What's to lose and what's to learn: Development under auditory deprivation, cochlear implants and limits of cortical plasticity

Layer-specific enhancement of visual-evoked activity in the audiovisual cortex following a mild degree of hearing loss in adult rats

Following adult-onset hearing impairment, crossmodal plasticity can occur within various sensory cortices, often characterized by increased neural responses to visual stimulation in not only the auditory cortex, but also in the visual and audiovisual cortices. In the present study, we used an established model of loud noise exposure in rats to examine, for the first time, whether the crossmodal plasticity in the audiovisual cortex that occurs following a relatively mild degree of hearing loss emerges solely from altered intracortical processing or if thalamocortical changes also contribute to the crossmodal effects. Using a combination of an established pharmacological 'cortical silencing' protocol and current source density analysis of the laminar activity recorded across the layers of the audiovisual cortex (i.e., the lateral extrastriate visual cortex, V2L), we observed layer-specific changes post-silencing in the strength of the residual visual, but not auditory, input in the noise exposed rats with mild hearing loss compared to rats with normal hearing. Furthermore, based on a comparison of the laminar profiles pre- versus post-silencing in both groups, we can conclude that noise exposure caused a re-allocation of the strength of visual inputs across the layers of the V2L cortex, including enhanced visual-evoked activity in the granular layer; findings consistent with thalamocortical plasticity. Finally, we confirmed that audiovisual integration within the V2L cortex depends on intact processing within intracortical circuits, and that this form of multisensory processing is vulnerable to disruption by noise-induced hearing loss. Ultimately, the present study furthers our understanding of the contribution of intracortical and thalamocortical processing to crossmodal plasticity as well as to audiovisual integration under both normal and mildly-impaired hearing conditions.

Sensory Stimulation-dependent Npas4 Expression in the Olfactory Bulb during Early Postnatal Development

The development of the olfactory system is influenced by sensory inputs, and it maintains neuronal generation and plasticity throughout the lifespan. The olfactory bulb contains a higher proportion of interneurons than other brain regions, particularly during the early postnatal period of neurogenesis. Although the relationship between sensory stimulation and olfactory bulb development during the postnatal period has been well studied, the molecular mechanisms have yet to be identified. In this study, we used western blotting and immunohistochemistry to analyze the expression of the transcription factor Npas4, a neuron-specific immediate-early gene that acts as a developmental regulator in many brain regions. We found that Npas4 is highly expressed in olfactory bulb interneurons during the early postnatal stages and gradually decreases toward the late postnatal stages. Npas4 expression was observed in all olfactory bulb layers, including the rostral migratory stream, where newborn neurons are generated and migrate to the olfactory bulb. Under sensory deprivation, the olfactory bulb size and the number of olfactory bulb interneurons were reduced. Furthermore, Npas4 expression and the expression of putative Npas4 downstream molecules were decreased. Collectively, these findings indicate that Npas4 expression induced by sensory input plays a role in the formation of neural circuits with excitatory mitral/tufted cells by regulating the survival of olfactory bulb interneurons during the early stages of postnatal development.

Connectome alterations following perinatal deafness in the cat

Following sensory deprivation, areas and networks in the brain may adapt and reorganize to compensate for the loss of input. These adaptations are manifestations of compensatory crossmodal plasticity, which has been documented in both human and animal models of deafness-including the domestic cat. Although there are abundant examples of structural plasticity in deaf felines from retrograde tracer-based studies, there is a lack of diffusion-based knowledge involving this model compared to the current breadth of human research. The purpose of this study was to explore white matter structural adaptations in the perinatally-deafened cat via tractography, increasing the methodological overlap between species. Plasticity was examined by identifying unique group connections and assessing altered connectional strength throughout the entirety of the brain. Results revealed a largely preserved connectome containing a limited number of group-specific or altered connections focused within and between sensory networks, which is generally corroborated by deaf feline anatomical tracer literature. Furthermore, five hubs of cortical plasticity and altered communication following perinatal deafness were observed. The limited differences found in the present study suggest that deafness-induced crossmodal plasticity is largely built upon intrinsic structural connections, with limited remodeling of underlying white matter.

Short-Term Effect of Auditory Stimulation on Neural Activities: A Scoping Review of Longitudinal Electroencephalography and Magnetoencephalography Studies

Explored through EEG/MEG, auditory stimuli function as a suitable research probe to reveal various neural activities, including event-related potentials, brain oscillations and functional connectivity. Accumulating evidence in this field stems from studies investigating neuroplasticity induced by long-term auditory training, specifically cross-sectional studies comparing musicians and non-musicians as well as longitudinal studies with musicians. In contrast, studies that address the neural effects of short-term interventions whose duration lasts from minutes to hours are only beginning to be featured. Over the past decade, an increasing body of evidence has shown that short-term auditory interventions evoke rapid changes in neural activities, and oscillatory fluctuations can be observed even in the prestimulus period. In this scoping review, we divided the extracted neurophysiological studies into three groups to discuss neural activities with short-term auditory interventions: the pre-stimulus period, during stimulation, and a comparison of before and after stimulation. We show that oscillatory activities vary depending on the context of the stimuli and are greatly affected by the interplay of bottom-up and top-down modulational mechanisms, including attention. We conclude that the observed rapid changes in neural activitiesin the auditory cortex and the higher-order cognitive part of the brain are causally attributed to short-term auditory interventions.

Features of the speech processing network in post- and prelingually deaf cochlear implant users

The onset of hearing loss can lead to altered brain structure and functions. However, hearing restoration may also result in distinct cortical reorganization. A differential pattern of functional remodeling was observed between post- and prelingual cochlear implant users, but it remains unclear how these speech processing networks are reorganized after cochlear implantation. To explore the impact of language acquisition and hearing restoration on speech perception in cochlear implant users, we conducted assessments of brain activation, functional connectivity, and graph theory-based analysis using functional near-infrared spectroscopy. We examined the effects of speech-in-noise stimuli on three groups: postlingual cochlear implant users (n = 12), prelingual cochlear implant users (n = 10), and age-matched individuals with hearing controls (HC) (n = 22). The activation of auditory-related areas in cochlear implant users showed a lower response compared with the HC group. Wernicke's area and Broca's area demonstrated differences network attributes in speech processing networks in post- and prelingual cochlear implant users. In addition, cochlear implant users maintain a high efficiency of the speech processing network to process speech information. Taken together, our results characterize the speech processing networks, in varying noise environments, in post- and prelingual cochlear implant users and provide new insights for theories of how implantation modes impact remodeling of the speech processing functional networks.

Comparison of Tonotopic and Default Frequency Fitting for Speech Understanding in Noise in New Cochlear Implantees: A Prospective, Randomized, Double-Blind, Cross-Over Study

OBJECTIVES

While cochlear implants (CIs) have provided benefits for speech recognition in quiet for subjects with severe-to-profound hearing loss, speech recognition in noise remains challenging. A body of evidence suggests that reducing frequency-to-place mismatch may positively affect speech perception. Thus, a fitting method based on a tonotopic map may improve speech perception results in quiet and noise. The aim of our study was to assess the impact of a tonotopic map on speech perception in noise and quiet in new CI users.

DESIGN

A prospective, randomized, double-blind, two-period cross-over study in 26 new CI users was performed over a 6-month period. New CI users older than 18 years with bilateral severe-to-profound sensorineural hearing loss or complete hearing loss for less than 5 years were selected in the University Hospital Centre of Rennes in France. An anatomical tonotopic map was created using postoperative flat-panel computed tomography and a reconstruction software based on the Greenwood function. Each participant was randomized to receive a conventional map followed by a tonotopic map or vice versa. Each setting was maintained for 6 weeks, at the end of which participants performed speech perception tasks. The primary outcome measure was speech recognition in noise. Participants were allocated to sequences by block randomization of size two with a ratio 1:1 (CONSORT Guidelines). Participants and those assessing the outcomes were blinded to the intervention.

