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PubMed1980

[Quantitative and qualitative characteristics of synapses in different layers of the auditory cortex].

The electron-microscopic examination of synapses in different layers of the cat auditory cortex was performed. 53% of them were located on dendritic spines, 37% on dendrites and 10% on neuronal soma. All synapses were separated into type I and type II according to Gray. The type I synapses amounted to 91% (69.5% were of type Ia and 21.5% of type Ib), the type II synapses constituted 9%. The type I synapses were located mainly on dendrites and dendritic spines, the type II--on neuronal soma, axon hillocks and large dendrites. 60 h after complete neuronal isolation of a portion of the auditory cortex 22.8% of synapses revealed signs of degeneration. No type II degenerating synapses were found. This indicates that they are formed by axons of intracortical neurons. Quantitative and qualitative composition of synapses in different layers of the auditory cortex is shown to be different.

Animals↗
PubMed1993

High metabolic activity demonstrated by positron emission tomography in human auditory cortex in case of deafness of early onset.

Glucose metabolism has been studied in the auditory cortex of human subjects with deafness of early onset, and compared to normal subjects with ears plugged. The metabolism in the auditory cortex and in the association auditory cortex was higher in deaf subjects than in normal subjects. This result is compared to similar observations that we made previously in the visual cortex of human subjects with blindness of early onset.

Adolescent↗
PubMed1989

Frequency and space representation in the primary auditory cortex of the frequency modulating bat Eptesicus fuscus.

1. Frequency and space representation in the auditory cortex of the big brown bat, Eptesicus fuscus, were studied by recording responses of 223 neurons to acoustic stimuli presented in the bat's frontal auditory space. 2. The majority of the auditory cortical neurons were recorded at a depth of less than 500 microns with a response latency between 8 and 20 ms. They generally discharged phasically and had nonmonotonic intensity-rate functions. The minimum threshold, (MT) of these neurons was between 8 and 82 dB sound pressure level (SPL). Half of the cortical neurons showed spontaneous activity. All 55 threshold curves are V-shaped and can be described as broad, intermediate, or narrow. 3. Auditory cortical neurons are tonotopically organized along the anteroposterior axis of the auditory cortex. High-frequency-sensitive neurons are located anteriorly and low-frequency-sensitive neurons posteriorly. An overwhelming majority of neurons were sensitive to a frequency range between 30 and 75 kHz. 4. When a sound was delivered from the response center of a neuron on the bat's frontal auditory space, the neuron had its lowest MT. When the stimulus amplitude was increased above the MT, the neuron responded to sound delivered within a defined spatial area. The response center was not always at the geometric center of the spatial response area. The latter also expanded with stimulus amplitude. High-frequency-sensitive neurons tended to have smaller spatial response areas than low-frequency-sensitive neurons. 5. Response centers of all 223 neurons were located between 0 degrees and 50 degrees in azimuth, 2 degrees up and 25 degrees down in elevation of the contralateral frontal auditory space. Response centers of auditory cortical neurons tended to move toward the midline and slightly downward with increasing best frequency. 6. Auditory space representation appears to be systematically arranged according to the tonotopic axis of the auditory cortex. Thus, the lateral space is represented posteriorly and the middle space anteriorly. Space representation, however, is less systematic in the vertical direction. 7. Auditory cortical neurons are columnarly organized. Thus, the BFs, MTs, threshold curves, azimuthal location of response centers, and auditory spatial response areas of neurons sequentially isolated from an orthogonal electrode penetration are similar.

Acoustic Stimulation↗
PubMed1988

Organization of auditory cortex in the albino rat: sound frequency.

1. Responses of neurons in the auditory cortex of the albino rat were examined using microelectrode mapping techniques. Characteristic frequencies were determined for numerous electrode penetrations across the cortical surface in individual animals. A primary auditory area was identified in the posterolateral neocortex that was characterized by short latency responses to tone bursts and tonotopic organization with high frequencies represented rostrally and low frequencies, caudally. Within this area cells with similar characteristic frequencies were aligned in a dorsoventral orientation to form isofrequency contours. 2. Tuning curves obtained from primary auditory cortex were characteristically "V" shaped with Q10's ranging from 0.97 to 28.4. Maximum Q10 values increased monotonically with characteristic frequency (CF). The lowest thresholds at CF closely approximated the behavioral audiogram for the albino rat. Many neurons, however, had CF thresholds well above the behavioral limit. 3. Areas were found dorsal and ventral to the primary auditory cortex in which CF's were clearly discontinuous with the neighboring isofrequency contours. These data suggest the presence of other auditory fields, the detailed characteristics of which have yet to be examined.

