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PubMed1993

Auditory projections to the anterior telencephalon in the budgerigar (Melopsittacus undulatus).

The connections of a higher order auditory area in the neostriatum intermedium pars ventrolateralis (NIVL) were mapped with pathway tracing techniques in order to elucidate possible pathways by which auditory feedback may influence vocal learning in the budgerigar (Melopsittacus undulatus). Previous research has shown that NIVL receives projections from Field 'L' as well as adjacent portions of the dorsolateral neostriatum intermedium (NIDL) and hyperstriatum ventrale (HV) and, therefore, may be homologous to previously described auditory centers in the dorsal and lateral portions of the auditory neostriatum of songbirds. The efferent connections of NIVL terminate within a small portion of the rostromedial archistriatum as well as a more rostrally situated area within the medial neostriatum intermedium (NI) and HV. Near by (but not overlapping) fields in NI and HV receive input from the nucleus dorsomedialis posterior thalami (DMP), the archistriatum and ectostriatum. Interestingly, only the DMP projection field overlaps a neural field known to be related to the vocal motor system. The DMP projection field corresponds to that previously described as the magnocellular nucleus of the anterior neostriatum; this nucleus is known to project to the higher vocal center in the budgerigar. In addition to projections from NIVL to medial NI and HIV, auditory information is relayed to the anterolateral telencephalon directly from the brainstem via the ventrolateral nucleus of the lateral lemniscus (VLV). This latter pathway appears comparable to that described in pigeons derived from the intermediate nucleus of the lateral lemniscus. The projection field of VLV overlaps a restricted portion of the caudal and medial aspect of nucleus basalis. These results support the notion that many aspects of telencephalic auditory pathways in birds are primitive characters, although a direct connection between auditory and vocal motor circuits was not found in the present study.

Animals↗
PubMed1968

Auditory detection and perception in normal man and in patients with adrenal cortical insufficiency: effect of adrenal cortical steroids.

Auditory detection thresholds for sinusoidal tones and various tests of auditory perception were determined in 12 patients with adrenal cortical insufficiency (seven with Addison's disease and five with panhypopituitarism) and compared to those in normal volunteers. In adrenal cortical insufficiency auditory detection sensitivity was significantly more acute than normal, and judgments of loudness and of the contralateral threshold shift were made at levels more than 20 db below those of normal subjects. Thus both the lower and the upper limits of the dynamic auditory range are significantly decreased in these patients. Speech discrimination ability of the patients was significantly impaired as was their difference limens, their alternate binaural loudness balances, and their ability to localize tones in space. Treatment of the patients with deoxycorticosterone acetate decreased serum potassium concentration, raised serum sodium concentration, and produced gains in body weight but did not alter auditory detection or perception. Treatment with prednisolone or with maintenance doses of carbohydrate-active steroids returned auditory detection and perception to normal in every patient tested. The inability of the untreated patients to perform the various auditory perception tasks indicates that they have a defect in their ability to integrate incoming sensory stimuli. This defect may be related to the alteration in the timing of transmission of neural impulses along axons and across synapses which occurs in these patients when their carbohydrate-active steroid is removed. This decreased integrative capacity occurs at the same time that they are able to detect many types of sensory stimuli significantly better than normal subjects. This interrelationship between increased detection sensitivity and decreased perceptual ability is dependent upon the absence of carbohydrate-active steroids, for when these steroids are replaced both detection sensitivity and perceptual ability revert to normal.

Addison Disease↗
PubMed2002

Early cochlear implantation in children allows normal development of central auditory pathways.

The goal of this study was to determine whether there is a sensitive period during early development when a cochlear implantation can occur into a minimally degenerate and/or highly plastic central auditory system. Our measure of central auditory deprivation was latency of the P1 auditory evoked potential, whose generators include auditory thalamocortical areas. Auditory evoked potentials were recorded in 18 congenitally deaf children who were fitted with cochlear implants by 3.5 years of age. The P1 latencies of the children with implants were compared with the P1 latencies of their age-matched peers with normal hearing. There was no significant difference between the P1 latencies of the children with implants and the children with normal hearing. The present results suggest that early implantation occurs in a central auditory system that is minimally degenerate and/or highly plastic. Studies are ongoing to assess the consequences to the developing central auditory system of initiating electrical stimulation at later ages.

Age Factors↗
PubMed1991

Cochlear nucleus cell size is regulated by auditory nerve electrical activity.

