A behavioral framework to guide research on central auditory development and plasticity

A complex acoustical environment is necessary for maintenance and development in the zebra finch auditory pallium

Postnatal experience is critical to auditory development in vertebrates. The zebra finch (Taeniopygia castanotis) provides a valuable model for understanding how complex social-acoustical environments influence development of the neural circuits that support perception of vocal communication signals. We previously showed that zebra finches raised in the rich acoustical environment of a breeding colony (colony-reared, CR) perform twice as well in an operant discrimination task as birds raised with only their families (pair-reared, PR), and we identified deficits in functional properties within the auditory pallium of PR birds that could explain this behavioral difference. Here, using single-unit extracellular recordings from the L3 subdivision of field L and caudomedial nidopallium (NCM) at three developmental timepoints (18-20, 30-35, and 90-110 days post hatch), we tracked how experience affects the emergence of these functional properties. Whereas CR birds showed stable single-unit response properties from fledging to adulthood alongside improvements in population-level encoding, PR birds exhibited progressive deterioration in neural function. Deficits in PR birds began emerging at 18 days for population metrics and by 30 days for single-unit properties, worsening into adulthood. These included altered spike waveforms, firing rates, selectivity, discriminability, coding efficiency, and noise invariance. Notably, these deficits occurred despite PR birds receiving normal exposure to the song of a male tutor, suggesting that learning to sing is robust enough to compensate for impaired auditory processing. Our findings demonstrate that a complex acoustical environment is necessary for both maintenance and development of the cortical-level auditory circuits that decode conspecific vocalizations.

Acoustic enrichment prevents early life stress-induced disruptions in sound azimuth processing

Early life stress (ELS) has been shown to disrupt cognitive and limbic functions, yet its impact on sensory systems, particularly the auditory system, remains insufficiently understood. In this study, we investigated the enduring effects of ELS induced by neonatal maternal separation (MS) on behavioral and cortical processing of sound azimuth in adult male rats. We found that MS significantly impairs sound-azimuth discrimination, paralleled by broader azimuth tuning and reduced dendritic branching and spine density in neurons within the primary auditory cortex. Notably, exposure to an enriched acoustic environment during the stress period effectively protects against these MS-induced alterations, restoring behavioral performance, cortical tuning, and dendritic spine density of neurons to levels comparable to controls. Further analyses reveal that epigenetic regulation of cortical brain-derived neurotrophic factor by histone H3 lysine 9 dimethylation may underlie the observed changes in cortical structure and function. These results underscore the profound and lasting impact of MS-induced ELS on auditory processing, particularly within cortical circuits involved in spatial processing. They suggest that sensory enrichment is a potential therapeutic strategy to ameliorate the adverse effects of ELS on sensory processing, with broader implications for understanding and treating sensory deficits in stress-related disorders.Significance Statement The contribution of early life stress (ELS) to sensory deficits in stress-related disorders remains largely unexplored. Here we show that ELS induced by neonatal maternal separation (MS) disrupts behavioral and cortical processing of sound azimuth in adult rats. Moreover, pairing MS with enriched acoustic exposure during the stress period alleviates these deficits in maternally separated rats. Epigenetic modulation of brain-derived neurotrophic factor gene expression by histone H3 lysine 9 dimethylation in the cortex may underlie the MS-effects and their reversal through acoustic enrichment. These findings reveal the enduring effects of ELS on sensory processing, emphasizing its broader implications for understanding stress-related disorders. Importantly, they highlight sensory enrichment as a promising therapeutic strategy to prevent sensory deficits associated with such conditions.

Consonant aspiration in Mandarin-speaking children: a developmental perspective from perception and production

Introduction

This study investigates Mandarin-speaking children's acquisition of aspirated/unaspirated voiceless consonants in terms of perception and production, to track children's developmental profile and explore the factors that may affect their acquisition, as well as the possible association between perception and production.

Methods

Mandarin-speaking children (N = 95) aged 3-5 and adults (N = 20) participated in (1) a perception test designed based on the minimal pairs of unaspirated/aspirated consonants in the quiet and noisy conditions respectively; (2) a production test where participants produced the target words, with syllable-initial consonants focusing on aspiration and non-aspiration. Six pairs of unaspirated/aspirated consonants in Mandarin were included.

Results

(1) Children's perception and production accuracy of aspirated and unaspirated consonants increased with age. Five-year-olds achieved high accuracy in the perception under the quiet condition and in the production (over 90%), though not yet adult-like. (2) Noise adversely affected children's perception, with all child groups showing poor performance in the noisy condition. In terms of perception, stops were more challenging to children than affricates, but in terms of production, children performed better on stops. Furthermore, the presence of noise had a greater detrimental effect on the perception of aspirated consonants compared to unaspirated ones. (3) A weak positive correlation was found between children's perception of consonant aspiration in the quiet condition and their production.

Discussion

The findings indicate that age, aspiration state, and manner of articulation (MOA) would affect children's acquisition of consonant aspiration. Although 5-year-olds have almost acquired aspirated/unaspirated consonants, compared to adults, the perception of consonant aspiration in noise remains a challenge for children.

Developmental encoding of natural sounds in the mouse auditory cortex

Mice communicate through high-frequency ultrasonic vocalizations, which are crucial for social interactions such as courtship and aggression. Although ultrasonic vocalization representation has been found in adult brain areas along the auditory pathway, including the auditory cortex, no evidence is available on the neuronal representation of ultrasonic vocalizations early in life. Using in vivo two-photon calcium imaging, we analyzed auditory cortex layer 2/3 neuronal responses to USVs, pure tones (4 to 90 kHz), and high-frequency modulated sweeps from postnatal day 12 (P12) to P21. We found that ACx neurons are tuned to respond to ultrasonic vocalization syllables as early as P12 to P13, with an increasing number of responsive cells as the mouse age. By P14, while pure tone responses showed a frequency preference, no syllable preference was observed. Additionally, at P14, USVs, pure tones, and modulated sweeps activate clusters of largely nonoverlapping responsive neurons. Finally, we show that while cell correlation decreases with increasing processing of peripheral auditory stimuli, neurons responding to the same stimulus maintain highly correlated spontaneous activity after circuits have attained mature organization, forming neuronal subnetworks sharing similar functional properties.