RESULTS

Thirteen participants were randomized to each sequence. Two of the 26 participants recruited (one in each sequence) had to be excluded due to the COVID-19 pandemic. Twenty-four participants were analyzed. Speech recognition in noise was significantly better with the tonotopic fitting at all signal-to-noise ratio (SNR) levels tested [SNR = +9 dB, p = 0.002, mean effect (ME) = 12.1%, 95% confidence interval (95% CI) = 4.9 to 19.2, standardized effect size (SES) = 0.71; SNR = +6 dB, p < 0.001, ME = 16.3%, 95% CI = 9.8 to 22.7, SES = 1.07; SNR = +3 dB, p < 0.001 ME = 13.8%, 95% CI = 6.9 to 20.6, SES = 0.84; SNR = 0 dB, p = 0.003, ME = 10.8%, 95% CI = 4.1 to 17.6, SES = 0.68]. Neither period nor interaction effects were observed for any signal level. Speech recognition in quiet ( p = 0.66) and tonal audiometry ( p = 0.203) did not significantly differ between the two settings. 92% of the participants kept the tonotopy-based map after the study period. No correlation was found between speech-in-noise perception and age, duration of hearing deprivation, angular insertion depth, or position or width of the frequency filters allocated to the electrodes.

CONCLUSION

For new CI users, tonotopic fitting appears to be more efficient than the default frequency fitting because it allows for better speech recognition in noise without compromising understanding in quiet.

Explaining neurological factors of hearing loss through digital technologies

The study investigated how inclusion of the considerable amount of knowledge generated through basic research in multisensory experiences can be brought into clinical paediatric audiology with a specific focus to enhance understanding of the neurological implications of childhood hearing loss.

OBJECTIVES

The overall aim of the project was to investigate how to use emerging technologies to enhance the understanding of the neurological impact of paediatric hearing loss. The specific objectives were to develop an app and to evaluate its ease of use and the understanding of neurology by all types of stakeholders and end-users.

METHODS

A collaborative participatory and human centred research design was used. This methodological approach brought stakeholders into the design process at an early point of time and workshops mapped the content and interaction of the iterative development of the app. Nine clinicians from Copenhagen Hearing and Balance Centre and 4 media technologists from Multisensory Experience Lab participated in the development of the app-prototype. Evaluations were made by use of questionnaires completed by stakeholders and end-users and focus group interviews. Eight parents with children with hearing loss, 13 internal stakeholders and 14 external stakeholders participated in the evaluation of the app.

RESULTS

The app was overall positively evaluated. End users/parents with children with hearing loss were slightly more positive than stakeholders/professionals in audiology.

CONCLUSIONS

Apps are a future media for providing health care information and it proved both relevant and applicable to start using apps also to provide complex information such as neurological implications of childhood hearing loss.

Beyond the Sound Waves: A Comprehensive Exploration of the Burn-In Phenomenon in Audio Equipment Across Physiological, Psychological, and Societal Domains

Audio burn-in, often referred to as the process by which audio equipment undergoes a series of played sounds to achieve optimal performance, remains a topic of significant debate within both audiophile communities and relevant scientific fields. While some attribute perceived changes in sound quality to actual physical changes in the equipment, an emerging perspective points to the interplay of physiological, psychological, and social factors that might influence these perceptions. This narrative review delves into the intricate layers of auditory physiology, cognitive sound interpretation, and the wider societal beliefs around burn-in. We underscore the importance of discerning between actual physical changes in audio gear and the multifaceted human factors that potentially modulate our perception of sound. Through a comprehensive exploration, this article illuminates the complexities of this phenomenon, offering insights for both medical professionals and passionate audio enthusiasts and proposing directions for future research.

Exploring Factors That Contribute to the Success of Rehabilitation With Hearing Aids

OBJECTIVES

Hearing aids are an essential and important part of hearing rehabilitation. The combination of technical data on hearing aids and individual rehabilitation needs can give insight into the factors that contribute to the success of rehabilitation. This study sets out to investigate if different subgroups of (comparable) hearing aids lead to differences in the success of rehabilitation, and whether these differences vary between different domains of auditory functioning.

DESIGN

This study explored the advantages of including patient-reported outcome measures (PROMs) in the process of purchasing new hearing aids in a large sample of successful hearing aid users. Subject data were obtained from 64 (commercial) hearing aid dispensers and 10 (noncommercial) audiological centers in the Netherlands. The PROM was a 32-item questionnaire and was used to determine the success of rehabilitation using hearing aids by measuring auditory disability over time. The items were mapped on six domains of auditory functioning: detection, discrimination, localization, speech in quiet, speech in noise, and noise tolerance, encompassing a variety of daily-life listening situations. Hearing aids were grouped by means of cluster analysis, resulting in nine subgroups. In total, 1149 subjects were included in this study. A general linear model was used to model the final PROM results. Model results were analyzed via a multifactor Analysis of Variance. Post hoc analyses provided detailed information on model variables.

RESULTS

Results showed a strong statistically significant effect of hearing aids on self-perceived auditory functioning in general. Clinically relevant differences were found for auditory domains including detection, speech in quiet, speech in noise, and localization. There was only a small, but significant, effect of the different subgroups of hearing aids on the final PROM results, where no differences were found between the auditory domains. Minor differences were found between results obtained in commercial and noncommercial settings, or between novice and experienced users. Severity of Hearing loss, age, gender, and hearing aid style (i.e., behind-the-ear versus receiver-in-canal type) did not have a clinically relevant effect on the final PROM results.

CONCLUSIONS

The use of hearing aids has a large positive effect on self-perceived auditory functioning. There was however no salient effect of the different subgroups of hearing aids on the final PROM results, indicating that technical properties of hearing aids only play a limited role in this respect. This study challenges the belief that premium devices outperform basic ones, highlighting the need for personalized rehabilitation strategies and the importance of evaluating factors contributing to successful rehabilitation for clinical practice.

Cochlear implantation in unilateral hearing loss: impact of short- to medium-term auditory deprivation

Introduction

Single sided deafness (SSD) results in profound cortical reorganization that presents clinically with a significant impact on sound localization and speech comprehension. Cochlear implantation (CI) has been approved for two manufacturers' devices in the United States to restore bilateral function in SSD patients with up to 10 years of auditory deprivation. However, there is great variability in auditory performance and it remains unclear how auditory deprivation affects CI benefits within this 10-year window. This prospective study explores how measured auditory performance relates to real-world experience and device use in a cohort of SSD-CI subjects who have between 0 and 10 years of auditory deprivation.

Methods

Subjects were assessed before implantation and 3-, 6-, and 12-months post-CI activation via Consonant-Nucleus-Consonant (CNC) word recognition and Arizona Biomedical Institute (AzBio) sentence recognition in varying spatial speech and noise presentations that simulate head shadow, squelch, and summation effects (S0N0, SSSDNNH, SNHNSSD; 0 = front, SSD = impacted ear, NH = normal hearing ear). Patient-centered assessments were performed using Tinnitus Handicap Inventory (THI), Spatial Hearing Questionnaire (SHQ), and Health Utility Index Mark 3 (HUI3). Device use data was acquired from manufacturer software. Further subgroup analysis was performed on data stratified by <5 years and 5-10 years duration of deafness.

Results

In the SSD ear, median (IQR) CNC word scores pre-implant and at 3-, 6-, and 12-months post-implant were 0% (0-0%), 24% (8-44%), 28% (4-44%), and 18% (7-33%), respectively. At 6 months post-activation, AzBio scores in S0N0 and SSSDNNH configurations (n = 25) demonstrated statistically significant increases in performance by 5% (p = 0.03) and 20% (p = 0.005), respectively. The median HUI3 score was 0.56 pre-implant, lower than scores for common conditions such as anxiety (0.68) and diabetes (0.77), and comparable to stroke (0.58). Scores improved to 0.83 (0.71-0.91) by 3  months post-activation. These audiologic and subjective benefits were observed even in patients with longer durations of deafness.

Discussion

By merging CI-associated changes in objective and patient-centered measures of auditory function, our findings implicate central mechanisms of auditory compensation and adaptation critical in auditory performance after SSD-CI and quantify the extent to which they affect the real-world experience reported by individuals.

