Central auditory development after long-term cochlear implant use

Significant influence of prelingual deafness but less impact of elderly age at implantation on long-term psychoacoustic CI programming parameters

OBJECTIVE

This study aimed to elucidate the long-term impact of prelingual deafness and elderly age at cochlear implantation on cochlear implant (CI) programming parameters and CI thresholds METHODS: We retrospectively reviewed patients who underwent cochlear implantation less than 5 years (Prelingual group) and equal and more than 18 years in our institute. The latter group was further divided into Adult and Elderly groups according to whether the patient was younger or older than 65 at implantation. From 152, 69, and 55 patients in the Prelingual, Adult, and Elderly groups, 242, 92, and 58 ears were included. We compared CI thresholds and CI programming parameters, including impedances, T/C levels, and dynamic ranges for 8 years after implantation between the Prelingual, Adult, and Elderly groups.

RESULTS

The Prelingual group showed consistently lower CI thresholds than the Adult and Elderly groups during the postoperative 2-8 years, but no difference was detected between the Elderly and Adult groups, except at the postoperative 4 years. The elderly group's CI thresholds did not deteriorate until postoperative 8 years. The Prelingual group showed consistently larger T/C levels (minimum/maximum current strength from CI), especially C levels, than the other two groups. At the same time, there was no significant difference between the Elderly and Adult groups except for smaller dynamic ranges in the Elderly group until postoperative 2 years. These results in the CI programming parameters might explain the lower CI thresholds in the Prelingual group than in the other groups. Focusing on CI maps 1 and 3 years after implantation, the strength of the T/C levels was similar for all channels in the Prelingual group, but the Adult and Elderly groups showed larger electrical stimuli in channels responsible for the middle frequencies than those for the lower or higher frequencies.

CONCLUSIONS

Our results suggest a significant influence of prelingual deafness but less impact of elderly age at implantation on long-term CI programming parameters and CI thresholds. The larger C levels and lower CI thresholds in the Prelingual group than in the Adult and Elderly groups implied that CI children with prelingual deafness tolerate and prefer larger CI stimuli, which may reflect the CI-dependent development of their auditory system before the critical period. No age-related reduction in hearing thresholds was observed in the Elderly group, probably because the CI compensates for age-related dysfunction of the peripheral auditory system.

Exploring the relationship between auditory late latency response and language age in children using cochlear implant

AIM & OBJECTIVES

The study aimed to compare P1 latency and P1-N1 amplitude with receptive and expressive language ages in children using cochlear implant (CI) in one ear and a hearing aid (HA) in non-implanted ear.

METHODS

The study included 30 children, consisting of 18 males and 12 females, aged between 48 and 96 months. The age at which the children received CI ranged from 42 to 69 months. A within-subject research design was utilized and participants were selected through purposive sampling. Auditory late latency responses (ALLR) were assessed using the Intelligent hearing system to measure P1 latency and P1-N1 amplitude. The assessment checklist for speech-language skills (ACSLS) was employed to evaluate receptive and expressive language age. Both assessments were conducted after cochlear implantation.

RESULTS

A total of 30 children participated in the study, with a mean implant age of 20.03 months (SD: 8.14 months). The mean P1 latency and P1-N1 amplitude was 129.50 ms (SD: 15.05 ms) and 6.93 μV (SD: 2.24 μV) respectively. Correlation analysis revealed no significant association between ALLR measures and receptive or expressive language ages. However, there was significant negative correlation between the P1 latency and implant age (Spearman's rho = -0.371, p = 0.043).

CONCLUSIONS

The study suggests that P1 latency which is an indicative of auditory maturation, may not be a reliable marker for predicting language outcomes. It can be concluded that language development is likely to be influenced by other factors beyond auditory maturation alone.

Relationships between bilateral auditory brainstem activity and inter-implant interval in children with cochlear implants

PURPOSE

To investigate the effect of the interval between bilateral cochlear implantation on the development of bilateral peripheral auditory pathways as revealed by the electrically evoked auditory brainstem response (EABR).

