of dendrites which accompanies advancing age is a tendency for the perikaryon to be smaller, but not distorted, in the old animals.

Aging↗

PubMed1986

A study on the tonotopic organization in the auditory cortex of the cat; an application of the glycine labelling method.

3H-glycine was locally applied to the auditory cortex of chloralose anaesthetized cats. Upon tonal stimulation the 3H-glycine was taken up and incorporated into the proteins of nerve cells. The selectively activated neurons were visualized by serial light microscopic autoradiography. Systematic application of this experimental setup revealed tonotopic organization in the primary auditory cortex. The distribution of nerve cells responding to spectrally pure, continuous tones of 0.34, 3.3, 8.0, 16 and 30 kHz was mapped. At these frequencies, distinct but overlapping representations were found, whose area increased in parallel with the elevation of frequencies. Tone pips and ramp stimuli resulted in generalized labelling, independently of pitch.

Animals↗

PubMed1990

[The connections of the parietal cortex with the lateral suprasylvian gyrus (the Clare-Bishop field) and the auditory cortex in the cat].

It has been shown that a parietal projection to the Clare--Bishop area is moderate and organized in a topographic manner. Associative fibres of area 5 terminate in the anterior part of the Clare--Bishop area, which corresponds to the intermediate and anterior part of the posterior suprasylvian sulcus belt. Area 7 projects to the posterior part of the intermediate and posterior suprasylvian sulcus belt. Area 5 and 7 send a few fibres to the auditory cortex. Associative fibres of area 5 terminate in the middle ectosylvian and sylvian gyri: areas 22, 50. Area 7 is connected only with the superior extremity of the middle ectosylvian gyrus or of areas 22, 50.

Afferent Pathways↗

PubMed1994

Transient and prolonged facilitation of tone-evoked responses induced by basal forebrain stimulations in the rat auditory cortex.

We investigated the relationships between cortical arousal and cholinergic facilitation of evoked responses in the auditory cortex. The basal forebrain (BF) was stimulated unilaterally, while cluster recordings were obtained simultaneously from both auditory cortices in urethane-anesthetized rats. The global electroencephalogram (EEG; large frontoparietal derivation) and the local EEG (from the auditory cortex) were recorded. The BF was stimulated at two intensities, a lower one which did not desynchronize the EEG and a higher one which did. Twenty pairing trials were delivered, during which a tone was presented 50 ms after the end of the BF stimulation. At low intensity, the pairing procedure led to a transient increase in the ipsilateral tone-evoked responses. At high intensity, the pairing increased the ipsilateral evoked responses up to 15 min after pairing. Such effects were not observed for the contralateral recordings. Systemic atropine injection prevented the facilitations observed ipsilaterally. BF stimulations alone did not induce any increased evoked response either at low or at high intensity. These results show (1) that a tone, presented while the cortex is activated by cholinergic neurons of the BF, evokes enhanced cortical responses, and (2) that the duration of this facilitation is dependent on the stimulation intensity. These results are discussed in the context of neural mechanisms involved in general arousal and cortical plasticity.

Acoustic Stimulation↗

PubMed1992

Auditory cortex of the long-eared hedgehog (Hemiechinus auritus): II. Tuning properties.

The forebrain of hedgehogs is considered by many investigators as one of the simplest and most primitive among extant placental mammals. In a recent study we have shown that the auditory cortex of the long-eared hedgehog (Hemiechinus auritus) comprises two distinct auditory fields, which are tonotopically organized. In this study, we describe tuning properties of single cells in these two fields. Application of the Q10dB and Square Root measures for determining sharpness of tuning revealed that, although most of the cells in the more anterior field, which is considered primary, are sharply tuned, on the average they are more broadly tuned than cells in the primary auditory cortex of other mammals. In the posterior field, the distribution of narrowly and broadly tuned cells is equal. Narrowly tuned cells in both fields are equally narrow, as are the broadly tuned cells. Latencies of single cells in both fields are frequency and intensity dependent and are somewhat longer than these found in other mammals. The distribution of BFs vs. threshold intensity matches fairly well the behavioral audiogram previously described. Our findings suggest that, in spite of the view that the isocortex of hedgehogs represents a 'primitive' condition, some basic tuning properties of their auditory cortex cells are comparable to those of other mammals.

