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PubMed2005

The auditory P300 at or near threshold.

Psychophysical and P300 (P3) thresholds and suprathreshold measures were obtained in 16 normal-hearing subjects. Subjects followed a classic oddball paradigm using 1000 (frequent) and 2000 Hz (rare) tones as stimuli. The P3 was obtained for all 16 subjects at or 5 dB above their behavioral threshold. The P3 was obtained more often at behavioral threshold and 5 dB SL than N1 and P2 late potentials. The P3 was larger in amplitude than either the N1 or the P2 at threshold and for 75 dB SPL stimuli. In comparing P3s obtained at threshold and for the 75 dB stimuli, significant effects were noted in latency and amplitude reflecting exogenous aspects to this endogenous potential. Differences in latency and amplitude were also noted in N1 and P2 waveforms obtained from the rare versus frequent stimuli. Clinical implications of these results are discussed.

Adolescent↗
PubMed2003

Effects of auditory stimulus intensity and hearing threshold on the relationship among P300, age, and cognitive function.

OBJECTIVE: Although P300 is regarded as cognitive or endogenous, studies have demonstrated that stimulus intensity influences the component. To isolate effects of hearing from cognition, two experiments were designed to compare the effects of variation in stimulus intensities with naturally occurring differences in hearing thresholds. METHODS: In experiment 1, 18 participants were tested with 5 auditory oddball event-related potential (ERP) paradigms with different intensities. In experiment 2, an auditory oddball ERP task was completed by 3 groups of participants with different hearing thresholds (n=57). P300 was then correlated with block design and matrices from Wechsler's abbreviated scale of intelligence. RESULTS: At Cz and Pz, manipulation of intensity had less effect on P300 than the observed differences between groups with different hearing thresholds. At Fz, however, the effect of manipulations of stimulus intensity was greater than the effect of naturally occurring differences in hearing thresholds. P300 still correlated in predicted directions with cognitive tests after correcting for the estimated effect of differences in hearing. CONCLUSIONS: The results indicate that P300 is an index of cognitive function even when the relationship is corrected for perceptual differences, at least at posterior scalp areas.

Acoustic Stimulation↗
PubMed1993

Electromagnetic stimulation of the auditory system: effects and side-effects.

Extracranial electromagnetic stimulation (EMS) is a recently developed clinical technique which may be used in place of conventional transcutaneous electrical stimulation to activate the central and peripheral nervous systems. This technique is widely used in neurology and otolaryngology for non-invasive stimulation of the brain and facial nerve. EMS uses electromagnetic field pulses which pass unimpeded through the cranium and soft tissues to activate excitable membranes of volume conductors. In this series of studies, the effects and side-effects of electromagnetic stimulation on the auditory system of humans and experimental animals were investigated. In the first study, 18 profoundly hard-of-hearing and deaf patients who were candidates for cochlear implants were examined by non-invasive EMS in an effort to determine whether EMS could stimulate residual neurons in the cochlea, 8th nerve proper, or higher auditory brain centers, and evoke auditory sensations. The patients were stimulated with a magnetic coil positioned at the (1) auricle, (2) mastoid process, and (3) the temporal lobe area. EMS elicited auditory sensations in 26 ears (of 14 patients/subjects). The lowest threshold of auditory sensation (TAS) at each stimulus position was found to be at the 20% EMS level, with a range of 20-50% of the maximum level (2.0 Tesla), and with equal sensitivity in each coil position. There was no correlation between the EMS/TAS and the immediate postoperative psychoacoustic tests in ten patients receiving cochlear implants. A prominent side effect of EMS was found to be the high intensity, high frequency impulse noise generated by the coil which causes severe cochlear damage and permanent sensorineural hearing loss in experimental animals. Measurements of the sound pressure level (SPL) of the magnetic coil acoustic artifact (MCAA) at the tympanic membrane of the rabbit ear showed levels of up to 160 dB for maximum EMS. Measurements of the spectral content and SPL of the MCAA in the ear canal of life size models of the human cranium with the stimulating coil placed at standard clinical positions indicated that the major acoustic energy of the pulse is concentrated in the 2-5 kHz range, and that the SPL of the pulse at some positions may place persons at risk for hearing loss. Studies on computer simulated impulse noises showed that the peak sound pressure rather than the rise time (in the range 0.1-1.0 ms) determined the permanent threshold shift (PTS). The MCAA was more harmful than a 128 dB SPL continuous noise with 100 times more energy.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1989

Aminoglycoside ototoxicity in cystic fibrosis. Evaluation by high-frequency audiometry.

