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PubMed1994

Work-related, noise-induced hearing loss: evaluation including evoked potential audiometry.

This article reviews the evaluation of 246 workers (492 ears) who underwent otologic and audiologic testing as part of a worker's compensation claim for work-related, noise-induced hearing loss. Tinnitus was present in 58% of the patients, but was rarely a major symptom. Other otologic symptoms or a history of ear disease were virtually nonexistent. Standard audiometry showed a downsloping, high-frequency sensorineural hearing loss in 85% of the ears tested, with only 37% having a characteristic "noise notch" at 4000 or 6000 hertz. Asymmetric hearing loss was not uncommon, with 48 patients (20%) undergoing magnetic resonance scanning, all of whom showed no central lesion responsible for the loss. Proven malingering was surprisingly uncommon (9%). In this study, evoked response audiometry was a valuable adjunct to confirm behavioral thresholds in the evaluation of possible work-related, noise-induced hearing loss. The middle latency response was more effective than the auditory brainstem response as a result of the high-frequency steepness of the audiometric curve.

Acoustic Stimulation↗
PubMed1987

Chronic ultrastructural changes in acoustic trauma: serial-section reconstruction of stereocilia and cuticular plates.

Two cochleas with permanent, noise-induced threshold shifts of 40 to 60 dB (as measured by responses of single, auditory-nerve fibers) were analyzed in detail, first at the light-microscopic level, and subsequently with transmission electron microscopy of serial sections. The light-microscopic analysis showed that there was little hair cell loss, but widespread damage to the stereocilia, especially those on the inner hair cells and first-row outer hair cells. Transmission electron microscopy revealed no pathology in any cells or organelles in the organ of Corti except for the stereocilia and their rootlets. Stereocilia tufts on first-row OHCs and IHCs were badly damaged; those on second- and third-row OHCs appeared ultrastructurally normal. Within the IHC tuft, the damage to the tall, outer row of stereocilia was often selective: the shorter rows could remain ultrastructurally normal even when the tall row was completely missing. The data suggested that most of the structures which appear normal in a careful light-microscopic analysis are also normal at the ultrastructural level. This strengthens earlier suggestions that the correlations between light-microscopic stereocilia changes and alterations in single-unit physiology are causal in nature. The most common stereocilia pathologies were fracture, attenuation or complete loss of the stereociliary rootlets, especially in the region of the cuticular plate near the endolymphatic surface of the cell. The degree and extent of these changes were well correlated with the degree and extent of stereocilia disarray. Abnormalities of the actin-filament matrix within the stereocilia were extremely rare in unfused stereocilia, however, they were common when the stereocilia were part of a fusion bundle. Fusion of stereocilia was always associated with ectopic supracuticular cytoplasm. Based on the ultrastructural observations, different sequences of structural changes preceding the generation of disarray, loss or fusion of stereocilia are suggested.

Animals↗
PubMed2004

Audiometric findings in children with a large vestibular aqueduct.

OBJECTIVE: To characterize audiometric findings in children with a large vestibular aqueduct (LVA). DESIGN: Retrospective review. METHODS: Audiometric records of children with an isolated LVA, diagnosed by computed tomography of the temporal bone, from 1995 through 1998 were reviewed. RESULTS: Nineteen children had an isolated LVA in one or both ears. In all, 26 ears with an isolated LVA were identified. An LVA was seen in association with another inner ear anomaly in an additional 7 ears. The hearing impairment was sensorineural in 22 ears (85%) with an isolated LVA and mixed in 3 (12%). The hearing was normal in 1 ear. The sensorineural hearing impairment (SNHI) was moderate-severe in 12 ears (46%) and severe-profound in 10 ears (38%). Thirteen (50%) of 26 ears had a downsloping or high-frequency SNHI, and 8 (31%) of 26 ears had a midfrequency-peaked audiogram. Bilateral LVAs were seen in 7 children, 6 of whom had bilateral and asymmetrical SNHI. Of 12 patients with a unilateral LVA, 5 had bilateral SNHI. CONCLUSIONS: In this series, the children with LVAs typically had moderate-severe or worse SNHI. An unusual midfrequency-peaked audiogram was present in approximately one third of the study patients. The majority of the patients had a unilateral LVA; however, nearly 50% of the patients with a unilateral LVA had bilateral SNHI. The patients with bilateral LVAs generally had asymmetrical SNHI.

