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At least 1,279 records · Page 71Linked to original sources
PubMed1985

Responses of single neurones in cat auditory cortex to time-varying stimuli: frequency-modulated tones of narrow excursion.

In the primary auditory cortex of cats anaesthetized with nitrous oxide, single neurones were examined with respect to their responses to tone bursts and linear modulations of the frequency of an on-going continuous tone. Using FM ramps of 2.0 kHz excursion and varying centre frequency, each of 39 neurones was examined for its preference for the direction of frequency change of a ramp whose centre frequency was varied in and around the neurone's response area. Direction preference was strictly associated with the slopes of the cell's spike count-versus-frequency function over the frequency range covered by the ramp. Preferences for upward- and downward-directed ramps were associated with the low- and high-frequency slopes of the spike count function, respectively. The strength of the cell's direction preference was associated with the relative steepness of the spike count function over the frequency range covered by the ramp. The timing of discharges elicited by the frequency modulations was found to be the sum of the cell's latent period for tone bursts plus the time after ramp onset that the stimulus frequency fell within the neurone's response area. The implications of these data for the processing of narrow and broad frequency-modulated ramps are discussed.

Animals↗
PubMed2006

Evaluation of hearing and cochlear function by DPOAE and audiometric tests in patients with ankylosing spondilitis.

The aim of this study was to investigate cochlear functions in patients with ankylosing spondilitis (AS). Prospective, case control study. Twenty-eight AS patients (56 ears) and 25 healthy control subjects (50 ears) were included in the study. Pure-tone audiometry at 250, 500, 1,000, 2,000, 4,000, 6,000 Hz and immittance measures including tympanometry and acoustic reflex and DPOAEs (Distortion Product Otoacoustic Emission) testing were performed in the patients and controls. Pure-tone audiometry findings of the patients and controls were significantly different in all frequencies (P < 0.05). Sensorineural hearing loss was found in 10 patients (35%) that was bilateral in seven and unilateral in three patients. On DPOAE testing, there was no statistically significant difference between the levels of noise floor of the patients and controls (P > 0.05). However, the DPOAE responses of the patients and controls were significantly different in 3,000, 4,000, 5,000 and 6,000 Hz frequencies (P < 0.05). There is a damage of outer hair cells in patients with AS, and damaged outer hair cell regions mostly corresponds to the basal and mid-portions of the cochlea.

Acoustic Impedance Tests↗
PubMed1982

Late onset of hearing in the ferret.

Onset of hearing in the ferret was judged by simple behavioral, physiological and anatomical indices. The ear canals do not open until the end of the first postnatal month. This coincides with the appearance of a startle response to loud hand claps and the recording of acoustically activated neurons in the midbrain. The late onset of hearing in the ferret (around 32 days postnatal) contrasts with the cat (6 days) and the mouse (12 days).

Aging↗
PubMed1990

Auditory dysfunction and cochlear vascular injury following trimethyltin exposure in the guinea pig.

Trimethyltin chloride (TMT) produces an auditory impairment in the rat due, presumably, to cochlear injury. The loss is unusual in that it persists for several weeks, but ultimately resolves at least at low to middle frequencies. Recovery of high frequency auditory loss is less predictable. Given this pattern of injury and recovery plus the known ability of TMT to impair oxidative phosphorylation, it was hypothesized that TMT would damage the stria vascularis which is the most metabolically active area and a structure containing one of the primary vascular networks in the cochlea. Trimethyltin chloride ototoxicity was evaluated in guinea pigs treated with the toxicant and then subjected to weekly tests of the auditory brainstem response evoked by tonal stimuli. A high frequency impairment was found which tended to improve within the first 2 weeks after exposure. Subjects were euthanized 6 weeks after TMT for histopathological study of the cochlea. At that time point most subjects showed full functional recovery. Subjects showed significant changes both in the number of outer hair cells and in the condition of the stria vascularis. Outer hair cell loss was observed in a restricted portion of the most basal turn of the cochlea which is responsible for encoding high frequency sound despite recovery of function in some animals. A very marked increase in the diameter of the vessels of the stria vascularis was observed along with signs of atrophy in the stria vascularis. Enlarged vessel diameters were particularly apparent in the apical and middle turns of the cochlea, which did not show significant hair cell loss. The data confirm that TMT does produce both hair cell damage and vascular pathology in the cochlea.

