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PubMed1990

[Neurological and pathophysiological analyses of patients with absent auditory brainstem evoked response].

Seventeen patients with no auditory brainstem evoked response (ABR) who suffered from various neurological disorders were reported. We evaluated the possibilities of co-existent brainstem lesions in addition to the peripheral impairment in the auditory pathway, by assessing neurological findings and other laboratory examinations, including cranial CT and electrically elicited blink reflex. Patients who showed cranial nerve symptoms other than that of the acoustic nerve or abnormal postural reflexes were suspected to have brainstem dysfunction. It was difficult, however, to exclude the influence from the dysfunction in the more central level CNS. Definite brainstem atrophy was revealed radiologically only in one case who was at the end stage of the degenerative disease. Blink reflex was studied in eleven cases, four of whom revealed abnormal responses, also suggesting brainstem dysfunction. All the five cases, consistent with these abnormal laboratory findings, had shown severe delay in motor development. Other five patients who showed rather good auditory behavior were considered to have 'desynchronization' response to ABR in the auditory pathway at the peripheral level. Many pathophysiological conditions may be involved in the phenomenon of absent ABR, which should be carefully evaluated from the viewpoints of clinical neurology.

Blinking↗
PubMed1980

The location by early auditory evoked potentials (EAEP) of acoustic nerve and brainstem demyelination in multiple sclerosis (MS).

Tone pips of suprathreshold intensities elicit an acoustic nerve response (I) and six low amplitude brainstem potentials (II-VII) during the initial 10 ms. Seven waves were studied in 40 control subjects and 5 waves (I-V) in 47 patients with MS. The results suggest involvement of the auditory pathway of 24 of 27 patients in the clinically "definite", of 5 of 9 cases in the "probable" and in none of 5 patients in the "possible" MS groups. EAEPs were normal in 6 cases with a spinal form with one exception where changes of potential were indicative of a midbrain lesion. Dysfunction within the acoustic pathway was observed at the level of the acoustic nerve and in the medulla oblongata, pons and midbrain. The significance of the bilateral EAEP abnormalities found in some patients at different levels is discussed with regard to a polytopic location of the underlying lesion.

Adult↗
PubMed2006

Neuromagnetic responses to binaural beat in human cerebral cortex.

The dichotic presentation of two sinusoids with a slight difference in frequency elicits subjective fluctuations called binaural beat (BB). BBs provide a classic example of binaural interaction considered to result from neural interaction in the central auditory pathway that receives input from both ears. To explore the cortical representation of the fluctuation of BB, we recorded magnetic fields evoked by slow BB of 4.00 or 6.66 Hz in nine normal subjects. The fields showed small amplitudes; however, they were strong enough to be distinguished from the noise accompanying the recordings. Spectral analyses of the magnetic fields recorded on single channels revealed that the responses evoked by BBs contained a specific spectral component of BB frequency, and the magnetic fields were confirmed to represent an auditory steady-state response (ASSR) to BB. The analyses of spatial distribution of BB-synchronized responses and minimum-norm current estimates revealed multiple BB ASSR sources in the parietal and frontal cortices in addition to the temporal areas, including auditory cortices. The phase of synchronized waveforms showed great variability, suggesting that BB ASSR does not represent changing interaural phase differences (IPD) per se, but instead it reflects a higher-order cognitive process corresponding to subjective fluctuations of BB. Our findings confirm that the activity of the human cerebral cortex can be synchronized with slow BB by using information on the IPD.

Acoustic Stimulation↗
PubMed2006

Discrimination of direction in fast frequency-modulated tones by rats.

