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PubMed2001

Functional specialization in rhesus monkey auditory cortex.

Neurons in the lateral belt areas of rhesus monkey auditory cortex prefer complex sounds to pure tones, but functional specializations of these multiple maps in the superior temporal region have not been determined. We tested the specificity of neurons in the lateral belt with species-specific communication calls presented at different azimuth positions. We found that neurons in the anterior belt are more selective for the type of call, whereas neurons in the caudal belt consistently show the greatest spatial selectivity. These results suggest that cortical processing of auditory spatial and pattern information is performed in specialized streams rather than one homogeneously distributed system.

Acoustic Stimulation↗
PubMed1997

Optical imaging of dynamic horizontal spread of excitation in rat auditory cortex slices.

Optical recordings using a voltage-sensitive dye (RH482) were conducted in brain slice preparations to investigate spatiotemporal patterns of excitation in the rat auditory cortex. Electrical stimulation of the border between the white matter and layer VI evoked vertical as well as horizontal spreading responses. While velocities of vertical and horizontal propagation of excitation were similar to those reported in non-disinhibited preparations, the horizontal propagation was widespread and strong especially in layers II/III in auditory cortex slices. This horizontal spread was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) but not by D-2-amino-5-phosphonopentanoic acid (D-AP5). These results suggest that the horizontal responses, especially in layers II/III, are prominent and are mediated primarily by non-N-methyl-D-aspartic acid (NMDA) receptors in the auditory cortex.

2-Amino-5-phosphonovalerate↗
PubMed1999

Sleep and wakefulness modulation of the neuronal firing in the auditory cortex of the guinea pig.

Sleep-related changes-including modification in sensory processing-that influence brain and body functions, occur during both slow wave and paradoxical sleep. Our aim was to investigate how cortical auditory neurons behave during the sleep/waking cycle, and to study cell firing patterns in relation to the processing of auditory information without the interference of anesthetic drugs. We recorded single cells in the A region of the auditory cortex in restrained, chronically-implanted guinea pigs, and compared their evoked and spontaneous activity during sleep stages and quiet wakefulness. A new classification of the unit's responses to simple sound during wakefulness is presented. Moreover, a number of the neurons in the primary auditory cortex exhibited significant quantitative changes in their evoked or spontaneous firing rates. These changes could be correlated to sleep stages or wakefulness in 42.2% to 58.3% of the sampled neurons. A similar population did not show behavioral related changes in firing rates. Our results indicate that the responsiveness of the auditory system during sleep may be considered partially preserved. An important result was that spontaneous and evoked activity may vary in opposite directions, i.e. , the evoked activity could increase while the spontaneous activity decrease or vice versa. Then, a general question was proposed: is the increased spontaneous activity in the auditory cortex, particularly during PS, related to auditory hypnic 'images'? The studied cortical auditory neurons exhibit changes in their firing rates in correlation to stages of sleep and wakefulness. This is consistent with the hypothesis that a general shift in the neuronal networks involved in sensory processing occurs during sleep.

Acoustic Stimulation↗
PubMed1999

Short-term plasticity of the human auditory cortex.

Magnetoencephalographic measurements (MEG) were used to examine the effect on the human auditory cortex of removing specific frequencies from the acoustic environment. Subjects listened for 3 h on three consecutive days to music "notched" by removal of a narrow frequency band centered on 1 kHz. Immediately after listening to the notched music, the neural representation for a 1-kHz test stimulus centered on the notch was found to be significantly diminished compared to the neural representation for a 0.5-kHz control stimulus centered one octave below the region of notching. The diminished neural representation for 1 kHz reversed to baseline between the successive listening sessions. These results suggest that rapid changes can occur in the tuning of neurons in the adult human auditory cortex following manipulation of the acoustic environment. A dynamic form of neural plasticity may underlie the phenomenon observed here.

Acoustic Stimulation↗
PubMed1998

Layer-specific NO dependence of long-term potentiation and biased NO release in layer V in the rat auditory cortex.

