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PubMed1985

A monaural space map in the guinea-pig superior colliculus.

Under anechoic conditions, a horizontal array of loudspeakers was used to investigate the representation of auditory space in the guinea-pig superior colliculus. We have previously demonstrated that in animals with both ears intact, there is a topographical representation of the azimuthal dimension of auditory space in the deep layers of this nucleus. In the present study, we have investigated the contribution of monaural and binaural cues to the generation of the auditory space map. Occlusion of one ear or unilateral cochlear destruction resulted in omnidirectional responses in all cells to white-noise stimuli more than 20 dB suprathreshold. The sensitivity of cells to the location of sound at or near threshold was, however, unchanged and we demonstrate the presence of a threshold, monaural auditory space map. This monaural space map was destroyed by removal of the contralateral pinna and concha which resulted in all cells responding best, at threshold, to sounds opposite the external auditory meatus. Measurements of cochlear microphonic (CM) potentials, although variable, revealed that the pinna and concha may result in location-specific changes in the spectral pattern at the tympanic membrane.

Animals↗

PubMed1983

Intracochlear electrical stimulation of normal and deaf cats investigated using brainstem response audiometry.

Brainstem response audiometry for intracochlear electrical stimulation of normal-hearing and deafened cats was investigated. In normal cochleas the brainstem response amplitude grew slowly near threshold as a current-amplitude dependent process, identified as electrophonic in origin. This terminated in a rapidly growing charge-dependent process at approximately 20 dB above threshold, identified as direct electrical stimulation of the auditory nerve. Small levels of white noise (25-35 dB SPL) were sufficient to mask most of the electrophonic response, leaving the direct stimulation process essentially unmodified. In cochleas damaged with d.c. currents and loud sounds, only a rapidly growing charge-dependent process was observed which grew similarly to that in normal-hearing cats but occurred at lower currents. This indicates that possibly the electrical properties of the cochlea were altered in the deafening process, suggesting the inadequacy of normal animals as deaf models for electrical stimulation. Using the technique of derived brainstem responses, it was shown that direct electrical stimulus components were localized to the vicinity of the stimulus electrode with electrophonic components distributed more widely. However, at high currents there was some evidence of the stimulus spreading into the internal auditory meatus.

Animals↗

PubMed1981

On the relationship of stapedial contraction to central masking.

The auditory masked threshold of a 1-kc/s pure tone was determined in quiet and with levels of white noise at 50-80 db SL in the non-test ear. Two groups of normal-hearing adults were tested, one (N:14, mn age = 27.4 yrs) with no history of middle-ear pathology, and another (N:12, mn age = 44.7 yrs) with the stapedial tendon severed. Significant differences in the amount of masked-threshold shift were observed, greater shifts being seen for the normal Ss, additional shifts ranging from 0.8-4.3 db as masking increased from 50-80 db SL. These differences were judged to be at least partly the result of stapedial contraction rather than having their origin entirely in central masking as often assumed.

Adolescent↗

PubMed1986

A psychophysiological study of insomnia.

Ten insomniacs with age- and sex-matched controls had studies of baseline sleep, relation of polygraphically defined sleep to retrospective reports, and arousal thresholds to electronic tones or to a recording of a voice calling out the subject's name. The two groups differed in 10 out of 13 questions about habitual sleep and daytime feelings. In contrast, polygraphic measures of baseline sleep indicated only that insomniacs tended to have slightly less total sleep and had a small but significant increase in early morning awakening time. Unlike the descriptions of habitual sleep, the subjects' retrospective reports of the previous night's sleep differed significantly only for the variable of total sleep time, and there were virtually no differences in the description of their status at a given moment. Auditory arousal thresholds were similar in the two groups, and both went back to sleep and stayed asleep with equal facility. These findings suggest that subjectively poor sleep is not necessarily "light" sleep. For both groups, arousal thresholds differed across the sleep stages, and thresholds to hearing the subject's name were lower than those in response to electronic tones. Although insomniacs had as much polygraphically defined sleep as controls between the forced awakenings of the arousal threshold studies, they perceived their sleep to be only approximately half as long. Insomniacs described themselves as having been awake more frequently than controls in 8 out of 10 forced awakening situations. In one case, insomniacs also overestimated the time between awakenings. In both groups, there was little relationship between reported habitual aspects of sleep and baseline polygraphically defined sleep variables. On questionnaires the following mornings, however, in both groups there was a positive correlation of subjective quality of sleep on the baseline nights with percentage of rapid eye movement sleep, and a negative correlation to various aspects of slow-wave sleep.