Fast frequency modulations (FM) are an essential part of species-specific auditory signals in animals as well as in human speech. Major parameters characterizing non-periodic frequency modulations are the direction of frequency change in the FM sweep (upward/downward) and the sweep speed, i.e., the speed of frequency change. While it is well established that both parameters are represented in the mammalian central auditory pathway, their importance at the perceptual level in animals is unclear. We determined the ability of rats to discriminate between upward and downward modulated FM-tones as a function of sweep speed in a two-alternative-forced-choice-paradigm. Directional discrimination in logarithmic FM-sweeps was reduced with increasing sweep speed between 20 and 1,000 octaves/s following a psychometric function. Average threshold sweep speed for FM directional discrimination was 96 octaves/s. This upper limit of perceptual FM discrimination fits well the upper limit of preferred sweep speeds in auditory neurons and the upper limit of neuronal direction selectivity in the rat auditory cortex and midbrain, as it is found in the literature. Influences of additional stimulus parameters on FM discrimination were determined using an adaptive testing-procedure for efficient threshold estimation based on a maximum likelihood approach. Directional discrimination improved with extended FM sweep range between two and five octaves. Discrimination performance declined with increasing lower frequency boundary of FM sweeps, showing an especially strong deterioration when the boundary was raised from 2 to 4 kHz. This deterioration corresponds to a frequency-dependent decline in direction selectivity of FM-encoding neurons in the rat auditory cortex, as described in the literature. Taken together, by investigating directional discrimination of FM sweeps in the rat we found characteristics at the perceptual level that can be related to several aspects of FM encoding in the central auditory pathway.

Acoustic Stimulation↗
PubMed2001

Rate-dependent activation of a prefrontal-insular-cerebellar network during passive listening to trains of click stimuli: an fMRI study.

Eight volunteers underwent fMRI during passive listening to click trains. Using a parametric approach, rate-response profiles across the frequency band considered (2-6 Hz) were determined. Several cerebral structures outside the central-auditory pathways and target areas displayed distinct activation patterns each: rate-response profiles resembling high-pass (left side) or low-pass filtered (right side) signal series emerged at the level of the anterior insula, band-pass like characteristics (center frequency: 3-4 Hz) were observed within the left inferior frontal gyrus, and click train rates > 4 Hz yielded enhanced activation of the right cerebellar hemisphere. A variety of clinical and experimental data indicate that the left and right cerebral hemispheres act as high- and low-pass filters, respectively, on auditory input (double filtering by frequency theory). In light of the present fMRI data, the anterior insula contributes to the assumed double filtering by frequency functions. Furthermore, these intrasylvian areas seem to join up with the right cerebellum and the left inferior frontal gyrus to a network subserving parsing/timing functions within the auditory-verbal domain.

Acoustic Stimulation↗
PubMed2006

Locating the initial stages of speech-sound processing in human temporal cortex.

It is commonly assumed that, in the cochlea and the brainstem, the auditory system processes speech sounds without differentiating them from any other sounds. At some stage, however, it must treat speech sounds and nonspeech sounds differently, since we perceive them as different. The purpose of this study was to delimit the first location in the auditory pathway that makes this distinction using functional MRI, by identifying regions that are differentially sensitive to the internal structure of speech sounds as opposed to closely matched control sounds. We analyzed data from nine right-handed volunteers who were scanned while listening to natural and synthetic vowels, or to nonspeech stimuli matched to the vowel sounds in terms of their long-term energy and both their spectral and temporal profiles. The vowels produced more activation than nonspeech sounds in a bilateral region of the superior temporal sulcus, lateral and inferior to regions of auditory cortex that were activated by both vowels and nonspeech stimuli. The results suggest that the perception of vowel sounds is compatible with a hierarchical model of primate auditory processing in which early cortical stages of processing respond indiscriminately to speech and nonspeech sounds, and only higher regions, beyond anatomically defined auditory cortex, show selectivity for speech sounds.

Adult↗
PubMed1984

Whole head sectioning in [3H] deoxyglucose mapping of auditory responses in gerbils.

Stimulus-specific neuronal responses in the central auditory pathway of Psammomys obesus were studied with deoxyglucose autoradiography. Responses were revealed mainly in the inferior colliculus. With whole head sectioning and subsequent gentle freeze-drying, excellent structural preservation was achieved. With the use of double-tritiated deoxyglucose, Ultrofilm 3H and vacuum-contact exposure, a mean spatial resolution of 43 micron Full Width Half Maximum was achieved.