Acoustic Stimulation↗
PubMed1994

Brain SPET and auditory cortex perfusion. Technical notes and preliminary results.

Auditory cortex stimulation was studied by 99Tcm-hexamethylpropyleneamine oxime (HMPAO) single photon emission tomography (SPET) in 11 patients with normal vestibular and auditory tests, as well as computed tomography. Markedly increased temporal and parietal blood flows were found in left brain cortex, contralateral to the stimulus. The right auditory areas showed moderate hyperactivity. The method might be useful for tonotopic mapping of auditory cortex, using various pure tonal stimuli.

Acoustic Stimulation↗
PubMed1994

Population responses to multifrequency sounds in the cat auditory cortex: one- and two-parameter families of sounds.

Population responses to multi-frequency sounds were recorded in primary auditory cortex of anesthetized cats. The sounds consisted of single-tone stimuli; two-tone stimuli; and nine-tone stimuli, with the tones evenly spaced on a linear frequency scale. The stimuli were presented through a sealed, calibrated sound delivery system. Single units, cluster activity (CA) and the short-time mean absolute value of the envelope of the neural signal (MABS) were recorded extracellularly from six microelectrodes simultaneously. The CA and MABS were interpreted as measures of the activity of large populations of neurons, in contrast with the single unit activity which is presumably recorded from single neurons. The responses of the MABS signal to simple stimuli were generally similar to those of the CA, but were more stable statistically. Thus, the MABS is better suited for studying the activity of populations of neurons. The responses to tones near the best frequency were strongly influenced by a second tone, even when the second tone was outside the single-tone response area. These influences could be both facilitatory and suppressory. They could not be predicted from the responses to single tones. The responses to the nine-tone stimuli could be explained qualitatively by the responses to the two-tone stimuli. It is concluded that the population responses in primary auditory cortex are shaped by the contributions of the individual frequencies appearing in the stimulus and by the interactions between pairs of frequencies. Interactions between stimulus components are therefore a necessary component of any attempt to explain the processing of complex sounds in the auditory cortex. They may play a role in a global representation of the stimulus spectrum in the primary auditory cortex. The presence of higher-order interactions cannot be excluded by the results presented here.

Acoustic Stimulation↗
PubMed1991

Landau-Kleffner syndrome: epileptic activity in the auditory cortex.

The Landau-Kleffner syndrome (LKS) is characterized by electroencephalographic spike discharges and verbal auditory agnosia in previously healthy children. We recorded magnetoencephalographic (MEG) spikes in a patient with LKS, and compared their sources with anatomical information from magnetic resonance imaging. All spikes originated close to the left auditory cortex. The evoked responses were contaminated by spikes in the left auditory area and suppressed in the right--the latter responses recovered when the spikes disappeared. We suggest that unilateral discharges at or near the auditory cortex disrupt auditory discrimination in the affected hemisphere, and lead to suppression of auditory information from the opposite hemisphere, thereby accounting for the two main criteria of LKS.

Aphasia↗
PubMed1995

Specific tonotopic organizations of different areas of the human auditory cortex revealed by simultaneous magnetic and electric recordings.

This paper presents data concerning auditory evoked responses in the middle latency range (wave Pam/Pa) and slow latency range (wave N1m/N1) recorded from 12 subjects. It is the first group study to report multi-channel data of both MEG and EEG recordings from the human auditory cortex. The experimental procedure involved potential and current density topographical brain mapping as well as magnetic and electric source analysis. Responses were compared for the following 3 stimulus frequencies: 500, 1000 and 4000 Hz. It was found that two areas of the auditory cortex showed mirrored tonotopic organization; one area, the source of N1m/N1 wave, exhibited higher frequencies at progressively deeper locations, while the second area, the source of the Pam/Pa wave, exhibited higher frequencies at progressively more superficial locations. The Pa tonotopic map was located in the primary auditory cortex anterior to the N1m/N1 mirror map. It is likely that N1m/N1 results from activation of secondary auditory areas. The location of the Pa map in A1, and its N1 mirror image in secondary auditory areas is in agreement with observations from animal studies.

