Biomedical subjects

S Khalfa

Publications and source records attributed to S Khalfa.

11 recordsLinked to original sources

PubMed2000

Frequency and temporal analysis of contralateral acoustic stimulation on evoked otoacoustic emissions in humans.

Previous studies have shown that the effect of contralateral acoustic stimulation (CAS) on ipsilateral evoked otoacoustic emissions (EOAE) depends somewhat upon the spectrum of the eliciting stimulus. The latency of the EOAE, however, is itself frequency-dependent. Consequently, two general ways of analyzing the effects of CAS may be considered: by frequency band or by temporal segment. In this study, we analyzed the effects of CAS both ways in the same subjects, essentially simultaneously. The frequency analysis of the EOAE derived from the wavelet transform (WT). The WT is known to provide a robust approach to the analysis of non-stationary signals and was anticipated to avoid possible time-frequency confounds of the cochlear mechanical system. For comparison, a more basic analysis - using a temporal moving window - was employed. The results largely support earlier findings and confirm that in humans the greatest suppression of EOAEs by CAS is obtained for lower frequency and/or longer latency EOAE components. Despite expectations for the WT analysis, the more basic, temporal, analysis tended to yield the clearer results.

Acoustic Stimulation↗

PubMed2000

Tones disappear faster in the right ear than in the left.

In order to gain further information on the characteristics and physiological correlates of tone decay in humans, the tone decay test was administered to 58 normal-hearing subjects, successively in the left and right ears and in absence and presence of a contralateral noise. The results revealed that tone decay was greater in the right than in the left ear and was increased by contralateral noise. The contralateral effect of this noise on cochlear biomechanisms was then estimated by measuring contralaterally induced variations in the amplitude of click-evoked otoacoustic emissions in the same subjects. In the right ear, the increase in tone decay and the decrease in otoacoustic emission amplitude--both induced by contralateral noise--were positively correlated (r = .315, p = .016). Furthermore, the contralateral changes in otoacoustic emission amplitude were found to be on average larger in the right than in the left ear, this asymmetry being correlated with that observed for the tone decay. These findings are discussed in relation to previous results on simple and induced loudness adaptation in the vicinity of threshold, on contralateral attenuation of otoacoustic emissions and on the influence of the auditory efferents on cochlear biomechanisms.

Adolescent↗

PubMed1999

Stronger bilateral efferent influences on cochlear biomechanical activity in musicians than in non-musicians.

The auditory sensory end organ is under the control of the central nervous system via efferent projections. Contralateral suppression of otoacoustic emissions (acoustic signatures of the cochlear biomechanical activity) provides a non-invasive approach to assess olivocochlear efferent activity in humans. Using this approach, the present study compared professional musicians with musically-inexperienced subjects. The results revealed stronger bilateral cochlear suppression, suggesting larger efferent influences in both ears, in musicians. Furthermore, in indicating no difference in left/right asymmetry of efferent-mediated suppression between the two groups, the present findings suggest that the observed differences in olivocochlear activity reflect bilaterally-enhanced activity of the cortical auditory structures in musicians rather than differences in cerebral hemispheric asymmetry between the two groups.

Acoustic Stimulation↗

PubMed1999

Clinical relevance of medial efferent auditory pathways.

Evoked otoacoustic emissions have been shown to be suppressed by sounds applied in the contralateral ear and this effect can be largely explained by the involvement of medial olivocochlear efferent fibers. Thus, EOAE recording during contralateral stimulation provides a non-invasive means of investigating auditory efferent system functioning in humans. The question remains, however, as to whether this test provides a tool, which could be useful in a variety of clinical applications. This review describes current clinical applications for this test, showing that it may prove useful for improving identification of retrocochlear pathologies. Some new areas are also identified. Methodological topics are discussed and suggestions for maximizing the value of this test are proposed.

Adult↗

PubMed1998

Peripheral auditory lateralization assessment using TEOAEs.

Previous studies indicate a left-right asymmetry in the function of peripheral auditory system. Contralateral acoustic suppression of TEOAEs (transient evoked otoacoustic emissions) enables assessment of medial olivocochlear efferent system functioning, and has demonstrated that this system is more effective in the right than in the left ear. Moreover, TEOAE amplitudes are lower in the left than in the right ear. The aim of the present experiment was to verify firstly the absence of a relationship between medial efferent system asymmetry and TEOAE amplitude asymmetry, and secondly to study TEOAE input/output function slopes. There was no link between the asymmetries in TEOAE amplitude and in the medial efferent system functioning. Further, as previously shown, the medial olivocochlear system increased the TEOAE input/output function slopes. These TEOAE input/output function slopes seem to be consistent factors in peripheral asymmetry since the slope is lower in the right than in the left ear. Moreover, the lower the TEOAE amplitudes, the greater the TEOAE slopes. The slope asymmetry of the two ears could correspond to earlier saturation or a lower augmentation ability of the TEOAE response in the right ear, where the TEOAE amplitude is higher. This asymmetry in growth slopes reinforces the notion of peripheral auditory lateralization.

Acoustic Stimulation↗

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

[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

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↗

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↗

PubMedDate not supplied

[Epidemiology of viral hepatitis in Algeria].

Viral hepatitis is endemoepidemic in Algeria. Recent serologic and epidemiological surveys have specified the importance of A, B and non A non B viruses respectively and brought out some details. -- Hepatitis A is very common: 96% of individuals have anti-HAV antibodies. Patients come into contact with the virus before the age of 10. No symptoms are found in 95% of cases. Icteric hepatitis occurs in infants. -- Hepatitis B infection includes 40 to 50% of icteric hepatitis in adults. Clinical and biological symptoms are similar to those described in the literature. The prevalence of HBs Ag carriers is within the range of 1,8 to 2,8%, but reach high level in Eastern and Saharian Regions of Algeria. It increases with age and low socio-economic status. In hospital environment, laboratory technicians and room servants is the most frequently contaminated personnel. -- Non A non B hepatitis is so far the least known in Algeria. In 1981, an epidemic of water-borne non A non B hepatitis was reported.

Adolescent↗