Accumulating evidence suggests that sensorineural hearing loss in animals is rapidly followed by degenerative changes in central auditory neurons. For example, cochlear removal in birds and mammals results in a reduction in central auditory neuron cell size within 48 hours. A similar decrease in cell size after pharmacologic blockade of auditory nerve electrical activity with tetrodotoxin has been reported. In the present study, we evaluate the reversibility of central auditory changes after a profound sensorineural hearing loss caused by blockade of auditory nerve actions potentials. Tetrodotoxin, which blocks voltage-sensitive sodium channels, was embedded in a slow-release vehicle and placed next to the round window membrane of gerbils. Tetrodotoxin diffused into perilymph and unilaterally blocked electrical activity in auditory nerve axons. Electrical activity blockade was confirmed with recordings of auditory brainstem response. Animals were killed immediately after 24 hours of electrical blockade or 7 days after a transient 24- or 48-hour blockade. Large spherical cells of the anteroventral cochlear nucleus ipsilateral to manipulation were measured and compared to large spherical cells on the opposite, unmanipulated side of the brain. Animals killed immediately after a 24-hour blockade of electrical activity showed a mean decrease of 16% in cell size ipsilateral to the blockade (p less than 0.05). In animals allowed to recover for 7 days after blockade for 24 or 48 hours, cell size returned to previous levels. There was no longer a consistent difference in cell size between the two sides of the brain in these animals (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

The neurochemical basis of human cortical auditory processing: combining proton magnetic resonance spectroscopy and magnetoencephalography.

BACKGROUND: A combination of magnetoencephalography and proton magnetic resonance spectroscopy was used to correlate the electrophysiology of rapid auditory processing and the neurochemistry of the auditory cortex in 15 healthy adults. To assess rapid auditory processing in the left auditory cortex, the amplitude and decrement of the N1m peak, the major component of the late auditory evoked response, were measured during rapidly successive presentation of acoustic stimuli. We tested the hypothesis that: (i) the amplitude of the N1m response and (ii) its decrement during rapid stimulation are associated with the cortical neurochemistry as determined by proton magnetic resonance spectroscopy. RESULTS: Our results demonstrated a significant association between the concentrations of N-acetylaspartate, a marker of neuronal integrity, and the amplitudes of individual N1m responses. In addition, the concentrations of choline-containing compounds, representing the functional integrity of membranes, were significantly associated with N1m amplitudes. No significant association was found between the concentrations of the glutamate/glutamine pool and the amplitudes of the first N1m. No significant associations were seen between the decrement of the N1m (the relative amplitude of the second N1m peak) and the concentrations of N-acetylaspartate, choline-containing compounds, or the glutamate/glutamine pool. However, there was a trend for higher glutamate/glutamine concentrations in individuals with higher relative N1m amplitude. CONCLUSION: These results suggest that neuronal and membrane functions are important for rapid auditory processing. This investigation provides a first link between the electrophysiology, as recorded by magnetoencephalography, and the neurochemistry, as assessed by proton magnetic resonance spectroscopy, of the auditory cortex.

Acoustic Stimulation↗
PubMed1990

Demonstration of prosthetic activation of central auditory pathways using [14C]-2-deoxyglucose.

The cochlear prosthesis is not applicable to patients who lack an implantable cochlea or an intact vestibulocochlear nerve. Direct electrical stimulation of the cochlear nucleus (CN) of the brain stem might provide a method for auditory rehabilitation of these patients. A penetrating CN electrode has been developed and tissue tolerance to this device demonstrated. This study was undertaken to evaluate metabolic activation of central nervous system (CNS) auditory tracts produced by such implants. Regional cerebral glucose use resulting from CN stimulation was estimated in a series of chronically implanted guinea pigs with the use of [14C]-2-deoxyglucose (2-DG). Enhanced 2-DG uptake was observed in structures of the auditory tract. The activation of central auditory structures achieved with CN stimulation was similar to that produced by acoustic stimulation and by electrical stimulation of the modiolar portion of the auditory nerve in control groups. An interesting banding pattern was observed in the inferior colliculus following CN stimulation, as previously described with acoustic stimulation. This study demonstrates that functional metabolic activation of central auditory pathways can be achieved with a penetrating CNS auditory prosthesis.

Animals↗
PubMed1982

Auditory brainstem responses (ABR) in the aged.