Acoustic Stimulation↗
PubMed1994

[Changes of auditory brainstem response and auditory cortex response after exposure to intensive noise].

Auditory brainstem response and auditory cortex response were recorded repeatedly in 35 guinea pigs after exposure to intensive white noise (125 dB, 150 min.) for 62 d. the amplitude of evoked potential of acoustic nerve was decreased by 29% (P < 0.05), of the cochlear nuclei by 28% (P < 0.05). However, the amplitude of response of superior olives nuclei was increased by 21% (P < 0.05), of the inferior colliculi by 37% (P < 0.05), of the cortical evoked response by 131% (P < 0.001). The results indicate that the amplitudes of auditory evoked potential showed a centripital augmentation after exposure to intensive noise. The centripital augmentation was observed not only during the period of the temporary threshold shift (TTS) but also during that of the permanent threshold shift (PTS).

Animals↗
PubMed1980

Anatomical and physiological evidence for a relationship between the 'cingular' vocalization area and the auditory cortex in the squirrel monkey.

With the aid of the autoradiographic tracing technique the projections from cortical limbic vocalization areas to the auditory cortex in the superior temporal gyrus were studied in the squirrel monkey. The vocalization areas were identified by exploring the anterior limbic cortex with moving electrodes until a site was found where electrical stimulation yielded vocalization. Projections from the region around the cingulate sulcus and supracallosal anterior cingulate gyrus have their terminal fields in the lower part of the superior temporal gyrus (STG) and upper bank of the superior temporal sulcus. Injections just in front of the genu of the corpus callosum and in the subcallosal gyrus and gyrus rectus lead to terminal fields in the middle part of STG. No projections were found in the upper part of STG, i.e. the primary auditory cortex. To test the functional properties of this pathway, action potentials of single neurons in the auditory cortex were recorded during electrical stimulation of the cingular vocalization area. From a total of 135 STG neurons, an effect on spontaneous activity was seen in 27 cells. All except one of these neurons also reacted to acoustic stimuli. In most cases, stimulation of the cingular area caused a decrease in the discharge rate of the STG neurons. In 4 neurons, stimulation of the vocalization area had an influence on the acoustic reactivity of the STG neurons. The results provide evidence that during phonation the 'cingular' vocalization area exerts a predominantly inhibitory influence on auditory cortex neurons. This effect probably is mediated via the extreme capsule. Its possible function is discussed.

Animals↗
PubMed1991

Morphology of corticothalamic terminals arising from the auditory cortex of the rat: a Phaseolus vulgaris-leucoagglutinin (PHA-L) tracing study.

Phaseolus vulgaris-leucoagglutinin (PHA-L) injection in the auditory cortex of the rat labeled anterogradely corticothalamic axons whose trajectory, morphology of terminals and their distribution were analyzed in light microscopy. From the primary auditory cortex, corticofugal axons ran in a rostral direction in the white matter (external capsule), and reached the internal capsule by crossing the caudate putamen. Then, they turned caudally, crossed the reticular nucleus (RE) of the thalamus, where some of them were seen to give off collaterals, ramifying in the 'auditory sector' of RE. From RE, the parent corticofugal axons continued in a caudal and medial direction to enter in the medial geniculate body (MGB). Corticofugal axons from the auditory cortex gave rise to 2 distinct types of terminals in the thalamus. First, small boutons (about 1 micron in diameter) were observed in the ventral division of the MGB (v-MGB; the main auditory relay nucleus in the thalamus), in RE, in the lateral part of the posterior thalamic nucleus, in the dorsal division of the MGB (d-MGB), as well as occasionally in the medial division of the MGB. Giant terminals (5-10 microns in diameter) formed the second type of cortical terminals, only present in a restricted zone of the ventral portion of d-MGB. Both types of terminals were observed as boutons 'terminaux' and 'en passant'. The zone of termination in v-MGB and RE varied as a function of the site of cortical injection. The similarity in the morphology and distribution of the terminals of corticothalamic axons arising from the primary auditory cortex with those of the primary somatosensory cortex of the mouse is striking and points to the existence of a basic pattern of connectivity used in corticothalamic processing of sensory information in rodents.

