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At least 127 records · Page 7Linked to original sources
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↗
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↗
PubMed1991

Habituation produces frequency-specific plasticity of receptive fields in the auditory cortex.

Associative learning produces conditioned stimulus (CS)-specific plasticity of frequency receptive fields (RFs) in the auditory cortex; responses to the CS frequency are increased, whereas responses to other frequencies are decreased. This study determined the effects of habituation on the RF of neurons in the auditory cortex of the guinea pig (Cavia porcellus). One frequency was presented repeatedly (REP) followed by redetermination of the RF. After REP, 26/36 (72%) RFs exhibited a substantial reduction (70-75%) of response to the repeated frequency, and this was highly specific (bandwidth less than 0.125 octave). This RF plasticity involves an initial decrease in response during REP but does not require attenuated responses at the end of REP. Incubation (i.e., development over time after cessation of REP) and long-term frequency-specific effects are evident. Thus, habituation induces a specific change in the processing of frequency information rather than a general reduction in responsivity.

Acoustic Stimulation↗
PubMed1990

Neural representation of sound amplitude in the auditory cortex: effects of noise masking.

Single auditory cortical neurons express their sensitivity to the amplitude of a preferred-frequency tone pulse as either a monotonic, saturating intensity profile or as a non-monotonic, bell-shaped intensity function. In the presence of continuous, wideband noise masking, the tone intensity profile is displaced toward higher tone levels. The magnitude of the tone threshold adjustments brought about by increments in noise level very closely match the elevations in noise amplitude. The mechanisms underlying the threshold adjustments likely include neural adaptation. This is because the tone threshold shifts seen in the spike count data are paralleled by spike latency data, and because recovery of tonal sensitivity following noise offset proceeds in a negatively-accelerating fashion. In some instances, the slope of the masked tone intensity profile is greater than that for unmasked tones. For masked tone levels evoking submaximal responses, this has the consequence that cortical responses to masked tones are somewhat more salient than those for unmasked tones of comparable suprathreshold level. These observations bolster our understanding of the psychophysics of noise-masking in normal listeners, and they provide a partial explanation of the difficulty shown by patients with temporal lobe lesions in discriminating signals in noise.

Animals↗
PubMedDate not supplied

Auditory evoked potentials from the primary auditory cortex of the cat: topographic and pharmacological studies.

Wave VI (8.4 msec) of the brain-stem auditory evoked potential (BAEP) was maximal in a discrete region of primary auditory cortex (AI) of the anesthetized cat. Wave VI underwent rapid amplitude decrease over millimeter distances in the AI region and followed high stimulation rates. Wave VI did not show intracortical polarity inversion nor was it abolished by epicortical or intracortical GABA administration. The data are compatible with a wave VI source in the terminal axons of the thalamo-cortical radiations. Middle latency auditory responses (MAEPs) generated 10-40 msec after auditory stimulation were also recorded in a circumscribed area of AI. In contrast to wave VI, these primary auditory cortex potentials (Pa 18.3 msec; Nb 31.9 msec) underwent transcortical polarity inversion, correlated with intracortical multi-unit activity in the AI region and were reversibly altered or abolished by epicortical or intracortical GABA administration to the AI region. The data suggest that the Pa and Nb components of the cat MAEP are intracortically generated by neuronal elements in the AI region.

Acoustic Stimulation↗
PubMed1992

Regional response differences within the human auditory cortex when listening to words.

The relationship between activity within the human auditory cortices and the presentation rate of heard words was investigated by measuring changes in regional cerebral blood flow with positron emission tomography. We demonstrate that in the primary auditory cortices and middle regions of the superior temporal gyri there is a linear relationship between the rate of presentation of heard words and blood flow response. In contrast, the blood flow response in an area of the left posterior superior temporal gyrus (Wernicke's area) is primarily dependent on the occurrence of words irrespective of their rate of presentation. The primary auditory cortices are associated with the early processing of complex acoustic signals whereas Wernicke's area is associated with the comprehension of heard words. This study demonstrates for the first time that time dependent sensory signals (heard words) detected in the primary auditory cortices are transformed into a time invariant output which is channelled to a functionally specialised region--Wernicke's area. Wernicke's area is therefore distinguished from other areas of the auditory cortex by direct observation of signal transformation rather than by association with a specific behavioural task.

Adult↗
PubMed1989

Unilateral auditory cortex ablation in macaques results in a contralateral hearing loss.

