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PubMed2005

Some quantitative measures of structural asymmetry in fields 41 and 22 of the human auditory cortex.

The aim of the present work was to perform a quantitative study of the cytoarchitectonic features of cortical fields 41 and 22 in the left and right hemispheres of the human brain. Studies addressed frontal sections of the brains of 10 subjects (right-handers) aged 29-59 years, stained with cresyl violet by the Nissl method; sections were 20 microm thick. The following quantitative parameters were measured: volume of field, thickness of cortex, and neuron field profile area. The results showed that field 22, which is the associative component in the processing of speech stimuli, was characterized by left-hemisphere asymmetry of measures of cortical volume, cortical thickness, and the neuron field profile area. Field 41, which is a projection field involved in the reception of sound stimuli, was characterized by right-hemisphere asymmetry for measures of neuron field profile area but no asymmetry in favour of either hemisphere for cortical volume or cortical thickness.

Adult↗
PubMed2006

Effects of prosodic emotional intensity on activation of associative auditory cortex.

Functional magnetic resonance imaging was used to investigate hemodynamic responses to adjectives pronounced in happy and angry intonations of varying emotional intensity. In separate sessions, participants judged the emotional valence of either intonation or semantics. To disentangle effects of emotional prosodic intensity from confounding acoustic parameters, mean and variability of volume and fundamental frequency of each stimulus were included as nuisance variables in the statistical models. A linear dependency between hemodynamic responses and emotional intensity of happy and angry intonations was found in the bilateral superior temporal sulcus during both tasks, indicating that increases of hemodynamic responses in this region are elicited by both positive and negative prosody independent of low-level acoustic properties and task instructions.

Acoustic Stimulation↗
PubMed2004

Is voice processing species-specific in human auditory cortex? An fMRI study.

Recent studies suggested a sensitivity of regions of the human superior temporal sulcus (STS) to the sound of the human voice. However, the question of the species specificity of this response is still open. Healthy adult volunteers were scanned in an event-related fMRI design to compare responses in the STS to human and animal vocalizations, as well as to control nonvocal sounds (e.g., musical instruments). Bilateral activation of anterior STS was observed for human vocalizations, when contrasted with both nonvocal sounds and animal vocalizations. Animal vocalizations, compared to nonvocal sounds, elicited a more restricted left STS activation, although this region responded even more strongly to human vocalizations. This study provides the first evidence suggesting a species specificity in STS responses to vocalizations in humans.

Acoustic Stimulation↗
PubMed2002

Neuromagnetic auditory cortex responses to duration and pitch changes in tones: cross-linguistic comparisons of human subjects in directions of acoustic changes.

Our recent magnetic mismatch field (MMF) study found that shortened-vowel duration changes and level-to-falling pitch changes in Japanese words elicited a prominent MMF in two hemispheres for both native and nonnative speakers (Inouchi, M., Kubota, M., Ferrari, P. and Roberts, T.P.L., Magnetic mismatch fields elicited by Japanese words: vowel duration and pitch by native and nonnative speakers, Poster presented at the 31st Annual Meeting of Society for Neuroscience, November 10-15, San Diego, CA, 2001). The current study investigated whether shortened duration changes and level-to-falling pitch changes in non-speech (tones) would elicit a more prominent MMF component than lengthened duration changes and falling-to-level pitch changes, respectively. Stimuli included three computer-synthesized tones with varying duration or frequency modulation: (1). short duration and level pitch; (2). long duration and level pitch; (3). long duration and falling pitch. Magnetoencephalography responses were recorded with a dual 37-channel gradiometer system. The results showed that the prominent MMF component was generated in long-to-short duration changes and level-to-falling pitch changes in each hemisphere for both Japanese and American subjects. The component peaked at around 100 ms after change onset for duration changes and 170 ms for pitch changes. The MMF component in tones, like in words, was particularly sensitive to duration shortening and pitch falling. In summary, changes in duration shortening and pitch falling are particularly salient cues for pre-attentive auditory change detection in each hemisphere.

Adult↗
PubMed2004

[Quantitative parameters of structural asymmetry of auditory cortex area 41 and 21 in the human brain].

