Littérature scientifique sur le sujet « Plasticity, deafness, cochlear implants, multisensory »

Purpose We review the evidence for attenuating visual input during intervention to enhance auditory development and ultimately improve spoken language outcomes in children with cochlear implants. Background Isolating the auditory sense is a long-standing tradition in many approaches for teaching children with hearing loss. However, the evidence base for this practice is surprisingly limited and not straightforward. We review four bodies of evidence that inform whether or not visual input inhibits auditory development in children with cochlear implants: (a) audiovisual benefits for speech perception and understanding for individuals with typical hearing, (b) audiovisual integration development in children with typical hearing, (c) sensory deprivation and neural plasticity, and (d) audiovisual processing in individuals with hearing loss. Conclusions Although there is a compelling theoretical rationale for reducing visual input to enhance auditory development, there is also a strong theoretical argument supporting simultaneous multisensory auditory and visual input to potentially enhance outcomes in children with hearing loss. Despite widespread and long-standing practice recommendations to limit visual input, there is a paucity of evidence supporting this recommendation and no evidence that simultaneous multisensory input is deleterious to children with cochlear implants. These findings have important implications for optimizing spoken language outcomes in children with cochlear implants.

Cochlear implantation is indicated in patients with severe to profound hearing loss that cannot be adequately treated by other auditory rehabilitation measures. The definitive indication of cochlear implantation is made on the basis of an extensive interdisciplinary clinical, audiological, radiological, and psychological diagnostic work-up. There are numerous changes are happening in cochlear implant candidacy. These have been associated with concomitant changes in surgical techniques, which enhanced the utility and safety of cochlear implantation. Currently, cochlear implants are approved for individuals with severe to profound unilateral hearing loss rather than previously needed for bilateral profound hearing loss. Studies have begun using the short electrode arrays for shallow insertion in patients with low-frequency residual hearing loss. The advancement in designs of the cochlear implant along with improvements in surgical techniques reduce the complications and result in the safety and efficacy of the cochlear implant which further encourages the use of these devices. This review article aims to discuss the new concepts in the candidacy of the cochlear implant, cochlear implant in younger children and hearing preservation, a cochlear implant for unilateral deafness, bilateral cochlear implant, and cochlear implant with neural plasticity and selection of patients for the cochlear implant.

Prelingual deafness deprives the auditory cortices areas from the physiological stimulus which is mandatory for the normal anatomical and physiological development of the cortex. In the absence of immediate intervention appropriate for auditory habilitation, the auditory cortex will lose its specific capacity to process the auditory information. This phenomenon is known as auditory deprivation. Due to the cerebral plasticity, conventional hearing aids or cochlear implants use allow the reorganization of the cerebral auditory structures in order to regain their capacity to process correctly the sounds and the child to hear. Age of implantation is determinant for the benefit obtained by deaf children with cochlear implants. As soon as the implantation occurs, the acoustic exposure of the hearing impaired children increases as well. Early exposure to sounds allows the deaf child to understand speech better and to develop language better. Prelingually deaf children, implanted by the age of two, develop speech and language skills similar to their normal hearing peers.

Numerous changes continue to occur in cochlear implant candidacy. In general, these have been accompanied by concomitant and satisfactory changes in surgical techniques. Together, this has advanced the utility and safety of cochlear implantation. Most devices are now approved for use in patients with severe to profound unilateral hearing loss rather then the prior requirement of a bilateral profound loss. Furthermore, studies have begun utilizing short electrode arrays for shallow insertion in patients with considerable low-frequency residual hearing. This technique will allow the recipient to continue to use acoustically amplified hearing for the low frequencies simultaneously with a cochlear implant for the high frequencies. The advances in design of, and indications for, cochlear implants have been matched by improvements in surgical techniques and decrease in complications. The resulting improvements in safety and efficacy have further encouraged the use of these devices. This paper will review the new concepts in the candidacy of cochlear implant. Medline data base was used to search articles dealing with the following topics: cochlear implant in younger children, cochlear implant and hearing preservation, cochlear implant for unilateral deafness and tinnitus, genetic hearing loss and cochlear implant, bilateral cochlear implant, neuropathy and cochlear implant and neural plasticity, and the selection of patients for cochlear implant.

