Auditory cortical plasticity in cochlear implant users

Current Opinion in Neurobiology, 2005

The cochlear implant arguably is the most successful neural prosthesis. Studies of the responses of the central auditory system to prosthetic electrical stimulation of the cochlea are revealing the success with which electrical stimulation of a deaf ear can mimic acoustic stimulation of a normal-hearing ear. Understanding of the physiology of central auditory structures can lead to improved restoration of hearing with cochlear implants. In turn, the cochlear implant can be exploited as an experimental tool for examining central hearing mechanisms isolated from the effects of cochlear mechanics and transduction. The cochlear implants Middlebrooks, Arenberg Bierer and Snyder 491 www.sciencedirect.com Current Opinion in Neurobiology 2005, 15:488-493 55. Bierer JA, Middlebrooks JC: Cortical responses to cochlear implant stimulation: channel interactions. J Assoc Res Otolaryngol 2004, 5:32-48. 56. Middlebrooks JC: Effects of cochlear-implant pulse rate and inter-channel timing on channel interactions and thresholds.

Advances in oto-rhino-laryngology, 2006

The benefit of cochlear implantation crucially depends on the ability of the brain to learn to classify neural activity evoked by the cochlear implant. Brain plasticity is a complex property with massive developmental changes after birth. The present paper reviews the experimental work on auditory plasticity and focuses on the plasticity required for adaptation to cochlear implant stimulation. It reviews the data on developmental sensitive periods in auditory plasticity of hearing, hearing-impaired and deaf, cochlear-implanted, animals. Based on the analysis of the above findings in animals and comparable data from humans, a cochlear implantation within the first 2 years of age is recommended.

International Journal of Pediatric Otorhinolaryngology, 1999

Previous animal research and clinical experiences in humans suggest the existence of an auditory critical period in language acquisition. We review the literature and present the changes within the cochlear nuclei in bilaterally deafferentated adult non-human primates. We also present and analyse the results of 98 prelingually deaf children and teenagers who underwent a cochlear implantation at the University of Navarra. Patients received a Nucleus 22 or 24 multichannel cochlear implant (CI). They were grouped in five categories according to their age at surgery. Performance is compared with a control group of 58 postlinguals. Only early-implanted prelingual children (before 6 years of age) achieved a complete open-set speech recognition, even with better performance than postlinguals. These results clearly demonstrate the existence of a period of high neural auditory plasticity within the first 6 years of life. The introduction of auditory stimulation with a CI can not restore the loss of neural plasticity out of this period. Prelingual children under 6 years of age should receive a CI as soon as there is a reliable diagnosis of bilateral sensorineural hearing loss.

Summary Currently, the most commonly used electrophysiological tests for cochlear implant evaluation are Averaged Electrical Voltages (AEV), Electrical Advisory Brainstem Responses (EABR) and Neural Response Telemetry (NRT). The present paper focuses on the study of acoustic auditory cortical responses, or slow vertex responses, which are not widely used due to the difficulty in recording, especially in young children. Aims of this study were validation of slow vertex responses and their possible applications in monitoring postimplant results, particularly restoration of hearing and auditory maturation. In practice, the use of tone-bursts, also through hearing aids or cochlear implants, as in slow vertex responses, allows many more frequencies to be investigated and louder intensities to be reached than with other tests based on a click as stimulus. Study design focused on latencies of N1 and P2 slow vertex response peaks in cochlear implants. The study population comprised 45 implant recipients (aged 2 to 70 years), divided into 5 different homogeneous groups according to chronological age, age at onset of deafness, and age at implantation. For each subject, slow vertex responses and free-field auditory responses (PTAS) were recorded for tone-bursts at 500 and 2000 Hz before cochlear implant surgery (using hearing aid amplification) and during scheduled sessions at 3 rd and 12 th month after implant activation. Results showed that N1 and P2 latencies decreased in all groups starting from 3 rd through 12 th month after activation. Subjects implanted before school age or at least before age 8 yrs showed the widest latency changes. All subjects showed a reduction in the gap between subjective thresholds (obtained with free field auditory responses) and objective thresholds (obtained with slow vertex responses), obtained in presurgery stage and after cochlear implant. In conclusion, a natural evolution of neurophysiological cortical activities of the auditory pathway, over time, was found especially in young children with prelingual deafness and implanted in preschool age. Cochlear implantation appears to provide hearing restoration, demonstrated by the sharp reduction of the gap between subjective free field auditory responses and slow vertex responses threshold obtained with hearing aids vs. cochlear implant.

World journal of otorhinolaryngology - head and neck surgery, 2017

Cochlear implants (CIs) often work very well for many children and adults with profound sensorineural (SNHL) hearing loss. Unfortunately, while many CI patients display substantial benefits in recognizing speech and understanding spoken language following cochlear implantation, a large number of patients achieve poor outcomes. Understanding and explaining the reasons for poor outcomes following implantation is a very challenging research problem that has received little attention despite the pressing clinical significance. In this paper, we discuss three challenges for future research on CIs. First, we consider the issue of individual differences and variability in outcomes following implantation. At the present time, we still do not have a complete and satisfactory account of the causal underlying factors that are responsible for the enormous individual differences and variability in outcomes. Second, we discuss issues related to the lack of preimplant predictors of outcomes. Very ...