METHODS

Fifty-eight children with profound bilateral sensorineural hearing loss were recruited. Among them, 33 children received sequential bilateral cochlear implants (CIs), and 25 children received simultaneous bilateral CIs. The bilateral EABRs evoked by electrical stimulation from the CI electrode were recorded on the day of second-side CI activation.

RESULTS

The latencies of wave III (eIII) and wave V (eV) were significantly shorter on the first CI side than on the second CI side in children with sequential bilateral CIs but were similar between the two sides in children with simultaneous bilateral CIs. Furthermore, the latencies were prolonged from apical to basal channels along the cochlea in the two groups. In children with sequential CIs, the inter-implant interval was negatively correlated with the eV latency on the first CI side and was positively correlated with bilateral differences in the eIII and eV latencies.

CONCLUSIONS

Unilateral CI use promotes the maturation of ipsilateral auditory conduction function. However, a longer inter-implant interval results in more unbalanced development of bilateral auditory brainstem pathways. Bilateral cochlear implantation with no or a short interval is recommended.

Prognostic factors in pediatric cochlear implant: an outcome-based study

OBJECTIVE

To determine the prognostic factors in the pediatric cochlear implant (CI) outcome.

MATERIALS AND METHODS

This prospective cohort study was conducted on 289 pediatric cases with prelingual hearing loss who received cochlear implantation. Several possible salient factors have been recorded. Auditory and speech evaluations were performed before CI, as well as 6 and 12 months after surgery, using Categories of Auditory Performance (CAP) and Speech Intelligibility Rating (SIR) tests.

RESULTS

According to univariate analysis, age at the time of surgery was a statistically significant factor. Neurological problems in the child, history of newborn infectious diseases, history of hearing aid use, proper parental cooperation, and round window approach were all significantly related to better auditory or speech outcomes. On the other hand, good parental cooperation and age (for CAP) and good parental cooperation, age, history of infectious disease, and hearing aids use (for SIR) are the significant factors in the multivariate setting.

CONCLUSION

As evidenced by the obtained results, age, background diseases, history of rehabilitation with hearing aids, and surgical details are essential factors to be taken into account in the case-selection process.

Effects of Sequential Bilateral Cochlear Implantation in Children: Evidence from Speech-Evoked Cortical Potentials and Tests of Speech Perception

INTRODUCTION

Benefits of bilateral cochlear implants (CI) may be compromised by delays to implantation of either ear. This study aimed to evaluate the effects of sequential bilateral CI use in children who received their first CI at young ages, using a clinical set-up.

METHODS

One-channel cortical auditory evoked potentials and speech perception in quiet and noise were evoked at repeated times (0, 3, 6, 12 months of bilateral CI use) by unilateral and bilateral stimulation in 28 children with early-onset deafness. These children were unilaterally implanted before 3.69 years of age (mean ± SD of 1.98 ± 0.73 years) and received a second CI after 5.13 ± 2.37 years of unilateral CI use. Comparisons between unilaterally evoked responses were used to measure asymmetric function between the ears and comparisons between bilateral responses and each unilateral response were used to measure the bilateral benefit.

RESULTS

Chronic bilateral CI promoted changes in cortical auditory responses and speech perception performance; however, large asymmetries were present between the two unilateral responses despite ongoing bilateral CI use. Persistent cortical differences between the two sides at 1 year of bilateral stimulation were predicted by increasing age at the first surgery and inter-implant delay. Larger asymmetries in speech perception occurred with longer inter-implant delays. Bilateral responses were more similar to the unilateral responses from the first rather than the second CI.

CONCLUSION

These findings are consistent with the development of the aural preference syndrome and reinforce the importance of providing bilateral CIs simultaneously or sequentially with very short delays.

