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PubMed2001

Multichannel auditory search: toward understanding control processes in polychotic auditory listening.

Two experiments are presented that serve as a framework for exploring auditory information processing. The framework is referred to as polychotic listening or auditory search, and it requires a listener to scan multiple simultaneous auditory streams for the appearance of a target word (the name of a letter such as A or M). Participants' ability to scan between two and six simultaneous auditory streams of letter and digit names for the name of a target letter was examined using six loudspeakers. The main independent variable was auditory load, or the number of active audio streams on a given trial. The primary dependent variables were target localization accuracy and reaction time. Results showed that as load increased, performance decreased. The performance decrease was evident in reaction time, accuracy, and sensitivity measures. The second study required participants to practice the same task for 10 sessions, for a total of 1800 trials. Results indicated that even with extensive practice, performance was still affected by auditory load. The present results are compared with findings in the visual search literature. The implications for the use of multiple auditory displays are discussed. Potential applications include cockpit and automobile warning displays, virtual reality systems, and training systems.

Adult↗
PubMed1985

Postnatal development of the mammalian central auditory system and the neural consequences of auditory deprivation.

The auditory system of many mammalian species is immature at the time of birth. Peripheral elements, particularly the middle ear and cochlea, account for much of the physiological immaturity observed in central auditory structures. However, there is now considerable evidence that the central pathway undergoes developmental changes that, at least partially, occur in parallel with peripheral development. Auditory nerve fibres and their terminals have been shown to be of smaller diameter and less extensively arborized in neonatal than in adult cats. These factors almost certainly contribute to many of the sluggish physiological properties of neurones in the kitten auditory nerve and cochlear nucleus. At higher levels of the cat auditory system (inferior colliculus, auditory cortex) mechanisms subserving binaural interaction also undergo a period of postnatal development. Recent studies of sound deprivation produced by either deafferentation or a conductive hearing loss have demonstrated that alteration of cochlear output during the immediate postnatal period may change the normal development of the central auditory system.

Animals↗
PubMed2006

[Preliminary study on the functional localization of auditory cortex in auditory pathology patients using magnetoencephalography].

OBJECTIVE: To access the pathological changes of the functional localization of the primary auditory cortex in auditory neuropathy patients using magnetoencephalography (MEG). METHODS: The M100 waves of cortical evoked magnetic fields (AEF) evoked by 0.5, 1, 2, 4, 6, 8 kHz pure tones were measured respectively in 10 auditory neuropathy patients (20 ears) and 15 healthy young subjects (30 ears) using a whole head 306 channel magnetoencephalography (MEG) system. The auditory cortex magnetic source imaging obtained by superimposing functional MEG data on structural magnetic resonance image (MRI). RESULTS: The M100 sources were obtained in all 15 healthy young subjects in all frequency except for 8 kHz in 16 ears. But in auditory neuropathy patients, the ratio of M100 from 0.5 to 6 kHz were 27.5% (11/40), 22.5% (9/40), 7.5% (3/40), 5% (2/40), 5% (2/40) respectively and no any waves in 8 kHz. The evoked ratio of M100 in low frequency was high and that decreased gradually with increasing of evoked pure tone frequency. The M100 latentencies and amplitudes were longer and lower in patient group than that in control group (P < 0.01). CONCLUSIONS: Auditory neuropathy is an audiology disease with pathological lesions from the VIII cranial nerve to auditory cortex. MEG might become an important reference in decision making for therapies.

Adolescent↗
PubMed2004

[Late auditory potentials (NC-ERP) in children with symptoms of auditory processing and perception disorder. With and without attention deficit disorder].