The effect of acoustically enriched environment on structure and function of the developing auditory system

It has long been known that environmental conditions, particularly during development, affect morphological and functional properties of the brain including sensory systems; manipulating the environment thus represents a viable way to explore experience-dependent plasticity of the brain as well as of sensory systems. In this review, we summarize our experience with the effects of acoustically enriched environment (AEE) consisting of spectrally and temporally modulated complex sounds applied during first weeks of the postnatal development in rats and compare it with the related knowledge from the literature. Compared to controls, rats exposed to AEE showed in neurons of several parts of the auditory system differences in the dendritic length and in number of spines and spine density. The AEE exposure permanently influenced neuronal representation of the sound frequency and intensity resulting in lower excitatory thresholds, increased frequency selectivity and steeper rate-intensity functions. These changes were present both in the neurons of the inferior colliculus and the auditory cortex (AC). In addition, the AEE changed the responsiveness of AC neurons to frequency modulated, and also to a lesser extent, amplitude-modulated stimuli. Rearing rat pups in AEE leads to an increased reliability of acoustical responses of AC neurons, affecting both the rate and the temporal codes. At the level of individual spikes, the discharge patterns of individual neurons show a higher degree of similarity across stimulus repetitions. Behaviorally, rearing pups in AEE resulted in an improvement in the frequency resolution and gap detection ability under conditions with a worsened stimulus clarity. Altogether, the results of experiments show that the exposure to AEE during the critical developmental period influences the frequency and temporal processing in the auditory system, and these changes persist until adulthood. The results may serve for interpretation of the effects of the application of enriched acoustical environment in human neonatal medicine, especially in the case of care for preterm born children.

Eight-Month-Old Infants Are Susceptible to the Auditory Continuity Illusion

The real world is full of noise and constantly overlapping sounds. However, our auditory system provides a solution to this, that is, the continuity illusion; when we hear a sound stream that is partially replaced by high-level noise, we can restore missing sound information and "fill in" the information as if it were smooth and continuous even against a background of noise. In the present study, we tested the preferences for familiar and novel melodies of 8-month-old infants after a 2-month memory retention interval following 1-week exposure to a specific melody. A preference for familiarity was seen not only when the melody was presented intact but also when it was periodically replaced by high-level noise, which elicits the continuity illusion in adults (Experiment 1). However, a trend toward preference for a novel melody was observed for stimuli periodically replaced by low-level noise that did not satisfy the ecological constraints for the elicitation of the illusion (Experiment 2). For the first time, this study showed that infants as young as 8 months of age are susceptible to the auditory continuity illusion. The study also revealed that the infants could recognize the melody they heard 2 months previously.

The Not-So-Slight Perceptual Consequences of Slight Hearing Loss in School-Age Children: A Scoping Review

PURPOSE

This study aimed to conduct a scoping review of research exploring the effects of slight hearing loss on auditory and speech perception in children.

METHOD

A comprehensive search conducted in August 2023 identified a total of 402 potential articles sourced from eight prominent bibliographic databases. These articles were subjected to rigorous evaluation for inclusion criteria, specifically focusing on their reporting of speech or auditory perception using psychoacoustic tasks. The selected studies exclusively examined school-age children, encompassing those between 5 and 18 years of age. Following rigorous evaluation, 10 articles meeting these criteria were selected for inclusion in the review.

RESULTS

The analysis of included articles consistently shows that even slight hearing loss in school-age children significantly affects their speech and auditory perception. Notably, most of the included articles highlighted a common trend, demonstrating that perceptual deficits originating due to slight hearing loss in children are particularly observable under challenging experimental conditions and/or in cognitively demanding listening tasks. Recent evidence further underscores that the negative impacts of slight hearing loss in school-age children cannot be solely predicted by their pure-tone thresholds alone. However, there is limited evidence concerning the effect of slight hearing loss on the segregation of competing speech, which may be a better representation of listening in the classroom.

CONCLUSION

This scoping review discusses the perceptual consequences of slight hearing loss in school-age children and provides insights into an array of methodological issues associated with studying perceptual skills in school-age children with slight hearing losses, offering guidance for future research endeavors.

Reduced processing efficiency impacts auditory detection of amplitude modulation in children: Evidence from an experimental and modeling study

Auditory detection of the Amplitude Modulation (AM) of sounds, crucial for speech perception, improves until 10 years of age. This protracted development may not only be explained by sensory maturation, but also by improvements in processing efficiency: the ability to make efficient use of available sensory information. This hypothesis was tested behaviorally on 86 6-to-9-year-olds and 15 adults using AM-detection tasks assessing absolute sensitivity, masking, and response consistency in the AM domain. Absolute sensitivity was estimated by the detection thresholds of a sinusoidal AM applied to a pure-tone carrier; AM masking was estimated as the elevation of AM-detection thresholds produced when replacing the pure-tone carrier by a narrowband noise; response consistency was estimated using a double-pass paradigm where the same set of stimuli was presented twice. Results showed that AM sensitivity improved from childhood to adulthood, but did not change between 6 and 9 years. AM masking did not change with age, suggesting that the selectivity of perceptual AM filters was adult-like by 6 years. However, response consistency increased developmentally, supporting the hypothesis of reduced processing efficiency in early childhood. At the group level, double-pass data of children and adults were well simulated by a model of the human auditory system assuming a higher level of internal noise for children. At the individual level, for both children and adults, double-pass data were better simulated when assuming a sub-optimal decision strategy in addition to differences in internal noise. In conclusion, processing efficiency for AM detection is reduced in childhood. Moreover, worse AM detection was linked to both systematic and stochastic inefficiencies, in both children and adults.

Early-life stress affects Mongolian gerbil interactions with conspecific vocalizations in a sex-specific manner

During development, early-life stress (ELS) impairs cognition, learning, and emotional regulation, in part by disrupting neural circuitry in regions underlying these higher-order functions. In addition, our recent work indicates that ELS also alters simple sensory perception: ELS impaired auditory perception and neural encoding of short gaps in sounds, which are essential for vocal communication. The combination of higher-order and basic sensory disruption suggests that ELS is likely to affect both the perception and interpretation of communication signals. We tested this hypothesis by measuring behavioral responses to conspecific vocalizations (those emitted by other gerbils) in ELS and untreated Mongolian gerbils. Because stress effects often differ by sex, we separately examined females and males. To induce ELS, pups were intermittently maternally separated and restrained from post-natal days (P) 9-24, a time window when the auditory cortex is most sensitive to external disruption. We measured the approach responses of juvenile (P31-32) gerbils to two types of conspecific vocalizations: an alarm call, which is emitted to alert other gerbils of a potential threat, and the prosocial contact call, which is emitted near familiar gerbils, especially after separation. Control males, Control females, and ELS females approached a speaker emitting pre-recorded alarm calls, while ELS males avoided this source, suggesting that ELS affects the response to alarm calls in male gerbils. During playback of the pre-recorded contact call, Control females and ELS males avoided the sound source, while Control males neither approached nor avoided, and ELS females approached the sound. These differences cannot be accounted for by changes in locomotion or baseline arousal. However, ELS gerbils slept more during playback, suggesting that ELS may reduce arousal during vocalization playback. Further, male gerbils made more errors than females on a measure of working memory, but the sex difference of cognition in this context may stem from novelty aversion rather than impaired memory. These data indicate that ELS influences behavioral responses to ethologically relevant communication sounds in a sex-specific manner, and are among the first to demonstrate an altered response to auditory stimuli following ELS. Such changes may arise from differences in auditory perception, cognition, or a combination of factors, and suggest that ELS may affect auditory communication in human adolescents.