Adult↗

PubMed1980

Threshold elevation at high frequencies of the auditory nerve action potentials in acute versus chronic recordings in guinea pigs.

Thresholds of the auditory nerve compound action potential (CAP) responses to filtered clicks from 0.5 to 40 kHz, defining a CAP frequency threshold curve, have been determined in the same guinea pigs: (1) in acute conditions, the animal still anesthetized at the end of the operation for permanent implantation of a round-window electrode, and (2) several days later in the implanted awake and unrestrained animal. The results show higher CAP thresholds for high frequencies in acute conditions as compared to chronic recordings. This difference appears above about 12.5 kHz and increases progressively to around 40 dB at 40 kHz. Similar effects, although somewhat less pronounced, were observed during anesthesia alone in already implanted guinea pigs. Thes observations could explain the discrepancies which appear between electrophysiological thresholds, acutely recorded either from single fibers or whole-nerve responses, and behavioral audiograms. Moreover, in the accurate evaluation of the cochlea, slight impairments may be masked by this phenomenon as illustrated in guinea pigs treated with low doses of ototoxic antibiotic.

Acoustic Stimulation↗

PubMed1996

Aging effects on monoamines in rat medial vestibular and cochlear nuclei.

Noradrenaline (NA), dopamine (DA); serotonin (5-HT) and their metabolites-3-methoxy, 4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA)-were determined using HPLC in medial vestibular nucleus (MVN), anteroventral cochlear nucleus (AVCN), dorsal+posteroventral cochlear nucleus (DCN+PVCN), locus coeruleus (LC) and raphe dorsalis of Dark Agouti-Hanovre (DA-HAN) rats aged 4, 21 and 24 months. In older rats, the main noradrenergic changes were a decrease of NA content with an increase of the MHPG/NA ratio in MVN and a selective NA increase in AVCN. 5-HT and 5-HIAA levels were increased in all the brainstem nuclei except raphe dorsalis. DA and DOPAC remained unchanged. These data show that noradrenergic neurons in sensory nuclei are differently affected by aging whereas serotonergic activation occurs in most of them possibly as a compensatory response to dysfunction of sensory input and processing. The increase of NA stores in the AVCN of aged rats is in line with the elevated auditory brainstem threshold reported in old rats and could improve the signal-to-noise ratio. Noradrenergic neurons in the MVN seem to be more sensitive to age effect than cochlear nuclei; however, even if neuronal loss occurs, NA synthesis and/or metabolism increase to ensure normal or increased noradrenergic activity.

3,4-Dihydroxyphenylacetic Acid↗

PubMed2003

Hyperexcitability and reduced low threshold potassium currents in auditory neurons of mice lacking the channel subunit Kv1.1.

