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Biomedical subjects

L Collet

Publications and source records attributed to L Collet.

At least 55 records · Page 3Linked to original sources
PubMed1998

Influence of handedness on peripheral auditory asymmetry.

It is well established that in humans many differences between right- and left-handers, anatomical, physiological and functional, exist. Left- and mixed-handedness is associated with greater bihemispheric representation of cognitive functions than in right-handers. Several studies indicate a left-right asymmetry in the function of hearing pathways between cochlea and auditory cortex, and furthermore, that this asymmetry is associated with handedness. Our investigation focuses on the medial olivo-cochlear system, which has been demonstrated to be more effective in the right than left ear in right-handers. The aim of the study was to investigate this auditory efferent system asymmetry according to handedness, gender, eyedness, footedness and the presence of spontaneous otoacoustic emissions. The medial efferent system has been found to be more effective in the right than left ear in right-handers, while functioning symmetrically in left-handers. Furthermore, the olivo-cochlear system, assumed to be involved in basic language processing, shows an asymmetrical pattern of functioning influenced by handedness as well as by hemispheric language representation. Reverse medial efferent system asymmetry was observed in left-handers compared to that in right-handers, on condition that only left-handed males were considered, or that the left-handers were also left-eyed, or that spontaneous otoacoustic emissions were present in the left ear of the left-handers, or when only left-handers without mixed-handers were considered.

Acoustic Stimulation↗
PubMed1998

Correlation between electrical auditory brainstem response and perceptual thresholds in Digisonic cochlear implant users.

OBJECTIVES: To examine the relationships between psychophysical perceptions and the electrically evoked auditory brainstem responses (EABRs) in multichannel cochlear implant (CI) users and to determine the effectiveness of EABRs in electrode failure. DESIGN: A descriptive study reported the EABR characteristics while the different electrodes were activated. Characteristics of the EABR and of the perceptual measures served as compared variables in a correlational study. SETTING: The study was carried out in the audiology clinic of an otolaryngology department at a university hospital. PATIENTS: The subjects consisted of nine consecutively selected habitual Digisonic DX1OR multichannel CI users. Seven patients were postlinguistically deafened adult patients; two were congenitally deaf children. MAIN OUTCOME MEASURES: Ipsilateral recordings were performed using a previously published method. Morphology, latency, and amplitude measures of the EABR recordings were described, computed, and compared with the literature data for EABRs obtained while activating other types of CI and for acoustically evoked ABRs. Correlations between EABRs and behavioral perception thresholds were analyzed using the parametric Pearson's correlation test. RESULTS: EABRs allowed the authors to detect failure of no. 10 electrode integrity in one child. Perceptual threshold measures were found to be highly significantly related to the EABR threshold across subjects and electrode position (n = 31, r = 0.98; P < 0.001; linear regression equation: perceptual threshold = 1.06 EABR threshold + 0.76). The latencies and amplitudes were found to be similar to those described in the literature. CONCLUSIONS: EABRs may be used to estimate settings for the Digisonic DX10 CI even in a pediatric population, although they cannot entirely replace behavioral measurements, especially in children. The EABR can be employed for electrode dysfunction diagnosis. Further studies are needed to determine whether recordings of EABR quality could contribute to the evaluation of functional prognosis during the rehabilitation.

Adult↗
PubMed1998

[Peripheral auditory lateralization].

Neuropsychological studies have demonstrated that language perception is lateralized at the hemispheric level. There is also much evidence for a peripheral lateralization of the auditory system in humans. Spontaneous otoacoustic emissions are more frequent in the right than in the left ear. The medial olivo-cochlear system is also more functional in the right than in the left ear in normal subjects. The study of specific samples shows that this asymmetry is found in professional musicians which have more functional efferent system in both ears. A link is hypothesized between peripheral and central laterality because of a dysfunctional peripheral asymmetry in pathological cases which show hemispheric lateralization disorders. Consequences of those pathological data will be discussed.

Adolescent↗
PubMed1997

Difference in cochlear efferent activity between musicians and non-musicians.

The present study aimed to confirm and extend the finding, suggested by the results of a previous study, of different auditory neural efferent functioning in musicians compared with non-musicians. The activity of the medial olivocochlear bundle (MOCB), an auditory efferent subsystem, was measured through the contralaterally induced attenuation of the amplitude of evoked otoacoustic emissions (EOAEs) in two groups, one of musicians and one of non-musicians, paired for age and sex. The results indicated a statistically significant difference between the two groups, with the musicians showing greater amplitude reduction upon contralateral noise stimulation than non-musicians (U-test, U = 204, p < 0.025, n = 32). These results indicate greater MOCB activity in musicians than in non-musicians. The possible origins and implications of this finding are discussed.

