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PubMed1985

5-year follow-up study of children with low-to-moderate lead absorption: electrophysiological evaluation.

Forty-nine children aged 6 to 12 years were evaluated for residual effects of lead exposure using psychometric, electrophysiological, and medical tests 5 years after initial assessment. The original range of blood lead (PbB) levels was 6-59 (mean = 28) micrograms/dl; the current range was 6-30 (mean = 14) micrograms/dl. A linear relationship between PbB and slow brain wave voltage during sensory conditioning was observed at initial evaluation and at 2-year follow-up. No significant relationship between PbB and slow wave voltage during passive conditioning was found at the 5-year follow-up, although a linear increase in slow wave negativity relative to the current PbB level during active conditioning was suggested by exploratory analyses. Another exploratory analysis revealed a significant linear relationship between the original PbB levels and the latency of waves III and V of the brainstem auditory evoked potential. The latency of both waves increased as a function of original PbB. Increased latency of these waves is suggestive of subclinical pathology of the auditory pathway rostral to the cochlear nucleus, although end-organ impairment cannot be ruled out. No threshold for the effect of Pb on auditory function was apparent.

Brain↗
PubMed1989

Timing of spike discharges in cat auditory cortex neurons: implications for encoding of stimulus periodicity.

Neurons at more central stations in the central auditory pathway show progressively poorer responses to high-frequency stimulus periodicities. This has been attributed to the relatively poorer spike timing in forebrain auditory neurons. This study directly examined the timing of spikes evoked by brief tone pulses which were varied in peak level and repetition rate. The experiments revealed that at tone repetition rates which produced progressively poorer entrainment, the timing of spike discharges remained sufficiently precise to support entrained responses. The fact that responses were poor indicates that imprecision in spike timing may not be the only factor limiting the encoding of temporal frequency. The data are discussed in relation to evidence on the temporal tuning of central neurons seen in studies using continuous amplitude modulations.

Acoustic Stimulation↗
PubMed2003

Patterns of calcium-binding proteins in human inferior colliculus: identification of subdivisions and evidence for putative parallel systems.

The subdivisions of human inferior colliculus are currently based on Golgi and Nissl-stained preparations. We have investigated the distribution of calcium-binding protein immunoreactivity in the human inferior colliculus and found complementary or mutually exclusive localisations of parvalbumin versus calbindin D-28k and calretinin staining. The central nucleus of the inferior colliculus but not the surrounding regions contained parvalbumin-positive neuronal somata and fibres. Calbindin-positive neurons and fibres were concentrated in the dorsal aspect of the central nucleus and in structures surrounding it: the dorsal cortex, the lateral lemniscus, the ventrolateral nucleus, and the intercollicular region. In the dorsal cortex, labelling of calbindin and calretinin revealed four distinct layers.Thus, calcium-binding protein reactivity reveals in the human inferior colliculus distinct neuronal populations that are anatomically segregated. The different calcium-binding protein-defined subdivisions may belong to parallel auditory pathways that were previously demonstrated in non-human primates, and they may constitute a first indication of parallel processing in human subcortical auditory structures.

Adult↗
PubMed1993

Auditory evoked potentials in cats with neonatal high frequency hearing loss. Evidence of abnormal frequency representation in the midbrain.

We have recorded auditory evoked potentials, of both neurogenic and myogenic origin, in cats having neonatal high frequency cochlear hearing loss. Using frequency specific stimuli (tone pips) and by measuring responses near to threshold, we have probed tonotopic (or cochleotopic) representation within the brainstem-midbrain auditory pathway. At stimulus frequencies corresponding to the high frequency cut-off of the cats' audiograms we have observed enhanced amplitudes of both auditory brainstem evoked responses (ABR) and postauricular myogenic (PAM) potentials. We interpret our findings as evidence of a larger than normal population of neurons tuned to this frequency region. We suggest that such abnormal frequency representation results from a long-term sensory deficit caused by lesions to the basal, high frequency region of the cochleas.

Animals↗
PubMed1994

Influence of efferent stimulation on acoustically responsive vestibular afferents in the cat.

