A ce jour, six millions de français sont atteints de troubles de l'audition. Face à ce problème de santé publique, des outils performants d'exploration de la fonction auditive sont indispensables. La Speech ABR (Speech Auditory Brainstem Response ou Réponse du tronc cérébral auditif à la parole) est un outil prometteur, comme marqueur électrophysiologique fin de l'encodage neuronal de la parole. Cependant, sa méthodologie reste peu développée, son origine neuronale incertaine et elle n'a jamais été enregistrée chez le malentendant porteur d'aides auditives. Le premier axe de cette thèse porte sur les générateurs neuronaux de la Speech ABR. Le développement d'une méthodologie de recueil topographique de cette réponse jusqu'alors décrite comme strictement sous-corticale, a d'abord suggéré la possibilité d'un générateur cortical. Une étude en stéréo-électroencéphalographie a ensuite confirmé l'existence d'une activité Speech ABR dans les cortex auditifs primaires bilatéraux. Ce résultat apporte un éclairage nouveau sur la représentation des sons de parole par système nerveux auditif. Le second axe concerne l'étude de la Speech ABR chez le malentendant appareillé. Après avoir développé une méthodologie de stimulation acoustique directement au travers des aides auditives, nous avons étudié la plasticité neuronale induite par le port d'aides auditives. Les résultats montrent une amélioration de l'identification des phonèmes amplifiés, liée à une représentation corticale modifiée et à un encodage fréquentiel rééquilibré. Ces toutes premières preuves de plasticité neuronales dès les 4 premiers mois d'utilisation des aides auditives ouvrent de nouveaux espoirs thérapeutiques / To date, six million French are hearing impaired. To address this public health issue, efficient tools for exploration of the hearing function are essentials. Speech ABR (Speech Auditory Brainstem Response) is a promising tool, being a fine electrophysiological marker of the neuronal encoding of speech. Though, its methodology remains underdeveloped, its neural origin is still uncertain, and it has never been recorded in hearing aid users. The first axis of this thesis focuses on the neural generators of Speech ABR. The development of a methodology for recording topographies of this response, up to now described as strictly subcortical, first suggested the possibility of a cortical generator. A stereo-electroencephalography study then confirmed the existence of Speech ABR activity in bilateral primary auditory cortices. This result sheds a new light on the representation of speech sounds within the auditory nervous system. The second axis concerns the study of Speech ABR in hearing aid users. After having developed a methodology of acoustic stimulation directly through hearing aids, we investigated neural plasticity induced by hearing aid use. Results show an improvement in the identification of amplified phonemes, linked to an altered cortical representation and a rebalanced frequency encoding. This very first evidence of neural plasticity as soon as the first four months of hearing aid use opens up new therapeutic hopes

There has always been a need for objective tests that assess auditory function in infants, young children, and/or any patient whose development level precludes the use of behavioral audiometric techniques. Although the Auditory Brainstem Response (ABR) is seen as the ‘gold standard’ in the field of objective audiometry, it presents with its own set of limitations. The Auditory Steady State Response (ASSR) has gained considerable attention and is seen as a promising addition to the AEP ‘family’ to address some of the limitations of the ABR. The ASSR promises to estimate all categories of hearing loss (mild to profound) in a frequency specific manner. It also indicates to the possibility to validate hearing aid fittings by determining functional gain of hearing aids by determining unaided and aided ASSR thresholds. An exploratory research design was selected in order to compare unaided thresholds, obtained through the use of three different procedures – ABR, ASSR and behavioral thresholds. Aided thresholds were also obtained and compared with two procedures – the aided ASSR (measured and predicted) and aided behavioral threshold. The results indicated that both the ABR (tone burst and click) and ASSR provided a reasonable estimation of the subsequently obtained behavioral audiograms. The ASSR, however, approximated the behavioral thresholds closer than the ABR and were furthermore able to quantify hearing thresholds accurately for subjects with severe and profound hearing losses. The result indicated further that the ASSR can be instrumental in the validation process of hearing aid fittings in infants. These results demonstrated however, that the ASSR measured thresholds underestimate the aided behavioral thresholds and the aided ASSR predicted thresholds overestimate the aided behavioral thresholds. The research concluded that the ASSR is useful in estimating frequency-specific behavioral thresholds accurately in infants and validating hearing aid fittings. Until evidence is sufficient to recommend the ASSR as primary electrophysiological measure of hearing in infants, the ASSR should be used in conjunction with the ABR – following a test battery approach in the diagnostic process of hearing loss in infants. The ASSR further shows great promise in validating hearing aid fittings, but this specific application of the ASSR needs further research evidence on large groups to validate the procedure. / Dissertation (Master of Communication Pathology)--University of Pretoria, 2007. / Speech-Language Pathology and Audiology / unrestricted