The aim of this work was to give a quantitative characteristic of cytoarchitectonic peculiarities of cortical areas 41 and 22 in the left and right hemispheres of human brain. 20 mm thick frontal brain sections of 10 right-handed adult persons aged 29-59 stained by Nissl's crezyl-violet method were studied. The following quantitative parameters determined included area volume, cortical thickness and neuron profile area. It was shown that area 22, which is considered to be an associative link in speech stimuli processing, possessed a leftward asymmetry in cortical volume, cortical thickness and neuron profile area. Area 41, which is known to be a projection zone and to participate in sound stimuli reception, was characterized by rightward asymmetry in neuron profile area, while no dominance of particular hemisphere was found as far as cortical volume and thickness were concerned.

Adult↗
PubMed1993

A possible neuronal basis for representation of acoustic scenes in auditory cortex of the big brown bat.

Behavioural studies and field observations demonstrate that echolocating bats simultaneously perceive range, direction and shape of multiple objects in the environment as acoustic images derived from echoes. Cortical echo delay-tuned neurons contribute to the perception of object range, because focal inactivation of these neurons disrupts behavioural discrimination of range. We report here that response properties of delay-tuned neurons in the cortical tonotopic area of the bat, Eptesicus, transform the sequential arrival times of echoes with different delays into a concurrent, accumulating neural representation of multiple objects at different ranges. The sharpness of delay tuning systematically increases at each best delay in a subpopulation of these neurons while responses to echoes at different delays are accumulated. The resulting concurrent, multiresolution representation of echo delay corresponds to neural implementation of a common representation of images used in computational vision and may provide the basis for representing acoustic images of multiple objects as acoustic 'scenes'.

Acoustic Stimulation↗
PubMed2003

Phonological grammar shapes the auditory cortex: a functional magnetic resonance imaging study.

Languages differ depending on the set of basic sounds they use (the inventory of consonants and vowels) and on the way in which these sounds can be combined to make up words and phrases (phonological grammar). Previous research has shown that our inventory of consonants and vowels affects the way in which our brains decode foreign sounds (Goto, 1971; Näätänen et al., 1997; Kuhl, 2000). Here, we show that phonological grammar has an equally potent effect. We build on previous research, which shows that stimuli that are phonologically ungrammatical are assimilated to the closest grammatical form in the language (Dupoux et al., 1999). In a cross-linguistic design using French and Japanese participants and a fast event-related functional magnetic resonance imaging (fMRI) paradigm, we show that phonological grammar involves the left superior temporal and the left anterior supramarginal gyri, two regions previously associated with the processing of human vocal sounds.

Acoustic Stimulation↗
PubMed1982

Structure of human auditory cortex. III. Statistical analysis of dendritic trees.

3-Dimensional coordinates of Golgi-impregnated neurons in left and right human areas TA, TB and TC were stored using computer microscopy. The tangential extent of neurons was taken to be an estimate of their effective radius, which is a compromise between their maximum radius and the average tangential projection of their dendrites. Analysis of variance and t-test comparisons were made among the areas and between the hemispheres on a total data base of 622 neurons. It was assumed that the neurons are organized in functional columns. The tangential extent of left-hemisphere columns is absolutely larger than on the right, but is smaller relative to the column-column interval. Neuropil on the left is packed more densely with dendrites belonging to the nearest column. It seems that during the course of evolution interconnected units (as in the right hemisphere) have become more disentangled (left hemisphere), yielding perhaps a greater capacity for differentiated responses in the latter case. A more detailed analysis revealed that much of the difference between areas and/or hemispheres was due to the pyramidal neurons. The structure of non-pyramidal cells is relatively consistent within each hemisphere and shows non-systematic differences between the hemispheres.

Aged↗
PubMed2005

Bistable network behavior of layer I interneurons in auditory cortex.

GABAergic interneurons in many areas of the neocortex are mutually connected via chemical and electrical synapses. Previous computational studies have explored how these coupling parameters influence the firing patterns of interneuronal networks. These models have predicted that the stable states of such interneuronal networks will be either synchrony (near zero phase lag) or antisynchrony (phase lag near one-half of the interspike interval), depending on network connectivity and firing rates. In certain parameter regimens, the network can be bistable, settling into either stable state depending on the initial conditions. Here, we investigated how connectivity parameters influence spike patterns in paired recordings from layer I interneurons in brain slices from juvenile mice. Observed properties of chemical and electrical synapses were used to simulate connections between uncoupled cells via dynamic clamp. In uncoupled pairs, action potentials induced by constant depolarizing currents had randomly distributed phase differences between the two cells. When coupled with simulated chemical (inhibitory) synapses, however, these pairs exhibited a bimodal firing pattern, tending to fire either in synchrony or in antisynchrony. Combining electrical with chemical synapses, prolonging tau(Decay) of inhibitory connections, or increasing the firing rate of the network all resulted in enhanced stability of the synchronous state. Thus, electrical and inhibitory synaptic coupling constrain the relative timing of spikes in a two-cell network to, at most, two stable states, the stability and precision of which depend on the exact parameters of coupling.