86 male subjects, aged between 60 and 86 years (M = 69.5), underwent pure-tone audiometry, impedance tests and brainstem response audiometry (BRA). Subjects have been classified into four age-related groups: 1) 34 subjects, aged between 60 and 65; 2) 22, aged between 66 and 70; 3) 22 aged between 71 and 75; 4) 8, aged between 76 and 86. They have also been classified into four groups on the basis of their mean auditory threshold at 0.5, 1, 2, 4 and 8 kHz: 1) 14 subjects with mean auditory threshold less than or equal to 30 dB HL; 2) 16, between 31 and 40; 3) 24, between 41 and 50; 4) 32, with mean auditory threshold greater than or equal to 51 dB HL. 19 normally hearing adults, aged between 28 and 42, were chosen as controls. Statistically significant correlations have been found between age and mean auditory threshold (P less than or equal to 0.001), between wave latency V and age (P less than or equal to 0.001), between wave latency V and the mean pure-tone auditory threshold at 0.5, 1, 2, 4 and 8 kHz (P less than or equal to 0.001) and between the V-I interval and age (P less than or equal to 0.001). The discrepancy between the mean auditory threshold and the ABR waveform, the overall amplitude's reduction of ABR waves and the progressive lengthening of V-I interval values, seem to indicate that age-related changes involve not only the end organ but also the brainstem auditory structures.

Age Factors↗
PubMed2000

Transformations of an auditory temporal code in the medulla of a sound-producing fish.

The fish auditory system provides important insights into the evolution and mechanisms of vertebrate hearing. Fish have relatively simple auditory systems, without a cochlea for mechanical frequency analysis. However, as in all vertebrates, the primary auditory afferents of fish represent sounds as stimulus-entrained spike trains. Thus, fish provide important models for studying how temporal spiking patterns are used in higher level neural computations. In this paper we demonstrate that one of the fundamental transformations of information in the auditory system of a sound-producing fish, Pollimyrus, takes place in the auditory medulla. We discovered a class of neurons in which evoked spiking patterns were relatively independent of the stimulus fine structure and appeared to reflect intrinsic properties of the neurons. These neurons generated sustained responses but were poorly phase-locked to tones compared with the primary afferents. The interval histograms showed that spike timing was regular. However, in contrast to primary afferents, the mode of the interspike interval distribution was independent of the period of tonal stimuli. The tuning of the neurons was broad, with best sensitivity in the same spectral region where these animals concentrate energy in their communication sounds. The physiology of these neurons was similar to that of the chopper neurons known in the auditory brainstem of mammals. Our findings suggest that this medullary transformation, from phase-locked afferent input to chopper-like physiology, is basic to vertebrate auditory processing, even within lineages that have not evolved a cochlea.

Acoustic Stimulation↗
PubMed2003

Seasonal plasticity of peripheral auditory frequency sensitivity.

Female midshipman fish (Porichthys notatus) use the auditory sense to detect and locate vocalizing males during the breeding season. Detection of conspecific vocal signals is essential to their reproductive success and can evoke strong phonotactic responses in gravid females but not in spent females that have released all of their eggs. Here, we test the hypothesis that seasonal variation in reproductive state affects the neurophysiological response properties of the peripheral auditory system in female midshipman fish. Iso-intensity responses of eighth nerve afferents from the sacculus, the main auditory end organ of the inner ear, to individual tones were measured for spike rate and vector strength (VS) of synchronization. Most auditory saccular units in reproductive, summer females showed robust temporal encoding up to 340 Hz, whereas nonreproductive winter females showed comparable encoding only up to 100 Hz. The dramatic upward shift in temporal encoding among summer fish was paralleled by increases in best frequency (BF), maximum evoked spike rate at BF, VS values at BF, and the percentage of units that showed significant VS to iso-intensity tones >140 Hz. Reproductive summer females were best suited to encode the higher harmonic components of male advertisement calls. This first demonstration of a natural cyclicity in peripheral auditory frequency sensitivity among vertebrates may represent, in this case, an adaptive plasticity of the female midshipman's auditory system to enhance the acquisition of auditory information needed for mate identification and localization during the breeding season.

Acoustic Stimulation↗
PubMed2003

Auditory cortical neurons respond to somatosensory stimulation.

The prevailing hierarchical model of cortical sensory processing holds that early processing is specific to individual modalities and that combination of information from different modalities is deferred until higher-order stages of processing. In this paper, we present physiological evidence of multisensory convergence at an early stage of cortical auditory processing. We used multi-neuron cluster recordings, along with a limited sample of single-unit recordings, to determine whether neurons in the macaque auditory cortex respond to cutaneous stimulation. We found coextensive cutaneous and auditory responses in caudomedial auditory cortex, an area lying adjacent to A1, and at the second stage of the auditory cortical hierarchy. Somatosensory-auditory convergence in auditory cortex may underlie effects observed in human studies. Convergence of inputs from different sensory modalities at very early stages of cortical sensory processing has important implications for both our developing understanding of multisensory processing and established views of unisensory processing.