Animals↗
PubMed1985

The owl's cochlear nuclei process different sound localization cues.

This paper discusses how the barn owl's brain stem auditory pathway is divided into two physiologically and anatomically segregated channels for separate processing of interaural phase and intensity cues for sound localization. The paper also points out the power of the "downstream" approach by which the emergence of a higher-order neuron's stimulus selectivity can be traced through lower-order stations.

Animals↗
PubMed1993

Evoked otoacoustic emissions in the study of adult sensorineural hearing loss.

In the present report the applicability of evoked otoacoustic emissions (EOAEs) in the clinical field for studying adult sensorineural hearing loss is discussed. Three topics are considered: (1) EOAEs replacing a testing procedure, (2) EOAEs integrating into the test battery thus validating the diagnostic outcome, (3) EOAEs implementing new diagnostic possibilities. The authors conclude that: (a) EOAEs could only be applied to replace pure-tone audiometry for assessing functional deafness, (b) EOAEs are a useful diagnostic tool complementing the audiological test battery, (c) EOAEs are a unique method that studies the efferent auditory pathways. It is suggested that EOAEs should be applied as a routine audiological test for adult sensorineural hearing loss not only in cases with a well-defined diagnostic profile, but also in those cases with a less clear diagnostic pattern, in order to collect more data and possibly gain better knowledge about the pathophysiology of the inner ear.

Acoustic Stimulation↗
PubMed2005

Avoiding spectral leakage in objective detection of auditory steady-state evoked responses in the inferior colliculus of rat using coherence.

Local field potentials (LFP) are bioelectric signals recorded from the brain that reflect neural activity in a high temporal resolution. Separating background activity from that evoked by specific somato-sensory input is a matter of great clinical relevance in neurology. The coherence function is a spectral coefficient that can be used as a detector of periodic responses in noisy environments. Auditory steady-state responses to amplitude-modulated tones generate periodic responses in neural networks that may be accessed by means of coherence between the stimulation signal and the LFP recorded from the auditory pathway. Such signal processing methodology was applied in this work to evaluate in vivo, anaesthetized Wistar rats, activation of neural networks due to single carrier sound stimulation frequencies, as well as to evaluate the effect of different modulating tones in the evoked responses. Our results show that an inappropriate choice of sound stimuli modulating frequencies can compromise coherence analysis, e.g. misleading conclusions due to mathematical artefact of signal processing. Two modulating frequency correction protocols were used: nearest integer and nearest prime number. The nearest prime number correction was successful in avoiding spectral leakage in the coherence analysis of steady-state auditory response, as predicted by Monte Carlo simulations.

Acoustic Stimulation↗
PubMedDate not supplied

Auditory ERP in extremely premature 5-year-old children.

The aim of this research was to test the hypothesis of a functional impairment in the automatic detection of deviant tones in 141 children born after 25 to 28 weeks of gestational age, as compared to 45 age-matched full-term control children. All of them were assessed at age 5 years 9 months and instructed to listen passively to two different pure tones (1000 vs 1200 Hz; 20 vs 80%) counterbalanced between ears. Rarity was thus defined by specific ear by tone combinations. The temporal N100 showed a clear contralateral functional organization of the central auditory pathway, especially for the left ear, but without group difference. By contrast, in full-term controls but not in premature children, the central N200 was specifically increased over frontal leads to rare stimuli as compared to frequent. Premature children demonstrated a lack of brain response when more complex processing integrating different informations was required.

Acoustic Stimulation↗
PubMed1979

Acoustic response characteristics of neurons in nonspecific areas of cat cerebral cortex.