A low voltage-activated potassium current, IKL, is found in auditory neuron types that have low excitability and precisely preserve the temporal pattern of activity present in their presynaptic inputs. The gene Kcna1 codes for Kv1.1 potassium channel subunits, which combine in expression systems to produce channel tetramers with properties similar to those of IKL, including sensitivity to dendrotoxin (DTX). Kv1.1 is strongly expressed in neurons with IKL, including auditory neurons of the medial nucleus of the trapezoid body (MNTB). We therefore decided to investigate how the absence of Kv1.1 affected channel properties and function in MNTB neurons from mice lacking Kcna1. We used the whole cell version of the patch clamp technique to record from MNTB neurons in brainstem slices from Kcna1-null (-/-) mice and their wild-type (+/+) and heterozygous (+/-) littermates. There was an IKL in voltage-clamped -/- MNTB neurons, but it was about half the amplitude of the IKL in +/+ neurons, with otherwise similar properties. Consistent with this, -/- MNTB neurons were more excitable than their +/+ counterparts; they fired more than twice as many action potentials (APs) during current steps, and the threshold current amplitude required to generate an AP was roughly halved. +/- MNTB neurons had excitability and IKL amplitudes identical to the +/+ neurons. The IKL remaining in -/- neurons was blocked by DTX, suggesting the underlying channels contained subunits Kv1.2 and/or Kv1.6 (also DTX-sensitive). DTX increased excitability further in the already hyperexcitable -/- MNTB neurons, suggesting that -/- IKL limited excitability despite its reduced amplitude in the absence of Kv1.1 subunits.

Animals↗

PubMed1976

Yes-no test for nonorganic hearing loss.

The Yes-No Test is a procedure that can be used in the diagnosis of nonorganic hearing loss in children. The test employs a pure tone audiometric technique in which the child is instructed to say "yes" when he hears the tone and "no" when he does not hear the tone. This article describes clinical findings in three cases involving nonorganic hearing loss in which the Yes-No Test was instrumental in determining the true organic hearing thresholds.

Adolescent↗

PubMed1989

A model of threshold for pulsatile electrical stimulation of cochlear implants.

Threshold measures have been made as a function of the repetition rate and pulse duration of biphasic electrical pulses applied to the cochlea through a cochlear implant (Shannon, 1985). Nonmonotonicities in those data suggest that at least two separate processes are involved in the translation of an electrical stimulus into a threshold perception. This paper presents a phenomenological model which accounts for the key features of the threshold data. The model consists of two parallel processes which are each power-law functions of the instantaneous current amplitude. The output of each process is then integrated with a short time constant (approximately 1-2 ms). The maximum of these two outputs represents the sensory magnitude of that electrical stimulus. Threshold data from 14 patients implanted with three different devices are compared to model predictions over a wide range of pulse durations and pulse rates. Since the model accurately predicts thresholds over such a wide range of stimuli, it is possible that it can predict the threshold of an arbitrary electrical stimulus. This model could be used to construct a speech processor that would convert any acoustic waveform into an equivalent electrical waveform that would preserve threshold relationships.

Auditory Threshold↗

PubMed2006

Pairwise fitting of mixed models for the joint modeling of multivariate longitudinal profiles.

A mixed model is a flexible tool for joint modeling purposes, especially when the gathered data are unbalanced. However, computational problems due to the dimension of the joint covariance matrix of the random effects arise as soon as the number of outcomes and/or the number of used random effects per outcome increases. We propose a pairwise approach in which all possible bivariate models are fitted, and where inference follows from pseudo-likelihood arguments. The approach is applicable for linear, generalized linear, and nonlinear mixed models, or for combinations of these. The methodology will be illustrated for linear mixed models in the analysis of 22-dimensional, highly unbalanced, longitudinal profiles of hearing thresholds.

Auditory Threshold↗

PubMedDate not supplied

Methodological problems in the determination of homolateral stapedius reflex threshold.

Generally, a bilateral symmetry of the acoustic stapedius reflex is assumed. But a homolaterally higher sensitivity has been described. We examined 71 patients with complete unilateral deafness. With a TDH 39 headphone, stimuli of intensities up to 133 dB were conveyed to the deaf ear. A fairly accurate estimate of the normal homolateral threshold is obtained by correcting for the cross-hearing loss and by mathematical consideration of the relative probabilities of the positive and negative cases. Methodology-specific influences are discussed and a correction made for them. The homolateral reflex threshold is 9-14 dB lower than the contralateral reflex threshold.

Acoustic Stimulation↗

PubMed1991

Unusual morphology of the stria vascularis in pigmented strain 2/NCR guinea pigs.