BACKGROUND: Auditory processing disorders (APD) result from dysfunctions of processes dedicated to audition and affect processing of information in the auditory modality. Children with APD exhibit symptoms similar to those with attention deficit disorders (ADHD). With regard to therapeutic strategies it seems mandatory to employ diagnostic procedures able to differentiate between APD and ADHD. Recently it was found that auditory evoked neutral condition event-related potentials (NC-ERP) correlate with results from psychoacoustic measures suitable to unveil dysfunctions of auditory processing, thus confirming APD. Here we investigated whether NC-ERP may be used as a tool to differentiate between APD and ADHD. METHODS: In a retrospective analysis, NC-ERP data from 99 children with (+ADHD) and 43 without ADHD symptoms (-ADHD) were examined. All patients suffered from symptoms consistent with information processing deficits in the auditory modality. Analysis of variance was applied. RESULTS: +ADHD children and -ADHD children did not show a significantly different distribution pattern of pathological NC-ERP. DISCUSSION: Since the probability of pathological NC-ERP is equally distributed in children with or without ADHD, all of whom suffered from auditory processing deficits, it seems fair to conclude that NC-ERP are not suitable to differentiate between APD and ADHD. This may be due to methodological limitations. Alternatively, APD and ADHD may indeed be overlapping entities with a common yet unidentified origin.

Adolescent↗
PubMed2003

Expression of c-fos in auditory and non-auditory brain regions of the gerbil after manipulations that induce tinnitus.

Subjective tinnitus is a phantom sound sensation that does not result from acoustic stimulation and is audible to the affected subject only. Tinnitus-like sensations in animals can be evoked by procedures that also cause tinnitus in humans. In gerbils, we investigated brain activation after systemic application of sodium salicylate or exposure to loud noise, both known to be reliable tinnitus-inductors. Brains were screened for neurons containing the c-fos protein. After salicylate injections, auditory cortex was the only auditory area with consistently increased numbers of immunoreactive neurons compared to controls. Exposure to impulse noise led to prolonged c-fos expression in auditory cortex and dorsal cochlear nucleus. After both manipulations c-fos expression was increased in the amygdala, in thalamic midline, and intralaminar areas, in frontal cortex, as well as in hypothalamic and brainstem regions involved in behavioral and physiological defensive reactions. Activation of these non-auditory areas was attributed to acute stress, to aversive-affective components and autonomous reactions associated with the treatments and a resulting tinnitus. The present findings are in accordance with former results that provided evidence for suppressed activation in auditory midbrain but enhanced activation of the auditory cortex after injecting high doses of salicylate. In addition, our present results provide evidence that acute stress coinciding with a disruption of hearing may evoke activation of the auditory cortex. We interpret these results in favor of our model of central tinnitus generation.

Animals↗
PubMed2005

Prenatal auditory enrichment with species-specific calls and sitar music modulates expression of Bcl-2 and Bax to alter programmed cell death in developing chick auditory nuclei.

Postnatal auditory stimulation influences early perceptual learning. Previously we reported morphological effects of prenatal auditory stimulation by species-specific and sitar musical sounds on the chick brainstem auditory nuclei-nucleus magnocellularis and nucleus laminaris. At hatching, these two nuclei of auditory enriched embryos showed higher neuronal numbers, amongst other morphological changes. There were also increases in synaptophysin and syntaxin1 expressions in the sound enriched groups and modulation of the developmental expression of transcription factors c-Fos and c-Jun. We hypothesized that prenatal auditory enrichment may have reduced embryonic apoptosis in these nuclei with possible alteration of molecular mechanisms enhancing the postsynaptic neuron's ability to survive. In the present study, therefore, we examined apoptotic cell death by TUNEL technique and Bcl-2 expression using immunohistochemistry and immunoblotting. In the controls, a peak percentage in the TUNEL-positive cells was noted in the auditory nuclei at embryonic day 12, which was reduced at embryonic day 16. Bcl-2 immunoreactivity decreased from embryonic day 8 to embryonic day 12 overlapping the period of embryonic cell death in these nuclei. The stimulated groups, however, showed fewer apoptotic neurons and higher Bcl-2 level than that in the controls. On the other hand, Bax immunohistochemistry showed correlated reverse changes compared to Bcl-2 expression. Thus prenatal extra-acoustic stimulation appears to alter Bcl-2 and Bax expression to support cell survival and differentiation, thereby augmenting the development of auditory nuclei.