1. Acoustic properties of single neurons in pericruciate, anterior lateral, and medial suprasylvian "association" areas were studied in chloralose-anesthetized cats using sealed stimulating systems incorporating probe microphone assemblies. 2. A total of 652 cells were isolated. Approximately 70% of the cells in each area were responsive to acoustic stimulation, and the majority of these cells were also driven by visual and/or somatosensory stimulation. 3. Association cortex neurons responded to tone- or noise-burst stimulation with an onset response of 16--50 ms latency. The onset response was found to be followed by a long period of suppression in those cases in which spontaneous activity was sufficiently high for this to be detected. 4. The majority of 56 units for which detailed frequency-tuning data were obtained had broad, irregular tuning curves extending over 5--6 octaves or more. A small proportion of association cortex cells exhibited sharp tuning comparable to that obtained in control recordings from cells in primary auditory cortex (AI). Although a number of broadly tuned units were rather insensitive, many cells--both broadly and sharply tuned--were of comparable sensitivity to AI cells. 5. Of the association cortex cells examined for binaural properties, 95% received excitatory input from each ear, and the dominant mode of binaural interaction in these cells was one of occlusion. The occurrence of occlusion at suprathreshold intensities reflected a tendency for monoaural and binaural intensity functions to asymptote at the same level. 6. The broad tuning, lability, and polysensory convergence exhibited by association cortex cells are similar to those of the so-called auditory lemniscal adjunct system. However, the binaural properties of association cells differ significantly from those of both the lemniscal line and adjuct components of the auditory pathway. 7. The homogeneity of acoustic and polysensory input to the three association fields is compatible with their input being derived from the single subcortical nonspecific projection system (reticular formation and medial/intralaminar thalamus) postulated by previous investigators. However, both neuroanatomical and neurophysiological evidence suggest that the lemniscal adjunct system and certain areas of periauditory cortex might also contribute to this input.

Acoustic Stimulation↗
PubMed2002

Disruption of primary auditory cortex by synchronous auditory inputs during a critical period.

In the primary auditory cortex (AI), the development of tone frequency selectivity and tonotopic organization is influenced by patterns of neural activity. Introduction of synchronous inputs into the auditory pathway achieved by exposing rat pups to pulsed white noise at a moderate intensity during P9-P28 resulted in a disrupted tonotopicity and degraded frequency-response selectivity for neurons in the adult AI. The latter was manifested by broader-than-normal tuning curves, multipeaks, and discontinuous, tone-evoked responses within AI-receptive fields. These effects correlated with the severe impairment of normal, developmental sharpening, and refinement of receptive fields and tonotopicity. In addition, paradoxically weaker than normal temporal correlations between the discharges of nearby AI neurons were recorded in exposed rats. In contrast, noise exposure of rats older than P30 did not cause significant change of auditory cortical maps. Thus, patterned auditory inputs appear to play a crucial role in shaping neuronal processing/decoding circuits in the primary auditory cortex during a critical period.

Age Factors↗
PubMed1986

On the mechanisms of call coding through auditory neurons in the squirrel monkey.

The main goal of the study was to investigate the neural processing of those acoustic signals through auditory neurons whose relevance for communication is either obvious or has been tested by psychoacoustic or behavioral experiments. Thus the activity of cortical, thalamic (MGB) and midbrain (IC) neurons of the auditory pathway were studied with periodically amplitude-modulated (AM) sounds, species-specific AM vocalizations and self-produced vocalizations. With regard to the processing of AM stimuli, there is evidence of a neural correlate to the psychoacoustic phenomenon "fluctuation strength": maximum of the Best Modulation Frequency (BMF) for the cortex was registered at 4 Hz. Furthermore, a relatively large number of units within the IC and the MGB can encode such amplitude changes which have been shown to be of communicative function; here too a neural correlate to the encoding processes of species-specific calls was indicated. Self-produced vocalizations do not seem to underlie a specific processing except that in higher auditory structures, they evoke quantitatively lower responses. In the midbrain, such less active areas are rare and were localized in regions belonging more to secondary auditory structures than primary ones.

Animals↗
PubMed2002

Ascending and descending projections from the superior olivary complex in guinea pigs: different cells project to the cochlear nucleus and the inferior colliculus.