Animals↗
PubMed1984

Infrasound responses in the midbrain of the guinea fowl.

The electrophysiological audiogram of the Guinea fowl has been obtained using auditory evoked potentials from the MLD of unanesthetized birds. In restricted regions of MLD, phase-coupled responses to extreme low-frequency sinusoids (2-10 Hz) could be recorded at moderate intensities. The tonotopy of MLD extends continuously to the infrasound region at the rostrodorsal margin. Single-cell recording of infrasound responses show phase-locked firing of neurons with different phase delays for different cells.

Animals↗
PubMed1984

Use of albino animals for auditory research.

Since Hearing Research commenced publication, 51% of reports involving the use of guinea pigs provide no information on whether the animals used were albino or pigmented. Recent evidence creates a strong suspicion that the albino mutation can influence both peripheral and central auditory function. It is concluded that information on pigmentation should always be provided in reports of auditory experiments on guinea pigs, and that the only justification for using albino animals in auditory research is to study effects of the albino mutation on hearing.

Animals↗
PubMed1991

Effects of the crossed acoustic reflex on distortion-product otoacoustic emissions in awake rabbits.

Recent studies in anesthetized cats suggest that contralateral-sound stimulation acts to suppress ipsilateral neural responses via the medial olivocochlear-efferent system. Activation of this descending efferent pathway presumably influences ipsilateral outer hair cell motility and, thus, cochlear micromechanics, resulting in reduced input to auditory-nerve fibers. The principal aim of the present study was to determine if contralateral-sound stimuli influence the generation of ipsilateral distortion-product otoacoustic emissions, in the ears of awake rabbits. The results showed no effects of contralateral stimuli on these emissions that could not be attributed to the crossed acoustic middle-ear reflex. The findings further indicate that distortion-product otoacoustic emission amplitudes over a wide range of frequencies can be dramatically reduced when the middle-ear reflex is activated.

Acoustic Stimulation↗
PubMed1992

The development and interpretation of the summating potential response.

The development of cochlear responses in the mouse was investigated, recording from the round window. Positive summating potentials (SP) could be detected as early as 7 days after birth in some individuals, the first signs of negative SP occurred in mice aged 10 days, and compound action potentials were first detected at 11 days of age. These early responses were obtained with relatively low frequency stimuli (usually 6 kHz). All waveforms recorded from 20 day old mice could be interpreted as simple additions of positive and negative SP and compound action potentials, each with different amplitudes and latencies. Positive SP showed both fast and slow components. Our observations are consistent with the positive SP with only a fast component arising from the basal turn inner hair cells, the positive SP with fast and slow components being generated by both inner and outer hair cells in the basal turn, and the negative SP seen at low frequencies of stimulation originating from depolarisation of hair cells in the apical turn. Summating potentials may thus be useful for investigating inner and outer hair cell function separately in abnormal cochleas in which it is not known which cell type primarily is affected.

Acoustic Stimulation↗
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↗
PubMed1995

Three-channel Lissajous' trajectory of the binaural interaction components of human auditory middle-latency evoked potentials.

Three-channel Lissajous' trajectories (3-CLTs) of the binaural interaction component (BI) of auditory middle latency evoked potentials (AMLEPs) were derived from 14 normally hearing adults by subtracting the response to binaural clicks from the algebraic sum of monaural responses. AMLEPs were recorded in response to 65 dB nHL, rarefaction clicks, presented at a rate of 3.3/s. A normative set of BI 3-CLT measures was calculated and compared with the corresponding measures of simultaneously recorded, single-channel vertex-left mastoid and vertex-neck derivations of BI and of AMLEP to binaural stimulation (B). 3-CLT measures included: apex latency, amplitude and orientation, as well as planar segment duration, orientation, size and shape. The results showed seven main apices and associated planar segments ('Be', 'Bf', 'Bg', 'Bh', 'Bi1', 'Bi2' and 'Bj') in the 3-CLT of BI. Apex latencies of the BI 3-CLT were comparable to peak latencies of the vertex-left mastoid and vertex-neck AMLEP and BI records, both in their absolute values and in intersubject variability. Durations of BI planar segments were approximately 5.0 ms. Apex amplitudes of BI 3-CLT were larger than the respective peak amplitudes of the vertex-mastoid and vertex-neck BI records, while their intersubject variabilities were comparable. The lateralization of BI components may indicate asymmetric processing of binaural auditory input, or may be connected with anatomical asymmetry such as skull thickness. Preliminary analyses did not reveal a clear correlation between the lateralization of the BI component 'Bi2' and the handedness of the subject. We suggest that BI components of AMLEP may be associated with the primary auditory cortex and subcortical ascending structures.

