Deafness in early development can alter how the brain responds to sound, compromising the restoration of hearing with cochlear implants. We asked how the naïve brain responds to initial cochlear implant stimulation in children who are deaf. Results indicated large variability in initial responses. Deafness associated with GJB-2 mutations led to more uniformity in cortical responses than other etiologies. Responses associated with GJB-2 mutations were characterized by a response peak with large contributions from temporal and frontal regions of the brain. This response may reflect an early stage of auditory development. By contrast, another response type, typical of normal hearing children, received less contribution from frontal regions. Through consistent cochlear implant use, frontal regions of the brain may not be as strongly recruited. Effects of deafness in early development are heterogeneous, which may reflect differences in etiology of deafness and different stages of auditory development.

Deafness in early development can alter how the brain responds to sound, compromising the restoration of hearing with cochlear implants. We asked how the naïve brain responds to initial cochlear implant stimulation in children who are deaf. Results indicated large variability in initial responses. Deafness associated with GJB-2 mutations led to more uniformity in cortical responses than other etiologies. Responses associated with GJB-2 mutations were characterized by a response peak with large contributions from temporal and frontal regions of the brain. This response may reflect an early stage of auditory development. By contrast, another response type, typical of normal hearing children, received less contribution from frontal regions. Through consistent cochlear implant use, frontal regions of the brain may not be as strongly recruited. Effects of deafness in early development are heterogeneous, which may reflect differences in etiology of deafness and different stages of auditory development.

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