1. We investigated the role of nitric oxide (NO) in the induction of long-term potentiation (LTP) in slices prepared from the rat auditory cortex. 2. Tetanic stimulation of layer IV elicited LTP of field potentials in layer II-III (LTPII-III) and in layer V (LTPV). The magnitude of LTPII-III measured at 30 min after tetanic stimulation was 171 +/- 9% (n = 15, mean +/- s.e.m.) of the control measured before tetanic stimulation, while that of LTPV was 138 +/- 3% (n = 17). 3. NO synthase (NOS) inhibitors had no apparent effect on LTPII-III, but LTPV was significantly suppressed (P < 0.001). This suppression of LTPV was significantly antagonized by a NO donor (P < 0.001) or a cGMP analogue (P < 0.001). 4. Small non-pyramidal neurones in the auditory cortex were stained with an anti-neuronal NOS antibody. More neurones were stained with the antibody in the deeper cortical layers. 5. We measured neocortical NO release with electrochemical NO probes. Layer IV stimulation elicited significantly more NO release in layer V than in layer II-III (P < 0.001). The amplitude of the increase in NO concentration elicited by stimulation at 20 Hz for 5 s was 380 +/- 14 pM (n = 55) in layer V and 55 +/- 8 pM (n = 5) in layer II-III. 6. NO release in layer V was partially but significantly suppressed by non-NMDA (P < 0.002) or NMDA (P < 0.002) receptor antagonists. Simultaneous application of the antagonists of the two types blocked NO release almost completely. 7. These results clearly indicate the NO dependence of the induction of LTPV, and the greater NO release in the deeper layer of the rat auditory cortex.

Animals↗
PubMed2004

Perceptual learning on an auditory frequency discrimination task by cats: association with changes in primary auditory cortex.

The aim of this study was to determine whether auditory perceptual learning is associated with changes in the frequency organization and/or neuronal response properties of primary auditory cortex (AI). Five out of six cats trained on an 8 kHz frequency discrimination task showed improvements in performance that reflected changes in discriminative capacity. Quantitative measures of the response characteristics and frequency organization of AI revealed that the frequency organization of AI in trained cats did not differ from that in controls, but there was a tendency for neurons with a CF immediately above 8 kHz to have slightly broader tuning in the trained cats than in controls, and neurons in one of these bands had significantly shorter latency. These results are in accord with recent reports that cortical topography in primary visual cortex is unchanged in animals trained on visual discrimination tasks, but are at variance with an earlier report of enlarged representations of training frequencies in AI of monkeys trained on a frequency discrimination task. It is concluded that substantial changes in perceptual discriminative capacity can occur without change in primary cortical topography and with only small changes in neuronal response characteristics.

Acoustic Stimulation↗
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↗
PubMed2002

Morphology of Heschl's gyrus reflects enhanced activation in the auditory cortex of musicians.

Using magnetoencephalography (MEG), we compared the processing of sinusoidal tones in the auditory cortex of 12 non-musicians, 12 professional musicians and 13 amateur musicians. We found neurophysiological and anatomical differences between groups. In professional musicians as compared to non-musicians, the activity evoked in primary auditory cortex 19-30 ms after stimulus onset was 102% larger, and the gray matter volume of the anteromedial portion of Heschl's gyrus was 130% larger. Both quantities were highly correlated with musical aptitude, as measured by psychometric evaluation. These results indicate that both the morphology and neurophysiology of Heschl's gyrus have an essential impact on musical aptitude.

Acoustic Stimulation↗
PubMed2004

Loudness dependence of primary auditory-cortex-evoked activity as predictor of therapeutic outcome to prophylactic lithium treatment in affective disorders--a retrospective study.

INTRODUCTION: Lithium has been found to be very effective in prophylactic treatment of affective disorders. However, approximately one-third of patients do not respond to this treatment, which does not become apparent until after a year or more of treatment. Therefore, predictors are needed to avoid a long and unsuccessful therapy with risk of severe side effects. Since lithium acts as a serotonin agonist in prophylactic treatment, a predictor of being able to identify patients with low serotonergic activity, who may be responders to lithium, is promising. To determine whether the loudness dependence (LDAEP) of primary, but not of secondary, auditory-cortex-evoked activity, which is inversely related to central serotonergic neurotransmission, could be such a predictor, responders and non-responders to prophylactic lithium treatment were compared. METHODS: Thirty patients with uni- and bipolar affective disorders, who have taken a prophylactic lithium medication continuously for at least 3 years, were included in the study. Patients were classified as responders if they had no hospitalization within the past 3 years. Dipole source analysis allowing us to separate evoked activity of the primary and secondary auditory cortex was used. RESULTS: The LDAEP of the primary, but not of the secondary, auditory cortex was significantly stronger in the responders to the lithium treatment than in the non-responders, implicating low serotonergic function in these patients. DISCUSSION: This finding, which is in line with previous studies, suggests that loudness dependence of primary auditory-cortex-evoked activity could be a clinically relevant predictor of prophylactic treatment with lithium in affective disorders.