Early-Life Stress Impairs Perception and Neural Encoding of Rapid Signals in the Auditory Pathway

During developmental critical periods (CPs), early-life stress (ELS) induces cognitive deficits and alters neural circuitry in regions underlying learning, memory, and attention. Mechanisms underlying critical period plasticity are shared by sensory cortices and these higher neural regions, suggesting that sensory processing may also be vulnerable to ELS. In particular, the perception and auditory cortical (ACx) encoding of temporally-varying sounds both mature gradually, even into adolescence, providing an extended postnatal window of susceptibility. To examine the effects of ELS on temporal processing, we developed a model of ELS in the Mongolian gerbil, a well-established model for auditory processing. In both male and female animals, ELS induction impaired the behavioral detection of short gaps in sound, which are critical for speech perception. This was accompanied by reduced neural responses to gaps in auditory cortex, the auditory periphery, and auditory brainstem. ELS thus degrades the fidelity of sensory representations available to higher regions, and could contribute to well-known ELS-induced problems with cognition.SIGNIFICANCE STATEMENT In children and animal models, early-life stress (ELS) leads to deficits in cognition, including problems with learning, memory, and attention. Such problems could arise in part from a low-fidelity representation of sensory information available to higher-level neural regions. Here, we demonstrate that ELS degrades sensory responses to rapid variations in sound at multiple levels of the auditory pathway, and concurrently impairs perception of these rapidly-varying sounds. As these sound variations are intrinsic to speech, ELS may thus pose a challenge to communication and cognition through impaired sensory encoding.

Effect of Musical Stimulation on Placental Programming and Neurodevelopment Outcome of Preterm Infants: A Systematic Review

BACKGROUND

The fetal environment is modulated by the placenta, which integrates and transduces information from the maternal environment to the fetal developmental program and adapts rapidly to changes through epigenetic mechanisms that respond to internal (hereditary) and external (environmental and social) signals. Consequently, the fetus corrects the trajectory of own development. During the last trimester of gestation, plasticity shapes the fetal brain, and prematurity can alter the typical developmental trajectories. In this period, prevention through activity-inducing (e.g., music stimulation) interventions are currently tested. The purpose of this review is to describe the potentialities of music exposure on fetus, and on preterm newborns in the Neonatal Intensive Care Unit evaluating its influence on neurobehavioral development.

METHODS

Databases were searched from 2010 to 2022 for studies investigating mechanisms of placental epigenetic regulation and effects of music exposure on the fetus and pre-term neonates.

RESULTS

In this case, 28 selected papers were distributed into three research lines: studies on placental epigenetic regulation (13 papers), experimental studies of music stimulation on fetus or newborns (6 papers), and clinical studies on premature babies (9 papers). Placental epigenetic changes of the genes involved in the cortisol and serotonin response resulted associated with different neurobehavioral phenotypes in newborns. Prenatal music stimulation had positive effects on fetus, newborn, and pregnant mother while post-natal exposure affected the neurodevelopment of the preterm infants and parental interaction.

CONCLUSIONS

The results testify the relevance of environmental stimuli for brain development during the pre- and perinatal periods and the beneficial effects of musical stimulation that can handle the fetal programming and the main neurobehavioral disorders.

Cortical tracking of lexical speech units in a multi-talker background is immature in school-aged children

Children have more difficulty perceiving speech in noise than adults. Whether this difficulty relates to an immature processing of prosodic or linguistic elements of the attended speech is still unclear. To address the impact of noise on linguistic processing per se, we assessed how babble noise impacts the cortical tracking of intelligible speech devoid of prosody in school-aged children and adults. Twenty adults and twenty children (7-9 years) listened to synthesized French monosyllabic words presented at 2.5 Hz, either randomly or in 4-word hierarchical structures wherein 2 words formed a phrase at 1.25 Hz, and 2 phrases formed a sentence at 0.625 Hz, with or without babble noise. Neuromagnetic responses to words, phrases and sentences were identified and source-localized. Children and adults displayed significant cortical tracking of words in all conditions, and of phrases and sentences only when words formed meaningful sentences. In children compared with adults, the cortical tracking was lower for all linguistic units in conditions without noise. In the presence of noise, the cortical tracking was similarly reduced for sentence units in both groups, but remained stable for phrase units. Critically, when there was noise, adults increased the cortical tracking of monosyllabic words in the inferior frontal gyri and supratemporal auditory cortices but children did not. This study demonstrates that the difficulties of school-aged children in understanding speech in a multi-talker background might be partly due to an immature tracking of lexical but not supra-lexical linguistic units.

Discrimination of consonants in quiet and in noise in Mandarin-speaking children with normal hearing

OBJECTIVE

Given the critical role of consonants in speech perception and the lack of knowledge on consonant perception in noise in Mandarin-speaking children, the current study aimed to investigate Mandarin consonant discrimination in normal-hearing children, in relation to the effects of age and signal-to-noise ratios (S/N).

DESIGN

A discrimination task consisting of 33 minimal pairs in monosyllabic words was designed to explore the development of consonant discrimination in five test conditions: 0, -5, -10, -15 dB S/Ns, and quiet.

STUDY SAMPLE

Forty Mandarin-speaking, normal-hearing children aged from 4;0 to 8;9 in one-year-age increment were recruited and their performance was compared to 10 adult listeners.

RESULTS

A significant main effect of age, test conditions, and an interaction effect between these variables was noted. Consonant discrimination in quiet and in noise improved as children became older. Consonants that were difficult to discriminate in quiet and in noise were mainly velar contrasts. Noise seemed to have less effect on the discrimination of affricates and fricatives, and plosives appeared to be to be more difficult to discriminate in noise than in quiet. Place contrasts between alveolar and palato-alveolar consonants were difficult in quiet.