In the preceding article (McCue and Guinan, 1994) we described a class of vestibular primary afferent fibers in the cat that responds vigorously to sounds at moderately high sound levels. Like their cochlear homologs, vestibular afferents and their associated hair cells receive efferent projections from brainstem neurons. In this report, we explore efferent influences on the background activity and tone-burst responses of the acoustically responsive vestibular afferents. Shock-burst stimulation of efferents excited acoustically responsive vestibular afferents; no inhibition was seen. A fast excitatory component built up within 100-200 msec of shock-burst onset and decayed with a similar time course at the end of each shock burst. During repeated 400 msec shock bursts at 1.5 sec intervals, a slow excitatory component grew over 20-40 sec and then decayed, even though the shock bursts continued. Efferent stimulation excited acoustically responsive vestibular afferents without appreciably changing an afferent's sound threshold or its average sound-evoked response. This evidence supports the hypothesis that excitation is due to efferent synapses on afferent fibers rather than on hair cells. Efferent stimulation enhanced the within-cycle modulation of afferent discharges evoked by a tone; that is, it increased the "AC gain." No appreciable change was noted in the degree of phase locking to low-frequency tones as measured by the synchronization index. Little or no improvement in the bidirectionality (linearity) of transduction was seen. Vestibular afferent responses to tones normally had one peak per cycle; however, during efferent stimulation, two peaks per cycle were sometimes seen. We hypothesize that this is caused by two driving components acting at different sound phases with the components differentially affected by efferent activity. We discuss the relationship of our findings to efferent influences on acoustic responses in cochlear afferent fibers. The acoustically responsive vestibular afferents provide a mammalian model for studying purely excitatory efferent effects in a hair cell system.

Animals↗
PubMed1983

Brainstem auditory evoked potentials in 20 patients with palatal myoclonus.

Brainstem auditory evoked potentials (BAEPs) were obtained in 20 patients with palatal myoclonus. The group included 14 men and six women whose ages ranged from 19 to 82 years. Six of the patients had abnormal BAEPs: two with severe head trauma and one each with a brainstem infarct, tumor, demyelination, and an indeterminate inflammatory process. The 14 patients with normal BAEPs had palatal myoclonus secondary to head trauma (five patients), brainstem infarcts (four patients), cerebellar tumors (two patients), degenerative processes (two patients), and an Arnold-Chiari malformation (one patient). Since the auditory pathways are separate from the structures associated with palatal myoclonus, it is possible to have discrete lesions producing palatal myoclonus with sparing of the auditory structures, whereas diffuse or multifocal lesions of the brainstem are more likely to be associated with abnormal BAEPs.

Adult↗
PubMedDate not supplied

Short- and middle-latency auditory evoked potentials in abstinent chronic alcoholics: preliminary findings.

Short- and middle-latency auditory evoked potentials (BAEPs and MAEPs) were studied in 15 chronic alcoholic patients after 1 month's abstinence and compared with those of 15 healthy controls, matching the patients pairwise for sex and age. Most of the parameters studied varied more within the alcoholic group than within the control group. The BAEP results agree with previous reports; in the alcoholic group, BAEP peak V was significantly delayed and the inter-peak intervals, III-V and I-V, were lengthened. The latencies of the MAEP components Na and Pa, on the other hand, were significantly shortened. These findings suggest that chronic abusive consumption of alcohol may bring about structural and/or neurochemical alterations at various levels in the auditory pathway.

Acoustic Stimulation↗
PubMed1984

Interaural intensity difference sensitivity based on facilitatory binaural interaction in cat superior colliculus.

Sensitivity to interaural intensity difference (IID) has generally been identified as a property of neurons exhibiting inhibitory binaural interaction, viz. contralateral excitatory and ipsilateral inhibitory input (EI cells). In the deep layers of the superior colliculus, however, almost 30% of IID-sensitive cells are characterised by facilitatory or mixed facilitatory/inhibitory interactions. Such cells typically have peaked IID sensitivity functions in contrast to the step functions characteristic of EI cells. There appears to be a continuum in IID sensitivity from pure step functions to sharply-peaked functions. The observation that a given form of IID sensitivity can be associated with patterns of binaural interaction other than that by which it is most commonly produced suggests that IID-sensitive neurons are better classified on the basis of the form of their IID sensitivity than their binaural input pattern. It seems probable that IID sensitivity based on facilitatory and mixed facilitatory/inhibitory binaural interactions is a general characteristic of the primary auditory pathway, although only fragmentary data are so far available.

Animals↗
PubMed1993

Sleep and active cochlear micromechanical properties in human subjects.

In this paper the effect of sleep on the cochlea is studied by transiently evoked otoacoustic emissions (TEOAEs). Amplitude increases considerably (e.g., 4 dB) and the effect of a contralateral noise on the TEOAEs decreases during the night. These modifications can be related to sleep, although there is no link to electroencephalographic sleep stage. During sleep onset, the effect of contralateral noise disappears: this could correspond to a functional rest of the auditory pathway during that period.

Acoustic Stimulation↗
PubMed1996

Transforming neural computations and representing time.