Adult↗
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↗
PubMed2002

Amplitopicity of the human auditory cortex: an fMRI study.

Whereas specialized frequency-encoding patterns in the human auditory cortex are generally accepted, termed tonotopicity, a similar principle of intensity encoding--amplitopicity--is debated controversially. This functional magnetic resonance imaging study describes the relationship of the activation volume and the spatial distribution of activated clusters under different sound pressure levels (SPL) across the temporal plane including the transverse temporal gyrus (TTG). Nine healthy subjects with no hearing deficiencies were investigated using an echo-planar imaging technique at 1.5 T. A boxcar stimulation paradigm was applied with a 5-Hz pulsed sine tone of 1000 Hz frequency at three SPLs of 70, 82, and 90 dB. Linear cross-correlation analysis (correlation coefficient > 0.3 corresponding to P < 0.08) of the functional data set revealed bilateral BOLD response within the auditory cortex of the nine subjects with moderate increase of activation volume for higher sound pressure levels. With increasing sound pressure a two-dimensional drift of cortical activation was observed (a) from the ventral to the dorsal edge and (b) from lateral to medial parts of TTG. This latero-medial drift therefore mimics the well-accepted principle of tonotopy for frequency-encoding neurons. This study demonstrates the existence of an amplitopic pattern of intensity-encoding neuronal clusters that in part resembles the tonotopic distribution of frequency-encoding neurons. This finding has to be integrated into the understanding of the auditory organization for the interpretation of higher auditory functions such as sound perception or speech.

Acoustic Stimulation↗
PubMed2003

Sustained blood oxygenation and volume response to repetition rate-modulated sound in human auditory cortex.

The blood oxygen level-dependent (BOLD) signal time course in the auditory cortex is characterized by two components, an initial transient peak and a subsequent sustained plateau with smaller amplitude. Because the T(2)(*) signal detected by functional magnetic resonance imaging (fMRI) depends on at least two counteracting factors, blood oxygenation and volume, we examined whether the reduction in the sustained BOLD signal results from decreased levels of oxygenation or from increased levels of blood volume. We used conventional fMRI to quantify the BOLD signal and fMRI in combination with superparamagnetic contrast agent to quantify blood volume and employed repetition rate-modulated sounds in a silent background to manipulate the response amplitude in the auditory cortex. In the BOLD signal, the initial peak reached 3.3% with pulsed sound and 1.9% with continuous sound, whereas the sustained BOLD signal fell to 2.2% with pulsed sound and to 0.5% with continuous sound, respectively. The repetition rate-dependent reduction in the sustained BOLD amplitude was accompanied by concordant changes in sustained blood volume levels, which, compared to silence, increased by approximately 30% with pulsed and by approximately 10% with continuous sound. Thus, our data suggest that the reduced amplitude of the sustained BOLD signal reflects stimulus-dependent modulation of blood oxygenation rather than blood volume-related effects.

Acoustic Stimulation↗
PubMed2002

Tonal response patterns of primary auditory cortex neurons in alert cats.

The firing rates of primary auditory cortex (A1) neurons are known to be modulated only at the onset, offset, and change of a tonal stimulus in anesthetized animals. The tonal response pattern has been rarely investigated in alert animals. We investigated the time-course of A1 neuron responses to a steady tonal stimulus in alert cats. We found four types of firing responses based on statistical evaluation of the time course of the firing rate. The tonic cells (38 cells) showed a significant (P<0.05) firing increase throughout the stimulus period after a relatively long latency (mean, 25.3 ms) with little tendency of adaptation. The phasic-tonic cells (22 cells) showed a significant firing increase throughout the stimulus period after a medium latency (19.8 ms) with tendency of adaptation to less than a half of the maximum excitation level. Phasic cells (15 cells) responded, after a short latency (10.2 ms), at onset and offset of the stimuli. The unresponsive cells (26 cells) did not show a significant firing increase during stimuli. The findings suggest that there is a functional difference between each type of cells: the tonic cells encode information of static auditory signals in their firing rates; the phasic-tonic cells, of the changing auditory signal during the stimulus period; and the phasic cells, of rapid change of the auditory signal at onset and offset.