Acoustic Stimulation↗
PubMed2004

Verbal dichotic listening in developmental stuttering: subgroups with atypical auditory processing.

OBJECTIVE: The major aim of this study was to determine whether adults with persistent developmental stuttering have atypical auditory processing. BACKGROUND: Stuttering has been attributed to aberrant hemispheric dominance, and auditory processing deficits have been found in some adults who stutter. Dichotic listening, an indirect measure of auditory processing, has not been used to study auditory laterality in right- and left-handers who stutter. Because left-handers and people who stutter may have aberrant hemispheric dominance, it is important to examine auditory neural systems in right- and left-handed people who do and do not stutter. METHODS: Adults with persistent developmental stuttering (n = 18) and matched controls (n = 28) were studied by simultaneous binaural (dichotic) presentation of consonant-vowel stimuli in three attention conditions: nondirected attention, attention directed right, and attention directed left. Sex-handedness groups (stutter and control) included right-handed men and women and left-handed men, but not left-handed women because this stutter subgroup could not be recruited. To study ear advantage and auditory laterality, two dependent measures were examined: percent left and right ear responses and lateralization shift magnitude. Potential relationships between degree of handedness and dichotic listening measures were also examined. RESULTS: Matched controls and right-handed men who stutter had the expected right-ear advantage (REA) in the nondirected attention condition. In contrast, left-handed men who stutter had a left-ear advantage (LEA), and right-handed women who stutter did not have a lateral ear bias in the nondirected attention condition. Right-handed women who stutter had the greatest tendency to hear a sound that was not presented to either ear, and were relatively unable to selectively direct attention left or right. In contrast, left-handed men who stutter were able to shift attention to the left and right ear better than any other group. For the fluent control group, there were no significant relationships among degree of handedness and dichotic-listening variables. For the stutter group, degree of handedness was significantly related to percentage left and right ear response and to the lateralization shift magnitude. CONCLUSIONS: Left-handed men who stutter and right-handed women who stutter have atypical auditory processing but differ in important ways. The left-ear bias found in left-handed men who stutter in the nondirected attention condition suggests that their right temporal lobe may be important in perceiving speech, and, therefore, they have mixed dominance. These subjects were also better at shifting attention in both directions in comparison to all other groups; thus, the right hemisphere, which is dominant for shifting attention to both right and left space, may be activated. In contrast, the right-handed women who stutter had no ear bias in the nondirected attention condition, made more perceptual errors, and had difficulty shifting attention to the left and right. Although these results suggest that right-handed women who stutter have attentional deficits, the relationship between attentional disorders and stuttering remains to be elucidated. Because right-handed men who stutter were not different from controls, aberrant hemispheric dominance cannot fully account for stuttering. Unfortunately, left-handed women were not examined in this study. Therefore, these interesting sex-handedness effects found in left-handed men and right-handed women who stutter must be interpreted with caution.

Adult↗
PubMedDate not supplied

[Brainstem auditory evoked potentials and vertex potentials in 5-year-old children with defective articulation of the phonemes /l/, /r/, /rr/ and /s/].

AIMS: In children with articulatory defects it is important to evaluate the central auditory level. We compared the results of the interwave intervals of brainstem auditory evoked potentials (BAEP) at 80 dB SPL (sound pressure level) and the latencies of the waves of long latency auditory evoked potentials (LLAEP) (vertex) in 5-year-old children with articulatory defects for /l/, /r/, /rr/ and /s/, and in controls. SUBJECTS AND METHODS: Fifty cases of 5-year-old children of both sexes were evaluated; 25 had articulatory defects and 25 with no articulatory defects were used as controls. Melgar's articulation test was applied to both groups. The following aspects were considered in the two groups: normal bilateral audition by means of tone audiometry, tympanometry and the revised Wechsler Intelligence Scale for preschool and primary school children, which were normal; there was no history of neurological damage. Interwave intervals for waves I-III, I-V and III-V of the BAEP and the latencies of the LLAEP (vertex) were evaluated. RESULTS: Data were analysed using SPSS 12, and descriptive statistics and Student's t test were carried out to appraise the differences between the two groups. No differences were found between the control group and the study group. CONCLUSIONS: It is important to determine whether children with articulatory defects have alterations in the auditory receptor or in their central auditory function. It can be concluded that the variables analysed in the two groups behave in the same way; no significant differences were found, which suggests that neither the auditory receptor nor the central auditory function are affected in the study group. Further studies are to be conducted to investigate the meaning of the difference in central nervous conduction between the two afferences in the study group.