Cortical imbalance following delayed restoration of bilateral hearing in deaf adolescents

Unilateral auditory deprivation in early childhood can lead to cortical strengthening of inputs from the stimulated side, yet the impact of this on bilateral processing when inputs are later restored beyond an early sensitive period is unknown. To address this, we conducted a longitudinal study with 13 bilaterally profoundly deaf adolescents who received unilateral access to sound via a cochlear implant (CI) in their right ear in early childhood before receiving bilateral access to sound a decade later via a second CI in their left ear. Auditory‐evoked cortical responses to unilateral and bilateral stimulation were measured repeatedly using electroencephalogram from 1 week to 14 months after activation of their second CI. Early cortical responses from the newly implanted ear and bilateral stimulation were atypically lateralized to the left ipsilateral auditory cortex. Duration of unilateral deafness predicted an unexpectedly stronger representation of inputs from the newly implanted, compared to the first implanted ear, in left auditory cortex. Significant initial reductions in responses were observed, yet a left‐hemisphere bias and unequal weighting of inputs favoring the long‐term deaf ear did not converge to a balanced state observed in the binaurally developed system. Bilateral response enhancement was significantly reduced in left auditory cortex suggesting deficits in ipsilateral response inhibition of new, dominant, inputs during bilateral processing. These findings paradoxically demonstrate the adaptive capacity of the adolescent auditory system beyond an early sensitive period for bilateral input, as well as restrictions on its potential to fully reverse cortical imbalances driven by long‐term unilateral deafness.

P-MMR and LDN beside MMN as Speech-evoked Neural Markers in Children with Cochlear Implants: A Review

This review mainly explores less-reported neural markers to speech-evoked contrasts in children with cochlear implants (CI). Databases and electronic journals were searched with keywords of "mismatch responses" AND "positive mismatch response" (p-MMR) AND "late discriminate negativity" (LDN). P-MMR likely is as a measurement of brain immaturity in CI children while the developmental trajectories of LDN remain unexplained in older CI children. In CI children, there is a p-MMR-MMN-LDN sequence to speech stimuli developmentally. Whereas these aforementioned neural responses anticipate developmental changes in CI groups, it is still uncertain about the cutoff age for disappearance of p-MMR and LDN.

The Importance of Access to Bilateral Hearing through Cochlear Implants in Children

Children with hearing loss require early access to sound in both ears to support their development. In this article, we describe barriers to providing bilateral hearing and developmental consequences of delays during early sensitive periods. Barriers include late identification of hearing loss in one or both ears and delayed access to intervention with hearing devices such as cochlear implants. Effects of delayed bilateral input on the auditory pathways and brain are discussed as well as behavioral effects on speech perception and other developmental outcomes including language and academics. Evidence for these effects has supported an evolution in cochlear implant candidacy in children that was started with unilateral implantation in children with profound deafness bilaterally to bilateral implantation to implantation of children with asymmetric hearing loss including children with single-side deafness. Opportunities to enhance the developmental benefits of bilateral hearing in children with hearing loss are also discussed including efforts to improve binaural/spatial hearing and consideration of concurrent vestibular deficits which are common in children with hearing loss.

Vestibular Evaluation and Management of Children with Sensorineural Hearing Loss

Vestibular dysfunction is the most common comorbidity associated with childhood sensorineural hearing loss. Early identification of vestibular dysfunction enables early intervention to mitigate its impact of motor, behavioral, and neurocognitive deficits of developing children. Screening for vestibular impairment can be achieved in the busy clinical setting.

Effects of long-term unilateral cochlear implant use on large-scale network synchronization in adolescents

Unilateral cochlear implantation (CI) limits deafness-related changes in the auditory pathways but promotes abnormal cortical preference for the stimulated ear and leaves the opposite ear with little protection from auditory deprivation. In the present study, time-frequency analyses of event-related potentials elicited from stimuli presented to each ear were used to determine effects of unilateral CI use on cortical synchrony. CI-elicited activity in 34 adolescents (15.4±1.9 years of age) who had listened with unilateral CIs for most of their lives prior to bilateral implantation were compared to responses elicited by a 500Hz tone-burst in normal hearing peers. Phase-locking values between 4 and 60Hz were calculated for 171 pairs of 19-cephalic recording electrodes. Ear specific results were found in the normal hearing group: higher synchronization in low frequency bands (theta and alpha) from left ear stimulation in the right hemisphere and more high frequency activity (gamma band) from right ear stimulation in the left hemisphere. In the CI group, increased phase synchronization in the theta and beta frequencies with bursts of gamma activity were elicited by the experienced-right CI between frontal, temporal and parietal cortical regions in both hemispheres, consistent with increased recruitment of cortical areas involved in attention and higher-order processes, potentially to support unilateral listening. By contrast, activity was globally desynchronized in response to initial stimulation of the naïve-left ear, suggesting decoupling of these pathways from the cortical hearing network. These data reveal asymmetric auditory development promoted by unilateral CI use, resulting in an abnormally mature neural network.