CONCLUSIONS

The findings were the first to reveal typical perceptual development of Mandarin consonant discrimination in children and can serve as a reference for comparison with children with disordered perceptual development, such as those with hearing loss.

Neurodevelopmental oscillatory basis of speech processing in noise

Humans' extraordinary ability to understand speech in noise relies on multiple processes that develop with age. Using magnetoencephalography (MEG), we characterize the underlying neuromaturational basis by quantifying how cortical oscillations in 144 participants (aged 5-27 years) track phrasal and syllabic structures in connected speech mixed with different types of noise. While the extraction of prosodic cues from clear speech was stable during development, its maintenance in a multi-talker background matured rapidly up to age 9 and was associated with speech comprehension. Furthermore, while the extraction of subtler information provided by syllables matured at age 9, its maintenance in noisy backgrounds progressively matured until adulthood. Altogether, these results highlight distinct behaviorally relevant maturational trajectories for the neuronal signatures of speech perception. In accordance with grain-size proposals, neuromaturational milestones are reached increasingly late for linguistic units of decreasing size, with further delays incurred by noise.

Auditory brainstem development of naked mole-rats (Heterocephalus glaber)

Life underground often leads to animals having specialized auditory systems to accommodate the constraints of acoustic transmission in tunnels. Despite living underground, naked mole-rats use a highly vocal communication system, implying that they rely on central auditory processing. However, little is known about these animals' central auditory system, and whether it follows a similar developmental time course as other rodents. Naked mole-rats show slowed development in the hippocampus suggesting they have altered brain development compared to other rodents. Here, we measured morphological characteristics and voltage-gated potassium channel Kv3.3 expression and protein levels at different key developmental time points (postnatal days 9, 14, 21 and adulthood) to determine whether the auditory brainstem (lateral superior olive and medial nucleus of the trapezoid body) develops similarly to two common auditory rodent model species: gerbils and mice. Additionally, we measured the hearing onset of naked mole-rats using auditory brainstem response recordings at the same developmental timepoints. In contrast with other work in naked mole-rats showing that they are highly divergent in many aspects of their physiology, we show that naked mole-rats have a similar hearing onset, between postnatal day (P) 9 and P14, to many other rodents. On the other hand, we show some developmental differences, such as a unique morphology and Kv3.3 protein levels in the brainstem.

Central auditory deficits associated with genetic forms of peripheral deafness

Since the 1990s, the study of inherited hearing disorders, mostly those detected at birth, in the prelingual period or in young adults, has led to the identification of their causal genes. The genes responsible for more than 140 isolated (non-syndromic) and about 400 syndromic forms of deafness have already been discovered. Studies of mouse models of these monogenic forms of deafness have provided considerable insight into the molecular mechanisms of hearing, particularly those involved in the development and/or physiology of the auditory sensory organ, the cochlea. In parallel, studies of these models have also made it possible to decipher the pathophysiological mechanisms underlying hearing impairment. This has led a number of laboratories to investigate the potential of gene therapy for curing these forms of deafness. Proof-of-concept has now been obtained for the treatment of several forms of deafness in mouse models, paving the way for clinical trials of cochlear gene therapy in patients in the near future. Nevertheless, peripheral deafness may also be associated with central auditory dysfunctions and may extend well beyond the auditory system itself, as a consequence of alterations to the encoded sensory inputs or involvement of the causal deafness genes in the development and/or functioning of central auditory circuits. Investigating the diversity, causes and underlying mechanisms of these central dysfunctions, the ways in which they could impede the expected benefits of hearing restoration by peripheral gene therapy, and determining how these problems could be remedied is becoming a research field in its own right. Here, we provide an overview of the current knowledge about the central deficits associated with genetic forms of deafness.

Electrophysiological Evidence of Enhanced Auditory Retrieval in Musically Trained Children

Abstract. Musical practice enhances auditory processing in children as related to pitch perception or tonal discrimination. The purpose of this study was to examine whether these benefits also occur in auditory working memory by influencing its neural substrates. Two groups of children aged between 7 and 11 years old were compared using an auditory retrieval task with three conditions: frequency retrieval, duration retrieval, and control. Musician children had weekly private violin or cello lessons for at least 14 months, whereas non-musician children had no musical training. Results showed that musicians’ scores on the Gordon’s Primary Measure of Music Audiation test were significantly higher than non-musicians’ scores in the rhythm and tone conditions. On memory tasks, musicians outperformed non-musicians in frequency retrieval but not in duration retrieval. Differences in retrieval performance were associated with a larger P200-like waveform over frontal sites in musicians and a larger N400-like waveform over centro-parietal sites in non-musicians. A source current density analysis revealed differences in frontal activities between musicians and non-musicians, suggesting that musical training influenced the neural mechanisms supporting auditory retrieval in children. These results are in agreement with previous studies that showed a better auditory memory in musicians. Furthermore, they suggest that in children, the effect of musical training can be strong enough to positively influence higher-order auditory memory processes such as active retrieval, as well as their neural correlates.

Auditory Behavior in Adult-Blinded Mice

Cross-modal plasticity occurs when the function of remaining senses is enhanced following deprivation or loss of a sensory modality. Auditory neural responses are enhanced in the auditory cortex, including increased sensitivity and frequency selectivity, following short-term visual deprivation in adult mice (Petrus et al. Neuron 81:664-673, 2014). Whether or not these visual deprivation-induced neural changes translate into improved auditory perception and performance remains unclear. As an initial investigation of the effects of adult visual deprivation on auditory behaviors, CBA/CaJ mice underwent binocular enucleation at 3-4 weeks old and were tested on a battery of learned behavioral tasks, acoustic startle response (ASR), and prepulse inhibition (PPI) tests beginning at least 2 weeks after the enucleation procedure. Auditory brain stem responses (ABRs) were also measured to screen for potential effects of visual deprivation on non-behavioral hearing function. Control and enucleated mice showed similar tone detection sensitivity and frequency discrimination in a conditioned lick suppression test. Both groups showed normal reactivity to sound as measured by ASR in a quiet background. However, when startle-eliciting stimuli were presented in noise, enucleated mice showed decreased ASR amplitude relative to controls. Control and enucleated mice displayed no significant differences in ASR habituation, PPI tests, or ABR thresholds, or wave morphology. Our findings suggest that while adult-onset visual deprivation induces cross-modal plasticity at the synaptic and circuit levels, it does not substantially influence simple auditory behavioral performance.