An imbalance of excitation and inhibition in the multisensory cortex impairs the temporal acuity of audiovisual processing and perception

The neural integration of closely timed auditory and visual stimuli can offer several behavioral advantages; however, an overly broad window of temporal integration-a phenomenon observed in various neurodevelopmental disorders-could have far-reaching perceptual consequences. Non-invasive studies in humans have suggested that the level of GABAergic inhibition in the multisensory cortex influences the temporal window over which auditory and visual stimuli are bound into a unified percept. Although this suggestion aligns with the theory that an imbalance of cortical excitation and inhibition alters multisensory processing, no prior studies have performed experimental manipulations to determine the causal effects of a reduction of GABAergic inhibition on audiovisual temporal perception. To that end, we used a combination of in vivo electrophysiology, neuropharmacology, and translational behavioral testing in rats to provide the first mechanistic evidence that a reduction of GABAergic inhibition in the audiovisual cortex is sufficient to disrupt unisensory and multisensory processing across the cortical layers, and ultimately impair the temporal acuity of audiovisual perception and its rapid adaptation to recent sensory experience. Looking forward, our findings provide support for using rat models to further investigate the neural mechanisms underlying the audiovisual perceptual alterations observed in neurodevelopmental disorders, such as autism, schizophrenia, and dyslexia.

Early retinal deprivation crossmodally alters nascent subplate circuits and activity in the auditory cortex during the precritical period

Sensory perturbation in one modality results in the adaptive reorganization of neural pathways within the spared modalities, a phenomenon known as "crossmodal plasticity," which has been examined during or after the classic "critical period." Because peripheral perturbations can alter the auditory cortex (ACX) activity and functional connectivity of the ACX subplate neurons (SPNs) even before the critical period, called the precritical period, we investigated if retinal deprivation at birth crossmodally alters the ACX activity and SPN circuits during the precritical period. We deprived newborn mice of visual inputs after birth by performing bilateral enucleation. We performed in vivo widefield imaging in the ACX of awake pups during the first two postnatal weeks to investigate cortical activity. We found that enucleation alters spontaneous and sound-evoked activities in the ACX in an age-dependent manner. Next, we performed whole-cell patch clamp recording combined with laser scanning photostimulation in ACX slices to investigate circuit changes in SPNs. We found that enucleation alters the intracortical inhibitory circuits impinging on SPNs, shifting the excitation-inhibition balance toward excitation and this shift persists after ear opening. Together, our results indicate that crossmodal functional changes exist in the developing sensory cortices at early ages before the onset of the classic critical period.

Cochlear implants: the effects of age on outcomes

INTRODUCTION

Cochlear implants (CIs) provide access to sound for children and adults who do not receive adequate benefit from hearing aids. Age at implantation is known to affect outcomes across the lifespan.

AREAS COVERED

The effects of age on CI outcomes are examined for infants, children, adolescents, and older adults. A variety of outcome measures are considered, including speech perception, language, cognition, and quality of life measures.

EXPERT OPINION/COMMENTARY

For those meeting candidacy criteria, CIs are beneficial at any age. In general, younger age is related to greater benefit when considering pre-lingual deafness. Other factors such as additional disabilities, may mitigate this effect. Post-lingually deafened adults demonstrate similar benefit regardless of age, though the oldest individuals (80+) may see smaller degrees of improvement from preoperative scores. Benefit can be measured in many ways, and the areas of greatest benefit may vary based on age: young children appear to see the greatest effects of age at implantation on language measures, whereas scores on cognitive measures appear to be most impacted for the oldest population. Future research should consider implantation at extreme ages (5-9 months or > 90 years), unconventional measures of CI benefit including qualitative assessments, and longitudinal designs.

Early retinal deprivation crossmodally alters nascent subplate circuits and activity in the auditory cortex during the precritical period

Sensory perturbation in one modality results in adaptive reorganization of neural pathways within the spared modalities, a phenomenon known as "crossmodal plasticity", which has been examined during or after the classic 'critical period'. Because peripheral perturbations can alter auditory cortex (ACX) activity and functional connectivity of the ACX subplate neurons (SPNs) even before the classic critical period, called the precritical period, we investigated if retinal deprivation at birth crossmodally alters ACX activity and SPN circuits during the precritical period. We deprived newborn mice of visual inputs after birth by performing bilateral enucleation. We performed in vivo imaging in the ACX of awake pups during the first two postnatal weeks to investigate cortical activity. We found that enucleation alters spontaneous and sound-evoked activity in the ACX in an age-dependent manner. Next, we performed whole-cell patch clamp recording combined with laser scanning photostimulation in ACX slices to investigate circuit changes in SPNs. We found that enucleation alters the intracortical inhibitory circuits impinging on SPNs shifting the excitation-inhibition balance towards excitation and this shift persists after ear opening. Together, our results indicate that crossmodal functional changes exist in the developing sensory cortices at early ages before the onset of the classic critical period.

Cortical and thalamic modulation of auditory gating in the posterior parietal cortex of awake mice

Auditory gating (AG) is an adaptive mechanism for filtering out redundant acoustic stimuli to protect the brain against information overload. AG deficits have been found in many mental illnesses, including schizophrenia (SZ). However, the neural correlates of AG remain poorly understood. Here, we found that the posterior parietal cortex (PPC) shows an intermediate level of AG in auditory thalamocortical circuits, with a laminar profile in which the strongest AG is in the granular layer. Furthermore, AG of the PPC was decreased and increased by optogenetic inactivation of the medial dorsal thalamic nucleus (MD) and auditory cortex (AC), respectively. Optogenetically activating the axons from the MD and AC drove neural activities in the PPC without an obvious AG. These results indicated that AG in the PPC is determined by the integrated signal streams from the MD and AC in a bottom-up manner. We also found that a mouse model of SZ (postnatal administration of noncompetitive N-methyl-d-aspartate receptor antagonist) presented an AG deficit in the PPC, which may be inherited from the dysfunction of MD. Together, our findings reveal a neural circuit underlying the generation of AG in the PPC and its involvement in the AG deficit of SZ.

Phoneme Categorization in Prelingually Deaf Adult Cochlear Implant Users

PURPOSE

Phoneme categorization (PC) for voice onset time and second formant transition was studied in adult cochlear implant (CI) users with early-onset deafness and hearing controls.

METHOD

Identification and discrimination tasks were administered to 30 participants implanted before 4 years of age, 21 participants implanted after 7 years of age, and 21 hearing individuals.

RESULTS

Distinctive identification and discrimination functions confirmed PC within all groups. Compared to hearing participants, the CI groups generally displayed longer/higher category boundaries, shallower identification function slopes, reduced identification consistency, and reduced discrimination performance. A principal component analysis revealed that identification consistency, discrimination accuracy, and identification function slope, but not boundary location, loaded on a single factor, reflecting general PC performance. Earlier implantation was associated with better PC performance within the early CI group, but not the late CI group. Within the early CI group, earlier implantation age but not PC performance was associated with better speech recognition. Conversely, within the late CI group, better PC performance but not earlier implantation age was associated with better speech recognition.

CONCLUSIONS

Results suggest that implantation timing within the sensitive period before 4 years of age partly determines the level of PC performance. They also suggest that early implantation may promote development of higher level processes that can compensate for relatively poor PC performance, as can occur in challenging listening conditions.

Gamma-Band Modulation in Parietal Area as the Electroencephalographic Signature for Performance in Auditory-Verbal Working Memory: An Exploratory Pilot Study in Hearing and Unilateral Cochlear Implant Children

This pilot study investigates the neurophysiological patterns of visual and auditory verbal working memory (VWM) in unilateral cochlear implant users (UCIs). We compared the task-related electroencephalogram (EEG) power spectral density of 7- to 13-year-old UCIs (n = 7) with a hearing control group (HC, n = 10) during the execution of a three-level n-back task with auditory and visual verbal (letters) stimuli. Performances improved as memory load decreased regardless of sensory modality (SM) and group factors. Theta EEG activation over the frontal area was proportionally influenced by task level; the left hemisphere (LH) showed greater activation in the gamma band, suggesting lateralization of VWM function regardless of SM. However, HCs showed stronger activation patterns in the LH than UCIs regardless of SM and in the parietal area (PA) during the most challenging audio condition. Linear regressions for gamma activation in the PA suggest the presence of a pattern-supporting auditory VWM only in HCs. Our findings seem to recognize gamma activation in the PA as the signature of effective auditory VWM. These results, although preliminary, highlight this EEG pattern as a possible cause of the variability found in VWM outcomes in deaf children, opening up new possibilities for interdisciplinary research and rehabilitation intervention.