Adolescent↗
PubMed1978

Influence of alcohol on the acoustic reflex and temporary threshold shift.

Blood alcohol levels between 0.09% and 0.15% were found to reduce the protective action of the acoustic reflex in five human subjects with normal hearing. Specifically, acoustic reflex thresholds were raised, reflex magnitude decreased, and temporary threshold shift increased under alcohol conditions. Stimuli consisted of a narrowband noise (500 to 1,000 Hz) and a 500-Hz pure tone. Measurements were made at blood alcohol concentrations from 0.05% to 0.15%. Temporary threshold shift at 1,000 Hz was determined three minutes after a ten minute exposure of narrowband noise at -5, +5, and +20 dB relative to the subject's prealcohol acoustic reflex threshold.

Adult↗
PubMed1998

Micromechanical models for the Brownian motion of hair cell stereocilia.

Brownian motion of the hairs (stereocilia) of amphibian hair cells has been shown in experiments to be in the range of some nm. Our models of the Brownian motion of coupled harmonic oscillators with mechanical properties of stereocilia lead to similar displacements. Computer simulation shows that stochastic fluctuations enhance the encoding of low level acoustic signals. Stochastic resonance lowers the detection threshold of auditory signals to amplitudes one order of magnitude lower than that of the Brownian motion.

Animals↗
PubMed1994

Influence of static middle ear pressure on transiently evoked otoacoustic emissions and distortion products.

Otoacoustic emissions (OAE) are influenced in their amplitude and frequency spectra by the middle ear. The effects of changes in the middle ear transmission mechanisms on transiently evoked OAE (TEOAE) and distortion product emissions (DPOAE) were investigated as a function of static ear canal pressure in 25 normal-hearing test persons aged 18-35 years. The ear canal pressure was varied stepwise between positive and negative values of 200 daPa. TEOAE and DPOAE amplitudes were attenuated significantly with changes of the static ear canal pressure, with greatest changes at low frequencies (< 2 kHz). The alterations of OAE amplitude were slightly dependent on the polarity of the pressure, with positive pressure producing a greater attenuation (0.6 dB). The results demonstrate that changes in middle ear impedance can cause a misinterpretation of OAE. To avoid this problem, tympanometry should always precede OAE measurements. Alternatively, both methods can be combined using one acoustic probe, so that the emissions can be evoked at the peak of middle ear compliance.

Acoustic Impedance Tests↗
PubMed1983

Processing of binaural stimuli by cat superior olivary complex neurons.

A method was developed to record sterotactically from the cat Superior Olivary Complex (SOC) using glass micropipettes. Sound stimulation was given through a closed system that permitted independent variation of interaural time (delta time) and intensity (delta int) differences. The most common binaural units found (n = 34) were ipsilateral excitatory, contralateral inhibitory (EI1), cells of the Lateral Superior Olive (LSO). Some Medial Superior Olive (MSO) cells and presumed MSO ascending afferents were found but, as noted by other authors, we found it difficult to obtain single unit recordings from this nucleus. The LSO EI cells were mostly sensitive to higher frequencies and showed Peristimulus Time Histograms (PSTHs) consisting of a sharp "On" response followed by a plateau when stimulated with Best Frequency (BF) tone bursts or noise bursts. This "On" response was sensitive to delta time and delta int such that ipsilateral time lead or intensity increase resulted in a stronger response. The response reached a minimum around zero delta time or delta int. No sharp peaks or dips were seen in the physiological range needed for localization, instead the response increased with increasing ipsilateral lead or intensity to the maximum values tested (2048 microseconds delta time, 30 dB delta int). In the physiological range the delta time and delta int response were complementary (both increasing response as ipsilaterality was increased). Provided enough sound energy in the unit's sensitive region was present, the same delta time curves were produced when BF tone bursts, masked tone bursts, "sharp onset" tone bursts or noise bursts were used. Changing the delta time of the carrier of the tone burst alone had no effect (except for one cell with a BF of 560 Hz), only the relative time of arrival of the stimulus envelope seemed to be important. In contrast to these LSO EI cells MSO-type units showed EI or EE predominantly low frequency phase-locked responses. When stimulated with interaurally phase shifted (delta pha) BF tones the unit response was a cyclic function of delta pha. Some cells (all that were tested, n = 6 including the 560 Hz LSO EI cell) showed these cyclic responses when stimulated with noise bursts or non-BF tones. However, these "characteristic delays" were not necessarily in the physiological range, i.e. we could find no evidence that these units were responding to delta time/delta pha values corresponding to a particular sound source direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Acoustic sensitivity and bimodal properties of cells in the anterior suprasylvian gyrus of the cat.