Acoustic Stimulation↗
PubMed2005

New composite index based on midlatency auditory evoked potential and electroencephalographic parameters to optimize correlation with propofol effect site concentration: comparison with bispectral index and solitary used fast extracting auditory evoked potential index.

BACKGROUND: This study investigates the accuracy of a composite index, the A-Line(R) auditory evoked potentials index version 1.6 (AAI1.6; Danmeter A/S, Odense, Denmark), as a measure of cerebral anesthetic drug effect in a model for predicting a calculated effect site concentration of propofol (CePROP). The AAI1.6 algorithm extracts information from the midlatency auditory evoked potentials, the spontaneous electroencephalographic activity, and the detection of burst suppression. The former version of this monitor, the A-Line auditory evoked potential index version 1.5, is only based on fast extracted midlatency auditory evoked potential information. METHODS: After institutional ethics committee approval (University Hospital, Ghent, Belgium), informed consent was obtained from 13 patients (10 women, 3 men) with an American Society of Anesthesiologists physical status of I, aged 18-65 yr, who were scheduled to undergo ambulatory gynecologic or urologic surgery. The authors evaluated for Bispectral Index, A-Line auditory evoked potential index, version 1.5, AAI1.6 scaled from 0 to 100 and AAI1.6 scaled from 0 to 60, the interpatient stability at baseline, the detection of burst suppression, prediction probability, and correlation with CePROP, during a constant infusion of 1% propofol at 300 ml/h. The authors developed pharmacodynamic models relating the predicted CePROP to each measure of cerebral anesthetic drug effect. RESULTS: Bispectral Index had the lowest interindividual baseline variability. No significant difference was found with prediction probability analysis for all measures. Comparisons for correlation were performed for all indices. The AAI1.6 scaled to 60 had a significantly higher correlation with CePROP compared with all other measures. The AAI1.6 scaled to 100 had a significant higher correlation with CePROP compared with the A-Line auditory evoked potential index version 1.5 (P < 0.05) CONCLUSIONS: The authors found that the application of AAI1.6 has a better correlation with a calculated CePROP compared with a solitary fast extracting midlatency auditory evoked potential measure. Whether this improvement in pharmacodynamic tracing is accompanied by an improved clinical performance should be investigated using clinical endpoints.

Adolescent↗
PubMed1999

Responses of neurons to click-pairs as simulated echoes: auditory nerve to auditory cortex.

When two identical sounds are presented from different locations with a short interval between them, the perception is of a single sound source at the location of the leading sound. This "precedence effect" is an important behavioral phenomenon whose neural basis is being increasingly studied. For this report, neural responses were recorded to paired clicks with varying interstimulus intervals, from several structures of the ascending auditory system in unanesthetized animals. The structures tested were the auditory nerve, anteroventral cochlear nucleus, superior olivary complex, inferior colliculus, and primary auditory cortex. The main finding is a progressive increase in the duration of the suppressive effect of the leading sound (the conditioner) on the response to the lagging sound (the probe). The first major increase occurred between the lower brainstem and inferior colliculus, and the second between the inferior colliculus and auditory cortex. In neurons from the auditory nerve, cochlear nucleus, and superior olivary complex, 50% recovery of the response to the probe occurred, on average, for conditioner and probe intervals of approximately 2 ms. In the inferior colliculus, 50% recovery occurred at an average separation of approximately 7 ms, and in the auditory cortex at approximately 20 ms. Despite these increases in average recovery times, some neurons in every structure showed large responses to the probe within the time window for precedence (approximately 1-4 ms for clicks). This indicates that during the period of the precedence effect, some information about echoes is retained. At the other extreme, for some cortical neurons the conditioner suppressed the probe response for intervals of up to 300 ms. This is in accord with behavioral results that show dominance of the leading sound for an extended period beyond that of the precedence effect. Other transformations as information ascended included an increased variety in the shapes of the recovery functions in structures subsequent to the nerve, and neurons "tuned" to particular conditioner-probe intervals in the auditory cortex. These latter are reminiscent of neurons tuned to echo delay in bats, and may contribute to the perception of the size of the acoustic space.