Animals↗

PubMed1990

Effect of bilateral auditory cortex lesions on sound localization in Japanese macaques.

1. The ability of four Japanese macaques (Macaca fuscata) to localize sound was determined after bilateral ablation of auditory cortex. The animals were given two tests: a "midline" test in which they had to discriminate noise bursts presented from a loudspeaker located to the left from identical noise bursts presented from a loudspeaker located to the right of midline, and a "hemifield" test in which both loudspeakers were located in their right hemifield. 2. Both of the tests were administered by the use of two different behavioral tasks: a conditioned-avoidance task in which the animals were trained to make or break contact with a water spout to indicate the location of a sound source, and a two-choice task that required the animals to walk to the source of the sound. 3. The results of both the conditioned-avoidance and the two-choice tasks demonstrated that the animals were able to perform the midline discrimination although their localization acuity was reduced. However, the animals had great difficulty in learning to walk to the source of a sound in spite of the fact that they had received previous sound-localization training in the conditioned-avoidance task. This difficulty suggested that the monkeys no longer associated the sound with a location in space. 4. The results of both the conditioned-avoidance and the two-choice tasks demonstrated that the animals were unable to discriminate the locus of a sound source when both loudspeakers were located in the same hemifield. 5. Bilateral ablation of auditory cortex results in both sensory and perceptual deficits. The presence of sensory deficits is indicated by the decreased acuity in the left-right discrimination and the inability to discriminate between two loudspeakers located in the same hemifield. The deficit in the perception of the locus of sound is indicated by the difficulty in learning to approach the source of a sound, an ability which normal monkeys exhibit without training. 6. There appear to be species' differences in the effect of auditory cortex lesions on sound localization. Although cortical lesions result in a sound-localization deficit in several species of primates and carnivores, they have little or no effect on rats.

Animals↗

PubMedDate not supplied

[Role of the auditory cortex in animal recognition of synthesized vowels].

Discrimination of synthesized vowels [a] and [i] was studied in intact dogs and animals with an ablated auditory cortex. Electro-defensive and conditioned reflex methods were used. It has been found that as a result of learning an auditory image of a stationary vowel can be formed in intact dogs, which is invariant relatively to any change in the basic frequency of the voice, the intensity and duration of presentation (300 to 75 msec), and that two formants are sufficent for discrimination. The auditory image of the vowel is preserved after a bilateral ablation of the auditory cortical projection zone. Discrimination of vowels is disturbed in animals with a removed auditory cortex when information redundancy is reduced (diminished number of formants and reduced signal duration).

Animals↗

PubMed1985

[Reactions of neurons of the auditory cortex of unanesthetized cats to tones of a characteristic frequency].

Extra- and intracellular responses of primary auditory cortex (AI) neurons were studied in acute experiments on non-anaesthetized cats. It was found that auditory cortex neurons having similar best frequencies revealed various forms of responses to corresponding frequency tones. Neurons responded to the tone by on reactions constituted about 40% of nerve cells studied. 27% of neurons revealed responses of on-off and off types. 27% of cortical neurons responded by steady excitation or by inhibition of background activity. About 6% of neurons did not respond to the tone. During intracellular recordings about 85% of neurons studied responded to switching on and/or off of the tone by a spike-IPSP sequence. 96% of cortical neurons generated IPSP as a constant component of the response to tone. Tonic responses of auditory cortical neurons were the result of powerful and lasting depolarization of the postsynaptic membranes. The conclusion is made that interaction of excitatory and inhibitory processes is the most significant in any kind of responses of the auditory cortical neurons to tones.

Animals↗

PubMed1987

Responses of the human auditory cortex to vowel onset after fricative consonants.

Neuromagnetic responses to different auditory stimuli (noise bursts and short speech stimuli) were mapped over both hemispheres of seven healthy subjects. The results indicate that a particular acoustic feature of speech, vowel onset after voiceless fricative consonants, evokes a prominent response in the human supratemporal auditory cortex. Although the observed response seems to be specific to acoustic rather than phonetic characteristics of the stimuli, it might reflect feature detection essential for further speech processing.