Electrophysiological Examination of Ambient Speech Processing in Children With Cochlear Implants

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.

Cross-modal functional connectivity supports speech understanding in cochlear implant users

Sensory deprivation can lead to cross-modal cortical changes, whereby sensory brain regions deprived of input may be recruited to perform atypical function. Enhanced cross-modal responses to visual stimuli observed in auditory cortex of postlingually deaf cochlear implant (CI) users are hypothesized to reflect increased activation of cortical language regions, but it is unclear if this cross-modal activity is "adaptive" or "mal-adaptive" for speech understanding. To determine if increased activation of language regions is correlated with better speech understanding in CI users, we assessed task-related activation and functional connectivity of auditory and visual cortices to auditory and visual speech and non-speech stimuli in CI users (n = 14) and normal-hearing listeners (n = 17) and used functional near-infrared spectroscopy to measure hemodynamic responses. We used visually presented speech and non-speech to investigate neural processes related to linguistic content and observed that CI users show beneficial cross-modal effects. Specifically, an increase in connectivity between the left auditory and visual cortices-presumed primary sites of cortical language processing-was positively correlated with CI users' abilities to understand speech in background noise. Cross-modal activity in auditory cortex of postlingually deaf CI users may reflect adaptive activity of a distributed, multimodal speech network, recruited to enhance speech understanding.

Children's Neural Sensitivity to Prosodic Features of Natural Speech and Its Significance to Speech Development in Cochlear Implanted Children

Catchy utterances, such as proverbs, verses, and nursery rhymes (i.e., "No pain, no gain" in English), contain strong-prosodic (SP) features and are child-friendly in repeating and memorizing; yet the way those prosodic features encoded by neural activity and their influence on speech development in children are still largely unknown. Using functional near-infrared spectroscopy (fNIRS), this study investigated the cortical responses to the perception of natural speech sentences with strong/weak-prosodic (SP/WP) features and evaluated the speech communication ability in 21 pre-lingually deaf children with cochlear implantation (CI) and 25 normal hearing (NH) children. A comprehensive evaluation of speech communication ability was conducted on all the participants to explore the potential correlations between neural activities and children's speech development. The SP information evoked right-lateralized cortical responses across a broad brain network in NH children and facilitated the early integration of linguistic information, highlighting children's neural sensitivity to natural SP sentences. In contrast, children with CI showed significantly weaker cortical activation and characteristic deficits in speech perception with SP features, suggesting hearing loss at the early age of life, causing significantly impaired sensitivity to prosodic features of sentences. Importantly, the level of neural sensitivity to SP sentences was significantly related to the speech behaviors of all children participants. These findings demonstrate the significance of speech prosodic features in children's speech development.

Aging Affects Subcortical Pitch Information Encoding Differently in Humans With Different Language Backgrounds

Aging and language background have been shown to affect pitch information encoding at the subcortical level. To study the individual and compounded effects on subcortical pitch information encoding, Frequency Following Responses were recorded from subjects across various ages and language backgrounds. Differences were found in pitch information encoding strength and accuracy among the groups, indicating that language experience and aging affect accuracy and magnitude of pitch information encoding ability at the subcortical level. Moreover, stronger effects of aging were seen in the magnitude of phase-locking in the native language speaker groups, while language background appears to have more impact on the accuracy of pitch tracking in older adult groups.

Resting-state EEG reveals global network deficiency in prelingually deaf children with late cochlear implantation

There are individual differences in rehabilitation after cochlear implantation that can be explained by brain plasticity. However, from the perspective of brain networks, the effect of implantation age on brain plasticity is unclear. The present study investigated electroencephalography functional networks in the resting state, including eyes-closed and eyes-open conditions, in 31 children with early cochlear implantation, 24 children with late cochlear implantation, and 29 children with normal hearing. Resting-state functional connectivity was measured with phase lag index, and we investigated the connectivity between the sensory regions for each frequency band. Network topology was examined using minimum spanning tree to obtain the network backbone characteristics. The results showed stronger connectivity between auditory and visual regions but reduced global network efficiency in children with late cochlear implantation in the theta and alpha bands. Significant correlations were observed between functional backbone characteristics and speech perception scores in children with cochlear implantation. Collectively, these results reveal an important effect of implantation age on the extent of brain plasticity from a network perspective and indicate that characteristics of the brain network can reflect the extent of rehabilitation of children with cochlear implantation.

Age and Hearing Ability Influence Selective Attention During Childhood

OBJECTIVES

The purpose of the present study was to determine whether age and hearing ability influence selective attention during childhood. Specifically, we hypothesized that immaturity and disrupted auditory experience impede selective attention during childhood.

DESIGN

Seventy-seven school-age children (5 to 12 years of age) participated in this study: 61 children with normal hearing and 16 children with bilateral hearing loss who use hearing aids and/or cochlear implants. Children performed selective attention-based behavioral change detection tasks comprised of target and distractor streams in the auditory and visual modalities. In the auditory modality, children were presented with two streams of single-syllable words spoken by a male and female talker. In the visual modality, children were presented with two streams of grayscale images. In each task, children were instructed to selectively attend to the target stream, inhibit attention to the distractor stream, and press a key as quickly as possible when they detected a frequency (auditory modality) or color (visual modality) deviant stimulus in the target, but not distractor, stream. Performance on the auditory and visual change detection tasks was quantified by response sensitivity, which reflects children's ability to selectively attend to deviants in the target stream and inhibit attention to those in the distractor stream. Children also completed a standardized measure of attention and inhibitory control.

RESULTS

Younger children and children with hearing loss demonstrated lower response sensitivity, and therefore poorer selective attention, than older children and children with normal hearing, respectively. The effect of hearing ability on selective attention was observed across the auditory and visual modalities, although the extent of this group difference was greater in the auditory modality than the visual modality due to differences in children's response patterns. Additionally, children's performance on a standardized measure of attention and inhibitory control related to their performance during the auditory and visual change detection tasks.

CONCLUSIONS

Overall, the findings from the present study suggest that age and hearing ability influence children's ability to selectively attend to a target stream in both the auditory and visual modalities. The observed differences in response patterns across modalities, however, reveal a complex interplay between hearing ability, task modality, and selective attention during childhood. While the effect of age on selective attention is expected to reflect the immaturity of cognitive and linguistic processes, the effect of hearing ability may reflect altered development of selective attention due to disrupted auditory experience early in life and/or a differential allocation of attentional resources to meet task demands.

Cognitive decline in acoustic neuroma patients: An investigation based on resting-state functional magnetic resonance imaging and voxel-based morphometry

OBJECTIVE

Acoustic neuroma (AN) is a clinically common benign tumor. There are few neuropsychological investigations for AN, especially cognitive neuropsychology. Herein, the study probed into cognitive function changes in AN patients and expounded possible mechanisms through structural and functional magnetic resonance imaging (fMRI).

MATERIALS AND METHODS

Neuropsychological tests were performed between 64 patients with AN and 67 healthy controls. Then, using resting-state fMRI, the possible mechanisms of cognitive decline in AN patients were further explored by calculating the amplitude of low-frequency fluctuations (ALFF) and regional homogeneity (ReHo). Furthermore, using high-resolution T1-weighted images, voxel-based morphometry (VBM) was adopted to investigate the changes in gray matter volume (GMV) and white matter volume (WMV) in AN patients.