In this study, we sought to determine the clinical usefulness of high-frequency audiometry (8000 to 20,000 Hz) in detecting aminoglycoside-induced increases in pure-tone hearing thresholds before they are noticed in conventionally tested frequencies. We measured hearing thresholds from 250 to 20,000 Hz in 22 patients with cystic fibrosis who were treated with aminoglycosides. The audiograms were age-matched and were compared with those from 13 patients with cystic fibrosis and 38 subjects without cystic fibrosis, all of whom had never received aminoglycoside therapy. In patients with cystic fibrosis who were treated with aminoglycosides (younger than 20 years), there were statistically significant elevations only in frequencies higher than 16,000 Hz. Patients with cystic fibrosis who were treated with aminoglycosides who were 20 years and older had elevated thresholds in all frequencies tested. Patients with cystic fibrosis who were not treated with aminoglycosides did not differ statistically from controls. High-frequency audiometry may serve as a useful measure of elevation in pure-tone hearing thresholds that precede noticeable loss of auditory acuity in patients with cystic fibrosis who are receiving long-term aminoglycoside therapy.

Adolescent↗
PubMed1982

The influence of chronic vitamin A deficiency on human and animal ears.

After feeding young rats a diet deficient in vitamin A, we examined the inner ear with the electron microscope. There were changes in the cuticle of the outer and inner hair cells. Furthermore, there were changes in the reticular system of the intermediate zone and massive degenerative changes in the ganglion cells of the VIII nerve. In a second experiment with older animals we found no significant changes in the sensory cells, though there was new bone formation in Rosenthal's canal and damage to the ganglion cells, of a lesser extent than was evident in the first experiment, however. In a further clinical study, we carefully chose human subjects suffering from alcoholic liver disease who also had a negative history of ear infection, noise exposure, head injury and use of streptomycin. Normal auditory function in the family was also a criterion. A decreased auditory function associated with low vitamin A levels was found in these patients. Those with liver disease showed not only a significant auditory dysfunction in the higher frequencies, but as well a poorer performance in the tone decay test. They were compared to a control group with normal hepatic, renal and thyroid status.

Animals↗
PubMed1980

The graph of loudness recruitment (ABLB-test).

The ABLB-test compares the subjective loudness in patients with unilateral sensorineural hearing loss. The graph of this comparison of loudness at different suprathreshold intensities is of interest for understanding the function of the hair cells.

Auditory Threshold↗
PubMed2000

Binaural interaction component and white-noise enhancement in middle latency responses: differential effects of anaesthesia in guinea pigs.

It is known that the response to binaural clicks is smaller in amplitude than the sum of two monaural responses. The difference is called the binaural interaction component (BIC). Also, an amplitude enlargement occurs in guinea pig middle latency responses (MLRs) to monaural clicks when white noise is applied to the other ear. This study was conducted to find out whether these two signs of binaural interaction result from the same mechanism. White noise enhancement (WNE) and BIC were computed from the evoked potential data simultaneously recorded in different phases of anaesthesia. WNE gradually decreased and disappeared with anaesthesia, but the relative amplitude of the BIC remained unchanged. This differential effect showed that different neural mechanisms must be responsible for BIC and WNE in guinea pig MLR.

Acoustic Stimulation↗
PubMed2006

Beaked whale auditory evoked potential hearing measurements.

Several mass strandings of beaked whales have recently been correlated with military exercises involving mid-frequency sonar highlighting unknowns regarding hearing sensitivity in these species. We report the hearing abilities of a stranded juvenile beaked whale (Mesoplodon europaeus) measured with auditory evoked potentials. The beaked whale's modulation rate transfer function (MRTF) measured with a 40-kHz carrier showed responses up to an 1,800 Hz amplitude modulation (AM) rate. The MRTF was strongest at the 1,000 and 1,200 Hz AM rates. The envelope following response (EFR) input-output functions were non-linear. The beaked whale was most sensitive to high frequency signals between 40 and 80 kHz, but produced smaller evoked potentials to 5 kHz, the lowest frequency tested. The beaked whale hearing range and sensitivity are similar to other odontocetes that have been measured.