Neuroplasticity following cochlear implants

The auditory cortex of people with sensorineural hearing loss can be re-afferented using a cochlear implant (CI): a neural prosthesis that bypasses the damaged cells in the cochlea to directly stimulate the auditory nerve. Although CIs are the most successful neural prosthesis to date, some CI users still do not achieve satisfactory outcomes using these devices. To explain variability in outcomes, clinicians and researchers have increasingly focused their attention on neuroscientific investigations that examined how the auditory cortices respond to the electric signals that originate from the CI. This chapter provides an overview of the literature that examined how the auditory cortex changes its functional properties in response to inputs from the CI, in animal models and in humans. We focus first on the basic responses to sounds delivered through electrical hearing and, next, we examine the integrity of two fundamental aspects of the auditory system: tonotopy and processing of binaural cues. When addressing the effects of CIs in humans, we also consider speech-evoked responses. We conclude by discussing to what extent this neuroscientific literature can contribute to clinical practices and help to overcome variability in outcomes.

Listening Difficulties in Children With Normal Audiograms: Relation to Hearing and Cognition

OBJECTIVES

Children presenting at audiology services with caregiver-reported listening difficulties often have normal audiograms. The appropriate approach for the further assessment and clinical management of these children is currently unclear. In this Sensitive Indicators of Childhood Listening Difficulties (SICLiD) study, we assessed listening ability using a reliable and validated caregiver questionnaire (the Evaluation of Children's Listening and Processing Skills [ECLiPS]) in a large (n = 146) and heterogeneous sample of 6- to 13-year-old children with normal audiograms. Scores on the ECLiPS were related to a multifaceted laboratory assessment of the children's audiological, psycho- and physiological-acoustic, and cognitive abilities. This report is an overview of the SICLiD study and focuses on the children's behavioral performance. The overall goals of SICLiD were to understand the auditory and other neural mechanisms underlying childhood listening difficulties and translate that understanding into clinical assessment and, ultimately, intervention.

DESIGN

Cross-sectional behavioral assessment of children with "listening difficulties" and an age-matched "typically developing" control group. Caregivers completed the ECLiPS, and the resulting total standardized composite score formed the basis of further descriptive statistics, univariate, and multivariate modeling of experimental data.

RESULTS

All scores of the ECLiPS, the SCAN-3:C, a standardized clinical test suite for auditory processing, and the National Institutes of Health (NIH) Cognition Toolbox were significantly lower for children with listening difficulties than for their typically developing peers using group comparisons via t-tests and Wilcoxon Rank-Sum tests. A similar effect was observed on the Listening in Spatialized Noise-Sentences (LiSN-S) test for speech sentence-in-noise intelligibility but only reached significance for the Low Cue and High Cue conditions and the Talker Advantage derived score. Stepwise regression to examine the factors contributing to the ECLiPS Total scaled score (pooled across groups) yielded a model that explained 42% of its variance based on the SCAN-3:C composite, LiSN-S Talker Advantage, and the NIH Toolbox Picture Vocabulary, and Dimensional Change Card Sorting scores (F[4, 95] = 17.35, p < 0.001). High correlations were observed between many test scores including the ECLiPS, SCAN-3:C, and NIH Toolbox composite measures. LiSN-S Advantage measures generally correlated weakly and nonsignificantly with non-LiSN-S measures. However, a significant interaction was found between extended high-frequency threshold and LiSN-S Talker Advantage.

CONCLUSIONS

Children with listening difficulties but normal audiograms have problems with the cognitive processing of auditory and nonauditory stimuli that include both fluid and crystallized reasoning. Analysis of poor performance on the LiSN-S Talker Advantage measure identified subclinical hearing loss as a minor contributing factor to talker segregation. Beyond auditory tests, evaluations of children with complaints of listening difficulties should include standardized caregiver observations and consideration of broad cognitive abilities.

Auditory neurophysiological development in early childhood: A growth curve modeling approach

OBJECTIVE

During early childhood, the development of communication skills, such as language and speech perception, relies in part on auditory system maturation. Because auditory behavioral tests engage cognition, mapping auditory maturation in the absence of cognitive influence remains a challenge. Furthermore, longitudinal investigations that capture auditory maturation within and between individuals in this age group are scarce. The goal of this study is to longitudinally measure auditory system maturation in early childhood using an objective approach.

METHODS

We collected frequency-following responses (FFR) to speech in 175 children, ages 3-8 years, annually for up to five years. The FFR is an objective measure of sound encoding that predominantly reflects auditory midbrain activity. Eliciting FFRs to speech provides rich details of various aspects of sound processing, namely, neural timing, spectral coding, and response stability. We used growth curve modeling to answer three questions: 1) does sound encoding change across childhood? 2) are there individual differences in sound encoding? and 3) are there individual differences in the development of sound encoding?

RESULTS

Subcortical auditory maturation develops linearly from 3-8 years. With age, FFRs became faster, more robust, and more consistent. Individual differences were evident in each aspect of sound processing, while individual differences in rates of change were observed for spectral coding alone.

CONCLUSIONS

By using an objective measure and a longitudinal approach, these results suggest subcortical auditory development continues throughout childhood, and that different facets of auditory processing follow distinct developmental trajectories.

SIGNIFICANCE

The present findings improve our understanding of auditory system development in typically-developing children, opening the door for future investigations of disordered sound processing in clinical populations.

Conductive hearing loss during development does not appreciably alter the sharpness of cochlear tuning

An increasing number of studies show that listeners often have difficulty hearing in situations with background noise, despite normal tuning curves in quiet. One potential source of this difficulty could be sensorineural changes in the auditory periphery (the ear). Signal in noise detection deficits also arise in animals raised with developmental conductive hearing loss (CHL), a manipulation that induces acoustic attenuation to model how sound deprivation changes the central auditory system. This model attributes perceptual deficits to central changes by assuming that CHL does not affect sensorineural elements in the periphery that could raise masked thresholds. However, because of efferent feedback, altering the auditory system could affect cochlear elements. Indeed, recent studies show that adult-onset CHL can cause cochlear synapse loss, potentially calling into question the assumption of an intact periphery in early-onset CHL. To resolve this issue, we tested the long-term peripheral effects of CHL via developmental bilateral malleus displacement. Using forward masking tuning curves, we compared peripheral tuning in animals raised with CHL vs age-matched controls. Using compound action potential measurements from the round window, we assessed inner hair cell synapse integrity. Results indicate that developmental CHL can cause minor synaptopathy. However, developmental CHL does not appreciably alter peripheral frequency tuning.