RESULTS

AN patients had worse cognitive performance than those in the healthy controls. Relative to the healthy individuals, the mALFF value was increased in the right caudate nucleus of the patients with left-sided AN (LAN) and the right rectus region of the patients with right-sided AN (RAN). The mReHo values of the bilateral superior frontal gyrus and middle frontal gyrus were decreased in LAN patients. Compared with healthy subjects, the GMV values were elevated in the left fusiform gyrus, parahippocampal gyrus, calcarine gyrus, and cuneus in LAN patients as well as in the right fusiform gyrus and parahippocampal gyrus in RAN patients. Meanwhile, the WMV values showed elevations in the bilateral putamen, left rectal gyrus, and thalamus in LAN patients.

CONCLUSION

Cognitive dysfunction occurs in AN patients. Cognitive decline in AN patients activates functional activity in some brain regions, thereby compensating for cognition decline. Additionally, the ReHo values were reduced in the frontal lobe in LAN patients, and the connectivity was decreased, affecting the functional differentiation and integration of the brain, which may be associated with the decline in cognitive function. Lateralized brain reorganization induced by unilateral hearing loss was presented in AN patients. LAN caused a more significant interference effect on the brain while RAN patients showed more stable cerebral cortices. Altogether, responding to cognition decline in AN patients, structural reorganization occurs, and compensative increases in cognitive-related brain regions, which compensates for cognitive impairment.

Cortical auditory evoked potentials with different acoustic stimuli: Evidence of differences and similarities in coding in auditory processing disorders

OBJECTIVES

The use of cortical auditory evoked potentials allows for the study of the processing of acoustic signals at the cortical level, an important step in the diagnostic evaluation process, and for the monitoring of the therapeutic process associated with auditory processing disorders (APD). The differences and similarities in the acoustic coding between different types of stimuli in the context of APD remain unknown to this date.

METHODS

A total of 37 children aged between 7 and 11 years, with and without APDs (identified based on verbal and non-verbal tests), all with a suitable intelligence quotient with respect to their chronological age, were assessed. Components P1 and N1 were studied using verbal and non-verbal stimuli.

RESULTS

The comparison between stimuli in each group revealed that the control group had higher latency and amplitude values for speech stimuli, except for the P1 amplitude, while the group with APDs had different results with respect to the amplitudes of P1 and N1, yielding higher values for speech sounds. The differences between the groups varied according to the type of stimulus: the difference was in amplitude for the verbal stimulus and latency for the non-verbal stimulus.

CONCLUSION

The records of components P1 and N1 revealed that the children with APDs performed the coding underlying the detection and identification of acoustic signals, whether verbal and non-verbal, according to a different pattern than the children in the control group.

Cortical Auditory Plasticity Following Cochlear Implantation in Children With Auditory Neuropathy Spectrum Disorder: A Prospective Study

OBJECTIVES

The cortical auditory evoked potential (CAEP) can provide an insight into the maturation of the central auditory nervous system by recording the auditory cortex responses to speech stimuli. This study aimed to explore the central auditory system development in children with auditory neuropathy spectrum disorder (ANSD) using cochlear implants (CIs) and to find the correlation of CAEP biomarkers with speech perception.

METHODS

This study was performed on 23 children with prelingual deafness, diagnosed with ANSD, as well as 23 children with prelingual deafness, without ANSD as the control group. All children underwent unilateral CI before the age of 3 years. Children with ANSD were classified into two groups, based on their CAEP results prior to implantation: children with a clear CAEP response (ANSD-I) and children without an identifiable CAEP (ANSD-II). The P1 component of CAEPs and speech intelligibility rating (SIR) were recorded before the initial device activation (baseline) and at 6, 12, and 24 months postimplantation.

RESULTS

The P1 CAEP responses were present in all children in the control group, while they were recorded in only 52% of ANSD children before the CI surgery. The longitudinal analysis revealed a significant reduction in the P1 latency and a significant improvement in the P1 amplitude across different time points in all study groups. However, the P1 latency and P1 amplitude were significantly shorter and larger in the control group than the ANSD group, respectively. Also, children in the ANSD-I group exhibited a slightly shorter P1 latency, a larger P1 amplitude, and a higher SIR score than the ANSD-II group after 2 years of follow-up. The P1 CAEP latency was significantly correlated with the SIR score.

CONCLUSION

The CAEP can be used as an objective indicator of auditory cortical maturation and a predictor of speech perception performance in implanted children with ANSD.

Cortical hemisphere preference and brainstem ear asymmetry reflect experience-dependent functional modulation of pitch

Temporal attributes of pitch processing at cortical and subcortical levels are differentially weighted and well-coordinated. The question is whether language experience induces functional modulation of hemispheric preference complemented by brainstem ear symmetry for pitch processing. Brainstem frequency-following and cortical pitch responses were recorded concurrently from Mandarin and English participants. A Mandarin syllable with a rising pitch contour was presented to both ears with monaural stimulation. At the cortical level, left ear stimulation in the Chinese group revealed an experience-dependent response for pitch processing in the right hemisphere, consistent with a functionalaccount. The English group revealed a contralateral hemisphere preference consistent with a structuralaccount. At the brainstem level, Chinese participants showed a functional leftward ear asymmetry, whereas English were consistent with a structural account. Overall, language experience modulates both cortical hemispheric preference and brainstem ear asymmetry in a complementary manner to optimize processing of temporal attributes of pitch.

The Critical Period Hypothesis for L2 Acquisition: An Unfalsifiable Embarrassment?

This article focuses on the uncertainty surrounding the issue of the Critical Period Hypothesis. It puts forward the case that, with regard to naturalistic situations, the hypothesis has the status of both “not proven” and unfalsified. The article analyzes a number of reasons for this situation, including the effects of multi-competence, which remove any possibility that competence in more than one language can ever be identical to monolingual competence. With regard to the formal instructional setting, it points to many decades of research showing that, as critical period advocates acknowledge, in a normal schooling situation, adolescent beginners in the long run do as well as younger beginners. The article laments the profusion of definitions of what the critical period for language actually is and the generally piecemeal nature of research into this important area. In particular, it calls for a fuller integration of recent neurolinguistic perspectives into discussion of the age factor in second language acquisition research.

Amount of Hearing Aid Use Impacts Neural Oscillatory Dynamics Underlying Verbal Working Memory Processing for Children With Hearing Loss

OBJECTIVES

Children with hearing loss (CHL) may exhibit spoken language delays and may also experience deficits in other cognitive domains including working memory. Consistent hearing aid use (i.e., more than 10 hours per day) ameliorates these language delays; however, the impact of hearing aid intervention on the neural dynamics serving working memory remains unknown. The objective of this study was to examine the association between the amount of hearing aid use and neural oscillatory activity during verbal working memory processing in children with mild-to-severe hearing loss.

DESIGN

Twenty-three CHL between 8 and 15 years-old performed a letter-based Sternberg working memory task during magnetoencephalography (MEG). Guardians also completed a questionnaire describing the participants' daily hearing aid use. Each participant's MEG data was coregistered to their structural MRI, epoched, and transformed into the time-frequency domain using complex demodulation. Significant oscillatory responses corresponding to working memory encoding and maintenance were independently imaged using beamforming. Finally, these whole-brain source images were correlated with the total number of hours of weekly hearing aid use, controlling for degree of hearing loss.

RESULTS

During the encoding period, hearing aid use negatively correlated with alpha-beta oscillatory activity in the bilateral occipital cortices and right precentral gyrus. In the occipital cortices, this relationship suggested that with greater hearing aid use, there was a larger suppression of occipital activity (i.e., more negative relative to baseline). In the precentral gyrus, greater hearing aid use was related to less synchronous activity (i.e., less positive relative to baseline). During the maintenance period, hearing aid use significantly correlated with alpha activity in the right prefrontal cortex, such that with greater hearing aid use, there was less right prefrontal maintenance-related activity (i.e., less positive relative to baseline).

CONCLUSIONS

This study is the first to investigate the impact of hearing aid use on the neural dynamics that underlie working memory function. These data show robust relationships between the amount of hearing aid use and phase-specific neural patterns during working memory encoding and maintenance after controlling for degree of hearing loss. Furthermore, our data demonstrate that wearing hearing aids for more than ~8.5 hours/day may serve to normalize these neural patterns. This study also demonstrates the potential for neuroimaging to help determine the locus of variability in outcomes in CHL.