Acoustic Stimulation↗
PubMed1997

Acoustical recognition of laryngeal pathology using the fundamental frequency and the first three formants of vowels.

The recognition of laryngeal pathology by analysis of the voice is investigated. The fundamental frequency and the first three formants are considered. The recognition strategy is based on comparison with normal ranges calculated over 200 ordinary voices, grouped in ten age classes ranging from 20 to 70 years, for males and females. 220 test voices are studied divided into four groups: normal voices, functional dysphonia, nodules and recurrent nerve palsy. Each subject is marked according to his/her normal range. Parameters (or items) are calculated on the Interactive Laboratory System workstation. The vocalic material is composed of 11 vowels taken from a sentence. Results are given in terms of the number of values out of the normal ranges. Statistical analysis considers both parameter ability and error rates in pathology recognition. Pathology recognition shows the following error percentages: 23% for dysphonia, 14% for nodules and 33% for recurrent nerve palsy. Parameters do not show the same efficiency for voice pathology characterisation. Formants appear to be better than the fundamental frequency.

Adult↗
PubMed1997

Effects of hypothermia on cochlear micromechanical properties in humans.

The aim of the present experiment was to investigate the influence of hypothermia on transient evoked otoacoustic emissions (TEOAEs) in humans. Hypothermic alterations were brought about directly by cooling the cardiovascular system of young children during open heart bypass surgery. This condition caused TEOAE levels to decrease with a significant positive correlation between total and frequency band TEOAE amplitudes during cooling. TEOAEs were totally abolished at tympanic temperatures around 30 degrees C, without it being possible to find differences in TEOAE alteration among the frequency components. During rewarming, the changes reversed and TEOAEs returned to their initial prehypothermia status, although sometimes only partially. Despite large possible metabolic changes caused by this hypothermic condition at various levels, it is concluded that the motile properties of outer hair cells (OHCs), that are related to TEOAEs, are temperature-sensitive. The total suppression found in deep hypothermia (above 30 degrees C) could conceivably be attributable to a process involving a temperature-dependent energy source.

Auditory Threshold↗
PubMed1997

Contralateral suppression and stimulus rate effects on evoked otoacoustic emissions.

Transiently evoked otoacoustic emissions (EOAE) were recorded in normal-hearing humans using pseudorandom pulse trains. This allowed the effect of increasing stimulus rate to be studied on EOAE amplitudes, input-output (I/O) functions and suppression by contralateral stimulation. EOAEs are very probably due to micromechanical properties of cochlear outer hair cells, and contralateral suppression is considered to result from olivo-cochlear efferent activation. EOAEs at various stimulus rates showed excellent reproducibility. Total EOAE amplitude diminished as interstimulus interval (ISI) decreased from 20 to 3 ms, but not for ISIs under 3 ms. The amplitude reduction was significant only on EOAE spectrum bands below 3.4 kHz. I/O functions, which kept a linear pattern, were steeper, and contralateral suppression was lower, with the highest stimulus rate (1111 c/s) relative to other rates. The EOAE decline with increasing stimulus rate might be due to incomplete recovery after adaptation of outer hair cells. The lower contralateral suppression at high stimulus rates suggests that crossed olivo-cochlear bundle action is lessened when outer hair cells are responding to a high-rate stimulus. An explanation may be that contralateral stimulation and a high-rate ipsilateral stimulus act via the same mechanisms, i.e., that high-rate stimulation activates an ipsilateral efferent loop.

Acoustic Stimulation↗
PubMed1997

Suppression of otoacoustic emission is unchanged after several minutes of contralateral acoustic stimulation.

The influence of variable durations of contralateral acoustic stimulation on the suppression of click-evoked otoacoustic emissions was investigated in order to determine whether olivocochlear efferent fibers are equally effective whatever the acoustical stimulation duration or if they show fatigue. The suppression effect was measured for contralateral stimulus durations ranging from 10 to 180 s prior to the onset of otoacoustic emission recording, and continuing throughout the recording time (60 s). No significant stimulus duration effect was found.

Acoustic Impedance Tests↗
PubMed1997

Medial olivocochlear system stabilizes active cochlear micromechanical properties in humans.