The properties of acoustically responsive neurons were studied in the anterior part of the gyrus suprasylvius (ASG) of the cat. The most important features of the responses given to pure tones of different frequencies were: short latency, sharp tuning curves with well definable best frequency (BF). In these respects the cells showed a close resemblance to those of primary acoustic area (AI), and at the same time they proved to be true bimodal cells (responding to somatosensory stimuli, too) like those of the associative areas.

Animals↗
PubMed1977

Filter function of the guinea pig cochlea after degeneration of outer hair cells.

After kanamycin induced degeneration of outer hair cells from guinea pigs the tuning properties of primary auditory nerve fibres are compared with those of normal untreated guinea pigs. The existence of fibres with no alteration of the tuning properties leads to the conclusion that there is no neural interaction between inner and outer hair cells needed to enhance the frequency selectivity.

Animals↗
PubMedDate not supplied

Characteristics of neuronal responses in the sensorimotor cortex of the cat to monaural and binaural stimulation.

The dependence of neuronal responses in the sensorimotor cortex (SMC) of the cat upon localization parameters of dichotically presented auditory signals was studied in acute experiments. Binaural stimulation was more effective than either monaural stimulation. It was shown that spatial-localization parameters of auditory-stimulus source such as interaural differences in intensity and time are reflected by the characteristics of neuronal responses in the SMC; moreover, in 67-88% of cases the most pronounced responses were observed for small, close to zero, temporal and amplitudinal interaural shifts. It was found that SMC neuronal background activity may be altered by signals simulating directed movement of the sound source in the horizontal plane.

Animals↗
PubMed2002

A comparative study of avian auditory brainstem responses: correlations with phylogeny and vocal complexity, and seasonal effects.

We conducted a comparative study of the peripheral auditory system in six avian species (downy woodpeckers, Carolina chickadees, tufted titmice, white-breasted nuthatches, house sparrows, and European starlings). These species differ in the complexity and frequency characteristics of their vocal repertoires. Physiological measures of hearing were collected on anesthetized birds using the auditory brainstem response to broadband click stimuli. If auditory brainstem response patterns are phylogenetically conserved, we predicted woodpeckers, sparrows, and starlings to be outliers relative to the other species, because woodpeckers are in a different Order (Piciformes) and, within the Order Passeriformes, sparrows and starlings are in different Superfamilies than the nuthatches, chickadees, and titmice. However, nuthatches and woodpeckers have the simplest vocal repertoires at the lowest frequencies of these six species. If auditory brainstem responses correlate with vocal complexity, therefore, we would predict nuthatches and woodpeckers to be outliers relative to the other four species. Our results indicate that auditory brainstem responses measures in the spring broadly correlated with both vocal complexity and, in some cases, phylogeny. However, these auditory brainstem response patterns shift from spring to winter due to species-specific seasonal changes. These seasonal changes suggest plasticity at the auditory periphery in adult birds.

Acoustic Stimulation↗
PubMed2002

The role of GABAergic inhibition in shaping directional selectivity of bat inferior collicular neurons determined with temporally patterned pulse trains.