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.

Oscillatory signatures of Repetition Suppression and Novelty Detection reveal altered induced visual responses in early deafness

The ability to differentiate between repeated and novel events represents a fundamental property of the visual system. Neural responses are typically reduced upon stimulus repetition, a phenomenon called Repetition Suppression (RS). On the contrary, following a novel visual stimulus, the neural response is generally enhanced, a phenomenon referred to as Novelty Detection (ND). Here, we aimed to investigate the impact of early deafness on the oscillatory signatures of RS and ND brain responses. To this aim, electrophysiological data were acquired in early deaf and hearing control individuals during processing of repeated and novel visual events unattended by participants. By studying evoked and induced oscillatory brain activities, as well as inter-trial phase coherence, we linked response modulations to feedback and/or feedforward processes. Results revealed selective experience-dependent changes on both RS and ND mechanisms. Compared to hearing controls, early deaf individuals displayed: (i) greater attenuation of the response following stimulus repetition, selectively in the induced theta-band (4-7 Hz); (ii) reduced desynchronization following the onset of novel visual stimuli, in the induced alpha and beta bands (8-12 and 13-25 Hz); (iii) comparable modulation of evoked responses and inter-trial phase coherence. The selectivity of the effects in the induced responses parallels findings observed in the auditory cortex of deaf animal models following intracochlear electric stimulation. The present results support the idea that early deafness alters induced oscillatory activity and the functional tuning of basic visual processing.

An event-related brain potential study of auditory attention in cochlear implant users

OBJECTIVE

Cochlear implants (CIs) provide access to the auditory world for deaf individuals. We investigated whether CIs enforce attentional alterations of auditory cortical processing in post-lingually deafened CI users compared to normal-hearing (NH) controls.

METHODS

Event-related potentials (ERPs) were recorded in 40 post-lingually deafened CI users and in a group of 40 NH controls using an auditory three-stimulus oddball task, which included frequent standard tones (Standards) and infrequent deviant tones (Targets), as well as infrequently occurring unique sounds (Novels). Participants were exposed twice to the three-stimulus oddball task, once under the instruction to ignore the stimuli (ignore condition), and once under the instruction to respond to infrequently occurring deviant tones (attend condition).

RESULTS

The allocation of attention to auditory oddball stimuli exerted stronger effects on N1 amplitudes at posterior electrodes in response to Standards and to Targets in CI users than in NH controls. Other ERP amplitudes showed similar attentional modulations in both groups (P2 in response to Standards, N2 in response to Targets and Novels, P3 in response to Targets). We also observed a statistical trend for an attenuated attentional modulation of Novelty P3 amplitudes in CI users compared to NH controls.

CONCLUSIONS

ERP correlates of enhanced CI-mediated auditory attention are confined to the latency range of the auditory N1, suggesting that enhanced attentional modulation during auditory stimulus discrimination occurs primarily in associative auditory cortices of CI users.

SIGNIFICANCE

The present ERP data support the hypothesis of attentional alterations of auditory cortical processing in CI users. These findings may be of clinical relevance for the CI rehabilitation.

Deafness Weakens Interareal Couplings in the Auditory Cortex

The function of the cerebral cortex essentially depends on the ability to form functional assemblies across different cortical areas serving different functions. Here we investigated how developmental hearing experience affects functional and effective interareal connectivity in the auditory cortex in an animal model with years-long and complete auditory deprivation (deafness) from birth, the congenitally deaf cat (CDC). Using intracortical multielectrode arrays, neuronal activity of adult hearing controls and CDCs was registered in the primary auditory cortex and the secondary posterior auditory field (PAF). Ongoing activity as well as responses to acoustic stimulation (in adult hearing controls) and electric stimulation applied via cochlear implants (in adult hearing controls and CDCs) were analyzed. As functional connectivity measures pairwise phase consistency and Granger causality were used. While the number of coupled sites was nearly identical between controls and CDCs, a reduced coupling strength between the primary and the higher order field was found in CDCs under auditory stimulation. Such stimulus-related decoupling was particularly pronounced in the alpha band and in top–down direction. Ongoing connectivity did not show such a decoupling. These findings suggest that developmental experience is essential for functional interareal interactions during sensory processing. The outcomes demonstrate that corticocortical couplings, particularly top-down connectivity, are compromised following congenital sensory deprivation.

Evidence for [Coronal] Underspecification in Typical and Atypical Phonological Development

The Featurally Underspecified Lexicon (FUL) theory predicts that [coronal] is the language universal default place of articulation for phonemes. This assumption has been consistently supported with adult behavioral and event-related potential (ERP) data; however, this underspecification claim has not been tested in developmental populations. The purpose of this study was to determine whether children demonstrate [coronal] underspecification patterns similar to those of adults. Two English consonants differing in place of articulation, [labial] /b/ and [coronal] /d/, were presented to 24 children (ages 4-6 years) characterized by either a typically developing phonological system (TD) or a phonological disorder (PD). Two syllables, /bɑ/ and /dɑ/, were presented in an ERP oddball paradigm where both syllables served as the standard and deviant stimulus in opposite stimulus sets. Underspecification was examined with three analyses: traditional mean amplitude measurements, cluster-based permutation tests, and single-trial general linear model (GLM) analyses of single-subject data. Contrary to previous adult findings, children with PD demonstrated a large positive mismatch response (PMR) to /bɑ/ while the children with TD exhibited a negative mismatch response (MMN); significant group differences were not observed in the /dɑ/ responses. Moreover, the /bɑ/ deviant ERP response was significantly larger in the TD children than in the children with PD. At the single-subject level, more children demonstrated mismatch responses to /dɑ/ than to /bɑ/, though some children had a /bɑ/ mismatch response and no /dɑ/ mismatch response. While both groups of children demonstrated similar responses to the underspecified /dɑ/, their neural responses to the more specified /bɑ/ varied. These findings are interpreted within a proposed developmental model of phonological underspecification, wherein children with PD are functioning at a developmentally less mature stage of phonological acquisition than their same-aged TD peers. Thus, phonological underspecification is a phenomenon that likely develops over time with experience and exposure to language.

The Benefit of Cross-Modal Reorganization on Speech Perception in Pediatric Cochlear Implant Recipients Revealed Using Functional Near-Infrared Spectroscopy

Cochlear implants (CIs) are the most successful treatment for severe-to-profound deafness in children. However, speech outcomes with a CI often lag behind those of normally-hearing children. Some authors have attributed these deficits to the takeover of the auditory temporal cortex by vision following deafness, which has prompted some clinicians to discourage the rehabilitation of pediatric CI recipients using visual speech. We studied this cross-modal activity in the temporal cortex, along with responses to auditory speech and non-speech stimuli, in experienced CI users and normally-hearing controls of school-age, using functional near-infrared spectroscopy. Strikingly, CI users displayed significantly greater cortical responses to visual speech, compared with controls. Importantly, in the same regions, the processing of auditory speech, compared with non-speech stimuli, did not significantly differ between the groups. This suggests that visual and auditory speech are processed synergistically in the temporal cortex of children with CIs, and they should be encouraged, rather than discouraged, to use visual speech.

Adult-Onset Hearing Impairment Induces Layer-Specific Cortical Reorganization: Evidence of Crossmodal Plasticity and Central Gain Enhancement

Adult-onset hearing impairment can lead to hyperactivity in the auditory pathway (i.e., central gain enhancement) as well as increased cortical responsiveness to nonauditory stimuli (i.e., crossmodal plasticity). However, it remained unclear to what extent hearing loss-induced hyperactivity is relayed beyond the auditory cortex, and thus, whether central gain enhancement competes or coexists with crossmodal plasticity throughout the distinct layers of the audiovisual cortex. To that end, we investigated the effects of partial hearing loss on laminar processing in the auditory, visual and audiovisual cortices of adult rats using extracellular electrophysiological recordings performed 2 weeks after loud noise exposure. Current-source density analyses revealed that central gain enhancement was not relayed to the audiovisual cortex (V2L), and was instead restricted to the granular layer of the higher order auditory area, AuD. In contrast, crossmodal plasticity was evident across multiple cortical layers within V2L, and also manifested in AuD. Surprisingly, despite this coexistence of central gain enhancement and crossmodal plasticity, noise exposure did not disrupt the responsiveness of these neighboring cortical regions to combined audiovisual stimuli. Overall, we have shown for the first time that adult-onset hearing impairment causes a complex assortment of intramodal and crossmodal changes across the layers of higher order sensory cortices.