Clinical Neurophysiology, 2005

Objective: This study determined the relationship between auditory evoked potential measures and speech perception in experienced adult cochlear implant (CI) users and compared the CI evoked potential results to those of a group of age-and sex-matched control subjects. Methods: CI subjects all used the Nucleus CI-22 implant. Middle latency response (MLR), obligatory cortical potentials (CAEP), mismatch negativity (MMN) and P3a auditory evoked potentials were recorded. Speech perception was evaluated using word and sentence tests. Results: Duration of deafness correlated with speech scores with poor scores reflecting greater years of deafness. Na amplitude correlated negatively with duration of deafness, with small amplitudes reflecting greater duration of deafness. Overall, N1 amplitude was smaller in CI than control subjects. Earlier P2 latencies were associated with shorter durations of deafness and higher speech scores. In general, MMN was absent or degraded in CI subjects with poor speech scores. Conclusions: Auditory evoked potentials are related to speech perception ability and provide objective evidence of central auditory processing differences across experienced CI users. Significance: Since auditory evoked potentials relate to CI performance, they may be a useful tool for objectively evaluating the efficacy of speech processing strategies and/or auditory training approaches in both adults and children with cochlear implants.

Hearing Research, 2008

Advances in implant technology and speech processing have provided great benefit to many cochlear implant patients. However, some patients receive little benefit from the latest technology, even after many years' experience with the device. Moreover, even the best cochlear implant performers have great difficulty understanding speech in background noise, and music perception and appreciation remain major challenges. Recent studies have shown that targeted auditory training can significantly improve cochlear implant patients' speech recognition performance. Such benefits are not only observed in poorly performing patients, but also in good performers under difficult listening conditions (e.g., speech noise, telephone speech, music, etc.). Targeted auditory training has also been shown to enhance performance gains provided by new implant devices and/or speech processing strategies. These studies suggest that cochlear implantation alone may not fully meet the needs of many patients, and that additional auditory rehabilitation may be needed to maximize the benefits of the implant device. Continuing research will aid in the development of efficient and effective training protocols and materials, thereby minimizing the costs (in terms of time, effort and resources) associated with auditory rehabilitation while maximizing the benefits of cochlear implantation for all recipients.

Cell and Tissue Research, 2014

Data from our laboratory show that the auditory brain is highly malleable by experience. We establish a base of knowledge that describes the normal structure and workings at the initial stages of the central auditory system. This research is expanded to include the associated pathology in the auditory brain stem created by hearing loss. Utilizing the congenitally deaf white cat, we demonstrate the way that cells, synapses, and circuits are pathologically affected by sound deprivation. We further show that the restoration of auditory nerve activity via electrical stimulation through cochlear implants serves to correct key features of brain pathology caused by hearing loss. The data suggest that rigorous training with cochlear implants and/or hearing aids offers the promise of heretofore unattained benefits.

Clinical linguistics & phonetics, 2013

In some cochlear implant users, success is not achieved in spite of optimal clinical factors (including age at implantation, duration of rehabilitation and post-implant hearing level), which may be attributed to disorders at higher levels of the auditory pathway. We used cortical auditory evoked potentials to investigate the ability to perceive and discriminate auditory stimuli in 10 unsuccessful implant users aged 8-10 years (CI) and 10 healthy age-matched controls with normal hearing (NH). Pure tones (1 and 2 kHz) and double consonant-vowel syllables were applied. The stimuli were presented in an oddball paradigm that required the subjects to react consciously. The latencies and amplitudes of the P1, N1, P2, N2 and P3 waves were analyzed, in addition to reaction times and number of responses. Significant differences in the average response times and number of responses were observed between the CI and NH groups. The latencies also indicate that the CI group took longer to perceive and discriminate between tonal and speech auditory stimuli than the NH group.