To investigate the involvement of the medial olivocochlear system (MOCS) in outer hair cell (OHC) motility stabilization, evoked otoacoustic emissions (EOAEs) were recorded in 20 normal-hearing subjects and in eight vestibular-neurotomized subjects, successively in the presence and absence of low-intensity contralateral acoustic stimulation. Intrasubject EOAE amplitude variability was assessed as the standard deviation computed over several successive recordings. In normal-hearing subjects, a significantly lower EOAE amplitude variability with contralateral acoustic stimulation (CAS) was observed in subjects in whom the CAS induced the greatest EOAE amplitude reduction. This result could not be attributed to the EOAE amplitude reduction itself, since variability was otherwise found to increase when EOAE amplitude decreased. Moreover, statistically significant correlations between EOAE amplitude attenuation and EOAE amplitude variability under CAS were observed. In the eight subjects operated for vestibular neurotomy, no such effect was found. Being sectioned in vestibular-neurotomized subjects, the MOCS can no longer exert its effects. These results strongly support the notion that MOCS activity, as induced by CAS, elicits a reduction in EOAE amplitude variability in normal-hearing subjects. This finding and some of its possible implications for understanding the role of the MOCS in hearing in humans are discussed.

Acoustic Stimulation↗
PubMed1997

Relationship between auditory intensity discrimination in noise and olivocochlear efferent system activity in humans.

Recent physiological data in animals suggest a role of the medial olivocochlear system (MOCS) in auditory intensity discrimination in noise. In this study, the existence of statistical relationships between intensity difference limens (IDLs) and MOCS functioning was tested in humans. IDLs were measured in conditions of quiet and of ipsilateral, contralateral, and dichotic noise. MOCS functioning was assessed through the contralateral evoked otoacoustic emission (EOAE) amplitude attenuation effect. A first finding was that IDLs measured in the presence of ipsilateral noise were reduced when contralateral noise was added. Furthermore, the observed shift in IDL appeared to be significantly correlated to the contralateral EOAE amplitude attenuation effect. These results support the hypothesis that MOCS functioning plays a role in intensity discrimination in dichotic noise in humans.

Adolescent↗
PubMed1997

Influence of contralateral noise on distortion product latency in humans: is the medial olivocochlear efferent system involved?

To test the hypothesis of temporal modifications of cochlear responses when medial efferents are activated, otoacoustic emission latencies were estimated in 16 normal human subjects, in the presence and absence of a contralateral broadband noise, using measurements of the phase of the 2f1-f2 distortion product (group latency method). Significant decrease in the latency of lower frequency (0.8-2.7 kHz) emissions was found in the presence of increasing levels of contralateral sound, and this effect disappeared when the primary-tone levels increased to 60 dB SPL. To ensure that effects were not attributable to mechanisms involving middle ear structures, susceptible to activation by contralateral sound, latency measures were performed in seven subjects whose efferents were severed during a vestibular neurotomy and in two subjects with paralyzed stapedial muscle. Results in patients were compared to those obtained in three surgical control patients with intact efferent bundle, and in eight other normal subjects. All the subject groups exhibited a decrease in latency under contralateral sound except the patients with the severed efferent system who showed increased latencies.

Acoustic Stimulation↗
PubMed1997

Medial olivocochlear efferent system in humans studied with amplitude-modulated tones.

Evoked otoacoustic emissions (EOAEs) are assumed to be generated by outer hair cells (OHCs). It is now generally accepted that EOAEs represent a means of functional exploration of the active micromechanical properties of OHCs. Efferent fibers of the medial olivocochlear system (MOCS) are connected along the sides and the bases of OHCs. Some studies have shown that a suppression effect on EOAE amplitude is induced by the MOCS neurons during contralateral stimulation, presumably by modification of OHC motility. The contralateral acoustic stimuli used in experiments on the EOAE suppression effect have consisted mainly of sounds without a slow temporal fluctuation in their envelopes (broad-band noise, narrow-band noise, pure tones, or clicks). To elucidate further the parameters of MOCS activation, in the present study we looked at the contralateral suppression effect of amplitude-modulated (AM) tones. The results showed that EOAE amplitude was reduced with AM tones compared with no contralateral acoustic stimulation. The suppression effect mainly depended on three parameters. 1) Contralateral stimulation intensity: EOAE suppression occurred only with intensities > or = 40 dB SL. 2) The greater the modulation depth, the greater the suppression effect: statistical analysis showed a significant effect for 75 and 100% modulation depth. 3) The 100- and 140-Hz modulation frequencies gave the greatest suppression effect for 100 and 75% modulation depths. The suppression effect was frequency specific. The greatest decreases were observed when the carrier frequency of the contralateral AM tone was close to the frequency of the EOAE under study, i.e., 1 and 2 kHz. Acoustic cross talk and middle ear effects, which cannot be completely excluded, are discussed. However, the demonstrated frequency specificity of the EOAE suppression effect, together with observed presence of contralateral EOAE suppression in patients without stapedial reflex and the very weak intensities used (i.e., below acoustic reflex threshold), suggested that it was unlikely that the observed effects were due merely to middle ear reflexes. Our results confirm further the contralateral suppression effect on human cochlea mechanisms and show that the suppression effect can be influenced by amplitude modulations of the suppressor, characteristic of sounds in the environment.