This study examined the role of GABAergic inhibition in shaping directional selectivity of neurons in the inferior colliculus of the big brown bat, Eptesicus fuscus. When determined with temporally patterned pulse trains at different pulse repetition rates, 93 inferior colliculus neurons displayed three types of directional selectivity curves. A directionally selective curve always showed a maximum to a certain azimuthal angle (the best angle). A hemifield curve showed a maximum to a range of contralateral azimuthal angles. A non-directional curve did not show a maximum to any particular azimuthal angles. Directional selectivity curves of 42% neurons changed from hemifield or non-directional to directionally selective and the best angles of 16-21% neurons shifted toward the midline with increasing pulse repetition rate of pulse trains. Directional selectivity curves of most (74%) neurons that discharged impulses to each pulse of a pulse train also became sharper with increasing pulse repetition rate of pulse trains. Bicuculline application produced more pronounced broadening of directional selective curves of inferior colliculus neurons at higher than at lower pulse repetition rates. As a result, pulse repetition rate-dependent directional selectivity of inferior colliculus neurons was abolished. Possible mechanisms and biological significance of these findings are discussed.

Action Potentials↗
PubMed1998

Encoding of acoustic directional information by saccular afferents of the sleeper goby, Dormitator latifrons.

This paper reports on directional response properties of saccular afferents of the sleeper goby, Dormitator latifrons, to 100-Hz acoustic particle motions with a focus on testing the hypothesis that the response directionality of a fish's auditory afferents derives from the morphological polarity of sensory hair cells in the otolithic organs. Spontaneous rates (SR) and best sensitivities (BS) of saccular afferents ranged from 0 to 162 spikes/sec and from 0.2-to 100-nm RMS displacement. SR did not vary with BS. Most saccular afferents were phase-locked to sinusoidal stimulation and had sustained temporal response patterns with some adaptation. All saccular afferents were directionally sensitive to the stimulus, and the sharpness of directional response curves was determined by a directionality index (DI). The DI ranged from 0.64 to 1.50 (mean = 1.02, SE = 0.02, n = 100) and gradually decreased with stimulus level throughout afferents' response dynamic range. Many afferents had approximately symmetric directional response curves relative to their best response axes (BRA). BRA of most afferents remained constant with stimulus level. The BRA distribution had a peak along an axis that correlates closely with the morphological polarity of saccular hair cells. Therefore, our results strongly support the hypothesis.

Acoustic Stimulation↗
PubMed1990

Psychophysiological correlates of posttraumatic stress disorder in Vietnam veterans.

We measured event-related brain potential (ERP) component amplitudes and heart rate (HR) to four intensities of randomly presented tones in two matched groups of drug-free male Vietnam veterans: 12 patients diagnosed with posttraumatic stress disorder (PTSD) and 6 normal combat veterans. Subjects were evaluated with structured diagnostic interviews and anxiety and depression rating scales. We found a significant group X intensity interaction for P2 peak amplitude at CZ. Subjects were classified as augmenters or reducers: positive P2 slopes as a function of stimulus intensity implying augmentation and negative slopes implying reduction. Nine of 12 PTSD subjects were reducers (sensitivity of 75%) and 5 of 6 normals were augmenters (specificity of 83.3%). By the third and fourth second following tone onset, the mean HR of PTSD subjects increased more than twice that of the normals. HR change scores were significantly responsive to the manipulation of stimulus intensity and to the difference between our two groups. P2 reduction differentiates Vietnam veterans with combat-related PTSD from combat veteran controls, and PTSD subjects are more autonomically arousable than their combat veteran peers.

Auditory Threshold↗
PubMed1992

P50 suppression is not affected by attentional manipulations.

Auditory evoked potentials (EP) to high or moderate intensity, single or paired clicks were recorded from normal young adult subjects. A choice-reaction-time paradigm had two sets of instructions, for intensity discrimination and for number (single versus paired stimulus) discrimination. For intensity discrimination, the second click had no informative value and its N100 amplitude was markedly reduced relative to the first click. For number discrimination, the presence or absence of the second click provided the salient information, and N100 amplitude was actually slightly larger for the second compared to the first click. In contrast, the attentional manipulation had no effect on P50 amplitude, which showed over 50% suppression from the first to the second click for both tasks. Thus, suppression of P50 amplitude to the second of a pair of clicks is insensitive to attentional manipulations that have major effects on N100 amplitude. These findings suggest that abnormalities of schizophrenic P50 suppression reflect neuronal rather than psychological phenomena.

Adult↗