Auditory Cortex↗

PubMed1993

Phonetic invariance in the human auditory cortex.

Neuromagnetic signals evoked by synthesized syllables (/bae/ and /gae/) were recorded over the left auditory cortex of healthy humans. The fundamental frequencies of the syllables varied as if the same speaker had pronounced them at 16 different pitches. Specific mismatch responses to infrequent syllables among frequent syllables of the other type indicated that phonetically invariant information had been extracted at the level of the auditory cortex from the extensive irrelevant pitch variation. Such a detection mechanism is necessary for perceiving speech sounds in natural situations with a great deal of acoustic variation present.

Acoustic Stimulation↗

PubMed1994

Plastic changes in ipsi-contralateral differences of auditory cortex and inferior colliculus evoked potentials after injury to one ear in the adult guinea pig.

In normal adult guinea pigs, evoked potentials recorded at the ipsilateral auditory cortex to monaural high-frequency acoustic stimuli present higher thresholds and lower amplitudes than at the contralateral cortex; in the inferior colliculus, such ipsi-contralateral differences (ICDs) are smaller than in the auditory cortex. Changes in the ICDs were studied after opposite ear injury. Following quasi-complete hair cell destruction induced by sisomicin injection into the contralateral inner ear, threshold ICDs almost disappeared after about two to six days and ipsilateral amplitudes progressively increased in two to three weeks. The occurrence of ICDs at higher auditory centers revealed in this study, indicates peculiar processing of high frequency stimuli in normal guinea pigs. The alteration of ICDs after opposite ear impairment provides a new possibility to study the auditory plasticity in adult animals.

Acoustic Stimulation↗

PubMed1990

Acquired word deafness, and the temporal grain of sound representation in the primary auditory cortex.

This paper explores the nature of the processing disorder which underlies the speech discrimination deficit in the syndrome of acquired word deafness following from pathology to the primary auditory cortex. A critical examination of the evidence on this disorder revealed the following. First, the most profound forms of the condition are expressed not only in an isolation of the cerebral linguistic processor from auditory input, but in a failure of even the perceptual elaboration of the relevant sounds. Second, in agreement with earlier studies, we conclude that the perceptual dimension disturbed in word deafness is a temporal one. We argue, however, that it is not a generalized disorder of auditory temporal processing, but one which is largely restricted to the processing of sounds with temporal content in the milliseconds to tens-of-milliseconds time frame. The perceptual elaboration of sounds with temporal content outside that range, in either direction, may survive the disorder. Third, we present neurophysiological evidence that the primary auditory cortex has a special role in the representation of auditory events in that time frame, but not in the representation of auditory events with temporal grains outside that range.

Animals↗

PubMed1985

Neuronal connections in the primary auditory cortex: an electrophysiological study in the cat.

Neuronal connections in the primary auditory cortex (AI) of the cat were studied electrophysiologically by using intracellular recording techniques. Fast-conducting fibers from the medial geniculate nucleus (MG) projected monosynaptically onto AI neurons in layers III-VI (mainly in layer IV), whereas slow-conducting MG-fibers projected monosynaptically onto AI neurons in layer I. AI neurons which received monosynaptic inputs from the auditory association cortices (AII and Ep) and/or from the contralateral AI were distributed in all layers of the AI; the commissural fibers from the contralateral AI were divided into fast- and slow-conducting ones. AI neurons were categorized into seven types: type I neurons which received monosynaptic inputs from slow-conducting MG-fibers were located in layer I. Type II neurons which received polysynaptic inputs from the MG were located in layers II-VI. Type III neurons which sent their axons to the AII or Ep were mainly located in layer III. Type IV neurons which sent their axons to the contralateral AI were located mainly in layer III. Type V neurons which received monosynaptic inputs from fast-conducting MG-fibers were located mainly in layer IV. Type VI neurons which projected onto the inferior colliculus were located in the upper part of the layer V. Type VII neurons which projected onto the MG were located in layers V and VI.

Animals↗

PubMed1995

Factors shaping the tone level sensitivity of single neurons in posterior field of cat auditory cortex.