This report highlights research projects relevant to binaural and spatial hearing in adults and children. In the past decade we have made progress in understanding the impact of bilateral cochlear implants (BiCIs) on performance in adults and children. However, BiCI users typically do not perform as well as normal hearing (NH) listeners. In this article we describe the benefits from BiCIs compared with a single cochlear implant (CI), focusing on measures of spatial hearing and speech understanding in noise. We highlight the fact that in BiCI listening the devices in the two ears are not coordinated; thus binaural spatial cues that are available to NH listeners are not available to BiCI users. Through the use of research processors that carefully control the stimulus delivered to each electrode in each ear, we are able to preserve binaural cues and deliver them with fidelity to BiCI users. Results from those studies are discussed as well, with a focus on the effect of age at onset of deafness and plasticity of binaural sensitivity. Our work with children has expanded both in number of subjects tested and age range included. We have now tested dozens of children ranging in age from 2 to 14 yr. Our findings suggest that spatial hearing abilities emerge with bilateral experience. While we originally focused on studying performance in free field, where real world listening experiments are conducted, more recently we have begun to conduct studies under carefully controlled binaural stimulation conditions with children as well. We have also studied language acquisition and speech perception and production in young CI users. Finally, a running theme of this research program is the systematic investigation of the numerous factors that contribute to spatial and binaural hearing in BiCI users. By using CI simulations (with vocoders) and studying NH listeners under degraded listening conditions, we are able to tease apart limitations due to the hardware/software of the CI systems from limitations due to neural pathology.

Purpose: This research examined the expression of cortical auditory evoked potentials in a cohort of children who received cochlear implants (CIs) for treatment of congenital deafness ( n = 28) and typically hearing controls ( n = 28). Method: We make use of a novel electroencephalography paradigm that permits the assessment of auditory responses to ambiently presented speech and evaluates the contributions of concurrent visual stimulation on this activity. Results: Our findings show group differences in the expression of auditory sensory and perceptual event-related potential components occurring in 80- to 200-ms and 200- to 300-ms time windows, with reductions in amplitude and a greater latency difference for CI-using children. Relative to typically hearing children, current source density analysis showed muted responses to concurrent visual stimulation in CI-using children, suggesting less cortical specialization and/or reduced responsiveness to auditory information that limits the detection of the interaction between sensory systems. Conclusion: These findings indicate that even in the face of early interventions, CI-using children may exhibit disruptions in the development of auditory and multisensory processing.

The present thesis investigates the effects of auditory deafferentation and reafferentation with a unimodal and multisensory perspective. Aim of the thesis is the understanding of issues concerning functional plasticity resulting from long-term auditory deprivation, and the effects of reafferentation through a cochlear implant (CI) on audition, vision, and their interaction. The thesis is divided into three parts: Part I explores the effects of auditory deafferentation on the visual modality to understand whether a long-term sensory deprivation leads one of the remaining senses to reorganise in a cross-modal fashion. In particular, Chapter 1 reviews animal and human findings on cross-modal plasticity after sensory deafferentation and introduces the particular case of deafness, focusing on the sensory modality that seems to reorganise the most after profound deafness: vision. In Chapter 2 I present the study we conducted to explore an underinvestigated issue of cross-modal reorganisation after long-term auditory deprivation. We investigated visual temporal processing in a group of profoundly deaf individuals by testing their ability to make temporal order judgments. Our results show comparable accuracy in processing visual temporal sequences in deaf individuals and hearing controls, but an enhanced reactivity in the deaf population particularly when responding to stimuli appearing towards the periphery of the visual field. Our findings suggest that long-term auditory deprivation does not alter temporal processing abilities, and that the reactivity observed in the deaf group may instead constitute a central aspect of the functional changes occurring after auditory deafferentation. Part II of the thesis addresses the effects of auditory reafferentation through a cochlear implant on the adult auditory system. Chapter 3 reviews findings that document plasticity in the adult brain and the role of experience in determining the extent for plasticity to occur. In addition, a review on auditory spatial hearing introduces the two studies we conducted to investigate the recovery of sound localisation abilities after bilateral and unilateral cochlear implantation (chapter 4 and 5, respectively). Results from the first study show that partial recovery of spatial hearing after bilateral implantation occur with different time course as a function of the recipient’s experience with auditory cues. Results from the second study show that some sound localisation abilities can emerge even in prelingually deafened adults fitted with a single implant, at least in a laboratory setting. Importantly, this ability appears to be constraint by the years of experience with the CI, and again as a function of previous auditory experience of the CI recipient. Part III addresses the question of the effects of auditory reafferentation on the visual system and its interaction with audition. Chapter 6 reviews the issue of crossmodal plasticity after auditory reafferentation. In particular, we investigated whether visual abilities are modified after cochlear implantation in a group of prelingual and postlingual deaf recipients (Chapter 7). In this study we found that prelingual deaf recipients, compared to postlingual deaf, had an advantage in detecting the onset of rapidly presented visual stimuli in the periphery of the visual field. In a further experiment (Chapter 8) we investigated whether auditory and visual information are integrated after cochlear implantation in prelingual and postlingual deaf recipients and found that their abilities are comparable to hearing controls. Finally, Chapter 9 summarises all the presented results and draws the major conclusions.