Acoustic Stimulation↗
PubMed2002

Auditory-somatosensory multisensory processing in auditory association cortex: an fMRI study.

Using high-field (3 Tesla) functional magnetic resonance imaging (fMRI), we demonstrate that auditory and somatosensory inputs converge in a subregion of human auditory cortex along the superior temporal gyrus. Further, simultaneous stimulation in both sensory modalities resulted in activity exceeding that predicted by summing the responses to the unisensory inputs, thereby showing multisensory integration in this convergence region. Recently, intracranial recordings in macaque monkeys have shown similar auditory-somatosensory convergence in a subregion of auditory cortex directly caudomedial to primary auditory cortex (area CM). The multisensory region identified in the present investigation may be the human homologue of CM. Our finding of auditory-somatosensory convergence in early auditory cortices contributes to mounting evidence for multisensory integration early in the cortical processing hierarchy, in brain regions that were previously assumed to be unisensory.

Acoustic Stimulation↗
PubMed1997

Protection of both auditory hair cells and auditory neurons from cisplatin induced damage.

Cisplatin is an effective anti-neoplastic agent used in the treatment of squamous cell cancer of the head and neck, but with serious side effects. One serious side effect is damage to both the auditory hair cells and the auditory neurons. The damage to the neurons has been shown to be a direct effect and not due to the loss of the neurotrophic support provided by the hair cells. Several neurotrophins have been shown to lessen the extent of cisplatin induced damage of auditory neurons in vitro, but these neurotrophins have had no effect on the extent of damage to the hair cells. D-methionine (D-met) has been demonstrated to provide protection against cisplatin's nephrotoxicity in vivo and ototoxicity in vitro. In this study the combination of brain derived neurotrophic factor (BDNF) with D-met has shown that both auditory neurons and auditory hair cells can be protected from cisplatin induced damage in vitro. These results demonstrate that this type of combination therapy (i.e. a neurotrophin combined with a free radical scavenger) can provide more complete protection for the auditory receptor against cisplatin toxicity than either of these agents alone. Because both BDNF and D-met have been shown to have trophic activity in vitro we proposed that the combination of these agents will also provide effective protection against cisplatin induced ototoxicity and neurotoxicity of the auditory receptor in vivo.

Animals↗
PubMed1993

Multiple brain systems generating the rat auditory evoked potential. I. Characterization of the auditory cortex response.

The objectives of this study were to characterize the auditory cortex response in the rat and to examine its contributions to the auditory evoked potentials (AEPs) recorded from the dorsal and lateral skull. This was accomplished by simultaneously recording AEPs from the cortical surface and from skull screw electrodes in anesthetized animals. The initial positive-negative response (P17-N32) was largely restricted to the cortical region corresponding to area 41. More detailed examination of the AEP mapping revealed multiple subcomponents (P9, P14, P17, P19) underlying the initial positivity, with differing topographies. Stimulus-response properties further dissociated the multiple positive subcomponents. Reversible local neurochemical suppression confirmed the auditory cortical origin of these AEPs. The auditory cortex-generated AEPs were refractory to barbiturate anesthesia which eliminated all dorsal skull AEPs, indicating that primary auditory cortical AEPs do not make a significant contribution to the dorsal skull-recorded ('vertex') AEPs. The findings raise issues regarding multiple parallel auditory processing systems and their associated AEPs.

Acoustic Stimulation↗
PubMed2003

Processing abstract auditory features in the human auditory cortex.

Using electric and magnetic brain responses we tested whether violations of an abstract auditory regularity are processed in auditory cortex and whether abstract auditory regularities are retained for at least 10 s. The mismatch negativity (MMN) event-related potential and its magnetic counterpart (MMNm) were recorded to infrequent tone pairs of descending pitch (the second tone having a lower frequency than the first one) embedded in a sequence of tone pairs of ascending pitch, whereas the absolute frequency of both ascending and descending tone pairs varied on seven levels. Results showed that the dominant generators of the electromagnetic activity elicited by violations of the pitch-ascension rule lie within auditory cortex. We also found that the memory representation of pitch-ascension is retained for at least 10 s. When short trains of ascending-pitched tone pairs were followed by a silent period of 8-12 s, descending-pitched probe tone pairs elicited the MMN component when a single reminding pair with ascending pitch was presented before the probe. The reactivating effect of the reminder was similar to what has been previously shown for concrete auditory regularities, such as the constancy of tone pitch. The present results support the view that auditory cortical functions can process sensory and categorical information in a similar manner.