Consistent and chronic cochlear implant use partially reverses cortical effects of single sided deafness in children

Potentially neuroprotective effects of CI use were studied in 22 children with single sided deafness (SSD). Auditory-evoked EEG confirmed strengthened representation of the intact ear in the ipsilateral auditory cortex at initial CI activation in children with early-onset SSD (n = 15) and late-onset SSD occurring suddenly in later childhood/adolescence (n = 7). In early-onset SSD, representation of the hearing ear decreased with chronic CI experience and expected lateralization to the contralateral auditory cortex from the CI increased with longer daily CI use. In late-onset SSD, abnormally high activity from the intact ear in the ipsilateral cortex reduced, but responses from the deaf ear weakened despite CI use. Results suggest that: (1) cortical reorganization driven by unilateral hearing can occur throughout childhood; (2) chronic and consistent CI use can partially reverse these effects; and (3) CI use may not protect children with late-onset SSD from ongoing deterioration of pathways from the deaf ear.

Advantages of double density alignment of fNIRS optodes to evaluate cortical activities related to phonological short-term memory using NIRS-SPM

Phonological short-term memory (STM) and working memory (WM) capacity, which is temporal storage of phonological information, facilitates language development. This capacity is often impaired in cochlear implant (CI) users who have congenital hearing loss. Functional near-infrared spectroscopy (fNIRS) is potentially useful to reveal underlying mechanisms of this impairment due to its tolerance to magnetic and electrical artifacts generated by CIs. The spatial resolution of the standard fNIRS, however, seems inadequate to evaluate cortical activity associated with the maintenance of phonological information in the STM/WM tasks. In the present study recruiting 14 normal hearing adults, we applied a double density alignment of fNIRS optodes to improve spatial resolution in the generalized linear model (GLM)-based statistical analysis using NIRS-SPM, in which cortical activities were estimated during each of three stages (encoding, maintenance, and retrieval) in pseudoword STM tasks with auditory or visual presentation. Since the double density alignment of fNIRS optodes contains two sets of standard density arrays, in the off-line analysis the measured cortical hemodynamic responses can be analyzed as data from two independent standard density arrays as well as those from one double density array (DD-array) which has two times higher density of channels. The two standard arrays demonstrated a similar pattern of cortical activation at each stage of the auditory and visual tasks, which proved the reliability of our fNIRS analysis, but failed to detect significant cortical activation in 2 of 12 conditions including the maintenance stage in the visual task. On the other hand, DD-array revealed significant cortical activation in all conditions. These differences were observed when estimated cortical activation was localized in small regions, which suggests higher spatial resolution in DD-array than the standard arrays. In our knowledge, this is the first clinical study supporting the previous experimental phantom study which demonstrated improvement of spatial resolution in the double density arrangement of fNIRS optodes. These findings imply that the double density alignment of fNIRS optodes improves reliability and spatial resolution in fNIRS-based estimation of cortical activity in the STM/WM studies, although further studies are required to determine usefulness of this method in the CI population.

The development of auditory performance and speech perception in CI children after long-period follow up

PURPOSE

The main purpose of the current study was to assess the development of auditory and speech perception and the effects of the age at implantation in CI children after long-period follow up.