Animals↗
PubMed1981

Tone-versus FM--induced patterns of excitation and suppression in the 14-C-2-deoxyglucose labeled auditory "cortex" of the guinea fowl.

The primary auditory "cortex" field L, of the Guinea fowl is a three layer tonotopically organized structure. Isofrequency planes as shown with the 2-deoxyglucose (2DG) method cut across these layers and with their second dimension extend in rostro-caudal direction. The input layer L2 exhibits "spontaneous" labeling due to high spontaneous activity of input terminals and units throughout the hearing range. The labeling is stronger locally along a rostro-caudal isofrequency contour of L2 after tone or narrow band FM stimulation. With tone stimuli the layers L1 and L3 are labeled within an isofrequency plane except for the rostral half of the field whereas frequency modulated tones do label these two layers throughout the corresponding isofrequency plane. FM stimuli in addition lead to a reduction of spontaneous labeling in frequency planes adjacent to those which are covered by the stimuli. Since these effects correlate with known inhibitory effects of such stimuli it is argued that the 2 DG method can identify the suppression of activity of neurons in suitable structures.

Animals↗
PubMed1991

Rate and synchronization measures of periodicity coding in cat primary auditory cortex.

Periodicity coding was studied in primary auditory cortex of the ketamine anesthetized cat by simultaneously recording with two electrodes from up to 6 neural units in response to one second long click trains presented once per 3 s. Trains with click rates of 1, 2, 4, 8, 16 and 32/s were used and the responses of the single units were quantified by both rate measures (entrainment and rate modulation transfer function, rMTF) and synchronization measures (vector strength VS and temporal modulation transfer functions, tMTF). The rate measures resulted in low-pass functions of click rate and the synchrony measures resulted in band-pass functions of click rate. Limiting rates (-6 dB point of maximum response) were in the range of 3-24 Hz depending on the measure used. Best modulating frequencies were in the range of 5-8 Hz again depending on the synchrony measure used. It appeared that especially the VS was highly sensitive to spontaneous firing rate, duration of the post click suppression and the size of the rebound response after the suppression. These factors were dominantly responsible for the band-pass character of the VS-rate function and the peak VS frequency was nearly identical to the inverse of the suppression period. It is concluded that the use of the VS and to a lesser extent also the tMTF as the sole measure for the characterization of periodicity coding is not recommended in cases where there is a strong suppression of spontaneous activity. The combination of entrainment and tMTF appeared to characterize the periodicity coding in an unambiguous way.

Acoustic Stimulation↗
PubMed1994

Detection of stimulus deviance within primate primary auditory cortex: intracortical mechanisms of mismatch negativity (MMN) generation.

Mismatch negativity (MMN) is a cognitive, auditory event-related potential (AEP) that reflects preattentive detection of stimulus deviance and indexes the operation of the auditory sensory ('echoic') memory system. MMN is elicited most commonly in an auditory oddball paradigm in which a sequence of repetitive standard stimuli is interrupted infrequently and unexpectedly by a physically deviant 'oddball' stimulus. Electro- and magnetoencephalographic dipole mapping studies have localized the generators of MMN to supratemporal auditory cortex in the vicinity of Heschl's gyrus, but have not determined the degree to which MMN reflects activation within primary auditory cortex (AI) itself. The present study, using moveable multichannel electrodes inserted acutely into superior temporal plane, demonstrates a significant contribution of AI to scalp-recorded MMN in the monkey, as reflected by greater response of AI to loud or soft clicks presented as deviants than to the same stimuli presented as repetitive standards. The MMN-like activity was localized primarily to supragranular laminae within AI. Thus, standard and deviant stimuli elicited similar degrees of initial, thalamocortical excitation. In contrast, responses within supragranular cortex were significantly larger to deviant stimuli than to standards. No MMN-like activity was detected in a limited number to passes that penetrated anterior and medial to AI. AI plays a well established role in the decoding of the acoustic properties of individual stimuli. The present study demonstrates that primary auditory cortex also plays an important role in processing the relationships between stimuli, and thus participates in cognitive, as well as purely sensory, processing of auditory information.

