Neuroplasticity behind the rehabilitation of asymmetrical hearing loss and tinnitus through cochlear implantation: from psychoacoustic evaluations to neuroimaging studies

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

La neuroplasticité derrière la réhabilitation des surdités profondes asymétriques et acouphènes via l'implantation cochléaire : évaluations psychoacoustiques et neuroimagerie

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

Evaluation of the pulse-spreading harmonic complex vocoder for simulating cochlear implant hearing

International audienceNoise- and sine-carrier vocoders are often used to acoustically simulate the information transmitted by a cochlear implant (CI). However, sinusoids fail to mimic the broad spread of excitation produced by a CI, and noise bands contain intrinsic modulations that are absent in CIs. Pulse spreading harmonic complexes (PSHCs) are complexes with a high-density spectrum that can be shaped spectrally and whose rate can be adjusted to minimize the amount of intrinsic modulations at the output of auditory filters, possibly providing a stimulus qualitatively similar to the electrical pulse trains of a CI. Here, we aimed to evaluate the PSHC vocoder in two experiments with single-sided deaf (SSD) CI listeners. In Experiment 1, electric-acoustic pitch matches were collected from 13 subjects. Electric stimulation was presented to an apical or a middle electrode. Acoustic stimulus types were either sinusoids (SINE), 1/3-octave wide narrow bands of Gaussian noises (NOISE), or 1/3-octave wide PSHCs. Assuming that electric-acoustic pitch matches should be less variable if the acoustic and electric stimuli are qualitatively similar, it was hypothesized that pitch matches of PSHC would yield a lower variance than those for SINE or NOISE. Although this hypothesis was not verified, the mean pitch matches showed significant effects of electrode position and stimulus type. In Experiment 2, 9 subjects were asked to compare the similarity of speech sentences presented through the audio input of their CI with different vocoder implementations that used PSHC, NOISE or SINE carriers. The vocoder using PSHC carriers was judged more similar to the sound of their CI compared to the other vocoders. However, it did not provide an exact match to the sound of their CI, prompting further research to better acoustically simulate CI hearing

Searching for the Sound of a Cochlear Implant: Evaluation of Different Vocoder Parameters by Cochlear Implant Users With Single-Sided Deafness

International audienceCochlear implantation in subjects with single-sided deafness (SSD) offers a unique opportunity to directly compare the percepts evoked by a cochlear implant (CI) with those evoked acoustically. Here, nine SSD-CI users performed a forcedchoice task evaluating the similarity of speech processed by their CI with speech processed by several vocoders presented to their healthy ear. In each trial, subjects heard two intervals: their CI followed by a certain vocoder in Interval 1 and their CI followed by a different vocoder in Interval 2. The vocoders differed either (i) in carrier type-(sinusoidal [SINE], bandfiltered noise [NOISE], and pulse-spreading harmonic complex) or (ii) in frequency mismatch between the analysis and synthesis frequency ranges-(no mismatch, and two frequency-mismatched conditions of 2 and 4 equivalent rectangular bandwidths [ERBs]). Subjects had to state in which of the two intervals the CI and vocoder sounds were more similar. Despite a large intersubject variability, the PSHC vocoder was judged significantly more similar to the CI than SINE or NOISE vocoders. Furthermore, the No-mismatch and 2-ERB mismatch vocoders were judged significantly more similar to the CI than the 4-ERB mismatch vocoder. The mismatch data were also interpreted by comparing spiral ganglion characteristic frequencies with electrode contact positions determined from postoperative computed tomography scans. Only one subject demonstrated a pattern of preference consistent with adaptation to the CI sound processor frequency-to-electrode allocation table and two subjects showed possible partial adaptation. Those subjects with adaptation patterns presented overall small and consistent frequency mismatches across their electrode arrays

The Effects of Multi-Mode Monophasic Stimulation with Capacitive Discharge on the Facial Nerve Stimulation Reduction in Young Children with Cochlear Implants: Intraoperative Recordings

Facial nerve stimulation (FNS) is a potential complication which may affect the auditory performance of children with cochlear implants (CIs). We carried out an exploratory prospective observational study to investigate the effects of the electrical stimulation pattern on FNS reduction in young children with CI. Ten ears of seven prelingually deafened children with ages up to 6 years old who undergone a unilateral or bilateral CI surgery were included in this study. Electromyographic (EMG) action potentials from orbicularis oculi muscle were recorded using monopolar biphasic stimulation (ST1) and multi-mode monophasic stimulation with capacitive discharge (ST2). Presence of EMG responses, facial nerve stimulation thresholds (T-FNS) and EMG amplitudes were compared between ST1 and ST2. Intra-cochlear electrodes placement, cochlear-nerve and electrode-nerve distances were also estimated to investigate their effects on EMG responses. The use of ST2 significantly reduced the presence of intraoperative EMG responses compared to ST1. Higher stimulation levels were required to elicit FNS with ST2, with smaller amplitudes, compared to ST1. No and weak correlation was observed between cochlea-nerve and electrode-nerve distances and EMG responses, respectively. ST2 may reduce FNS in young children with CI. Differently from the electrical stimulation pattern, the cochlea-nerve and electrode-nerve distances seem to have limited effects on FNS in this population

Auditory cortical plasticity after cochlear implantation in asymmetric hearing loss is related to spatial hearing: a PET H215O study