Acoustic Stimulation↗
PubMed2001

Neural correlates of auditory stream segregation in primary auditory cortex of the awake monkey.

An important feature of auditory scene analysis is the perceptual organization of sequential sound components, or 'auditory stream segregation'. Auditory stream segregation can be demonstrated by presenting a sequence of high and low frequency tones in an alternating pattern, ABAB. When the tone presentation rate (PR) is slow or the frequency separation (DeltaF) between the tones is small (<10%), a connected alternating sequence ABAB is perceived. When the PR is fast or the DeltaF is large, however, the alternating sequence perceptually splits into two parallel auditory streams, one composed of interrupted 'A' tones, and the other of interrupted 'B' tones. The neurophysiological basis of this perceptual phenomenon is unknown. Neural correlates of auditory stream segregation were examined in A1 of the awake monkey using neuronal ensemble techniques (multiunit activity and current source density). Responses evoked by alternating frequency sequences of tones, ABAB, were studied as a function of PR (5, 10, 20 and 40 Hz). 'A' tones corresponded to the best frequency (BF) of the cortical site, while 'B' tones were situated away from the BF by an amount DeltaF. At slow PRs, 'A' and 'B' tones evoked responses that generated an overall pattern of activity at the stimulus PR. In contrast, at fast PRs, 'B' tone responses were differentially suppressed, resulting in a pattern of activity consisting predominantly of 'A' tone responses at half the PR. The magnitude of 'B' tone response suppression increased with DeltaF. Differential suppression of BF and non-BF tone responses at high PRs can be explained by physiological principles of forward masking. The effect of DeltaF is explained by the hypothesis that responses to tones distant from the BF are more susceptible to suppression by BF tones than responses to tones near the BF. These results parallel human psychoacoustics of auditory stream segregation and suggest a cortical basis for the perceptual phenomenon.

Acoustic Stimulation↗
PubMed1991

Absence of both auditory evoked potentials and auditory percepts dependent on timing cues.

An 11-yr-old girl had an absence of sensory components of auditory evoked potentials (brainstem, middle and long-latency) to click and tone burst stimuli that she could clearly hear. Psychoacoustic tests revealed a marked impairment of those auditory perceptions dependent on temporal cues, that is, lateralization of binaural clicks, change of binaural masked threshold with changes in signal phase, binaural beats, detection of paired monaural clicks, monaural detection of a silent gap in a sound, and monaural threshold elevation for short duration tones. In contrast, auditory functions reflecting intensity or frequency discriminations (difference limens) were only minimally impaired. Pure tone audiometry showed a moderate (50 dB) bilateral hearing loss with a disproportionate severe loss of word intelligibility. Those auditory evoked potentials that were preserved included (1) cochlear microphonics reflecting hair cell activity; (2) cortical sustained potentials reflecting processing of slowly changing signals; and (3) long-latency cognitive components (P300, processing negativity) reflecting endogenous auditory cognitive processes. Both the evoked potential and perceptual deficits are attributed to changes in temporal encoding of acoustic signals perhaps occurring at the synapse between hair cell and eighth nerve dendrites. The results from this patient are discussed in relation to previously published cases with absent auditory evoked potentials and preserved hearing.

Acoustic Stimulation↗
PubMed2004

Auditory perception vs. recognition: representation of complex communication sounds in the mouse auditory cortical fields.