MATERIALS AND METHODS

Five hundred and forty-four young children participated in this study (339 males and 205 females). The age at implantation ranged from 6 months to 36 months. All subjects were prelingually bilateral profound sensorineural hearing loss. They were divided into 3 groups according to the implant ages: group 1 (age at implantation < 12 months, n = 109); group 2 (12 months < age at implantation < 24 months, n = 284); and group 3 (24 months < age at implantation < 36 months, n = 151). The categorical auditory performance (CAP) was used to assess auditory abilities and the speech intelligibility rating (SIR) was used to assess the speech intelligibility of these CI children. The tests were administered at pre-surgery and 1, 3, 6, 12, 24, 36, 48- and 60-months post-surgery.

RESULTS

All the subjects demonstrated improvements of auditory abilities and speech intelligibility after CI surgery. The auditory ability developed quickly in 12 months after implantation. However, the speech intelligibility scores show rapid improvement within 24 months post implantation. Significant difference was found between group 1 and group 3, group 2 and group 3 before 12 months post-implantation for CAP and SIR. The three groups of children showed similar development pattern for their auditory abilities and speech intelligibility.

CONCLUSION

The results of this study suggested dramatic and continuous improvement of the auditory and speech abilities post implantation in these CI children. Furthermore, the age at implantation played a considerably smaller role in the improvement of hearing and speech abilities. However, earlier implantation still benefits the language development.

Cortical auditory evoked potential in babies and children listeners

Introduction

Cortical auditory evoked potentials have been increasingly used in research and audiological routines. However, there is a lack of studies with a large number of children who are stratified by age group. These would help clarify the variations in latency and amplitude of cortical auditory evoked potentials, and thus help establish reference values in children of different ages.

Objective

To identify the variation in latency and amplitude of the cortical auditory evoked potentials and to establish reference values for the pediatric population.

Methods

This was a cross-sectional study. Subjects were born at term and presented with no auditory complaints. A total of 105 children, of up to 6 years and eleven months old, who were divided into 7 age groups, named 1, 2, 3, 4, 5, 6 and 7, participated in the study. The tests were carried out using Biologic Navigator Pro. Initially, brainstem auditory evoked potential testing was performed in order to investigate the electrophysiological threshold of the subjects. Then, cortical auditory evoked potentials were elicited through oddball paradigm with tone burst differing in frequency, 750 Hz (frequent) and 1000 Hz (rare), and stimuli differing in speech: /ba/ (frequent) and /da/ (rare). In this study, descriptive and comparative analyzes of tonal and speech stimuli were performed for the age groups.

Results

Significant differences were observed when comparing cortical auditory evoked potentials with speech stimulus in the right ear for P2 amplitude, for P1 latency the left ear, for P2 amplitude of the left ear; and for P1 amplitude of the left ear when performed with tonal stimuli.

Conclusion

The obtained results can be considered as reference values of latency and amplitude of cortical auditory potentials in infants and children, and be used for monitoring their cortical auditory development.

Cochlear Implants and Children with Vestibular Impairments

Sensorineural hearing loss (SNHL) in children occurs in 1 to 3% of live births and acquired hearing loss can additionally occur. This sensory deficit has far reaching consequences that have been shown to extend beyond speech and language development. Thankfully there are many therapeutic options that exist for these children with the aim of decreasing the morbidity of their hearing impairment. Of late, focus has shifted beyond speech and language outcomes to the overall performance of children with SNHL in real-world environments. To account for their residual deficits in such environments, clinicians must understand the extent of their sensory impairments. SNHL commonly coexists with other sensory deficits such as vestibular loss. Vestibular impairment is exceedingly common in children with SNHL with nearly half of children exhibiting vestibular end-organ dysfunction. These deficits naturally lead to impairments in balance and delay in motor milestones. However, this additional sensory deficit likely leads to further impairment in the performance of these children. This article focuses on the following: 1. Defining the coexistence of vestibular impairment in children with SNHL and cochlear implants. 2. Describing screening methods aimed at identifying vestibular dysfunction in children with SNHL. 3. Understanding the functional implications of this dual-sensory impairment. 4. Exploring possible rehabilitative strategies to minimize the impact of vestibular impairment in children with SNHL.