Basic Measures of Auditory Perception in Children: No Evidence for Mediation by Auditory Working Memory Capacity

Immature auditory perception in children has generally been ascribed to deficiencies in cognitive factors, such as working memory and inattention. This notion appears to be commonly accepted for all children despite limited empirical evidence. In the present work, we examined whether working memory capacity would predict basic aspects of hearing, pure-tone frequency discrimination and temporal gap detection, in typically-developing, normal-hearing children (7–12 years). Contrary to our expectation, working memory capacity, as measured by digit spans, or intrinsic auditory attention (on- and off-task response variability) did not consistently predict the individual variability in auditory perception. Present results provide no evidence for a role of working memory capacity in basic measures of auditory perception in children. This lack of a relationship may partly explain why some children with perceptual deficits despite normal audiograms (commonly referred to as auditory processing disorders) may have typical cognitive abilities.

Effects of Gap Position on Perceptual Gap Detection Across Late Childhood and Adolescence

The ability to detect a silent gap within a sound is critical for accurate speech perception, and gap detection has been shown to have an extended developmental trajectory. In certain conditions, the detectability of the gap decreases as the gap is placed closer to the beginning of the signal. Early in development, the detection of gaps shortly after signal onset may be especially difficult due to immaturities in the encoding and perception of rapidly changing sounds. The present study explored the development of gap detection from age 8 to 19 years, specifically when the temporal placement of the gap varied. Performance improved with age for all temporal placements of the gap, demonstrating a gradual maturation of gap detection abilities throughout adolescence. Younger adolescents did not benefit from increasing gap onset times, while older adolescents' thresholds gradually improved as gap onset time lengthened. Regardless of age, listeners learned between the two testing days but did not improve within days. Younger adolescents had poorer thresholds for the last block of testing on the second day, returning to baseline performance despite learning between days. These data support earlier studies showing that gaps are harder to detect near stimulus onset and confirm that gap detection abilities continue to mature into adolescence. The data also suggest that younger adolescents do not receive the same benefit of increasing gap onset time and respond differently to repeated testing than older adolescents and young adults.

Regulation of auditory plasticity during critical periods and following hearing loss

Sensory input has profound effects on neuronal organization and sensory maps in the brain. The mechanisms regulating plasticity of the auditory pathway have been revealed by examining the consequences of altered auditory input during both developmental critical periods—when plasticity facilitates the optimization of neural circuits in concert with the external environment—and in adulthood—when hearing loss is linked to the generation of tinnitus. In this review, we summarize research identifying the molecular, cellular, and circuit-level mechanisms regulating neuronal organization and tonotopic map plasticity during developmental critical periods and in adulthood. These mechanisms are shared in both the juvenile and adult brain and along the length of the auditory pathway, where they serve to regulate disinhibitory networks, synaptic structure and function, as well as structural barriers to plasticity. Regulation of plasticity also involves both neuromodulatory circuits, which link plasticity with learning and attention, as well as ascending and descending auditory circuits, which link the auditory cortex and lower structures. Further work identifying the interplay of molecular and cellular mechanisms associating hearing loss-induced plasticity with tinnitus will continue to advance our understanding of this disorder and lead to new approaches to its treatment.

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During CPs, brain plasticity is enhanced and sensitive to acoustic experience.

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Enhanced plasticity can be reinstated in the adult brain following hearing loss.

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Molecular, cellular, and circuit-level mechanisms regulate CP and adult plasticity.

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Plasticity resulting from hearing loss may contribute to the emergence of tinnitus.

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Modifying plasticity in the adult brain may offer new treatments for tinnitus.

Development of the mandarin hearing in noise test for children

Objectives: To develop a Mandarin version of the Hearing in Noise Test for Children (MHINT-C) and examine the maturational effects on sentence recognition.Design: Sentences suitable for evaluating children aged 6-18 years were selected from the adult MHINT to form 12 lists of 10 MHINT-C sentences (Study 1). List equivalence, inter-list reliability, response variability, and maturational effects on sentence recognition were examined using the MHINT-C (Study 2).Study sample: A total of 246 children aged 6.1-17.11 years were included. Six children participated in Study 1; the rest were included in Study 2. To compare these results with adults, 20 native Mandarin-speaking adults aged 18 or above were included in Study 2.Results: MHINT-C list equivalency, inter-list reliability, and response variability were similar to those of the adult MHINT and the Cantonese HINT for children. Sentence recognition in children reached adult-like performance around age 8 in quiet and at ages 15 and 14 in front and side noise conditions, respectively.Conclusions: The MHINT-C can reliably measure sentence recognition in quiet and noise in Mandarin-speaking children. Age-specific correction factors were established.

Experience- and Sex-Dependent Intrinsic Plasticity in the Zebra Finch Auditory Cortex during Song Memorization

For vocal communicators like humans and songbirds, survival and reproduction depend on highly developed auditory processing systems that can detect and differentiate nuanced differences in vocalizations, even amid noisy environments. Early auditory experience is critical to the development of these systems. In zebra finches and other songbirds, there is a sensitive period when young birds memorize a song that will serve as a model for their own vocal production. In addition to learning a specific tutor's song, the auditory system may also undergo critical developmental processes that support auditory perception of vocalizations more generally. Here, we investigate changes in intrinsic spiking dynamics among neurons in the caudal mesopallium, a cortical-level auditory area implicated in discriminating and learning species-specific vocalizations. A subset of neurons in this area only fire transiently at the onset of current injections (i.e., phasic firing), a dynamical property that can enhance the reliability and selectivity of neural responses to complex acoustic stimuli. At the beginning of the sensitive period, just after zebra finches have fledged from the nest, there is an increase in the proportion of caudal mesopallium neurons with phasic excitability, and in the proportion of neurons expressing Kv1.1, a low-threshold channel that facilitates phasic firing. This plasticity requires exposure to a complex, noisy environment and is greater in males, the only sex that sings in this species. This shift to more phasic dynamics is therefore an experience-dependent adaptation that could facilitate auditory processing in noisy, acoustically complex conditions during a key stage of vocal development.SIGNIFICANCE STATEMENT Auditory experience early in life shapes how humans and songbirds perceive the vocal communication sounds produced by their species. However, the changes that occur in the brain as this learning takes place are poorly understood. In this study, we show that in young zebra finches that are just beginning to learn the structure of their species' song, neurons in a key cortical area adapt their intrinsic firing patterns in response to the acoustic environment. In the complex, cocktail-party-like environment of a colony, more neurons adopt transient firing dynamics, which can facilitate neural coding of songs amid such challenging conditions.