Acoustic Stimulation↗
PubMed1995

Generation of human auditory steady-state responses (SSRs). I: Stimulus rate effects.

Auditory evoked responses were recorded in 16 normally hearing subjects in order to investigate the mechanisms underlying the generation of the 40 Hz steady-state response (SSR). In the first part of our study, auditory potentials were evoked by 0.1 ms clicks presented at 105 dB p.e. SPL with repetition rates of 7.9 (to obtain middle latency response, MLR), 20, 30, 40, 50, 60 Hz. In each subject predictions of the responses recorded at stimulus repetition rates of 30, 40, 50, 60 Hz were synthesized by superimposing MLRs at suitable time intervals. The calculated mean amplitude/rate and phase/rate functions behaved similarly for the recorded and predicted curves, showing the highest amplitude at 40 Hz and a linear increase of phase values when increasing the stimulus rate. Nevertheless the synthetic curves closely predicted amplitude and phase values of the recorded responses only at 40 Hz. At frequencies below 40 Hz, the mean amplitude of the predicted curve was lower than that of the recorded one while at frequencies above 40 Hz the mean amplitude was higher. Predicted phase values were found lagging at 30 Hz, and leading at 50 Hz and 60 Hz in comparison to phase values calculated on the recorded responses. Our findings suggest that a model based on the linear addition of transient MLRs is not able to adequately predict steady-state responses at stimulus rates other than at 40 Hz. Other mechanisms related to the recovery cycle of the activated system come into play in the steady-state response generation causing a decrease in amplitude and an increase in phase lag when increasing the stimulus repetition rate.

Acoustic Stimulation↗
PubMed1994

Pure-tone masking profiles for human auditory brainstem and middle latency responses to 500-Hz tones.

A simultaneous masking paradigm was used to determine the frequency selectivity of human auditory brainstem (ABR) and middle latency (MLR) responses to 60 dB pe SPL 500-Hz probe tones in 12 normal adults. Masking profiles for simultaneous recordings of the ABR and MLR were obtained in the presence of pure-tone maskers presented at 60- and 70-dB SPL. Results show sharp amplitude profiles with maximum reduction in amplitude seen using the 500-Hz maskers. There were no significant differences in the masking profiles for the ABR and MLR waves to the 500-Hz probe tones. An additional measure of frequency selectivity, bandwidth at 50% reduction in amplitude (W50), also demonstrated no significant difference between the ABR and MLR waves. In summary, the results of this study and those of an earlier study (Mackersie et al., 1993) suggest no significant difference in the frequency selectivity of the ABR and MLR to low-intensity (60 dB pe SPL) 500- and 2000-Hz tones.

Acoustic Stimulation↗
PubMed1994

Evidence of sharp frequency tuning in the human auditory cortex.

The frequency tuning of the human auditory cortex was studied by masking 100-ms tones of 1 and 2 kHz by continuous white-noise maskers with frequency notches around the tone frequencies. The subjects ignored the stimuli and concentrated on a reading task. The neuronal activity elicited by the test tones in the auditory cortex was measured with a 24-channel neuromagnetometer. The masker affected the amplitude and latency of the neuromagnetic N100m response, peaking about at 100 ms after stimulus onset, in a systematic way: the wider the notch, the shorter was the latency and the larger the amplitude. The source location of N100m in the auditory cortex did not depend on the notch width. Auditory filters at 1 and 2 kHz were modelled by a single-parameter rounded-exponential [Roex(p)] filter, based on the amplitude changes of N100m. The filters revealed sharp tuning of the auditory cortex, resembling that obtained in psychoacoustical masking studies. The results demonstrate that frequency tuning of the neurons or neuron ensembles in the human auditory cortex can be studied completely noninvasively. Moreover, since the stimuli were ignored by the subjects, the filter shape is not affected by the criterion adopted by the subject in the discrimination task.