Animals↗
PubMed2005

Quantitative proton MR spectroscopic findings of cortical reorganization in the auditory cortex of musicians.

BACKGROUND AND PURPOSE: Brain has a capacity for reorganization that enables use-dependent adaptations to acquire skills. Previous studies demonstrated morphometric and functional use-dependent changes in the brains of musicians. The purpose of this study was to investigate the differences in metabolite concentrations in the planum temporale, an area strongly associated with the processing of music perception, between trained musicians and non-musicians. We hypothesized that the microscopic changes leading to use-dependent adaptations in brain might cause neurometabolite changes that could be detected with quantitative proton MR spectroscopy. METHODS: We performed quantitative proton MR spectroscopy in the left planum temporale of 10 musicians (six men and four women; age range, 20-37 years) and in those of 10 age- and sex-matched control subjects who had no musical training. We calculated the major metabolite concentrations in the left planum temporale. RESULTS: The difference in N-acetylaspartate (NAA) concentrations between the musicians and the non-musician control subjects was statistically significant (P <.01). No significant difference was noted in the choline and creatine concentrations between the musicians and the non-musician control subjects (P >.05). The NAA concentration of the musicians correlated with the total duration of musical training and activity (r=0.733, P <.05). CONCLUSION: Long-term, professional musical activity caused significant changes in the neurometabolite concentrations that might reflect the physiologic mechanism(s) of use-dependent adaptation in the brains of musicians.

Adult↗
PubMed1992

Processing of pure-tone and FM stimuli in the auditory cortex of the FM bat, Myotis lucifugus.

FM bats perceive their surroundings during echolocation by analyzing frequency-modulated (FM) acoustic signals. Results from this study indicate a cortical organization in Myotis lucifugus which is largely made up of neurons sensitive to FM sounds (FM-sensitive neurons). Three types of neurons were distinguished by their responses to pure-tone and FM stimuli: (1) Type I FM-sensitive units (83%), Type II FM-sensitive units (13%) and pure-tone sensitive units (4%). Type I FM-sensitive units responded to pure tones, but exhibited greater response magnitudes to FM stimuli when the best FM swept through the BF. An orderly frequency representation was found when the frequencies of pure tones essential for response (EPTs) in Type I units were mapped along the cortical surface. The EPTs for Type I neurons were usually found within the last millisecond of a downward FM sweep. As outlined by two neuronal network models, both the responses of Type I and II units could likely result from the convergence of excitatory and inhibitory lower level neurons with slightly differing BFs. Type II units were selective for an FM sweep and showed negligible to no response to pure-tone stimuli. Pure-tone sensitive units exhibited weak or no responses to FM stimuli. These neurons were clustered in a small area located rostrodorsal to the tonotopic zone and had significantly lower best frequencies than adjacent EPT frequencies of Type I FM-sensitive neurons.

Acoustic Stimulation↗
PubMed2000

Multiple representations of information in the primary auditory cortex of cats. II. Stability and change in early (<32 ms), rapid components of activity after conditioning with a click conditioned stimulus.

Activity was recorded from single units of the A(I) cortex of awake animals to identify early (<32 ms) components of the population response to a 70 dB click and establish if they changed after using the click as a CS for conditioning. A 70 dB hiss was used as a discriminative stimulus. Responses to these stimuli were compared before and after a forward order of pairing that produced conditioning and a backward order of pairing that produced weak sensitization (backward conditioning). Averages of discharges in 2 and 4 ms bins distinguished primary (8-12 ms) from secondary (12-16 ms) temporal components of response to the click, and confirmed that the onset of the response was shorter in A(I) (8 ms, mean of 647 units) than in the adjacent, A(II) cortex (16 ms, mean of 95 units). (All times include a 1.6 ms transmission delay in sound arrival.) Primary and secondary components of A(I) responses to click did not change uniformly after changes in behavioral state, and were affected differently by both conditioning and backward conditioning. The percentage of cells with onsets of response to the click at secondary latencies (and to the hiss at tertiary latencies) increased after backward conditioning but not after conditioning, as did the magnitude of activity in response to the click. (The latter had a lesser degree of increase after conditioning.) The primary response to the click did not show these increases. The non-uniform changes suggested that temporal processing of the click was conducted differently in the 8-12 ms post stimulus period than in the 12-16 ms period. Within the total population of cells, it was possible to identify a small subgroup (13%) of highly auditory-responsive units that showed an increased primary response to the click as a CS selectively after conditioning and not after backward conditioning. The secondary component of response in these cells increased after both conditioning and backward conditioning. The percentages of cells responding to the click and hiss at primary latencies did not change significantly after conditioning, even in the subgroup of highly responsive cells. The results characterize differently timed components of rapid responses to acoustic stimuli in the A(I) cortex, disclose significant temporal differences in primary, secondary and tertiary information processing that affect the representations of the transmitted acoustic message across different behavioral states, and find one representation in a small subgroup of cells that supports the hypothesis that cells of the A(I) cortex have a selectively potentiated response to the CS after conditioning.