This paper reports an abnormality in the morphology of the apical stria vascularis of inbred 2/NCR guinea pigs as compared to outbred animals. Cochleas were embedded in plastic, sectioned, and examined in the light and electron microscopes. In the 2/NCR animals, the apical stria vascularis consisted of a cuboidal epithelium composed of a monolayer of poorly differentiated cells. Few or no capillaries were associated with this epithelium. No melanin pigment was present in the abnormal region of the stria in these animals, although pigmentation appeared normal in lower turns of the cochlea. Measurements of compound action potential thresholds between 2 and 40 kHz revealed no differences in auditory function between the two strains.

Action Potentials↗

PubMed1999

Sleep spindles and arousal: the effects of age and sensory stimulation.

This study assessed a proposed sleep-preserving role for sleep spindles by evaluating variations in this activity as a function of factors, both naturally occurring and experimentally induced, known to affect and effect arousal from sleep. These factors included age, auditory stimulation, and experimentally induced arousal from sleep. Analyses were based on data from 84 males (5-49 yrs. old) from normal and clinical (hyperactive, enuretic, and chronic pain) populations who had participated in sleep auditory arousal threshold studies involving adaptation and 1-2 experimental nights. Spindles on experimental nights were visually analyzed and incidence determined for the two minutes preceding and throughout all Stage 2 arousal attempts. Prestimulation spindle occurrence in 39 preadolescent subjects with two experimental nights did not vary significantly from night-to-night, and prestimulation period comparisons between clinical groups and their respective controls were also non-significant. Anticipated relationships between spindle activity and indices of arousal-either inverse with respect to known variations in arousal threshold, i.e., decreases with age and across the night, or direct with respect to stimulus intensity particularly on trials when arousal did not occur-were not observed. Instead, all age groups showed significant decreases in spindle density as an increasing negative function of stimulus intensity. These findings suggest that to the extent to which sleep spindles can be considered to play a role in sleep preservation by inhibiting or attenuating potentially arousing stimuli, these effects appear to be restricted to endogenously generated stimuli and are passive rather than reactive in nature.

Acoustic Stimulation↗

PubMed1987

Auditory steady-state responses: threshold prediction using phase coherence.

These experiments add a measure of response phase variance--'phase coherence'--to the analysis procedures applied to auditory steady-state responses (SSR). The effects of stimulus frequency, intensity, rate and total number (i.e., recording time) were studied using 11 normal adult subjects. In a first experiment, SSR phase coherence was found to be highest at presentation rates near 40/sec, even when response amplitudes were higher at other rates. Further, phase coherence was observed to be linearly related (r = 0.91) to signal-to-noise ratio. Two further experiments demonstrated that phase coherence can correctly detect responses to near-threshold stimuli. In 15 min runs, significant phase coherence was detected within 6 dB of behavioral threshold in 6 subjects for 0.5 and 2.0 kHz signals, while phase coherence in no-stimulus control runs did not reach significance. Minimum data collection time required to record significant (P less than 0.01) responses was studied for 10 subjects. In 2 of 40 recordings at 10 dB SL phase coherence remained insignificant after even 15 min. However, average recording time to reach significance at 10 dB SL was less than 4 min in 38 of 40 recordings, and less than 1 min at 25 dB SL (18 of 18 recordings). These results indicate that using phase coherence to detect the presence of the 40/sec auditory steady-state response, efficient threshold search procedures may be devised to provide fast, accurate, and objective estimates of auditory behavioral thresholds in nearly all normal adults.

Acoustic Stimulation↗

PubMed1986

Rate responses of auditory nerve fibers to tones in noise near masked threshold.