1. The posterior field (field P) of the cat's auditory cortex contains a higher proportion of neurons whose response/level functions for characteristic frequency (CF) tones are nonmonotonic than does the primary field (AI). The general purpose of the present study is to assess whether the response/level functions of field P neurons are generated by the same mechanisms as those of cells in AI. All of the data came from single neurons in the cortices of barbiturate-anesthetized cats, to which we presented tonal stimuli through sealed, calibrated stimulating systems. 2. We obtained quantitative data from 123 neurons, of which 108 were located in field P. Of the 108 field P cells, 70% had nonmonotonic response/level functions for 5-ms rise time tones of CF. For cells of any given CF, both CF thresholds and best SPLs (i.e., SPLs associated with maximal responses) varied widely. A correlation analysis revealed that a linear relation between best SPL and CF threshold accounted for 73% of the data variance in the association between those response variables. An analysis of data from 83 nonmonotonic cells in AI revealed a similar relation. 3. Field P neurons whose response/level functions were non-monotonic for 5-ms rise time CF tones became even more narrowly tuned to SPL when the rise time of the tone bursts was reduced to 1 ms. Lengthening the rise time to 20 ms reduced or eliminated the SPL tuning in almost all of these neurons. The general form of monotonic tone response/level functions was commonly unaffected by variation in signal rise time. In a few instances, cells with monotonic response/level functions for 5- and 20-ms rise time tones developed nonmonotonic functions for 1-ms rise time tones. 4. Field P neurons with nonmonotonic response/level functions for CF tones usually failed to respond to wideband noise pulses, or, less commonly, responded to noise only at low SPLs. In contrast, field P cells with a monotonic response to CF tones usually responded monotonically to noise. 5. The minimal mean first-spike latencies of field P neurons were generally longer than those of AI cells studied under similar conditions. The precision of first-spike timing, measured using the SD of the mean first-spike latency, was commonly poorer than that of AI cells. 6. The properties of field P cells followed the same rules as those seen in AI.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1993

Functional organization of auditory cortex in the mongolian gerbil (Meriones unguiculatus). II. Tonotopic 2-deoxyglucose.

The tonotopic organization of the auditory cortex in the Mongolian gerbil was mapped with 2-deoxyfluoro-D-glucose (2DG) using narrow-band frequency-modulated tones of different centre frequency (FM tones) and tones periodically alternating between two different frequencies (alternating tones) as stimuli. Continuous tone bursts of a constant frequency and repetition rate were used in initial experiments. Continuous tones produced 2DG patterns similar to those observed in animals that were not specifically stimulated. With tone bursts of constant frequency and repetition rate variable patterns were observed, some of which could be interpreted only in retrospect in the light of results obtained with FM tones and alternating tones. These stimuli, in contrast, produced differential metabolic responses which in conjunction with 2DG data from monaural animals and electrophysiological data made it possible to distinguish a primary auditory field AI with its dorsal region Ald, an anterior auditory field AAF, a ventral field V, a dorsoposterior field DP and a ventroposterior field VP, a dorsal field D, and in addition an anteroventral field AV. In the largest field (AI) and the smaller rostrally adjacent field AAF, frequency-specific dorsoventral bands of labelling (isofrequency contours) were mapped quantitatively. Bands shifted as a function of frequency relative to each other and to an independent spatial reference line in the lateral hippocampus. Spatial analysis of the single bands obtained with FM tones, and of the double bands obtained with alternating tones in both fields, revealed roughly mirror-imaged tonotopic maps of AI and AAF. In AI the progression from low to high frequencies was from caudal to rostral and in AAF the gradient was reversed, leading to a common high-frequency border of the two fields. In AI, the spatial resolution for frequencies below 16 kHz was in similar intervals per octave and higher for frequencies below 1 kHz. AI showed a somewhat higher spatial resolution for frequencies (at least below 1 kHz) as well as longer isofrequency contours than AAF. The 2-deoxyglucose patterns provided average tonotopic maps and topological data on various fields, as well as reliable landmarks in the gerbil's auditory cortex.

Acoustic Stimulation↗