Acoustic Stimulation↗
PubMed1991

GABA neuronal subpopulations in cat primary auditory cortex: co-localization with calcium binding proteins.

GABA immunoreactive neurons are present in all layers of cat AI and in the subjacent white matter; they are most numerous in layer II, the superficial half of layer III and layer IV. Double labeling immunofluorescence reveals that subpopulations of the GABA neurons are immunoreactive for the calcium binding proteins (CaBP), calbindin (28 kDa vitamin D-dependent calcium binding protein) and parvalbumin. Both proteins are present exclusively with GABA neurons but in subpopulations that are entirely separate. The two proteins together are present in approximately 70-75% of the GABA neurons; the largest group of GABA neurons displaying no CaBP immunoreactivity is in layers I-IIIA and VI. Calbindin immunoreactive neurons are present in two bands within cat AI: a superficial band, made up of numerous stained somata and processes, that includes layers II and IIIA and a deeper band, containing fewer neurons, that is coextensive with layer VI. Isolated calbindin somata are scattered between the two bands and very rarely in the subcortical white matter. Parvalbumin immunoreactive neurons are very densely packed in layers IIIB and layer IV, and include the majority of GABA neurons in layer IV; they are also numerous in layer VI. Parvalbumin immunoreactive neurons are much less numerous in layers II, IIIA and V and are absent from layer I. Light microscopic analyses suggest that the two subpopulations of GABA/CaBP neurons include several morphological types. In addition to the intrinsic somata and processes, numerous axons in white matter subjacent to AI are immunoreactive for either or both of the two proteins. These data demonstrate that cat AI is similar to other cortical areas in other species in possessing subpopulations of GABA neurons that express the CaBPs, calbindin and parvalbumin.

Acetylcholinesterase↗
PubMed2001

Analysis of transient expression of estrogen receptor-alpha in newborn rat primary auditory cortex.

In the primary temporal cortex (Te1) of newborn rats, we detected transient expression of alpha-type estrogen receptor (ER alpha). Since they have a pyramidal-like shape, they are considered neurons. By immunohistochemistry we found that they were absolutely devoid of glial fibrillary acidic protein but some of them contained calretinin, a calcium binding protein. It is already known that neurons in layer V of the Te1 extend their projections to the contralateral side of the Te1, the ipsilateral inferior colliculus, or the ipsilateral medial geniculate nucleus. Thus, we applied a retrograde track tracer into those regions of newborn rats and examined the possible colocalization of ER alpha signals and the tracer in the same cells. So far no clear colocalization of both signals has been detected in cells in the Te1. Thus, the cells expressing ER alpha transiently are not projecting to the assumed regions, at least at the newborn age examined in the present experiment. The possibility exists that (1) they are not projection neurons but local interneurons, (2) even though they are projection neurons, they did not have any synaptic contacts with their target region(s), (3) they may die after they are attached to the target neurons. Further analyses are needed to clarify the biological roles of ER alpha expressed transiently in these neurons. On the other hand, no ER beta cells were detected in the same region of the brain under the same condition. Thus, this finding was limited to the ER alpha.

Animals↗
PubMed1976

Single unit study of binaural interaction in the auditory cortex of the chinchilla.