Birds of a different feather sing together

A new study sheds light on how sensitivity to communication sounds is established in the brain. Juvenile finches raised with tutors of either the same or different species always learned the tutors’ songs. Cortical neurons developed selectivity for the learned song by tuning for its secondary acoustic features.

Emergent tuning for learned vocalizations in auditory cortex

Vocal learners use early social experience to develop auditory skills specialized for communication. However, it is unknown where in the auditory pathway neural responses become selective for vocalizations or how the underlying encoding mechanisms change with experience. We used a vocal tutoring manipulation in two species of songbird to reveal that tuning for conspecific song arises within the primary auditory cortical circuit. Neurons in the deep region of primary auditory cortex responded more to conspecific songs than to other species' songs and more to species-typical spectrotemporal modulations, but neurons in the intermediate (thalamorecipient) region did not. Moreover, birds that learned song from another species exhibited parallel shifts in selectivity and tuning toward the tutor species' songs in the deep but not the intermediate region. Our results locate a region in the auditory processing hierarchy where an experience-dependent coding mechanism aligns auditory responses with the output of a learned vocal motor behavior.

British children's performance on the listening in spatialised noise-sentences test (LISN-S)

Objective: To investigate whether British children's performance is equivalent to North American norms on the listening in spatialised noise-sentences test (LiSN-S). Design: Prospective study comparing the performance of a single British group of children to North-American norms on the LiSN-S (North American version). Study sample: The British group was composed of 46 typically developing children, aged 6-11 years 11 months, from a mainstream primary school in London. Results: No significant difference was observed between the British's group performance and the North-American norms for Low-cue, High-cue, Spatial Advantage and Total Advantage measure. The British group presented a significantly lower performance only for Talker Advantage measure (z-score: 0.35, 95% confidence interval -0.12 to -0.59). Age was significantly correlated with all unstandardised measures. Conclusion: Our results indicate that, when assessing British children, it would be appropriate to add a corrective factor of 0.35 to the z-score value obtained for the Talker Advantage in order to compare it to the North-American norms. This strategy would enable the use of LiSN-S in the UK to assess auditory stream segregation based on spatial cues.

Pspan: A New Tool for Assessing Pitch Temporal Processing and Patterning Capacity

Purpose The purpose of this study was to evaluate whether merging the clinical pitch pattern test procedure with psychoacoustic adaptive methods would create a new tool feasible to capture individual differences in pitch temporal processing and patterning capacity of children and adults. Method Sixty-six individuals, young children (ages 10-12 years, n = 22), older children (ages 13-15 years, n = 23), and adults (ages 18-33 years, n = 21), were recruited and assigned to subgroups based on reported duration (years) of instrumental music instruction. Additional background information was collected in order to assess if the pitch temporal processing and patterning span developed, the Pspan, was sensitive to individual differences across participants. Results The evaluation of the Pspan task as a scale indicated good parallel reliability across runs assessed by Cronbach's alpha, and scores were normally distributed. Between-subjects analysis of variance indicated main effects for both age groups and music groups recruited for the study. A multiple regression analysis with the Pspan scores as the dependent variable found that 3 measures of music instruction, age in years, and paternal education were predictive of enhanced temporal processing and patterning capacity for pitch input. Conclusions The outcomes suggest that the Pspan task is a time-efficient data collection tool that is sensitive to the duration of instrumental music instruction, maturation, and paternal education. In addition, results indicate that the task is sensitive to age-related auditory temporal processing and patterning performance changes during adolescence when children are 10-15 years old.

Amplitude modulation detection and temporal modulation cutoff frequency in normal hearing infants

The goal of this study was to determine if temporal modulation cutoff frequency was mature in three-month-old infants. Normal-hearing infants and young adults were tested in a single-interval forced-choice observer-based psychoacoustic procedure. Two parameters of the temporal modulation transfer function (TMTF) were estimated to separate temporal resolution from amplitude modulation sensitivity. The modulation detection threshold (MDT) of a broadband noise amplitude modulated at 10 Hz estimated the y-intercept of the TMTF. The cutoff frequency of the TMTF, measured at a modulation depth 4 dB greater than the MDT, provided an estimate of temporal resolution. MDT was obtained in 27 of 33 infants while both MDT and cutoff frequency was obtained in 15 infants and in 16 of 16 adults. Mean MDT was approximately 10 dB poorer in infants compared to adults. In contrast, mean temporal modulation cutoff frequency did not differ significantly between age groups. These results suggest that temporal resolution is mature, on average, by three months of age in normal hearing children despite immature sensitivity to amplitude modulation. The temporal modulation cutoff frequency approach used here may be a feasible way to examine development of temporal resolution in young listeners with markedly immature sensitivity to amplitude modulation.

Speech Recognition Abilities in Normal-Hearing Children 4 to 12 Years of Age in Stationary and Interrupted Noise

Objectives:

The main purpose of this study was to examine developmental effects for speech recognition in noise abilities for normal-hearing children in several listening conditions, relevant for daily life. Our aim was to study the auditory component in these listening abilities by using a test that was designed to minimize the dependency on nonauditory factors, the digits-in-noise (DIN) test. Secondary aims were to examine the feasibility of the DIN test for children, and to establish age-dependent normative data for diotic and dichotic listening conditions in both stationary and interrupted noise.

Design:

In experiment 1, a newly designed pediatric DIN (pDIN) test was compared with the standard DIN test. Major differences with the DIN test are that the pDIN test uses 79% correct instead of 50% correct as a target point, single digits (except 0) instead of triplets, and animations in the test procedure. In this experiment, 43 normal-hearing subjects between 4 and 12 years of age and 10 adult subjects participated. The authors measured the monaural speech reception threshold for both DIN test and pDIN test using headphones. Experiment 2 used the standard DIN test to measure speech reception thresholds in noise in 112 normal-hearing children between 4 and 12 years of age and 33 adults. The DIN test was applied using headphones in stationary and interrupted noise, and in diotic and dichotic conditions, to study also binaural unmasking and the benefit of listening in the gaps.

Results:

Most children could reliably do both pDIN test and DIN test, and measurement errors for the pDIN test were comparable between children and adults. There was no significant difference between the score for the pDIN test and that of the DIN test. Speech recognition scores increase with age for all conditions tested, and performance is adult-like by 10 to 12 years of age in stationary noise but not interrupted noise. The youngest, 4-year-old children have speech reception thresholds 3 to 7 dB less favorable than adults, depending on test conditions. The authors found significant age effects on binaural unmasking and fluctuating masker benefit, even after correction for the lower baseline speech reception threshold of adults in stationary noise.