A potential neurophysiological correlate of electric-acoustic pitch matching in adult cochlear implant users: Pilot data

The overall goal of this study was to identify an objective physiological correlate of electric-acoustic pitch matching in unilaterally implanted cochlear implant (CI) participants with residual hearing in the non-implanted ear. Electrical and acoustic stimuli were presented in a continuously alternating fashion across ears. The acoustic stimulus and the electrical stimulus were either matched or mismatched in pitch. Auditory evoked potentials were obtained from nine CI users. Results indicated that N1 latency was stimulus-dependent, decreasing when the acoustic frequency of the tone presented to the non-implanted ear was increased. More importantly, there was an additional decrease in N1 latency in the pitch-matched condition. These results indicate the potential utility of N1 latency as an index of pitch matching in CI users.

A mismatch negativity study in Mandarin-speaking children with sensorineural hearing loss

OBJECTIVE

a) To examine the effects of sensorineural hearing loss on the discriminability of linguistic and non-linguistic stimuli at the cortical level, and b) to examine whether the cortical responses differ based on the chronological age at intervention, the degree of hearing loss, or the acoustic stimulation mode in children with severe and profound hearing loss.

METHODS

Mismatch negativity (MMN) responses were collected from 43 children with severe and profound bilateral sensorineural hearing loss, and 20 children with normal hearing (age: 3-6 years). In the non-verbal stimulation condition, pure tones with frequencies of 1 kHz and 1.1 kHz were used as the standard and the deviant respectively. In the verbal stimulation condition, the Chinese mandarin tokens/ba2/and/ba4/were used as the standard and the deviant respectively. Latency and amplitude of the MMN responses were collected and analyzed.

RESULTS

Overall, children with hearing loss showed longer latencies and lower amplitudes of the MMN responses to both non-verbal and verbal stimulations. The latency of the verbal/ba2/-/ba4/pair was longer than that of the nonverbal 1 kHz-1.1 kHz pair in both groups of children.

CONCLUSIONS

Children with hearing loss, especially those who received intervention after 2 years of age, showed substantial weakness in the neural responses to lexical tones and pure tones. Thus, the chronological age when the children receive hearing intervention may have an impact on the effectiveness of discriminating between verbal and non-verbal signals.

Bilateral cochlear implants in children: Effects of auditory experience and deprivation on auditory perception

Spatial hearing skills are essential for children as they grow, learn and play. These skills provide critical cues for determining the locations of sources in the environment, and enable segregation of important sounds, such as speech, from background maskers or interferers. Spatial hearing depends on availability of monaural cues and binaural cues. The latter result from integration of inputs arriving at the two ears from sounds that vary in location. The binaural system has exquisite mechanisms for capturing differences between the ears in both time of arrival and intensity. The major cues that are thus referred to as being vital for binaural hearing are: interaural differences in time (ITDs) and interaural differences in levels (ILDs). In children with normal hearing (NH), spatial hearing abilities are fairly well developed by age 4-5 years. In contrast, most children who are deaf and hear through cochlear implants (CIs) do not have an opportunity to experience normal, binaural acoustic hearing early in life. These children may function by having to utilize auditory cues that are degraded with regard to numerous stimulus features. In recent years there has been a notable increase in the number of children receiving bilateral CIs, and evidence suggests that while having two CIs helps them function better than when listening through a single CI, these children generally perform worse than their NH peers. This paper reviews some of the recent work on bilaterally implanted children. The focus is on measures of spatial hearing, including sound localization, release from masking for speech understanding in noise and binaural sensitivity using research processors. Data from behavioral and electrophysiological studies are included, with a focus on the recent work of the authors and their collaborators. The effects of auditory plasticity and deprivation on the emergence of binaural and spatial hearing are discussed along with evidence for reorganized processing from both behavioral and electrophysiological studies. The consequences of both unilateral and bilateral auditory deprivation during development suggest that the relevant set of issues is highly complex with regard to successes and the limitations experienced by children receiving bilateral cochlear implants. This article is part of a Special Issue entitled .