Acoustic Stimulation↗
PubMed1997

EABRs and surface potentials with a transcutaneous multielectrode cochlear implant.

In a previous study, the authors described a technique for recording ipsilateral EABRs using the DIGISONIC MXM cochlear implant (Gallégo et al, Acta Otolaryngol (Stockh) 1996; 116: 228-33) and showed that the EABR input/output functions were very similar across electrodes. In the present study a test of electrode functioning based on the recording of surface potentials is presented. Then, for each electrode the relationship between EABR thresholds and hearing thresholds was determined. Lastly, the relationship between EABR parameters and patients' performances was studied. The results show that the functioning of each implanted electrode can be assessed quickly, accurately and objectively. Furthermore it is demonstrated that a strong correlation between EABR and hearing threshold can be obtained using an automatic EABR wave detection technique. Finally it is shown that EABR inter-peak intervals are related to patient performance. These results are of the utmost importance for cochlear implant setting in children as they indicate a method of objective assessment of the functioning of each electrode and of the corresponding hearing threshold.

Adolescent↗
PubMed1997

Evidence of peripheral hearing asymmetry in humans: clinical implications.

Auditory system hemispheric asymmetry in language processing is well-established, and there are many indications of lateralization as of the peripheral auditory system i.e., as of the cochlea. The left ear is more susceptible to noise damage; tinnitus is more predominant there, while spontaneous otoacoustic emissions (SOAEs) are more often found in the right ear. The present study addressed the following two questions: Does this right-ear SOAE prevalence exist as early as preterm birth? Is there any functional asymmetry in the medial olivo-cochlear (MOC) efferent system, known to modulate outer hair cell contractions? The study involved 483 preterm neonates (gestional age: 24-37 weeks) and 70 right-handed adults (age: 18-31 years). In each ear, SOAEs and evoked otoacoustic emissions (EOAEs) were recorded and analysed, and, for the adults, functional MOC system assessment was made. Results showed SOAEs and EOAE amplitude to be right-predominant and in adults a right MOC functional predominance. These results indicate peripheral auditory system lateralisation, and an early origin thereof. The MOC system being thought to play a protective role, its physiological lateralisation may be relevant to the left prevalence of tinnitus and of auditory fatigue.

Acoustic Stimulation↗
PubMed1997

[Value of auditory evoked potentials of the brain stem in patients with a Digisonic cochlear implant].

We report our techniques of electrically elicited Auditory Brainstem Responses (eABR) in Digisonic DX 10 cochlear implanted patients and summarize the theoretical interests of objectives measures in pre-, per- and post-operative periods of the cochlear implantation process. This report demonstrates the major interest of eABR during rehabilitation with a cochlear implant. EABR allowed us to detect the lack of device integrity in one electrode in one patient. The quality of electrically elicited responses can contribute to appreciate the electrophysiological responses during electrical stimulation. We found a very strong correlation between the objective thresholds (obtained by means of eABR) and subjective ones (obtained by means of behavioral methods); this is of major interest in the pediatric populations.

Acoustic Stimulation↗
PubMed1996

Development of cochlear active mechanisms in humans differs between gender.

Despite onset of function early during the third term of gestation, the human auditory system demonstrates continued maturation, thought previously to occur primarily at the neural level. The electromotile properties of outer hair cells appear to contribute substantially to hearing sensitivity and frequency selectivity and lead to the generation of otoacoustic emissions (OAEs). This report demonstrates continued development of cochlear active mechanisms (i.e. end-organ level) after onset of cochlear function, as reflected by OAEs. Significant gender differences also are reported, corresponding to recently observed intersex differences in cochlear length and precursory to gender differences observed in the adult.

Cochlea↗
PubMed1996

Functional asymmetry of medial olivocochlear system in humans. Towards a peripheral auditory lateralization.

The aim of this study was to investigate the human peripheral auditory system in either ear to allow comparison of right and left medial olivocochlear inhibition during contralateral ear stimulation with a broad band noise. The efferent system showed a statistically significant greater right-side activity among 44 young subjects. This laterality appeared to be related to the presence of spontaneous otoacoustic emission but not to gender. This efferent asymmetry and the parallel spontaneous otoacoustic emission asymmetry could explain the lateralization of auditory sensitivity, temporary threshold shift and tinnitus.

Acoustic Stimulation↗