Ce travail de thèse visait à étudier les adaptations périphériques et centrales du système auditif liées à l'effet bénéfique des implants cochléaires (IC) chez les sujets présentant une perte auditive asymétrique (AHL) et des acouphènes. En ce sens, notre principal intérêt était d'étudier la possibilité d'une fusion entre le signal électrique de l'IC et le signal acoustique de l'oreille auditive et de déterminer si cette fusion restaure les mécanismes d'intégration binaurale, comme chez les sujets ayant une audition normale (NH), tant sur le niveau comportemental qu'au niveau central. D'un point de vue clinique, ces études sur la récupération de l'audition chez les sujets souffrant d'AHL fourniront des informations cruciales sur les capacités plastiques du cerveau à s'adapter à la stimulation électrique et guideront ainsi les stratégies thérapeutiques permettant de mieux récupérer les capacités binaurales et la perception linguistique et paralinguistique. Nous avons combiné différents types de tests comportementaux et audiologiques, des analyses radiologiques et une évaluation en neuroimagerie (imagerie PET Scan H2O15). En outre, nous avons pu décrire certaines propriétés qualitatives du son perçu du côté implanté et évaluer la réponse centrale à cette incohérence spectrale - lorsque les deux signaux de nature différente sont présentés, nous renseignant potentiellement sur des stratégies adaptatives possibles. Par ailleurs, nous avons confirmé que les principaux avantages de la réafférentation électrique via l'IC sont principalement la diminution et, dans certains cas, la suppression des acouphènes. Nous avons également envisagé plusieurs stratégies thérapeutiques pour le masquage des acouphènes impliquant non seulement l'oreille IC, mais également l'oreille NH. Dans l'ensemble, nous estimons que les sujets AHL bénéficient réellement de l'implantation cochléaire. Par conséquent, nos données indiquent que les adaptations plastiques induites par la réafférentation électrique chez les sujets AHL pourraient jouer un rôle déterminant dans la restauration des capacités binaurales, dans l'adaptation aux caractéristiques spectrales du signal IC et dans la suppression des acouphènes, ce qui permettrait potentiellement d'apporter un peu plus d'informations sur leurs mécanismes sous-jacents
This thesis work aimed to investigate the peripheral and central adaptations of the auditory system related to the beneficial effect of cochlear implants (CI) in subjects with asymmetrical hearing loss (AHL) and tinnitus. In this sense, our main interest was to study the possible fusion between the electric signal of the CI and the acoustic signal from the hearing ear and assess if it restores the binaural integration mechanisms as in normal-hearing (NH) subjects, both on behavioral and central levels. From the clinical standpoint, these studies on hearing recovery in AHL CI subjects will provide crucial information on the plastic abilities of the brain to adapt to electrical stimulation and thus to guide therapeutic strategies to better recover binaural abilities, and linguistic and para-linguistic perception. We combined behavioral and audiological testing, radiological analysis and neuroimaging investigation (H2O15PET Scan imaging). Besides, we were able to describe some qualitative properties of the perceived sound on the implanted side and to evaluate the central response to this spectral inconsistency- when the two signals of different nature are presented, potentially informing on possible adaptive strategies. In addition, we confirmed that the main benefits of electrical reafferentation via the CI is mostly the decrease, and in some cases the suppression, of tinnitus. We also considered several therapeutic strategies for tinnitus masking involving not only the CI ear but also the NH ear. Overall, we strongly believe that AHL subjects truly benefit from cochlear implantation. Hence, our data indicate that plastic adaptations to the CI input in AHL subjects may play a key role on restoring binaural hearing abilities, accommodation to CI signal spectral characteristics and tinnitus suppression which may shed some light on its underlying mechanisms

This study examined the effects of bilateral and unilateral deafness by measuring cortical auditory evoked potential (CAEP) responses in children at initial stages of bilateral cochlear implant (CI) use. We recorded cortical responses evoked by right and left CI stimulation in 127 children with early onset (< 12 months) deafness, with 72 children receiving the two devices in the same surgery (simultaneously implanted) and 55 children receiving the devices in separate procedures (sequentially implanted). Three different types of responses were identified in children with bilateral CIs. No significant effects of duration of deafness, age at implantation, or duration of unilateral CI use were found on response latencies and amplitudes within each type of cortical response, but there were clear differences in responses types between groups and ears. In the context of these findings, the effects of bilateral and unilateral deafness to the auditory pathways were discussed.