The relationship between cortical auditory evoked potentials (CAEPs) and speech perception in children with Nurotron(®) cochlear implants during four years of follow-up

OBJECTIVE

The purpose of the current study was to evaluate the relationship between the presence or absence of cortical auditory evoked potentials (CAEPs) to speech stimuli and the performance of speech perception in Chinese pediatric recipients of the Nurotron(®) cochlear implant (CI).We also wanted to determine how the CAEPs might be used as an indicator for predicting early speech perception and could provide objective evidence for clinical applications of CAEPs.

METHODS

23 pediatric unilateral CI recipients participated in this study. 15 males 8 females, and their ages at implantation ranged from 13 to 68 months, with a mean age of 36 months. CAEPs and Mandarin Early Speech Perception (MESP) tests were used to evaluate the audibility and speech perception of these CI users. The tests were administered at the first, second, third, and fourth year after the CI surgery.

RESULTS

All the subjects demonstrated improvements in detection of speech sounds with CI. The percentages of participants who could detect all three stimuli were 26% (6/23) at first year, to 100% (23/23) at the fourth year post-implantation. The percentages of participants who passed the Category 6 of MESP were from 9% (2/23) at first year, to 91% (21/23) at the fourth year post-implantation. Significant correlations (p<0.05) were found between CAEP scores and MESP at the first, second, third year after the CI surgery. The multiple regression equation for prediction of MESP categories from CAEP scores and hearing ages was MESP=1.088+(0.504×CAEP score)+(0.964×hearing ages) (F=72.919, p<0.001, R(2)=0.621).

CONCLUSION

The results of this study suggested that aided cortical assessment was a useful tool to evaluate the outcomes of cochlear implantation. Cortical outcomes had a significant positive relationship with the MESP, which predicted the early speech perception of CI recipients.

Early unilateral cochlear implantation promotes mature cortical asymmetries in adolescents who are deaf

Unilateral cochlear implant (CI) stimulation establishes hearing to children who are deaf but compromises bilateral auditory development if a second implant is not provided within ∼ 1.5 years. In this study we asked: 1) What are the cortical consequences of missing this early sensitive period once children reach adolescence? 2) What are the effects of unilateral deprivation on the pathways from the opposite ear? Cortical responses were recorded from 64-cephalic electrodes within the first week of bilateral CI activation in 34 adolescents who had over 10 years of unilateral right CI experience and in 16 normal hearing peers. Cortical activation underlying the evoked peaks was localized to areas of the brain using beamformer imaging. The first CI evoked activity which was more strongly lateralized to the contralateral left hemisphere than normal, with abnormal recruitment of the left prefrontal cortex (involved in cognition/attention), left temporo-parietal-occipital junction (multi-modal integration), and right precuneus (visual processing) region. CI stimulation in the opposite deprived ear evoked atypical cortical responses with abnormally large and widespread dipole activity across the cortex. Thus, using a unilateral CI to hear beyond the period of cortical maturation causes lasting asymmetries in the auditory system, requires recruitment of additional cortical areas to support hearing, and does little to protect the unstimulated pathways from effects of auditory deprivation. The persistence of this reorganization into maturity could signal a closing of a sensitive period for promoting auditory development on the deprived side.

Binaural fusion and listening effort in children who use bilateral cochlear implants: a psychoacoustic and pupillometric study

Bilateral cochlear implants aim to provide hearing to both ears for children who are deaf and promote binaural/spatial hearing. Benefits are limited by mismatched devices and unilaterally-driven development which could compromise the normal integration of left and right ear input. We thus asked whether children hear a fused image (ie. 1 vs 2 sounds) from their bilateral implants and if this “binaural fusion” reduces listening effort. Binaural fusion was assessed by asking 25 deaf children with cochlear implants and 24 peers with normal hearing whether they heard one or two sounds when listening to bilaterally presented acoustic click-trains/electric pulses (250 Hz trains of 36 ms presented at 1 Hz). Reaction times and pupillary changes were recorded simultaneously to measure listening effort. Bilaterally implanted children heard one image of bilateral input less frequently than normal hearing peers, particularly when intensity levels on each side were balanced. Binaural fusion declined as brainstem asymmetries increased and age at implantation decreased. Children implanted later had access to acoustic input prior to implantation due to progressive deterioration of hearing. Increases in both pupil diameter and reaction time occurred as perception of binaural fusion decreased. Results indicate that, without binaural level cues, children have difficulty fusing input from their bilateral implants to perceive one sound which costs them increased listening effort. Brainstem asymmetries exacerbate this issue. By contrast, later implantation, reflecting longer access to bilateral acoustic hearing, may have supported development of auditory pathways underlying binaural fusion. Improved integration of bilateral cochlear implant signals for children is required to improve their binaural hearing.