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Introduction: Auditory neuropathy spectrum disorder (ANSD) is a disorder characterized by impaired temporal coding of acoustic signals due to a deficiency in neural synchrony or neural transmission. Despite variations in speech perception outcomes within both patients and studies, current evidence demonstrates that children with ANSD, who use hearing aids (HAs) or cochlear implants (CIs), generally achieve speech perception performance comparable to peers with sensorineural hearing loss (SNHL). However, limited studies have reported factors that have prognostic value for auditory intervention outcomes. The objectives of this doctoral thesis, consisting of three consecutive associated projects on children with ANSD, were (1) to determine factors with predictive value for post-intervention (CIs and/or HAs) outcomes through a retrospective study, (2) to systematically summarize and critically appraise existing evidence of the prognostic value of early auditory electrophysiologic tests and MRI findings for CI outcomes through a systematic review (SR), and (3) to systematically overview, summarize, and critically appraise evidence of CI outcomes through an umbrella review of current SRs (overview of SRs). -- Methods: For the first project, the records of 38 children with ANSD between 5 and 18 years old, 63.20% males, who used CIs (71%) and/or HAs, identified at the Children's Hospital of Eastern Ontario (CHEO) were reviewed. For the second and third projects, the SRs were guided by the PRISMA 2020 statement, and electronic databases were searched without restrictions on language, publication status, or year of publication. In the second project, studies on children with ANSD (including those with cochlear nerve deficiency [CND]), cochleovestibular nerve (CVN) abnormalities, or SNHL reporting the relevance of preoperative and/or postoperative electric compound action potential (eCAP), electric auditory brainstem response (eABR), and/or MRI results to CI outcomes were included. The methodological quality and strength of evidence were assessed using the Crowe Critical Appraisal Tool (CCAT) and Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) tool, respectively. In the third project, all SRs that reported CI outcomes in children with ANSD were included. The methodological quality of the selected SRs was evaluated using the Assessment of Multiple Systematic Reviews 2 (AMSTAR-2) checklist, and the risk of bias in evidence was assessed using the Risk of Bias in Systematic Reviews (ROBIS) tool. -- Results: In the retrospective chart review (first project), ages at HL diagnosis and CI activation and the length of follow-up with CI/HA showed a significant relationship with open-set speech perception outcomes (i.e., the scores of Phonetically Balanced Kindergarten [PBK] test with word and phoneme speech materials and Hearing in Noise Test [HINT] in quiet and noise conditions). Using a Forward Linear Multiple Regression Model, the length of follow-up with CI/HA and bilateral amplification showed prognostic value for speech perception performance. In the second project, 25 papers were included in the review. While it was difficult to draw a firm conclusion about the eCAP findings, current evidence strongly supports the prognostic value of eABR and MRI for post-CI speech perception outcomes. According to the eight SRs selected for the third project, children with ANSD achieve CI outcomes comparable to their peers with SNHL. However, in children with postsynaptic ANSD (i.e., those with CND), cochlear nerve hypoplasia is associated with better speech recognition outcomes compared to cochlear nerve aplasia, especially in the absence of additional disabilities and/or medical comorbidities (ADs/MCs). -- Conclusion: Children with ANSD, especially those without cochlear nerve aplasia and ADs/MCs, achieve speech perception outcomes comparable to their peers with SNHL. In addition, age at HL diagnosis, age at CI activation, the length of follow-up with CI/HA, bilateral amplification, and eABR and MRI findings are associated with or have predictive value for intervention outcomes. The findings of the SRs should be interpreted with caution given the low quality of evidence and risk of bias in the studies selected for SRs.

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