International audienceIn asymmetric hearing loss (AHL), the normal pattern of contralateral hemispheric dominance for monaural stimulation is modified, with a shift towards the hemisphere ipsilateral to the better ear. The extent of this shift has been shown to relate to sound localization deficits. In this study, we examined whether cochlear implantation to treat postlingual AHL can restore the normal functional pattern of auditory cortical activity and whether this relates to improved sound localization. The auditory cortical activity was found to be lower in the AHL cochlear implanted (AHL-CI) participants. A cortical asymmetry index was calculated and showed that a normal contralateral dominance was restored in the AHL-CI patients for the nonimplanted ear, but not for the ear with the cochlear implant. It was found that the contralateral dominance for the nonimplanted ear strongly correlated with sound localization performance (rho = 0.8, P < 0.05). We conclude that the reorganization of binaural mechanisms in AHL-CI subjects reverses the abnormal lateralization pattern induced by the deafness, and that this leads to improved spatial hearing. Our results suggest that cochlear implantation enables the reconstruction of the cortical mechanisms of spatial selectivity needed for sound localization

Anatomical Variations of the Human Cochlea Using an Image Analysis Tool

Understanding cochlear anatomy is crucial for developing less traumatic electrode arrays and insertion guidance for cochlear implantation. The human cochlea shows considerable variability in size and morphology. This study analyses 1000+ clinical temporal bone CT images using a web-based image analysis tool. Cochlear size and shape parameters were obtained to determine population statistics and perform regression and correlation analysis. The analysis revealed that cochlear morphology follows Gaussian distribution, while cochlear dimensions A and B are not well-correlated to each other. Additionally, dimension B is more correlated to duct lengths, the wrapping factor and volume than dimension A. The scala tympani size varies considerably among the population, with the size generally decreasing along insertion depth with dimensional jumps through the trajectory. The mean scala tympani radius was 0.32 mm near the 720° insertion angle. Inter-individual variability was four times that of intra-individual variation. On average, the dimensions of both ears are similar. However, statistically significant differences in clinical dimensions were observed between ears of the same patient, suggesting that size and shape are not the same. Harnessing deep learning-based, automated image analysis tools, our results yielded important insights into cochlear morphology and implant development, helping to reduce insertion trauma and preserving residual hearing

Clinical efficiency and safety of the oticon medical neuro cochlear implant system: a multicenter prospective longitudinal study

Objective This prospective longitudinal cohort study at six tertiary referral centers in Canada and Denmark describes the clinical efficiency and surgical safety of cochlear implantation with the Oticon Medical Neuro cochlear implant system, including the Neuro Zti implant, the EVO electrode array, and the Neuro One sound processor. Methods Patients were adult cochlear implant candidates with bilateral sensorineural hearing loss. Results The mean HINT scores in quiet pre-operatively and at 3, 6, and 12 months post-activation were 13%, 58%, 67%, and 72%, respectively, and in noise (+10 dB SNR) 13%, 46%, 53%, and 59%, respectively. The mean improvement from baseline to 6 months post-activation was 54% in quiet and 40% in noise. The surgical major complication incidence rate was 0% and the post-surgical major complication incidence rate (until 12 months post-activation) was 4%. There was no adverse event that was fatal, that required explantation, or that resulted in sound processor nonuse, and no implant failure. Conclusion Cochlear implantation with the Oticon Medical Neuro system enables speech identification both in quiet and in noise and audiologic outcomes continue to improve in the year following activation. No substantial adverse events occurred during the surgical implantation procedure and during the 12 months post-activation.Funding Agencies|Oticon Medical</p

The Development of the “Telislife” Questionnaire for the Evaluation of Telephone Use in Cochlear Implant Users

Purpose For cochlear implant users, the ability to use the telephone is often seen as an important landmark during rehabilitation and an indicator of cochlear implant benefit. The goal of this study was to develop a short questionnaire exploring the ability to use the telephone in cochlear implant users, named Telislife, and test it in a group of experienced users. Method This prospective multicenter study was based on the completion of self-administrated questionnaires. The Telislife includes 20 items using a 5-point Likert scale for answers. Speech recognition scores were obtained with monosyllabic word lists at 70 dB HL. Quality of life was evaluated with the Nijmegen Cochlear Implant Questionnaire. This study included 55 adult patients wearing a cochlear implant for over 1 year. Results The Telislife questionnaire showed excellent reliability (Cronbach's α = .91). A significant correlation was found between Telislife scores and Nijmegen Cochlear Implant Questionnaire scores (r = .69, p &lt; .001) and speech recognition scores (r = .35, p = .007). Conclusion Given significant correlations between Telislife scores and both speech recognition and quality of life and given its short form, the Telislife questionnaire appears to be a reliable tool to evaluate cochlear implant outcomes in clinical practice

Adult Users of the Oticon Medical Neuro Cochlear Implant System Benefit from Beamforming in the High Frequencies

The Oticon Medical Neuro cochlear implant system includes the modes Opti Omni and Speech Omni, the latter providing beamforming (i.e., directional selectivity) in the high frequencies. Two studies compared sentence identification scores of adult cochlear implant users with Opti Omni and Speech Omni. In Study 1, a double-blind longitudinal crossover study, 12 new users trialed Opti Omni or Speech Omni (random allocation) for three months, and their sentence identification in quiet and noise (+10 dB signal-to-noise ratio) with the trialed mode were measured. The same procedure was repeated for the second mode. In Study 2, a single-blind study, 11 experienced users performed a speech identification task in quiet and at relative signal-to-noise ratios ranging from -3 to +18 dB with Opti Omni and Speech Omni. The Study 1 scores in quiet and in noise were significantly better with Speech Omni than with Opti Omni. Study 2 scores were significantly better with Speech Omni than with Opti Omni at +6 and +9 dB signal-to-noise ratios. Beamforming in the high frequencies, as implemented in Speech Omni, leads to improved speech identification in medium levels of background noise, where cochlear implant users spend most of their day.Funding Agencies|Oticon Medical; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (Coordination for the Improvement of Higher Education Personnel) from the Ministry of Education of Brazil</p