Acoustic Stimulation↗
PubMed1989

Prefrontal cortex gating of auditory transmission in humans.

Middle-latency auditory evoked potentials (MAEPs) were recorded in controls and patients with focal lesions in dorsolateral prefrontal cortex. Unilateral prefrontal lesions increased the amplitude of the Pa component of the MAEP beginning at 25-35 ms poststimulus. The data suggest that prefrontal cortex exerts early inhibitory modulation of input to primary auditory cortex in humans.

Acoustic Stimulation↗
PubMedDate not supplied

Aging decreases auditory event-related potentials to unexpected stimuli in humans.

A P300 event-related potential (P3a) was recorded to unexpected, deviant auditory stimuli requiring no behavioral response. This brain potential underwent systematic latency prolongation and amplitude decrease with advancing age. The age-related changes paralleled those of the P300 (P3b) recorded in target detection tasks. These results provide physiological evidence of a decremented CNS response to unexpected stimuli with aging.

Acoustic Stimulation↗
PubMed1982

Quantitative analysis of intensity--rate and intensity--latency functions in peripheral auditory nerve fibers of northern leopard frogs (Rana p. pipiens).

The intensity--rate and intensity--latency functions were analyzed quantitatively from single auditory fibers in the eighth nerve of northern leopard frogs (Rana p. pipiens). There was a firing rate change of as high as 15 impulses/s and a latency shift of as much as 1.4 ms per dB change in sound intensity. These rates of change were different for units with the same best excitatory frequency and greater for each unit studied at lower intensities than at high intensities. The significance of the latency function on central binaural time processing was discussed.

Acoustic Stimulation↗
PubMed1983

Damage to sensory hairs of inner hair cells after exposure to noise in rabbits without outer hair cells.

We investigated if the noise-induced damage to the stereocilia of inner hair cells (IHCs) was dependent on the integrity of the outer hair cells (OHCs) in rabbit. Prior to the noise exposure a total loss of OHCs in the basal 1.5 to 2 turns was induced by administration of kanamycin (400 mg/kg for 10 days). This left the IHCs apparently normal as observed in the scanning electron microscope. These animals exhibited a 20-60 dB hearing loss before noise exposure. In spite of this pronounced hearing loss, the fusion and inclination of the IHC stereocilia were extensive in these noise-exposed ears. The stereocilia damage occurred at the same noise exposure and was as prominent or even more pronounced than has been noted in ears exposed to noise only. Under the assumption that kanamycin causes selective destruction of OHCs, the results can be interpreted as evidence that the OHCs facilitate the IHCs at low sound levels without being involved in the process which damages IHC stereocilia at high levels of noise.

Animals↗
PubMed1983

Frequency selectivity of phase-locking of complex sounds in the auditory nerve of the rat.

Frequency selectivity of single auditory nerve fibers in the auditory nerve of the rat was studied using pseudorandom noise as the stimulus. The noise was lowpass filtered ternary m-sequences. Period histograms of the discharges of single auditory nerve fibers, locked to the periodicity of the noise, were cross-correlated with one period of the noise to obtain estimates of the impulse response. These cross-correlograms were subsequently Fourier transformed to obtain estimates of the frequency transfer functions. Earlier results obtained using noise that was based on binary sequences as the stimulus showed a systematic dependence on stimulus intensity of the bandwidth and center frequency of the computer transfer functions. The results of the present study confirmed this dependence and showed that a linear model based upon first-order cross-correlations fit the histograms of response. It is concluded that phase-locked activity of single auditory nerve fibers accurately reproduces the half-wave rectified motion of the basilar membrane over a large range of sound intensities.

Animals↗
PubMed1983

Ultrastructural studies of stereocilia in noise-exposed rabbits.