Acoustic Stimulation↗
PubMed1995

Tetraethylammonium effects on cochlear potentials in the guinea pig.

Voltage-dependent K+ channels in the basolateral membrane of hair cells in guinea-pig cochlea might contribute to the non-linear current-voltage relationships in these hair cells and, thereby, to generation of the extracellular summating potential (SP). To evaluate the role of K+ channels in the generation of the SP the perilymphatic perfusion technique was used to introduce the K(+)-channel blocker tetraethylammonium (TEA) into the cochlea. Sound-evoked cochlear potentials were measured subsequently. Without blocking nerve activity TEA induced reversible shifts of the SP in the negative direction, irrespective of whether we recorded from scala vestibuli or scala tympani. Shifts in the negative direction were probably due to TEA acting directly on the afferent fibres, since removal of nerve activity by the potent Na(+)-channel blocker tetrodotoxin (TTX) prevented TEA from shifting the SP in the negative direction. Once nerve activity had been removed by TTX, administration of TEA caused a small decrease in the magnitude of the SP, both in scala vestibuli and in scala tympani, irrespective of its polarity. The decrease was significant for the highest test frequencies only (8-12 kHz), and completely reversible. The rapidly activated K+ channel in the inner hair cell (IHC) is probably blocked by TEA and this blocking might be responsible for the small decrease in magnitude of the SP. The asymmetric contribution from this K+ channel to the IHC's current-voltage relationship seems to be only partly responsible for the generation of the SP, since blocking of this K+ channel with TEA caused relatively small decreases in the amplitude of the SP. TEA did not affect the endocochlear potential.

Acoustic Stimulation↗
PubMed1995

Suppression of stimulus frequency otoacoustic emissions by contralateral noise.

The effect of different bands of contralaterally presented noise at low and moderate intensities on stimulus frequency otoacoustic emissions (SFOAE) from human ears is examined. A SFOAE evoked by a continuous stimulus tone and suppressed by a second tone to produce an SFOAE residual was chosen as the probe to determine the effect of the efferent input. At low levels of contralateral noise, a band centred on the ipsilateral stimulus frequency was the most effective suppressor of the SFOAE residual. For higher levels of the contralateral stimulus, noise bands containing higher frequency components produced most reductions in the SFOAE residual. Small changes in the phase of the SFOAE residual during the contralateral noise were also recorded. Increases in the SFOAE residual onset latency were also found to be small, being around 1 ms. In some cases increases in the level of the SFOAE residual produced by low-frequency suppressors were recorded during the contralateral noise presentation. The results are discussed in the context of current knowledge of the functioning of the auditory efferent innervation, and it is suggested that the method of evoking SFOAEs presents a viable method for determining the effect of efferent stimulation on cochlear mechanics which also allows possible artifact contamination to be readily identified.

Acoustic Stimulation↗
PubMed1995

Envelope-following response and modulation transfer function in the dolphin's auditory system.

Potentials following the envelopes of sinusoidally amplitude-modulated tones (envelope response, EFR) were recorded from the head surface in bottle-nosed dolphins. EFR appeared at modulation rates from 300 to 3400 Hz. EFR amplitude was higher at rates from 500 to 1400 Hz with peaks at 600 and 1000 Hz and troughs at 700-850, 1200, and 2000 Hz; at rates above 1700 Hz it fell steeply. EFR dependence on modulation depth was linear except at the highest response amplitudes, which made it possible to obtain the modulation transfer function (MTF). EFR appears to be generated by several sources. One source had a latency of about 4 ms and followed modulation rates up to 1700 Hz, while another had a latency of 2 ms and followed modulation rates up to 3.4 kHz. The latencies of both sources coincided with those of waves of the auditory brainstem response (ABR). Comparison of MTF with the ABR spectrum had shown that several MTF peaks and troughs reflected the ABR spectrum. The latencies of the two sources were consistent with origins in the midbrain and auditory nerve, respectively.

Acoustic Stimulation↗