Indian Journal of Otolaryngology and Head & Neck Surgery, 2012

Normal maturation of central auditory pathways is a precondition for the optimal development of speech and language skills in children. The temporal cortex gets acoustically tagged due to auditory stimulation and important changes occur in the higher auditory centers due to hearing loss of any type and degree. Cochlear implantation increases auditory sensitivity by direct electrical activation of auditory nerve fibers, enabling phonemic awareness, discrimination and identification ultimately yielding speech understanding. Early implantation stimulates a brain that has not been re-organized and will therefore be more receptive to auditory input and greater auditory capacity. Cortical potentials have enabled us to objectively study this phenomenon. To assess the outcomes of Cochlear implants on the auditory cortex by analyzing cortical auditory evoked potentials (CAEPs) in the habilitation period. This prospective clinical study was performed in 30 pre-lingual candidates with varied etiology of deafness who underwent cochlear implantation at our institute over the last 1 year. The study group had two cohorts (group-1: 0-8 years and group-2: 8-15 years) which included candidates with normal inner ear and no syndromes or handicaps. All implantees in the study group underwent CAEP testing at 6 months and 1 year post-implantation and comparison of the CAEP wave parameters (P1 amplitude, P1 latency and P1 morphology) were done between the two cohorts. In children Implanted early (group-1) there was an early onset rapid increase in P1 amplitude along with a decrease in P1 latency during the follow-up period. Significant change in the CAEP wave morphology was also notable in group-1 unlike in group-2. Candidates who experienced less than 3 years of auditory deprivation before implantation showed P1 latencies, which fell into the range of normal children within 6 months of habilitation. Children with more than 6 years of auditory deprivation, however, generally did not develop normal P1 latencies or morphology even after 1 year of habilitation. The overall outcome with CAEP was much better in group-1 as compared to group-2 and the observations were is in comparison with the existing world literature. The advent of CAEP has objectively proved beyond doubt that there is a critical age for stimulating the auditory brain via cochlear implantation. There is considerable evidence for a developmental sensitive period, during which the auditory cortex is highly plastic. If sensory input is deprived to the auditory system during this sensitive period, then the central auditory system is susceptible to large scale reorganization. Restoring input to the auditory system by Cochlear Implant at an early age can provide the stimulation necessary to preserve the auditory pathways. However, if auditory input is not restored until after this developmental period, then the cross-modal reorganized pathways may exhibits abnormal functional characteristics as observed in recorded P1 amplitude, latencies and morphologies of CAEPs.

Cochlear Implants International, 2004

Although there was variation among these patients in the rate and amount of improvement in auditory-recognition skills and speech-production abilities, all ten patients demonstrated substantial benefit from their implants. We also found cochlear implantation of patients under 3 to be most rewarding, the outcome can be as good as or even better than other patients without LVAS. The hearing function, speech development and quality of life have significant improvement, especially in postlingually deafened patients with LVAS. Cochlear implantation should be considered when patients with LVAS progress to profound levels of hearing loss and cannot be salvaged by traditional hearing aids. Regular and continuous auditory rehabilitation and speech training after implantation are mandatory.

Clinical Neurophysiology, 2013

Little is known about the long-term development and maturation of the auditory cortex in children who have used a cochlear implant to hear for most of their lives. Early latency cortical activity follows a normal-like developmental trajectory with time-in-sound experience. Differences from normal emerge in later latency cortical activity despite long-term chronic stimulation of the auditory system for up to 16 years, in children using cochlear implants to hear.

Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology, 2016

Considerable unexplained variability and large individual differences exist in speech recognition outcomes for postlingually deaf adults who use cochlear implants (CIs), and a sizeable fraction of CI users can be considered "poor performers." This article summarizes our current knowledge of poor CI performance, and provides suggestions to clinicians managing these patients. Studies are reviewed pertaining to speech recognition variability in adults with hearing loss. Findings are augmented by recent studies in our laboratories examining outcomes in postlingually deaf adults with CIs. In addition to conventional clinical predictors of CI performance (e.g., amount of residual hearing, duration of deafness), factors pertaining to both "bottom-up" auditory sensitivity to the spectro-temporal details of speech, and "top-down" linguistic knowledge and neurocognitive functions contribute to CI outcomes. The broad array of factors that contribute to speech reco...

Brain, 2012

Cross-modal reorganization in the auditory cortex has been reported in deaf individuals. However, it is not well understood whether this compensatory reorganization induced by auditory deprivation recedes once the sensation of hearing is partially restored through a cochlear implant. The current study used electroencephalography source localization to examine cross-modal reorganization in the auditory cortex of post-lingually deafened cochlear implant users. We analysed visual-evoked potentials to parametrically modulated reversing chequerboard images between cochlear implant users (n = 11) and normal-hearing listeners (n = 11). The results revealed smaller P100 amplitudes and reduced visual cortex activation in cochlear implant users compared with normal-hearing listeners. At the P100 latency, cochlear implant users also showed activation in the right auditory cortex, which was inversely related to speech recognition ability with the cochlear implant. These results confirm a visual take-over in the auditory cortex of cochlear implant users. Incomplete reversal of this deafness-induced cortical reorganization might limit clinical benefit from a cochlear implant and help explain the high inter-subject variability in auditory speech comprehension.

2013

The most dramatic progress in the restoration of hearing takes place in the first months after cochlear implantation. To map the brain activity underlying this process, we used positron emission tomography at three time points: within 14 days, three months, and six months after switch-on. Fifteen recently implanted adult implant recipients listened to running speech or speech-like noise in four sequential PET sessions at each milestone. CI listeners with postlingual hearing loss showed differential activation of left superior temporal gyrus during speech and speech-like stimuli, unlike CI listeners with prelingual hearing loss. Furthermore, Broca's area was activated as an effect of time, but only in CI listeners with postlingual hearing loss. The study demonstrates that adaptation to the cochlear implant is highly related to the history of hearing loss. Speech processing in patients whose hearing loss occurred after the acquisition of language involves brain areas associated with speech comprehension, which is not the case for patients whose hearing loss occurred before the acquisition of language. Finally, the findings confirm the key role of Broca's area in restoration of speech perception, but only in individuals in whom Broca's area has been active prior to the loss of hearing.