Motifs of neural circuitry seem surprisingly conserved over different areas of neocortex or of paleocortex, while performing quite different sensory processing tasks. This apparent paradox may be resolved by the fact that seemingly different problems in sensory information processing are related by transformations (changes of variables) that convert one problem into another. The same basic algorithm that is appropriate to the recognition of a known odor quality, independent of the strength of the odor, can be used to recognize a vocalization (e.g., a spoken syllable), independent of whether it is spoken quickly or slowly. To convert one problem into the other, a new representation of time sequences is needed. The time that has elapsed since a recent event must be represented in neural activity. The electrophysiological hallmarks of cells that are involved in generating such a representation of time are discussed. The anatomical relationships between olfactory and auditory pathways suggest relevant experiments. The neurophysiological mechanism for the psychophysical logarithmic encoding of time duration would be of direct use for interconverting olfactory and auditory processing problems. Such reuse of old algorithms in new settings and representations is related to the way that evolution develops new biochemistry.

Action Potentials↗
PubMedDate not supplied

Auditory effects of aircraft noise on people living near an airport.

Two groups of randomly chosen individuals who lived in two communities located different distances from the airport were studied. We monitored audiometry and brainstem auditory-evoked potentials to evaluate cochlear and retrocochlear functions in the individuals studied. The results of audiometry measurements indicated that hearing ability was reduced significantly in individuals who lived near the airport and who were exposed frequently to aircraft noise. Values of pure-tone average, high pure-tone average, and threshold at 4 kHz were all higher in individuals who lived near the airport, compared with those who lived farther away. With respect to brainstem auditory-evoked potentials, latencies between the two groups were not consistently different; however, the abnormality rate of such potentials was significantly higher in volunteers who lived near the airport, compared with less-exposed counterparts. In addition, a positive correlation was found between brainstem auditory-evoked potential latency and behavioral hearing threshold of high-frequency tone in exposed volunteers. We not only confirmed that damage to the peripheral cochlear organs occurred in individuals exposed frequently to aircraft noise, but we demonstrated involvement of the central auditory pathway.

Adult↗
PubMedDate not supplied

The influence of aging on auditory brainstem response and electrocochleography in the elderly.

Auditory brainstem responses and simultaneous transtympanic electrocochleographies were investigated in 92 subjects aged between 50 and 89 years with normal hearing or mild presbycusis. Subjects were classified into four age-related groups: 16 subjects in the sixth decade, 28 in the seventh decade, 32 in the eighth decade and 16 in the ninth decade. Thirty young subjects with normal hearing aged 20-29 years were chosen as controls. The result showed progressive delay of wave I (or action potential: AP), wave III and wave V and lengthening of the interpeak intervals (IPIs) of waves III-V and I-V in the subjects aged 50-79 years. In the subjects in the ninth decade, shortening of IPIs of waves I-III and I-V was noted in spite of further delays of wave I. The amplitude of APs on electrocochleography decreased in the groups with mild presbycusis. Both the lengthening and shortening of IPIs might be electrophysiological alterations occurring with aging in the central auditory pathways.

Age Factors↗
PubMed2002

Audiological assessment in Ramsay Hunt syndrome.

Ramsay Hunt syndrome is known to cause symptoms and signs of vestibulocochlear dysfunction, including sensorineural hearing loss. The present study investigates the audiological features of a group of 15 patients with this syndrome. A complete otolaryngological, neurologic, and audiological workup was performed in every patient, including auditory brain stem response measurements and recording of transiently evoked otoacoustic emissions. In most patients, some degree of hearing loss was evident, and abnormal latencies and interpeak latencies of the auditory brain stem response, or even absence of the waves, were observed. Transiently evoked otoacoustic emissions were present in only 6 cases, and caloric tests showed unilateral weakness in the majority of the patients. In all of the performed tests, abnormalities were present only on the affected side. The audiological data suggested cochlear or retrocochlear involvement or involvement at more than one site along the auditory pathway.

Adolescent↗
PubMed1994

Audiologic manifestations in fetal alcohol syndrome assessed by brainstem auditory-evoked potentials.

In 29 of 36 children with fetal alcohol syndrome brainstem auditory-evoked potentials were performed and the auditory threshold was determined. The hearing of patients with a pathologic finding was then subject to a thorough ear-nose-throat examination. Additionally the IQ was determined and an audiolinguistic examination was carried out. Seventy-five % of the children showed a peripheral hearing disorder on the basis of conductive hearing loss. In two children (7%) sensorineural hearing loss was located to the inner ear. A dysfunction of the auditory pathway was found in 6 patients (21%). The results of an isolated ear-nose-throat examination in 7 further children supported these findings. The mean performances in the linguistic tests were far below average and displayed a strong relation to the IQ. This study shows that a peripheral hearing disorder, especially an obstruction of the auditory tube as well as dysfunctions of the inner ear and the central hearing pathway, are different manifestations of the fetal alcohol syndrome. An etiologic connection between craniofacial abnormalities in these children and an increased susceptibility to peripheral hearing disorders could not be demonstrated. To avoid a retardation of the linguistic development in addition to the intellectual deficits a strong emphasis must be put on an early and comprehensive auditory examination of children with FAS.