In rabbits with noise-induced, permanent hearing loss of more than 20 dB the stereocilia of the inner hair cells (IHCs) showed widespread signs of damage: fracturing, folding, fusion, and formation of giant hairs. Damage to the stereocilia on outer hair cells (OHCs) was much less pronounced in corresponding regions. On damaged OHCs the stereocilia were usually missing, except in the apical turn where fusion of stereocilia and formation of giant stereocilia occurred. On both IHCs and OHCs the 'neck' of the stereocilium appeared to be a site of fracture of the actin skeleton. On IHCs the actin cores of the former stereocilia were enclosed in a bulge of the apical cytoplasm to form a giant hair, with portions of the stereocilia projecting from the bulge. Inside the giant hairs profiles of the original stereocilia could be recognized, and these often retained their original circular form at least at the base of a giant hair. In the distal portion of the giant hair the actin filaments frequently formed a single thick bundle where the individual stereocilia could not be distinguished. Material had condensed between the surface membrane enclosing the former stereocilia and the actin cores. A thin kinocilium was often identified on IHCs. together with giant hairs possibly indicating a regenerative activation of the cell. It is suggested that fracture and fusion of stereocilia are due to different pathophysiological mechanisms, and that the actin of damaged cilia may undergo a slow reorganization and regeneration.

Actins↗
PubMed1987

Current source density analysis of frequency coding in the inferior colliculus.

Current source density (CSD) analysis is a technique that provides information about the time course and spatial location of transmembrane currents derived from a laminar collection of evoked potentials. Restrictive conditions for acquisition of evoked potentials are required in order to yield a one-dimensional CSD analysis that is an accurate estimate of synaptic activity. Satisfaction of these conditions was assumed in recordings of tone-burst-evoked potentials along the axis of symmetry (tonotopic) in the inferior colliculus of adult mongolian gerbils. Off-line these data were converted into distance/voltage functions. The second spatial derivatives of these functions gave a family of profiles of the spatial distribution of current source and sink densities at discrete latencies relative to the stimulus. Results indicate a frequency-dependent spatial shift in the evoked current sink of about 280 microns octave. This sink, indicative of local excitatory synaptic drive, is surrounded, both spatially and temporally, by current sources. The spatial extent of excitation as estimated from CSD analysis, compares well quantitatively with predictions from an across-neuron model that is based on single unit data.

Acoustic Stimulation↗
PubMed1991

Sound frequency and binaural response properties of single neurons in rat inferior colliculus.

Sound frequency and binaural response properties were determined for single neurons in the rat's inferior colliculus. Nerve cell responses in the central nucleus of the inferior colliculus were narrowly tuned and had clearly defined characteristic frequencies (CF). The central nucleus was tonotopically organized with low frequencies represented dorsolaterally and high frequencies ventromedially from 0.87 to 45 kHz. Sharpness of tuning, as indicated by Q10, covered a wide range of values for neurons with the same CF, but the maximum Q10 at each frequency increased monotonically with CF. Maximum Q10s were larger than previously reported for auditory cortex at the same CF. Binaural responses were classified as either suppression, summation or mixed. Most of the units encountered exhibited binaural suppression but there were substantial numbers of both summation and mixed responses. Each major binaural response type was distributed broadly across sound frequencies within the rat's hearing range. Binaural suppression responses were most numerous at high frequencies and summation responses at low frequencies. The binaural response types, their relative proportions and their distribution by CF were similar for neurons in the central nucleus of inferior colliculus and primary auditory cortex of the albino rat.

Acoustic Stimulation↗
PubMed1992

Single-fibre and whole-nerve responses to clicks as a function of sound intensity in the guinea pig.

This paper describes a study of the intensity dependence of click-evoked responses of auditory-nerve fibres in relation to the simultaneously recorded compound action potential (CAP). Condensation and rarefaction clicks were presented to normal hearing guinea pigs over an intensity range of 60 dB. The recorded poststimulus time histograms (PSTHs) were characterized by the latency (tp), amplitude (Ap) and synchronization (Sp) of their dominant peak, parameters that are particularly important for the understanding of the CAP. For all fibres tp decreased monotonically with increasing intensity, in a continuous way for fibres with high characteristic frequency (CF greater than 3 kHz), and in discrete steps of one CF-cycle for low-CF (CF less than or equal to 3 kHz) fibres. An additional analysis of PSTH envelopes revealed that average latency shifts with intensity are similar for all CFs above 2 kHz. For all fibres Ap increased monotonically with intensity; the increase was stronger and maximum values were larger for low-CF than for high-CF fibres. A schematic model PSTH was then formulated on the basis of the experimental data. A sum of these model PSTHs from a hypothesized fibre population was convolved with an elemental unit response (Versnel et al., 1992) in order to simulate the compound action potential. Synthesized CAPs agreed with experimental CAPs in their main aspects.

Acoustic Stimulation↗