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R C de Sauvage

Publications and source records attributed to R C de Sauvage.

12 recordsLinked to original sources
PubMed1997

Fast, slow, and steady-state effects of contralateral acoustic activation of the medial olivocochlear efferent system in awake guinea pigs: action of gentamicin.

The function of the medial olivocochlear efferent system was observed in awake guinea pigs by recording, in the absence of ipsilateral external acoustic stimulation, the ensemble background activity (EBA) of the VIIIth nerve from an electrode chronically implanted on the round window of one ear. The EBA was measured by calculating the power value of the round window signal in the 0.5- to 2.5-kHz band after digital or analog (active) filtering. This EBA was compared with and without the addition of a low-level broadband noise to the opposite ear. The contralateral broadband noise (CLBN, 55 dB SPL) induced, via the efferent system, a decrease (suppression) of this EBA. With the use of noise bursts of different durations, two components in this suppression could be observed. After the onset of a 1-s CLBN, the power value of the EBA decreased rapidly by 38.0 +/- 4.2% (mean +/- SD, n = 3), with a latency of <10 ms and a decay time constant of 13.1 +/- 1.0 ms (fast effect). At the offset of the 1-s CLBN, EBA came back to prestimulation values with a similar latency and a time constant of 15.5 +/- 2.9 ms. During longer CLBN stimulation (>/=1 min), EBA presented, after the fast decrease, an additional, slower decrease of 15.6 +/- 3.1%, with a delay of 9.8 +/- 1.3 s and a decay time constant of 16.1 +/- 5.0 s (n = 12, slow effect), and then remained remarkably constant for as long as observed, i.e., >2 h (steady state). The average global suppression was thus up to 47.8 +/- 5.8% of the basal, pre-CLBN-stimulation EBA value. At the offset of the CLBN, EBA returned to pre-CLBN level with fast and slow phases, with, for the slow phase, no delay and a time constant of 32.1 +/- 8.1 s. Fast and slow changes in EBA power values were observed after a single injection of gentamicin (GM) at different doses (150, 200, and 250 mg/kg). At 150 and 200 mg/kg, GM progressively and reversibly blocked the rapid effect, but the slow component of the efferent medial suppression remained remarkably unchanged. However, at higher doses both the fast and slow suppressions were totally yet still reversibly blocked. These observations indicate that the medial olivocochlear efferent system exerts sustained influences on outer hair cells and that this effect develops in two different steps that may have different basic cellular mechanisms.

Acoustic Stimulation↗
PubMed1985

Derived evoked potentials for continuous tones using a hybrid electrical-acoustical stimulation.

Averaged VIIIth nerve and brainstem potentials are recorded in normal guinea pigs in response to electrical stimulation of the ear presented once without and once with a simultaneous masking continuous pure tone. The waveform difference yields a well synchronized 'derived signal' which is the response to the electrical stimulation of only the group of fibers masked by the pure tone. Study of very low frequency activation is a new possibility brought by this method which is efficient whatever the sound frequency. Pure tone thresholds obtained are similar to previous measurements. Response amplitudes are likely a measure of the number of fibers stimulated by the sounds.

Acoustic Stimulation↗
PubMed1984

40 Hz middle latency responses to low frequency tone pips in normally hearing adults.

Middle latency auditory evoked potentials can be rapidly obtained using a 40/second stimulous rate, taking advantage of response periodicity to accelerate the averaging procedure. This technique was used in 31 normally hearing adults for low frequency response evaluation. Tone pips at 250, 500, and 1000 Hz were employed. The average difference between the middle latency evoked potential threshold and the subjective threshold was 17.9 dB at 250 Hz, 14.5 dB at 500 Hz, and 13 dB at 1000 Hz. The waveform of the response and the latency and amplitude of its main peaks were also analyzed. Thresholds at 500 and 1000 Hz were also determined using brainstem evoked responses in 15 of the subjects. These differed, on average, by 30 dB from subjective thresholds. The 40 Hz MLR paradigm thus appears to be an accurate and rapid method for low frequency threshold evaluation in adults, but it is greatly influenced by the state of arousal. During sleep, response amplitude decreases and threshold increases by about 15 dB. This may be of great concern when interpreting the results in children, in whom low frequency threshold evaluation is of primary importance.

Adolescent↗
PubMed1983

Acoustically derived auditory nerve action potential evoked by electrical stimulation: an estimation of the waveform of single unit contribution.