Details of brain areas for acoustical Gestalt perception and the recognition of species-specific vocalizations are not known. Here we show how spectral properties and the recognition of the acoustical Gestalt of wriggling calls of mouse pups based on a temporal property are represented in auditory cortical fields and an association area (dorsal field) of the pups' mothers. We stimulated either with a call model releasing maternal behaviour at a high rate (call recognition) or with two models of low behavioural significance (perception without recognition). Brain activation was quantified using c-Fos immunocytochemistry, counting Fos-positive cells in electrophysiologically mapped auditory cortical fields and the dorsal field. A frequency-specific labelling in two primary auditory fields is related to call perception but not to the discrimination of the biological significance of the call models used. Labelling related to call recognition is present in the second auditory field (AII). A left hemisphere advantage of labelling in the dorsoposterior field seems to reflect an integration of call recognition with maternal responsiveness. The dorsal field is activated only in the left hemisphere. The spatial extent of Fos-positive cells within the auditory cortex and its fields is larger in the left than in the right hemisphere. Our data show that a left hemisphere advantage in processing of a species-specific vocalization up to recognition is present in mice. The differential representation of vocalizations of high vs. low biological significance, as seen only in higher-order and not in primary fields of the auditory cortex, is discussed in the context of perceptual strategies.

Acoustic Stimulation↗
PubMed2006

The formation of auditory fear memory requires the synthesis of protein and mRNA in the auditory thalamus.

The medial geniculate nucleus of the thalamus responds to auditory information and is a critical part of the neural circuitry underlying aversive conditioning with auditory signals for shock. Prior work has shown that lesions of this brain area selectively disrupt conditioning with auditory stimuli and that neurons in the medial geniculate demonstrate plastic changes during fear conditioning. However, recent evidence is less clear as to whether or not this area plays a role in the storage of auditory fear memories. In the current set of experiments rats were given infusions of protein or messenger RNA (mRNA) synthesis inhibitors into the medial geniculate nucleus of the thalamus 30 min prior to auditory fear conditioning. The next day animals were tested to the auditory cue and conditioning context. Results showed that rats infused with either inhibitor demonstrated less freezing to the auditory cue 24 h after training, while freezing to the context was normal. Autoradiography confirmed that the doses used were effective in disrupting synthesis. Taken together with prior work, these data suggest that the formation of fear memory requires the synthesis of new protein and mRNA at multiple brain sites across the neural circuit that supports fear conditioning.

Acoustic Stimulation↗
PubMed2005

Are auditory-verbal hallucinations associated with auditory affective processing deficits?

We investigated whether the presence of auditory-verbal hallucinations (AVH) was associated with impaired auditory affect perception. Controls, schizophrenia patients with a history of AVH (AVH) or with no history of AVH (NAVH) completed four perceptual auditory affect tasks. The tasks used either non-verbal/non-semantic or verbal/semantic stimuli. AVH patients showed significant impairments on a non-verbal task requiring the recognition of environmental sounds, this was particularly so for the affective stimuli and not the neutral valance stimuli. Thus, confirming auditory affect deficits in AVH patients. AVH patients also showed reduced right ear performance on a dichotic listening task. Conversely, both patient groups showed impairments on auditory affect tasks that used verbal/semantic stimuli; as these tasks require proficient semantic processing we speculated that significant semantic impairments in schizophrenia masked the additional auditory affect deficits present in the AVH group. The overall results support the notion that patients with AVH have increased liability for auditory affect perception deficits.

Adult↗
PubMed1985

The auditory pathology of brain death as revealed by auditory evoked potentials.

A case of brain death is reported in which the auditory brainstem response, middle latency component, and slow vertex response were recorded before and after the cessation of cortical activity, and in which histological examination of the temporal bone and central auditory pathways was performed post mortem. Brain death of at least 48 hours' duration was demonstrated by neurological examination, flat electroencephalographic recording, and persistent absence of auditory evoked responses. The postmortem examination was performed 3 hours after death. The pathological studies of the whole length of the auditory pathway revealed total autolysis of the organ of Corti, marked cell loss in the dorsal cochlear nucleus, and moderate cell loss in other nuclei of the central auditory pathway. It should be considered that total autolysis of the organ of Corti and severe cell loss of the cochlear nucleus may occur if the auditory brainstem response becomes absent in comatose patients.

Adult↗