1. The behavioral audiograms of four Japanese macaques (Macaca fuscata) were assessed before and after unilateral ablation of auditory cortex. The tones were presented via insertion earphones so that each ear could be tested separately. 2. Each animal had a hearing loss in the ear contralateral to the lesion, whereas the ipsilateral ear showed no change in sensitivity. The hearing loss initially appeared as a large shift in thresholds followed by rapid but incomplete recovery during the first 3-5 wk after surgery. The initial hearing loss ranged as high as 68 dB at some frequencies, although thresholds at other frequencies were occasionally unchanged. A threshold shift could be demonstrated with broadband noise as well as with tones. Although thresholds for some tones returned to normal within a few weeks, most were still elevated 16 wk after surgery when testing was discontinued. The largest long-term hearing losses occurred at frequencies from 4 to 25 kHz. 3. Analysis of the animals' psychophysical functions suggested that the hearing loss resembled a sensory deficit, as opposed to a nonsensory deficit in attention or vigilance. 4. Testing with binaural stimuli indicated that the hearing loss could best be described as a contralateral "ear" deficit, as opposed to a contralateral "auditory field" deficit. 5. It is suggested that a similar hearing loss occurs in humans after unilateral damage to auditory cortex.

Animals↗
PubMed1988

Spect-studies of the brain with stimulation of the auditory cortex.

The radiopharmaceutical N-isopropyl-p-J-Amphetamin (IMP) permits a new approach in the study of cerebral perfusion and function. We advanced the hypothesis for an increased IMP-uptake on auditory cortex during stimulation by white noise. Auditory stimulation activates the auditory cortex. This is marked by an increased IMP-uptake. IMP-uptake by the auditory region on the left side during stimulation on the right ear is another evidence of the crossing of central auditory pathways to the contralateral side.

Acoustic Stimulation↗
PubMed1983

Intrinsic organization of the cat's medial geniculate body identified by projections to binaural response-specific bands in the primary auditory cortex.

The area of the cat's primary auditory cortex (AI) within which high frequency sounds are represented can be subdivided using functional criteria. Within each subdivision, or "binaural interaction band," all recorded neurons display similar responses to binaural stimulation. The current study distinguishes the thalamic sources of input to these subdivisions of AI and characterizes the topography within the thalamic projection to each class of bands. The borders of binaural bands in AI were mapped using microelectrode recording with diotic tonal stimulation, then injections of one to three retrograde tracers were introduced into identified bands. Within the ventral division (V) of the medial geniculate body (the major thalamic source of input to AI), the neuronal populations that projected to different classes of binaural bands were strictly segregated from each other. This segregation of class-specific thalamic sources constitutes a laminar organization within an axis of V that is orthogonal to the previously described tonotopic organization. Excitatory/excitatory (EE) binaural neurons in AI were found to be segregated from excitatory/inhibitory (EI) neurons in alternating "bands." We consistently identified: (1) a ventral pair of rostrocaudally continuous EI and EE bands, (2) a middle area within which the pattern of binaural subdivisions was more variable and within which bands often were discontinuous rostrocaudally, and (3) a dorsal zone (DZ) within which the responses of neurons differed in binaural properties and in frequency specificity from the response patterns that were characteristic of neurons elsewhere in AI. Each EI band apparently derived input that converged from three thickened laminae of cells in V that were oriented approximately horizontally. The most ventral of these laminae encompassed the ovoidal part of V (Vo), suggesting that EI bands are the only recipients in AI of a projection from Vo. All of the EE bands and DZ derived their input from a single continuous structure which included the dorsal two-thirds of the rostral pole of V and a horizontal lamina interposed between the two dorsalmost EI-projecting laminae. Restricted portions of the complex EE-projecting structure in V projected preferentially to particular EE subdivisions of AI. The V-to-AI thalamocortical topography exhibited a high degree of convergence and divergence within the projections to each cortical binaural band and within the projections to each class of bands. These observations indicate that the high frequency representation in AI and its principal thalamic source of input, the ventral division of the medial geniculate body, may be thought of as assemblies of spatially discrete, functionally distinguishable subunits. The significance of this intrinsic organization is discussed in regard to the requirements for analysis of sound stimuli.

Animals↗
PubMed1988

Combination-sensitive neurons in the ventroanterior area of the auditory cortex of the mustached bat.