Adolescent↗
PubMed2006

A comparison between exocytic control mechanisms in adrenal chromaffin cells and a glutamatergic synapse.

It has been known since the work of Katz and collaborators in the early 1950s that an increase in intracellular Ca(++) concentration ([Ca(++)]) is the immediate trigger for neurotransmitter release. Later work has shown that, next to Ca(++), many other signaling pathways, particularly via cyclic AMP, modulate the release of both neurotransmitters and hormones. However, regulated secretion is a multistep process and the signaling mechanisms involved act at many stages. Biochemical and traditional electrophysiological techniques very often cannot distinguish whether a change in secretion is caused by regulation of ion channels, vesicle trafficking, or the exocytic process itself. My laboratory has made an effort to dissect the stimulus secretion pathway by developing assays in chromaffin cells (for catecholamine release) and at a glutamatergic central nervous synapse (the calyx of Held, a component of the auditory pathway), which permit the study of secretion in single cells under voltage clamp conditions. This enables us to clearly distinguish between consequences of changes in electrical signaling, from those regarding the process of vesicle recruitment or the process of exocytosis.

Adrenal Medulla↗
PubMed2001

Auditory edge detection: a neural model for physiological and psychoacoustical responses to amplitude transients.

Primary segmentation of visual scenes is based on spatiotemporal edges that are presumably detected by neurons throughout the visual system. In contrast, the way in which the auditory system decomposes complex auditory scenes is substantially less clear. There is diverse physiological and psychophysical evidence for the sensitivity of the auditory system to amplitude transients, which can be considered as a partial analogue to visual spatiotemporal edges. However, there is currently no theoretical framework in which these phenomena can be associated or related to the perceptual task of auditory source segregation. We propose a neural model for an auditory temporal edge detector, whose underlying principles are similar to classical visual edge detector models. Our main result is that this model reproduces published physiological responses to amplitude transients collected at multiple levels of the auditory pathways using a variety of experimental procedures. Moreover, the model successfully predicts physiological responses to a new set of amplitude transients, collected in cat primary auditory cortex and medial geniculate body. Additionally, the model reproduces several published psychoacoustical responses to amplitude transients as well as the psychoacoustical data for amplitude edge detection reported here for the first time. These results support the hypothesis that the response of auditory neurons to amplitude transients is the correlate of psychoacoustical edge detection.

Animals↗
PubMed1991

Auditory nerve compound action potentials and brain stem auditory evoked potentials in patients with various degrees of hearing loss.

Click-evoked compound action potentials recorded in normal-hearing patients through a monopolar electrode placed on the intracranial portion of the eighth nerve were compared with the responses recorded in patients with high-frequency hearing loss or with high- and low-frequency hearing losses. That multiple peaks appear in the compound action potential in patients with hearing loss implies that click sounds elicit successive and separated volleys of neural excitation in the ascending auditory pathway, whereas click sounds in patients with normal hearing mainly give rise to a single volley of neural activity. This difference in the pattern of auditory nerve activity might explain why there are often multiple peaks in the brain stem auditory evoked potentials in patients with hearing loss and that the peaks are often less well-defined than peaks in patients with normal hearing.

Audiometry, Evoked Response↗
PubMed2005

Brainstem origins for cortical 'what' and 'where' pathways in the auditory system.

We have developed a data-driven conceptual framework that links two areas of science: the source-filter model of acoustics and cortical sensory processing streams. The source-filter model describes the mechanics behind speech production: the identity of the speaker is carried largely in the vocal cord source and the message is shaped by the ever-changing filters of the vocal tract. Sensory processing streams, popularly called 'what' and 'where' pathways, are well established in the visual system as a neural scheme for separately carrying different facets of visual objects, namely their identity and their position/motion, to the cortex. A similar functional organization has been postulated in the auditory system. Both speaker identity and the spoken message, which are simultaneously conveyed in the acoustic structure of speech, can be disentangled into discrete brainstem response components. We argue that these two response classes are early manifestations of auditory 'what' and 'where' streams in the cortex. This brainstem link forges a new understanding of the relationship between the acoustics of speech and cortical processing streams, unites two hitherto separate areas in science, and provides a model for future investigations of auditory function.

Animals↗