The rate responses of auditory nerve fibers were measured for best frequency (BF) tone bursts in the presence of continuous background noise. Rate functions for BF tones were constructed over a 32-dB range of levels, centered on the behavioral masked thresholds of cats. The tone level at which noticeable rate changes are evoked by the tones corresponds closely to behavioral masked threshold at all noise levels used (-10- to 30-dB spectrum level). As the noise level increases, the response rate to the background noise approaches saturation, and the incremental rate response to tones decreases. At high noise levels, the rate responses to tones of low and medium spontaneous rate fibers are larger than those of high spontaneous rate fibers. Empirical statistics of auditory nerve fiber spike counts are reported; these differ from those expected of a Poisson process in that the variance is smaller than the mean. A new measure of discharge rate is described that allows rate changes to be expressed in units of a standard deviation. This measure allows tone-evoked responses to be interpreted in terms of their detectability in a signal detection task. Rate responses of low and medium spontaneous rate fibers are more detectable than those of high spontaneous rate fibers, especially at high noise levels. There appears to be sufficient information in the rate response of a small number of auditory nerve fibers to support behaviorally observed levels of detection performance.

Acoustic Stimulation↗

PubMed1990

Stapedius reflex thresholds in relation to tails of auditory nerve fiber frequency tuning curves.

The acoustic stapedius reflex (ASR) threshold on non-anesthetized rabbits was compared to some measures of the single auditory nerve fiber activity of rabbits. The observations were made on normal-hearing animals, with some additional data from noise-exposed individuals. The results showed that the ASR threshold was reached at a sound level above saturation of discharge rate for individual neurons at their characteristic frequency (CF) in normal animals. It was found, on the other hand, that the ASR threshold measured across frequencies from 0.25 to 12.0 kHz were at a level similar to that of the tails of the frequency tuning curves (FTCs). Cochlear lesions-induced changes in FTC tail levels were paralleled by changes in ASR threshold levels. The raise of ASR threshold was, however, somewhat larger than the raise of the tails which might be explained by the significant relative decrease in the total number of units found in the frequency region corresponding to the lesion. There was also a decrease in the high spontaneous rate (SR) compared to the low and medium SR fibers for higher frequencies. It is concluded that the FTC tails can be a major eighth-nerve correlate to ASR activation.

Acoustic Stimulation↗

PubMed1990

The role of non-auditory factors in measured and self-reported disability.

The effect of age per se on auditory disability in relation to other non-auditory factors, including personality and IQ, is unclear because of the close link with hearing threshold level. Auditory disability may be assessed in terms of either performance or self-report. It was measured using two tasks identifying words in sentences: (1) sentence identification in noise for spatially separated signal sources, and (2) identification of sensible and nonsensical sentences given at normal and artificially accelerated rates. Self-reported disability was assessed using the MRC Institute of Hearing Research's Hearing Disability Questionnaire and the American Hearing Performance Inventory. The sample of 240 individuals aged 50-75 years was constructed to provide a balance across the major stratification parameters of hearing level and age. In accordance with much of the published literature, the performance indices exhibited significant age effects: for a given hearing threshold level, older individuals are more disabled. Conversely, the indices of self-reported disability exhibit a trend whereby individuals with a given hearing threshold level, report a lower degree of disability with increasing age. There were no significant effects of personality, verbal or non-verbal IQ on the performance indices. However, these variables had large effects on reported disability, increasing the explained variance by approximately 20% more than the variance explained by hearing threshold level and age. Thus, the effect of age has the expected direction for performance-based disability, but for reported disability has the counter-intuitive direction. This finding, together with the additional large significant effects of other nonauditory variables, implies that indices of self-reported disability have to be controlled for these other major determinants if they are to be useful in an overall assessment of auditory disability.

Aged↗

PubMed1991

Comparison of compound action potential audiograms with distortion product otoacoustic emissions in experimentally induced hydrops.

Endolymphatic hydrops was induced in a series of adult pigmented guinea pigs. Distortion product oto-acoustic emissions in general reflected the typical form of the hydropic compound action potential (CAP) audiogram, either with predominant low-frequency losses or a relatively flat audiogram. However, at certain two-tone combinations in some control ears the emissions could be smaller than expected from respective CAP audiograms, while in some hydropic ears the emissions could be larger than expected. The data presented here suggest that whilst the diagnostic value of distortion product emissions in the clinical situation might, at this time, be limited, the data from these emissions can give some insight into tonotopic hair cell function.

Action Potentials↗