Acoustic Stimulation↗
PubMed1984

[Primary inhibitory responses of neurons of a chronically isolated band of auditory cortex to intracortical stimulation].

The reactions of 579 neurons to intracortical stimulation of an auditory cortex slab (three weeks after its isolation) were studied intracellularly in three series of experiments on cats. The distances between stimulating and recording electrodes were 0.5, 1.0 and 2.0 mm. It was shown that 67.7% of neurons responded to intracortical stimulation by primary IPSP, which is by 10% more than that in acute isolated slab. The distribution of neurons reacting by primary IPSP was analysed according to the depth of location in the isolated slab and to the duration of IPSPs and their latent periods depending on the distance between the point of stimulating and recording microelectrodes. Latent periods of IPSPs did not exceed 10 ms like in an acute isolated slab. Amplitude and duration of IPSP were in the same range as in acute isolated slab and intact auditory cortex of cat brain. The histological structure of the chronically isolated auditory cortex slab is described.

Animals↗
PubMed1996

Stimulus-induced spike bursts in two fields of cat auditory cortex.

The sound-evoked responses of extracellularly recorded cat primary auditory cortical neurons usually consist of a single spike or a short-term burst of 2-4 spikes, irrespective of the nature of the acoustic signal. In the cat's auditory cortex, the properties of such responses have to date been described only for cells in the primary field (AI). The purpose of the present study was to describe the properties of stimulus-evoked spike-burst responses seen in neurons of the posterior auditory field (P) and to compare those properties with those of a sample of AI neurons studied under similar conditions. The data come from 80 field P and 31 AI neurons studied with tonal and noise-burst stimuli in barbiturate-anesthetized cats, using calibrated, sealed stimulus delivery systems and conventional extracellular recording techniques. The mean inter-spike intervals (ISI) seen in the transient burst responses of posterior field cells were typically short (2-5 ms) and, where it was possible to test them, independent of the rise time of tonal signals, suggesting that they were also independent of the onset spectrum of the stimulus. The mean ISIs were often independent of the stimulus amplitude, even though the signal level had profound effects on the number of spikes evoked and the latency and regularity with which the responses were initiated. Each neuron was assigned a 'characteristic ISI', i.e., the mean ISI seen in the most vigorous responses. The distribution of characteristic ISIs for AI and P neurons overlapped, but were significantly different, with the characteristic ISIs of field P neurons being longer. In both AI and P populations, characteristic ISI was significantly correlated with minimal first-spike latency. The slopes of the regression lines of characteristic ISI on minimal latency for AI and for P cells were not significantly different from each other. Since the minimal latencies of AI neurons were usually shorter than those of field P neurons, the shorter characteristic ISIs of AI cells may thus be interpreted as secondary to their shorter latent periods. The general properties of stimulus-evoked spike bursts seen in field P neurons were thus very similar those previously described for AI cells. These data are consistent with the view that the majority of extracellular recordings in the cat's auditory cortex come from pyramidal neurons and are appropriate as a specialization for transfer of information to nonpyramidal, inhibitory interneurons.

Acoustic Stimulation↗
PubMed1990

Auditory cortex of the long-eared hedgehog (Hemiechinus auritus). I. Boundaries and frequency representation.

The boundaries of the primary auditory cortex of the long-eared hedgehog, Hemiechinus auritus, were determined by single-cell recordings, myeloarchitecture and retrograde horseradish peroxidase labeling in the medial geniculate, using anesthetized animals. The auditory cortex is located on the lateral surface of the temporal cortex, medial to the rhinal fissure. Responses to pure tones revealed an orderly representation of best frequencies in the primary auditory cortex, with low frequencies represented rostrally and high frequencies caudally. A second auditory field caudal to the primary one was indicated.

Animals↗