Articulation Disorders↗
PubMed2006

[Role of ion channel Na-K-2Cl and alpha2 Na, K-ATPase in cochlear potassium cycling and auditory function].

OBJECTIVE: To investigate the auditory function and the role of NKCC1 and alpha2 Na, K-ATPase in the potassium recycling of cochlea. METHODS: NKCC1(+/-) / alpha2 Na, K-ATPase(+/-) mice model was established from NKCC1(+/-) and alpha2 Na, K-ATPase(+/-) mice. The auditory function of all strain mice were detected by auditory brainstem response (ABR) and endocochlear potential (EP) to investigate the role of NKCC1 and alpha2 Na, K-ATPase in the potassium recycling of cochlea. Furosemide and ouabain were applied to block the two channels in Castel mice line which can long-time maintain normal auditory function and then their auditory function was detected by ABR to authenticate the mode of potassium recycling in vivo and the relationship between cochlear potassium recycling and NKCC1(+/-) and alpha2 Na, K-ATPase. RESULTS: The mean value for ABR thresholds in response to stimulus was elevated in NKCC1(+/-) and alpha2 Na, K-ATPase (+/-) mice [(38.49 +/- 12.29) dB and (53.32 +/- 7.62) dB) ] respectively, which was significantly increased compared with that observed in wild type mice [(23.13 +/- 3.78) dB, P < 0.05) ]; The EP value of NKCC1(+/-) [(78 +/- 7) mV] and alpha2 Na, K-ATPase(+/-) mice [(71 +/- 14) mV] was decreased compared with that of NKCC1(+/-) / alpha2 Na, K-ATPase(+/-) mice [( 86 +/- 11) mV]. The auditory function of NKCC1(+/-) / alpha2 Na, K-ATPase(+/-) mice could simulate the model of cochlear potassium recycling well. NKCC1 and Na, K-ATPase were great of importance in the potassium recycling, while the two ion channels were in restrict dynamic equilibrium. Castel mice line after administration with furosemide developed significant ABR threshold shifts (P < 0.05) compared with control group. Castel mice line after administration with ouabain also developed greatly significant ABR threshold shifts (P < 0.05) compared with control group. ABR threshold shifts in mice after administration both furosemide and ouabain was attenuated compared with only administration with furosemide (P < 0.01). CONCLUSIONS: Ion channel NKCC1 and alpha2 Na, K-ATPase played important roles in the inner ear potassium recycling. Dysfunction of either of them could influence potassium concentration in the endolymph and lead to hearing loss subsequently. The role of NKCC1 and alpha2 Na, K-ATPase in cochlear potassium recycling was authenticated in vivo. The two ion channels contribute the key role for dynamic equilibrium in cochlear potassium recycling and are of great importance for the metabolism of potassium in the inner ear to maintain the normal auditory function.

Animals↗
PubMed1987

[Auditory hallucinations in lesions of the brain stem].

Since the publication by Jean Lhermitte in 1922 of his paper on hallucinosis, the peduncular type has been described as a purely visual phenomenon. However, limited brain stem lesions can give rise to analogous manifestations in the auditory field. Five cases of auditory hallucinosis are reviewed, the first four resulting from a lesion of tegmentum of pons responsible for contralateral hemi-anesthesia and homolateral facial palsy with paralysis of laterality. Central type hypoacusis and a severe disorder of localization of sounds revealed a lesion of trapezoid body. The fifth case resulted from a peduncular lesion in region supplied by superior cerebellar artery, the auditory deficit being related to a lesion of inferior corpus quadrigeminum. In one patient, the auditory hallucinosis was followed by a period of visual hallucinations and oneiric delusions. Both auditory and visual hallucinosis can be related to hypnagogic hallucinations. Dream mechanisms (the geniculo-occipital spikes system) escape from normal inhibitory control exerted by the raphe nuclei. Auditory deafferentation could predispose to auditory hallucinosis.

Aged↗
PubMed1978

Response variability in the mammalian auditory cortex: an objection to feature detection?