An experimental study of the electrical stimulation of the guinea pig cochlea is made using an electrode on the round window for both stimulation and recording. The neural response is separated from the electrical artifact with a masking procedure combined with a low amplification, "statistical" averaging method [Charlet de Sauvage et al., Hear. Res. 2, 343-346 (1980)]. The high electrical impedance required for recording physiological responses implies the use of a current pulse generator. Monitoring of evoked potentials from the auditory cortex provides evidence that the effects of electrical stimulation (and of masking noise) are of auditory origin. The electrically evoked round window response is of very short latency (less than 0.2 ms). There is a response threshold for both electrical stimulus and masking noise. The response amplitude varies monotonically as a function of masking noise or electrical stimulus intensity. Experiments with high-pass noise masking suggest that the electrical stimulus is mainly acting on basal fibers. The response latency and waveform are independent of electrical stimulus intensity, repetition rate, masker level, or spectrum. Little intersubject variation is noted. Our experiments (reciprocal forward masking by electrical and acoustic stimuli) suggest that a direct, instantaneous electrical stimulation of the fibers occurs. We believe that this response to electrical stimulation represents the mean unit response of the auditory nerve fibers. This approach may be useful in the separate study of cochlear and VIIIth nerve functions and in the analysis (deconvolution) of the acoustically evoked compound AP.

Acoustic Stimulation↗
PubMedDate not supplied

Normal and pathological adaptation of compound viii nerve responses in the guinea pig.

Adaptation of VIII nerve compound action potentials in response to trains of broad frequency spectrum clicks and high frequency filtered clicks is studied at various intensities in normal guinea pig under normal conditions, while masking with white noise and under pathological conditions after ototoxic antibiotic treatment. The results are discussed with respect to the clinical electro-cochleographic adaptation studies in man and the so-called two populations of receptors and nerve fibres in the cochlea.

Acoustic Stimulation↗
PubMedDate not supplied

Evolution of CM, SP and AP during etacrynic acid intoxication in the guinea pig.

During etacrynic acid intoxication in the guinea pig, patterns of click-evoked compound electrocochleographic responses are similar to those observed in Menière and retro-cochlear human pathologies. Using high frequency tone bursts, SP, CM and AP were studied after intracardiac injection of etacrynic acid. The evolution of SP precedes that of CM and AP. Its change in polarity could be related to that reported for EP by Bosher et al. (1973). While during the recovery period SP overshoots (after 90 min), CM and AP increase more slowly (up to about 7 days) and in most cases AP amplitudes do not exceed 70-80% of their original value (25 days). N1, when present, keeps its classical pattern durint the entire evolution, whatever its amplitude and latency variations are. The early positive peak or negative shift observed in click-evoked human pathological electrocochleography can therefore be identified as SP. Thus this response is the indication of the presence of hair cells and of the impairment of the nerve fibre stimulation or response.

Acoustic Stimulation↗
PubMedDate not supplied

Role of the efferent medial olivocochlear system in contralateral masking and binaural interactions: an electrophysiological study in guinea pigs.

Contralateral broadband noise (BBN) elevates ipsilateral auditory thresholds (central masking) and reduces the amplitude of ipsilateral brainstem auditory evoked potentials (BAEPs). Binaural interactions are complex psychophysical phenomena, but binaural interaction components are easily extracted from BAEPs to monaural versus binaural click stimulation. However, contralateral, or binaural, acoustical stimulation is known to activate simultaneously the crossed and uncrossed medial olivocochlear (MOC) efferent systems and decrease activity in both cochleas. Particularly, contralateral BBN stimulation suppresses in part ipsilateral peripheral activity. What is the role of such contralaterally induced peripheral suppression in the overall changes in central BAEPs observed during contralateral masking or binaural stimulation? Compound action potentials (CAPs) of the auditory nerve and BAEPs were recorded simultaneously in awake guinea pigs from electrodes chronically implanted on the round window of the cochlea and the surface of the brain. Peripheral and central measures of contralateral masking and binaural interactions were obtained from responses to monaural or binaural clicks, with or without contralateral BBN, recorded before, during, and after the reversible blockade of the MOC function following a single intramuscular injection of gentamicin. Contralateral BBN effectively reduced the amplitudes of CAP and of all BAEP peaks. CAP to ipsilateral click did not, however, change significantly from monaural to binaural click stimulation; still, normal binaural interaction components developed in the BAEPs. When the medial efferent function was blocked by gentamicin, the normal contralateral BBN suppression of CAP and of the earliest BAEP peak was lost; however, the later BAEP peaks were suppressed by contralateral BBN as before gentamicin, and the central binaural interaction components were unchanged. In these experimental conditions, the MOC efferent system seems to play little role in centrally recorded contralateral masking and binaural interactions.

Animals↗