The primary aim of this investigation was to systematically compare for various stimulus conditions the relative influences of contralateral and ipsilateral acoustic stimulation on cortical single units in an unanesthetized preparation and to study the effects upon single unit responses of the dominant stimulus cues for sound localization--interaural intensity difference (deltaI) and interaural time difference (deltat). Recordings were obtained from 133 units in chinchillas immobilized by gallamine triethiodide. All units were found to be influenced by input from both ears. Unit thresholds for contralateral stimulation were lower and more discharges were elicited than for ipsilateral stimulation over a range of intensities from unit threshold intensity to 80 dB sound-pressure level. A predominance of contralateral influence was also observed when the number of stimulus-evoked discharges was plotted as a function of the deltaI or deltat. For 62% of the deltaI functions maximal responsiveness occurred for binaural stimuli that were more intense at the contralateral ear. Similarly, of the 36 units that showed sensitivity to deltat parameters for tone stimuli, 22 (61%) were maximally responsive at the contralateral-leading deltat intervals. For click stimuli, maximal responsiveness for all 21 deltat-sensitive units also occured for contralateral-leading stimuli. Certain observations in the study question the generality of the hypothesis that a particular cell invariantly encodes a specific deltat, i.e., that cells have 'characteristic delays'. First, most units tested at more than two frequencies showed maximal responsiveness at different deltat intervals depending upon stimulus frequency. Second, the deltat intervals for maximal responsiveness for half of the units tested were greater than the maximal interaural delays the animal could encounter naturally. Third, deltat functions from the same unit for click and tone stimuli showed poor correspondence. These findings suggest that the encoding of interaural time and intensity might depend on an inter-hemispheric comparison of the activity of neural populations as originally proposed by von Bekesy.

Acoustic Stimulation↗
PubMed1998

Motor, somatosensory and auditory cortex localization by fMRI and MEG.

Functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were performed in six subjects during self-paced finger movement performance, tactile somatosensory stimulation and binaural auditory stimulation using identical stimulation paradigms. Both functional imaging modalities localized brain activity in adjacent areas of anatomically correct cortex. The mean distances measured between fMRI activity and the corresponding MEG dipoles were 10.1 mm (motor), 10.7 mm (somatosensory), 13.5 mm (auditory right hemisphere) and 14.3 mm (auditory left hemisphere). The distances found may reflect the correlation between electrophysiological and hemodynamic responses due to the different underlying substrates of neurophysiology measured by fMRI and MEG: BOLD contrast vs neuronal biomagnetic activity.

Adult↗
PubMed2001

Architectonic identification of the core region in auditory cortex of macaques, chimpanzees, and humans.

The goal of the present study was to determine whether the architectonic criteria used to identify the core region in macaque monkeys (Macaca mulatta, M. nemestrina) could be used to identify a homologous region in chimpanzees (Pan troglodytes) and humans (Homo sapiens). Current models of auditory cortical organization in primates describe a centrally located core region containing two or three subdivisions including the primary auditory area (AI), a surrounding belt of cortex with perhaps seven divisions, and a lateral parabelt region comprised of at least two fields. In monkeys the core region can be identified on the basis of specific anatomical and physiological features. In this study, the core was identified from serial sets of adjacent sections processed for cytoarchitecture, myeloarchitecture, acetylcholinesterase, and cytochrome oxidase. Qualitative and quantitative criteria were used to identify the borders of the core region in individual sections. Serial reconstructions of each brain were made showing the location of the core with respect to gross anatomical landmarks. The position of the core with respect to major sulci and gyri in the superior temporal region varied most in the chimpanzee and human specimens. Although the architectonic appearance of the core areas did vary in certain respects across taxonomic groups, the numerous similarities made it possible to identify unambiguously a homologous cortical region in macaques, chimpanzees, and humans.

Acetylcholinesterase↗
PubMed1991

Chemoarchitectonic organization of the cat primary auditory cortex.

Acetylcholinesterase (AChE) activity, demonstrated histochemically, defines an area of cortex on the middle ectosylvian gyrus that appears to correspond to the cytoarchitectonically defined area 41 and the physiologically defined primary auditory area (AI). In this area there are high levels of AChE in layers III, IV and VI while in the surrounding areas there are comparatively low levels of enzyme in these layers. The monoclonal antibody CAT 301, which was raised against a cell surface proteoglycan, also defines this area. There are high levels of CAT 301 immunoreactivity in cell bodies and the neuropil of layer III and an absence of very large immunoreactive neurons in layer V. Furthermore there are higher levels of the calcium binding protein, parvalbumin and the metabolic enzyme, cytochrome oxidase, in layers III and IV of AI, than in most of the surrounding cortex. By contrast the distribution of the calcium binding protein, calbindin and the distribution of myelinated fibers are similar in area 41 and the surrounding areas.

Acetylcholinesterase↗