Acoustic Stimulation↗
PubMed2002

Temporal resolution of the human primary auditory cortex in gap detection.

The temporal resolution of the primary auditory cortex was studied by recording the magnetic middle latency fields (MAEF) evoked by gaps of 3, 6 and 9 ms inserted in the middle of 600 ms broadband noise bursts. Spatio-temporal source modelling showed that a significant neural representation as reflected by MAEF responses is present at gap durations as low as 3 sms. The comparison of the MAEF waveforms elicited by the onset, gap and offset of the noise bursts indicates that the gap related response near threshold is largely determined by the onset to the burst following the gap. The electro-physiologically derived minimum detectable gap closely resembled the psychoacoustic threshold of 2.0 ms obtained in the same subjects.

Acoustic Stimulation↗
PubMed2005

Mapping auditory cortex in the La Plata dolphin (Pontoporia blainvillei).

This study deals with the mapping of the primary and secondary auditory cortex. Due to their important role in echolocation they were the first areas to be examined [P.J. Morgane, M.S. Jacobs, in: R.J. Harrison (Ed.), Functional Anatomy of Marine Mammals, Comparative Anatomy of the Cetacean Nervous System, vol. 1, Academic Press, London, 1972, pp. 117-144]. We analysed the brain of a La Plata dolphin (Pontoporia blainvillei), which had been fixed in formaldehyde, embedded in paraffin, cut in sections of 20mum thickness and stained with cresyl violet. The experimental approach being impossible, we used cytoarchitectonic variations in the neocortex. Former electrophysiological data [T.F. Ladygina, A.Y. Supin, Localization of the projectional sensory areas in the cortex of the porpoise Tursiops truncates, Zh. Evol. Biokhim. Fiziol. 13 (1978) 712-718] [Sokolov, T.F. Ladygina, A.Y. Supin, Location of sensory zones in cerebral cortex of dolphin, Dokl. Biol. Sci., Russian Original 202 (1-6) (1972)] provided the framework for the exact determination of borders between functional cortical areas. We used a stereological observer-independent procedure based on changes in volume density of cell bodies throughout the neocortex [A. Schleicher, et al., Stereological approach to human cortical architecture: Identification and delineation of cortical areas, J. Chem. Neuroanat. 20 (2000) 31-47]. Due to the computer program's high sensitivity to changes in volume density it was possible to analyse the poorly laminated dolphin cortex. The 3D-reconstruction of the auditory cortex was processed using the AMIRA 3.0 Graphics software package comparing the main primary gyri in the histological sections with those in coronal magnetic resonance imaging scans of another intact Pontoporia brain.

Animals↗
PubMed1997

Frequency resolution and spectral integration (critical band analysis) in single units of the cat primary auditory cortex.

Frequency resolution and spectral filtering in the cat primary auditory cortex (AI) were mapped by extracellular recordings of tone responses in white noise of various bandwidths. Single-tone excitatory tuning curves, critical bandwidths, and critical ratios were determined as a function of neuronal characteristic frequency and tone level. Single-tone excitatory tuning curves are inadequate measures of frequency resolution and spectral filtering in the AI, because their shapes (in most neurons) deviated substantially from the shapes of "tuning curves for complex sound analysis", the curves determined by the band limits of the critical bandwidths. Perceptual characteristics of spectral filtering (intensity independence and frequency dependence) were found in average critical bandwidths of neurons from the central and ventral AI. The highest frequency resolution (smallest critical bandwidths) reached by neurons in the central and ventral AI equaled the psychophysical frequency resolution. The dorsal AI is special, since most neurons there had response properties incompatible with psychophysical features of frequency resolution. Perceptual characteristics of critical ratios were not found in the average neuronal responses in any area of the AI. It seems that spectral integration in the way proposed to be the basis for the perception of tones in noise is not present at the level of the AI.

Acoustic Stimulation↗
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↗