Research strategy in the auditory system has tended to parallel that in the visual system, where neurons have been shown to respond selectively to specific stimulus parameters. Auditory neurons have been shown to be sensitive to changes in acoustic parameters, but only rarely have neurons been reported that respond exclusively to only one biologically significant sound. Even at higher levels of the auditory system very few cells have been found that could be described as "vocalization detectors." In addition, variability in responses to artificial sounds have been reported for auditory cortical neurons similar to the response variability that has been reported in the visual system. Recent evidence indicates that the responses of auditory cortical neurons to species-specific vocalizations can also be labile, varying in both strength and selectivity. This is especially true of the secondary auditory cortex. This variability, coupled with the lack of extreme specificity in the secondary auditory cortex, suggests that secondary cortical neurons are not well suited for the role of "vocalization detectors."

Acoustic Stimulation↗
PubMed1986

Auditory response properties of neurons in the claustrum and putamen of the cat.

The auditory response properties of single neurons in claustrum and putamen were studied in response to simple dichotic stimuli (viz. noise-and tone-bursts) in chloralose-anaesthetized cats. Neurons in claustrum were commonly weakly driven with long latency, were broadly tuned and were excited by stimulation of either ear (EE). Putamen neurons, in contrast, were securely driven with short latency, showed irregular tuning with a preference for low frequencies and were either EE or excited only by the contralateral ear (EO). The differences between claustrum and putamen responses can be related to differences in connections with the auditory cortical fields and with auditory thalamus. Some neurons were also tested for visual responsiveness: auditory and visual cells were intermingled in both nuclei and only a small percentage of cells were bimodal. In contrast to the visual and somatosensory input to claustrum, which are derived from primary cortical fields, the auditory input to claustrum is apparently derived from non-primary cortical regions, suggesting a fundamentally different role for processing of auditory information in claustrum.

Animals↗
PubMed1993

Extralemniscal co-activation is not indispensable for behavioral detection of auditory stimuli.

Thresholds for triggering summed auditory evoked responses (ERs) were measured in non-auditory (= extralemniscal--EL) nuclei receiving direct auditory projections from the lateral lemniscus. Primary EL ERs with onset latency of 3-6 ms reflecting activation of direct EL projections of lemniscal auditory nuclei were registered in caudal pontine reticular nucleus (CPRN), in deep layers of superior colliculus (SC) and in ventromedial hypothalamus (VMH). Secondary EL ERs (waves of EL ERs with onset latency above 10 ms) reflecting diffuse auditory EL co-activation of the brain, were registered besides the above mentioned nuclei also in the medial amygdala (MA). Threshold sound intensities for evoking primary EL ERs in CPRN, SC and VMH, for secondary EL ERs in all extralemniscal nuclei tested, and for conditioned avoidance behavior in a two-way shuttle box, were compared mutually. There were no significant mutual differences among thresholds for inducing secondary EL ERs in all EL nuclei tested. Thresholds for evoking secondary EL ERs were lower than those for evoking primary EL ERs in deep layers of the SC, equaled to thresholds for primary EL ERs in the VMH and were higher than thresholds for primary EL ERs in the CPRN. The results suggest that auditory EL projections into SC and/or VMH (but not into CPRN) might represent the primary triggering source for secondary EL ERs in various extralemniscal nuclei. Although conditioning lowered the threshold intensities for inducing secondary EL ERs, the threshold sound intensity for triggering conditioned behavior was lower than the threshold for secondary EL ERs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Evidence of sharp frequency tuning in the human auditory cortex.

The frequency tuning of the human auditory cortex was studied by masking 100-ms tones of 1 and 2 kHz by continuous white-noise maskers with frequency notches around the tone frequencies. The subjects ignored the stimuli and concentrated on a reading task. The neuronal activity elicited by the test tones in the auditory cortex was measured with a 24-channel neuromagnetometer. The masker affected the amplitude and latency of the neuromagnetic N100m response, peaking about at 100 ms after stimulus onset, in a systematic way: the wider the notch, the shorter was the latency and the larger the amplitude. The source location of N100m in the auditory cortex did not depend on the notch width. Auditory filters at 1 and 2 kHz were modelled by a single-parameter rounded-exponential [Roex(p)] filter, based on the amplitude changes of N100m. The filters revealed sharp tuning of the auditory cortex, resembling that obtained in psychoacoustical masking studies. The results demonstrate that frequency tuning of the neurons or neuron ensembles in the human auditory cortex can be studied completely noninvasively. Moreover, since the stimuli were ignored by the subjects, the filter shape is not affected by the criterion adopted by the subject in the discrimination task.

Acoustic Stimulation↗