Music Training for Children With Sensorineural Hearing Loss Improves Speech-in-Noise Perception

Purpose A growing body of evidence suggests that long-term music training provides benefits to auditory abilities for typical-hearing adults and children. The purpose of this study was to evaluate how music training may provide perceptual benefits (such as speech-in-noise, spectral resolution, and prosody) for children with hearing loss. Method Fourteen children aged 6-9 years with prelingual sensorineural hearing loss using bilateral cochlear implants, bilateral hearing aids, or bimodal configuration participated in a 12-week music training program, with nine participants completing the full testing requirements of the music training. Activities included weekly group-based music therapy and take-home music apps three times a week. The design was a pseudorandomized, longitudinal study (half the cohort was wait-listed, initially serving as a passive control group prior to music training). The test battery consisted of tasks related to music perception, music appreciation, and speech perception. As a comparison, 16 age-matched children with typical hearing also completed this test battery, but without participation in the music training. Results There were no changes for any outcomes for the passive control group. After music training, perception of speech-in-noise, question/statement prosody, musical timbre, and spectral resolution improved significantly, as did measures of music appreciation. There were no benefits for emotional prosody or pitch perception. Conclusion The findings suggest even a modest amount of music training has benefits for music and speech outcomes. These preliminary results provide further evidence that music training is a suitable complementary means of habilitation to improve the outcomes for children with hearing loss.

Clinical evaluation of cochlear implantation in children younger than 12 months of age

IMPORTANCE

Cochlear implantation (CI) is an effective therapy for patients with severe to profound sensorineural hearing loss. It remains controversial whether children younger than 12 months of age should undergo CI.

OBJECTIVE

To evaluate the safety and effectiveness of CI in children younger than 12 months of age.

METHODS

We performed a retrospective study of clinical data of pediatric patients younger than 12 months of age who underwent CI and were followed up for 1 to 2 years. Patients' developmental levels were evaluated by the Gesell score before CI. Intraoperative and postoperative complications were recorded to evaluate the safety of CI. Auditory and speech abilities were scored by the LittlEARS® auditory questionnaire (LEAQ), categories of auditory performance (CAP), speech intelligibility rating (SIR), infant-toddler meaningful auditory integration scale (IT-MAIS), and meaningful use of speech scale (MUSS) at 1, 2, 3, 6, 9, and 12 months after CI. The associations between clinical characteristics before CI and postoperative scores at 1 year after CI were analyzed by the linear mixed-effects model.

RESULTS

Eighty-nine children (47 boys and 42 girls) were included in this study (mean age at CI, 9.2 ± 1.6 months). Sixteen patients were diagnosed with cochlear malformation and 16 underwent bilateral CI. No severe complications occurred in any patients. The mean developmental quotient of the Gesell score was 78.00 ± 10.03. The median LEAQ scores were 0, 5, 10, 16, 22, 26 and 30 before and at 1, 2, 3, 6, 9, and 12 months after CI, respectively. These findings implied that the LEAQ score greatly improved in the first year after CI. The overall CAP, SIR, IT-MAIS, and MUSS scores also increased with increasing duration after CI. No significant associations were detected between clinical characteristics (age, sex, implant number, pre-CI Gesell score, and inner ear malformation) and LEAQ outcomes at 12 months after CI.

INTERPRETATION

With increasing duration after CI, auditory and speech behavior dramatically improve in young children. Our findings indicate that CI is feasible for children younger than 12 months of age.

How does the brain learn environmental structure? Ten core principles for understanding the neurocognitive mechanisms of statistical learning

Despite a growing body of research devoted to the study of how humans encode environmental patterns, there is still no clear consensus about the nature of the neurocognitive mechanisms underpinning statistical learning nor what factors constrain or promote its emergence across individuals, species, and learning situations. Based on a review of research examining the roles of input modality and domain, input structure and complexity, attention, neuroanatomical bases, ontogeny, and phylogeny, ten core principles are proposed. Specifically, there exist two sets of neurocognitive mechanisms underlying statistical learning. First, a "suite" of associative-based, automatic, modality-specific learning mechanisms are mediated by the general principle of cortical plasticity, which results in improved processing and perceptual facilitation of encountered stimuli. Second, an attention-dependent system, mediated by the prefrontal cortex and related attentional and working memory networks, can modulate or gate learning and is necessary in order to learn nonadjacent dependencies and to integrate global patterns across time. This theoretical framework helps clarify conflicting research findings and provides the basis for future empirical and theoretical endeavors.

Long-term Change in the Speech Perception Ability in Pediatric Cochlear Implants and the Effect of the Age at Implantation

OBJECTIVE

We analyzed the long-term changes in speech perception ability of pediatric cochlear implants (CIs) to evaluate the effect of the age at the time of surgery.

STUDY DESIGN

Retrospective.

SETTING

Tertiary care academic center.

PATIENTS

One hundred fourteen prelingually deaf children with CI use duration >10 years.

MAIN OUTCOME MEASURES

Categories of auditory performance (CAP) scores and monosyllabic word recognition scores using the Asan-Samsung Korean word list (ASK-WRS) and a conventional word list (KS-WRS) were the main outcomes. Outcomes were compared according to the age at surgery (group I, 1-2 yr; II, 2.1-3 yr; III, 3.1-7 yr; IV, 7.1-13 yr).

RESULTS

CAP scores reached plateaus at 2.6 to 3.3 years post-CI; groups I to III showed better scores than group IV. The maximum CAP score was obtained in all children of groups I to III and in 65% of group IV. ASK-WRSs reached plateaus at 3.2 to 4.8 years post-CI. Younger patients at CI operation showed better ASK-WRSs (97, 93, 90, and 54% in groups I-IV, respectively), but the differences were not significant (I versus II and II versus III). Ceiling effect (perfect score) was observed in early groups (67, 44, 30, and 0% in groups I-IV). KS-WRSs, which is a challenging test, reached plateaus at 7.2 to 8.4 years postsurgery with no ceiling effect. Early implantees showed significantly better scores (88, 82, 73, and 46% in groups I-IV).

CONCLUSIONS

Speech perception ability after CI showed audiological age-specific improvement evaluated by various test methods. The most challenging test demonstrated long-term performance differences by the age at CI operation.

Usefulness of cochlear implantation in children with single sided deafness

OBJECTIVES

Children with single sided deafness (SSD) show a poorer performance at school, which is attributable to reduced speech discrimination in noise, to reduced localization ability, and to a decreased power of concentration due to faster hearing exhaustion. Therefore, it is important to provide children with SSD with adequate hearing amplification to restore binaural hearing. This can only be achieved by provision with a cochlear implant (CI). But these treatment option in children with SSD is still under discussion. The aim of the present study is to evaluate audiological and clinical results in children with SSD following cochlear implantation. A special focus was placed on the duration of deafness before implantation and on the frequency of CI-use in everyday life.

METHODS

Seven children with SSD of different etiologies who were provided with a CI between 3 and 16 years of age were evaluated. Every child underwent multiple audiological tests before and after cochlear implantation. After cochlear implantation speech recognition tests in noise using the HSM (Hochmair, Schulz and Moser 1997) test and localization tests were performed. Furthermore, the frequency of implant use was evaluated.

RESULTS

Speech recognition in noise with CI compared to the unaided condition significantly improved in all children in different settings. Improvement of the localization ability measured by the root mean square error (RMSE) was shown in all children. All children are very satisfied with the decision to have undergone cochlear implantation and are all full-time users.

CONCLUSIONS

Cochlear implantation benefits speech recognition in noise and sound localization ability in children with SSD at different ages. All implanted children are full-time users regardless of age or duration of deafness before implantation.

Cochlear implantation in adults with auditory deprivation: What do we know about it?