1. Because the ventroanterior (VA) area is one of the target areas of the FM-FM area in the auditory cortex of the mustached bat, Pteronotus parnellii parnellii, response properties of combination-sensitive neurons in this area were studied with constant-frequency (CF) tones, frequency-modulated (FM) sounds, and sounds similar to the bat's biosonar signal (pulse), which consisted of long CF components (CF1-4) and short FM components (FM1-4). CF1-4 and FM1-4 are the components in the four harmonics (H1-4) of the pulse. 2. Combination-sensitive neurons are clustered in a small area immediately anteroventral to the Doppler-shifted CF processing (DSCF) area and posteroventral to the anterior division of the primary auditory cortex. Because this cluster in the VA area is small, it was difficult to record a sufficient number of combination-sensitive neurons to explore the functional organization of the cluster, but it was found that the response properties of these VA neurons were unique. 3. Combination-sensitive neurons in the VA area are tuned to particular combinations of signal elements similar to the first and second harmonics of the pulse and/or echo. Unlike neurons in the FM-FM, dorsal fringe (DF), and CF/CF areas, no neurons in the VA area are tuned to the signal elements in the first and third or fourth harmonics. 4. The great majority of combination-sensitive neurons in the VA area can not be easily classified into either FM-FM or CF/CF neurons, because they show facilitative responses to combinations of CF1/CF2, FM1-FM2, and FM1-CF2. Therefore, they are called H1-H2 neurons. In the FM-FM and CF/CF areas, all the neurons could be easily classified as FM-FM or CF/CF. This uniqueness of H1-H2 neurons is related to the fact that their best frequencies for facilitation are predominantly between 61.0 and 62.0 kHz, i.e., within the frequency range of stabilized Doppler-shifted echo CF2. 5. In addition to 27 H1-H2 neurons, 7 FM1-FM2 neurons were also recorded in the VA area. The best delays of these H1-H2 and FM1-FM2 neurons measured with FM1-FM2 pairs are between 1 and 10 ms. Unlike neurons in the FM-FM and DF areas, their delay-tuning curves are very broad, even if their best delays are short, and extend beyond zero delay to several millisecond "negative" delays of the FM2 from the FM1, i.e., several millisecond delays of the FM1 from the FM2.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1988

[Spreading excitation in the upper (I-III) layers of an isolated strip of cat auditory cortex].

Lower layers of the isolated slab in the auditory cortex were cut, one, two or three cortical layers under the pial surface remaining intact. Impulse reactions of neurons to the intracortical stimulation applied on the other side of this additional cut were investigated in acute experiments on unanaesthetized immobilized cats. It was shown that stimulation of layer IV generated a flow of excitation ascending to the upper cortical layers and activating mono- and polysynaptically neurons of all layers through the vertical bundles of apical dendrites of pyramidal cells. Suggestion is made about an important role a large bundle of axons of layer III plays in the horizontal spread of excitation in the cerebral cortex.

Animals↗
PubMed1984

[Connections between area AIV and areas AI, AII and Ep of the auditory cortex in the cat].

Zones AI A11 and Ep in the cat auditory corex have been studied layer-by-layer electron microscopically after the zone AIV has been removed. Terminals having degeneration signs according to the dark type are mainly found in the layers V-VI of all the auditory cortex zones studied. Additional degenerative zones are revealed in the layer I of the zone AII and in the layer II of the zone Ep. Not any additional foci of degeneration are found in the zone AI. A suggestion is made concerning a physiological significance of the afferent distribution in the connective systems investigated. The corticocortical connections are formed by axodendritic and axospine synapses.

Animals↗
PubMed1976

Proprioceptive effects on evoked responses to sounds in the cat auditory cortex.

With a view to analyse the influence of neck proprioceptors on directional hearing, evoked potentials (EPs) to dichotically or monaurally presented clicks were recorded from the auditory cortex of cats under deep Nembutal anaesthesia with their head pointing to the front, and then to the right or to the left side at 45 degrees. The change in the head position produced considerable changes in the amplitude of the two primary EP components and in their thresholds. The changes were of two kinds: either decrease or increase of the amplitude. At symmetrical points of the auditory cortex they went in the same direction. The also appeared in the associative zone with the same sign. With monaurally presented clicks, the change of the side of stimulation for the most part resulted in a reversal of the sign of the proprioceptive effect. Similar proprioceptive influences were recorded when the clicks were presented not through earphones but in an open acoustic field.

Animals↗