The superior olivary complex is a source of ascending projections to the inferior colliculus and descending projections to the cochlear nucleus. We used multiple-labeling techniques with fluorescent retrograde tracers to determine whether individual superior olivary cells project to the inferior colliculus and the cochlear nucleus. Almost all labeled cells contained one tracer, suggesting that they projected to only one of the injected targets. A small number of cells sent collateral projections to the ipsilateral cochlear nucleus and ipsilateral inferior colliculus. The double-labeled cells constituted fewer than 2% of the cells that projected to the cochlear nucleus or to the inferior colliculus. There was no evidence for cells projecting to both contralateral targets or to one ipsilateral target and one contralateral target. We conclude that the ascending projections to the inferior colliculus and the descending projections to the cochlear nucleus arise almost exclusively from separate populations of cells in the superior olivary complex. Their separate origins suggest that these projections are sending different information to higher and lower centers of the auditory pathways.

Animals↗
PubMed1996

Point process models of single-neuron discharges.

In most neural systems, neurons communicate via sequences of action potentials. Contemporary models assume that the action potentials' times of occurrence rather than their waveforms convey information. The mathematical tool for describing sequences of events occurring in time and/or space is the theory of point processes. Using this theory, we show that neural discharge patterns convey time-varying information intermingled with the neuron's response characteristics. We review the basic techniques for analyzing single-neuron discharge patterns and describe what they reveal about the underlying point process model. By applying information theory and estimation theory to point processes, we describe the fundamental limits on how well information can be represented by and extracted from neural discharges. We illustrate applying these results by considering recordings from the lower auditory pathway.

Animals↗
PubMedDate not supplied

Evoked cerebral potential audiometry and hearing threshold.

Audiometric testing by means of the nonspecific evoked cerebral potential (NECP) was performed in 20 children (11 with normal hearing, 6 with conductive and 3 with sensorineural hearing loss). The threshold as determined by this method was 20-30 dB higher than the threshold of the subjective tonal audiograms in the majority of the cases. Only in two cases the difference was up to 70 dB. There were no significant differences between the results of the methods in the three groups of children. The possible reasons for the described discrepancy between the thresholds of the ECP audiometry and the subjective tonal audiometry are discussed. It is pointed out that either of the two methods explores one of two different functional systems: the nonspecific activating system of the brain stem and the auditory pathway. It is suggested that the observed discrepancy between the results of the two methods may mainly be due to different thresholds of the two systems. To avoid false negative results of the ECP audiometry in subjects with 'constitutionally' low amplitude of the NECP it is proposed to routinely determine the amplitude of the NECP produced by somatosensory stimuli. Careful evaluation of the recorded data can improve the diagnostic value of ECP audiometry.

Acoustic Stimulation↗
PubMed2006

Contralateral white noise selectively changes left human auditory cortex activity in a lexical decision task.

In a previous study, we hypothesized that the approach of presenting information-bearing stimuli to one ear and noise to the other ear may be a general strategy to determine hemispheric specialization in auditory cortex (AC). In that study, we confirmed the dominant role of the right AC in directional categorization of frequency modulations by showing that fMRI activation of right but not left AC was sharply emphasized when masking noise was presented to the contralateral ear. Here, we tested this hypothesis using a lexical decision task supposed to be mainly processed in the left hemisphere. Subjects had to distinguish between pseudowords and natural words presented monaurally to the left or right ear either with or without white noise to the other ear. According to our hypothesis, we expected a strong effect of contralateral noise on fMRI activity in left AC. For the control conditions without noise, we found that activation in both auditory cortices was stronger on contralateral than on ipsilateral word stimulation consistent with a more influential contralateral than ipsilateral auditory pathway. Additional presentation of contralateral noise did not significantly change activation in right AC, whereas it led to a significant increase of activation in left AC compared with the condition without noise. This is consistent with a left hemispheric specialization for lexical decisions. Thus our results support the hypothesis that activation by ipsilateral information-bearing stimuli is upregulated mainly in the hemisphere specialized for a given task when noise is presented to the more influential contralateral ear.

Acoustic Stimulation↗