INTRODUCTION

In the ENT community, auditory deprivation is frequently considered as a negative prognostic factor for a good hearing outcome of cochlear implantation (CI), even if a growing literature suggests that this is not completely true. The purpose of this study is to evaluate the results of CI in patients with hearing deprivation, to compare them to results from non-deprived patients and then estimate how time of deprivation impacts on CI outcome and how a bilateral deprivation can affect the outcome compared to a unilateral deprivation.

METHODS

Seventy-eight adults with severe to profound post-verbal hearing loss, with and without auditory deprivation history, received CI; audiological results obtained at 3-6-12-24 months follow up post CI were analyzed.

RESULTS

No differences were founded between patients with unilateral deprivation and patients with no deprivation. Patients with bilateral deprivation seem to have a worse hearing outcome compared to that of those patients with unilateral deprivation or no deprivation at all. Long time deprivation (>15 years) seems to have a negative influence on the hearing outcome but results with CI remain excellent.

CONCLUSIONS

Auditory deprivation should not be considered a contraindication to CI. The duration of auditory deprivation in the implanted ear seems to be a negative prognostic factor only for ears deprived from more of 15 years.

Critical periods of brain development

Brain plasticity is maximal at specific time windows during early development known as critical periods (CPs), during which sensory experience is necessary to establish optimal cortical representations of the surrounding environment. After CP closure, a range of functional and structural elements prevent passive experience from eliciting significant plastic changes in the brain. The transition from a plastic to a more fixed state is advantageous as it allows for the sequential consolidation and retention of new and more complex perceptual, motor, and cognitive functions. However, the formation of stable neural representations may pose limitations on future revisions to the circuitry. If sensory experience is abnormal or absent during this time, it can have profound effects on sensory representations in adulthood, resulting in quasi-permanent adaptations that can make it nearly impossible to learn certain skills or process certain stimulus properties later on in life. This chapter begins with a brief introduction to experience-dependent plasticity throughout the lifespan (Section Introduction). Next, we define what constitutes a CP (Section What Are Critical Periods?) and review some of the key CPs in the visual and auditory systems (Section Key Critical Periods of Sensory Systems). We then discuss the mechanisms whereby cortical plasticity is regulated both locally and through neuromodulatory systems (Section How Are Critical Periods Regulated?). Finally, we highlight studies showing that CPs can be extended beyond their normal epochs, closed prematurely, or reopened during adult life by merely altering sensory inputs (Section Timing of Critical Periods: Can CP Plasticity Be Extended, Limited, or Reactivated?).

Structural neuroimaging of the altered brain stemming from pediatric and adolescent hearing loss-Scientific and clinical challenges

There has been a spurt in structural neuroimaging studies of the effect of hearing loss on the brain. Specifically, magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) technologies provide an opportunity to quantify changes in gray and white matter structures at the macroscopic scale. To date, there have been 32 MRI and 23 DTI studies that have analyzed structural differences accruing from pre- or peri-lingual pediatric hearing loss with congenital or early onset etiology and postlingual hearing loss in pre-to-late adolescence. Additionally, there have been 15 prospective clinical structural neuroimaging studies of children and adolescents being evaluated for cochlear implants. The results of the 70 studies are summarized in two figures and three tables. Plastic changes in the brain are seen to be multifocal rather than diffuse, that is, differences are consistent across regions implicated in the hearing, speech and language networks regardless of modes of communication and amplification. Structures in that play an important role in cognition are affected to a lesser extent. A limitation of these studies is the emphasis on volumetric measures and on homogeneous groups of subjects with hearing loss. It is suggested that additional measures of morphometry and connectivity could contribute to a greater understanding of the effect of hearing loss on the brain. Then an interpretation of the observed macroscopic structural differences is given. This is followed by discussion of how structural imaging can be combined with functional imaging to provide biomarkers for longitudinal tracking of amplification. This article is categorized under: Developmental Biology > Developmental Processes in Health and Disease Translational, Genomic, and Systems Medicine > Translational Medicine Laboratory Methods and Technologies > Imaging.

The Cross-Modal Effects of Sensory Deprivation on Spatial and Temporal Processes in Vision and Audition: A Systematic Review on Behavioral and Neuroimaging Research since 2000

One of the most significant effects of neural plasticity manifests in the case of sensory deprivation when cortical areas that were originally specialized for the functions of the deprived sense take over the processing of another modality. Vision and audition represent two important senses needed to navigate through space and time. Therefore, the current systematic review discusses the cross-modal behavioral and neural consequences of deafness and blindness by focusing on spatial and temporal processing abilities, respectively. In addition, movement processing is evaluated as compiling both spatial and temporal information. We examine whether the sense that is not primarily affected changes in its own properties or in the properties of the deprived modality (i.e., temporal processing as the main specialization of audition and spatial processing as the main specialization of vision). References to the metamodal organization, supramodal functioning, and the revised neural recycling theory are made to address global brain organization and plasticity principles. Generally, according to the reviewed studies, behavioral performance is enhanced in those aspects for which both the deprived and the overtaking senses provide adequate processing resources. Furthermore, the behavioral enhancements observed in the overtaking sense (i.e., vision in the case of deafness and audition in the case of blindness) are clearly limited by the processing resources of the overtaking modality. Thus, the brain regions that were previously recruited during the behavioral performance of the deprived sense now support a similar behavioral performance for the overtaking sense. This finding suggests a more input-unspecific and processing principle-based organization of the brain. Finally, we highlight the importance of controlling for and stating factors that might impact neural plasticity and the need for further research into visual temporal processing in deaf subjects.

Early general development and central auditory system maturation in children with cochlear implants - A case series

OBJECTIVES

A cochlear implant (CI) has the potential to improve the functioning of a deaf child in many aspects. Nevertheless, the dynamics of the general development, beyond the typically measured language abilities, directly after CI, is still unknown, especially if a child is implanted early. In this study we present a methodological framework for assessment of different domains of development, as well as the central auditory nervous system (CANS) maturation in infants and toddlers with a CI.

METHODS

Three children with bilateral congenital hearing loss and a unilateral CI, aged below 2.5 years, participated in a longitudinal study. Children were tested at three time points after cochlear implantation using the Polish Children Development Scale (CDS) consisting of a comprehensive battery of tests, as well as recordings of Cortical Auditory Evoked Potentials (CAEP).

RESULTS

All three children revealed gradual improvement in the overall CDS result as well as most of the CDS subscales. After 9 months of CI experience two younger children showed age-appropriate performance. In CAEP measurements a decrease of latency of the P1 component (an established biomarker of cortical auditory maturation) was observed in the same two children, with one achieving normal ranges of P1 latency after 9 months of CI use.

CONCLUSIONS

Our novel methodological framework can be successfully applied in small children with cochlear implants. It contributes to better understanding of the general development in early implanted children. The preliminary results indicate variability in children's performance in various developmental domains and thus the need to monitor the development of each child individually and holistically.

Literature overview on P3 measurement as an objective measure of auditory performance in post-lingually deaf adults with a cochlear implant

Objective: Cochlear implantation results in restoration of hearing, potential cortical reorganisation and the reallocation of attentional resources to the auditory system. Hence, the distorted cortical activity of patients with profound sensorineural hearing loss may be partially reversed. The measurement of auditory event-related potentials (ERPs) forms a promising electrophysiological evaluation of the central auditory nervous system. In particular, the P3 component is hypothesised to be a differential indicator of subjective auditory discrimination. This overview discusses the association between the cortical P3 component and the performance on auditory tests in post-lingually deaf adults using a CI. Moreover, the current article proposes important guidelines on eliciting, recording and analysing ERPs in CI users.Design: The literature search was conducted in PubMed.Study sample: Articles were included if they focussed on the relationship between P3 and auditory performance of an adult CI population.Results: The higher-order processing of speech in quiet and in noise of adult CI users is correlated with the ERP components, including the P3, shedding light on neurophysiological foundations for auditory performance differences.Conclusions: There is a need for replicating studies with larger sample sizes to fully comprehend the relationship between P3 and the auditory performance of CI users.