Altered cortical activity in prelingually deafened cochlear implant users following long periods of auditory deprivation

Auditory stimulation during childhood is critical for the development of the auditory cortex in humans and with that for hearing in adulthood. Age-related changes in morphology and peak latencies of the cortical auditory evoked potential (CAEP) have led to the use of this cortical response as a biomarker of auditory cortical maturation including studies of cortical development after deafness and subsequent cochlear implantation. To date, it is unknown whether prelingually deaf adults, with early onset deafness (before the age of 2 years) and who received a cochlear implant (CI) only during adulthood, would display absent or aberrant CAEP waveforms as predicted from CAEP studies in late implanted prelingually deaf children. In the current study, CAEP waveforms were recorded in response to electric stimuli in prelingually deaf adults, who received their CI after the age of 21 years. Waveform morphology and peak latencies were compared to the CAEP responses obtained in postlingually deaf adults, who became deaf after the age of 16. Unexpectedly, typical CAEP waveforms with adult-like P1-N1-P2 morphology could be recorded in the prelingually deaf adult CI users. On visual inspection, waveform morphology was comparable to the CAEP waveforms recorded in the postlingually deaf CI users. Interestingly, however, latencies of the N1 peak were significantly shorter and amplitudes were significantly larger in the prelingual group than in the postlingual group. The presence of the CAEP together with an early and large N1 peak might represent activation of the more innate and less complex components of the auditory cortex of the prelingually deaf CI user, whereas the CAEP in postlingually deaf CI users might reflect activation of the mature neural network still present in these patients. The CAEPs may therefore be helpful in the assessment of developmental state of the auditory cortex.

Long latency auditory evoked potentials in children with cochlear implants: systematic review

The aim of this study was to analyze the findings on Cortical Auditory Evoked Potentials in children with cochlear implant through a systematic literature review. After formulation of research question and search of studies in four data bases with the following descriptors: electrophysiology (eletrofisiologia), cochlear implantation (implante coclear), child (criança), neuronal plasticity (plasticidade neuronal) and audiology (audiologia), were selected articles (original and complete) published between 2002 and 2013 in Brazilian Portuguese or English. A total of 208 studies were found; however, only 13 contemplated the established criteria and were further analyzed; was made data extraction for analysis of methodology and content of the studies. The results described suggest rapid changes in P1 component of Cortical Auditory Evoked Potentials in children with cochlear implants. Although there are few studies on the theme, cochlear implant has been shown to produce effective changes in central auditory path ways especially in children implanted before 3 years and 6 months of age.

Benefits and detriments of unilateral cochlear implant use on bilateral auditory development in children who are deaf

We have explored both the benefits and detriments of providing electrical input through a cochlear implant in one ear to the auditory system of young children. A cochlear implant delivers electrical pulses to stimulate the auditory nerve, providing children who are deaf with access to sound. The goals of implantation are to restrict reorganization of the deprived immature auditory brain and promote development of hearing and spoken language. It is clear that limiting the duration of deprivation is a key factor. Additional considerations are the onset, etiology, and use of residual hearing as each of these can have unique effects on auditory development in the pre-implant period. New findings show that many children receiving unilateral cochlear implants are developing mature-like brainstem and thalamo-cortical responses to sound with long term use despite these sources of variability; however, there remain considerable abnormalities in cortical function. The most apparent, determined by implanting the other ear and measuring responses to acute stimulation, is a loss of normal cortical response from the deprived ear. Recent data reveal that this can be avoided in children by early implantation of both ears simultaneously or with limited delay. We conclude that auditory development requires input early in development and from both ears.