Conclusions:

Speech recognition in noise abilities develop well into adolescence, and young children need a more favorable signal-to-noise ratio than adults for all listening conditions. Speech recognition abilities in children in stationary and interrupted noise can accurately and reliably be tested using the DIN test. A pediatric version of the test was shown to be unnecessary. Normative data were established for the DIN test in stationary and fluctuating maskers, and in diotic and dichotic conditions. The DIN test can thus be used to test speech recognition abilities for normal-hearing children from the age of 4 years and older.

Cortical Tracking of Speech-in-Noise Develops from Childhood to Adulthood

In multitalker backgrounds, the auditory cortex of adult humans tracks the attended speech stream rather than the global auditory scene. Still, it is unknown whether such preferential tracking also occurs in children whose speech-in-noise (SiN) abilities are typically lower compared with adults. We used magnetoencephalography (MEG) to investigate the frequency-specific cortical tracking of different elements of a cocktail party auditory scene in 20 children (age range, 6-9 years; 8 females) and 20 adults (age range, 21-40 years; 10 females). During MEG recordings, subjects attended to four different 5 min stories, mixed with different levels of multitalker background at four signal-to-noise ratios (SNRs; noiseless, +5, 0, and -5 dB). Coherence analysis quantified the coupling between the time courses of the MEG activity and attended speech stream, multitalker background, or global auditory scene, respectively. In adults, statistically significant coherence was observed between MEG signals originating from the auditory system and the attended stream at <1, 1-4, and 4-8 Hz in all SNR conditions. Children displayed similar coupling at <1 and 1-4 Hz, but increasing noise impaired the coupling more strongly than in adults. Also, children displayed drastically lower coherence at 4-8 Hz in all SNR conditions. These results suggest that children's difficulties to understand speech in noisy conditions are related to an immature selective cortical tracking of the attended speech streams. Our results also provide unprecedented evidence for an acquired cortical tracking of speech at syllable rate and argue for a progressive development of SiN abilities in humans.SIGNIFICANCE STATEMENT Behaviorally, children are less proficient than adults at understanding speech-in-noise. Here, neuromagnetic signals were recorded while healthy adults and typically developing 6- to 9-year-old children attended to a speech stream embedded in a multitalker background noise with varying intensity. Results demonstrate that auditory cortices of both children and adults selectively track the attended speaker's voice rather than the global acoustic input at phrasal and word rates. However, increments of noise compromised the tracking significantly more in children than in adults. Unexpectedly, children displayed limited tracking of both the attended voice and the global acoustic input at the 4-8 Hz syllable rhythm. Thus, both speech-in-noise abilities and cortical tracking of speech syllable repetition rate seem to mature later in adolescence.

Duration of unilateral auditory deprivation is associated with reduced speech perception after cochlear implantation: A single-sided deafness study

OBJECTIVE

Examine the relationship between duration of unilateral deafness and speech perception outcomes after cochlear implantation in adults with single-sided deafness.

METHODS

A systematic review of PubMed articles containing individual speech perception and duration of deafness data from single-sided deaf adults. Studies were selected for detailed review and duration of deafness and speech perception outcomes were extracted, with speech scores reported as percent correct. A linear regression as a function of study and length of deafness was performed.

RESULTS

A statistically significant negative effect of duration of unilateral deafness on speech perception was found, but there was substantial uncertainty regarding the strength of the effect.

DISCUSSION

Existing data make it difficult to either support or reject a hard 5- or 10-year unilateral auditory deprivation limit on cochlear implant (CI) candidacy for patients with single-sided deafness. This is because the totality of available data are consistent with a very small effect, perhaps negligible in practical terms, and just as consistent with a very large effect. Regardless of effect size, the present results have important basic implications. They suggest that unilateral sound deprivation may have a deleterious effect on auditory processing even though more central parts of the auditory system have continued to receive input from a contralateral normal ear.

CONCLUSIONS

Speech perception scores in SSD patients are negatively correlated with duration of deafness, but the limited amount of data from cochlear implant users with long-term single-sided deafness leads to substantial uncertainly, which in turn precludes any strong clinical recommendations. Further study of SSD CI users with long-term deafness will be necessary to generate evidence-based guidelines for implantation criteria in this population.

Adenosine A1 Receptor mRNA Expression by Neurons and Glia in the Auditory Forebrain

In the brain, purines such as ATP and adenosine can function as neurotransmitters and co‐transmitters, or serve as signals in neuron–glial interactions. In thalamocortical (TC) projections to sensory cortex, adenosine functions as a negative regulator of glutamate release via activation of the presynaptic adenosine A1 receptor (A₁R). In the auditory forebrain, restriction of A₁R‐adenosine signaling in medial geniculate (MG) neurons is sufficient to extend LTP, LTD, and tonotopic map plasticity in adult mice for months beyond the critical period. Interfering with adenosine signaling in primary auditory cortex (A1) does not contribute to these forms of plasticity, suggesting regional differences in the roles of A₁R‐mediated adenosine signaling in the forebrain. To advance understanding of the circuitry, in situ hybridization was used to localize neuronal and glial cell types in the auditory forebrain that express A₁R transcripts (Adora1), based on co‐expression with cell‐specific markers for neuronal and glial subtypes. In A1, Adora1 transcripts were concentrated in L3/4 and L6 of glutamatergic neurons. Subpopulations of GABAergic neurons, astrocytes, oligodendrocytes, and microglia expressed lower levels of Adora1. In MG, Adora1 was expressed by glutamatergic neurons in all divisions, and subpopulations of all glial classes. The collective findings imply that A₁R‐mediated signaling broadly extends to all subdivisions of auditory cortex and MG. Selective expression by neuronal and glial subpopulations suggests that experimental manipulations of A₁R‐adenosine signaling could impact several cell types, depending on their location. Strategies to target Adora1 in specific cell types can be developed from the data generated here. Anat Rec, 301:1882–1905, 2018. © 2018 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Developmental deprivation-induced perceptual and cortical processing deficits in awake-behaving animals

Sensory deprivation during development induces lifelong changes to central nervous system function that are associated with perceptual impairments. However, the relationship between neural and behavioral deficits is uncertain due to a lack of simultaneous measurements during task performance. Therefore, we telemetrically recorded from auditory cortex neurons in gerbils reared with developmental conductive hearing loss as they performed an auditory task in which rapid fluctuations in amplitude are detected. These data were compared to a measure of auditory brainstem temporal processing from each animal. We found that developmental HL diminished behavioral performance, but did not alter brainstem temporal processing. However, the simultaneous assessment of neural and behavioral processing revealed that perceptual deficits were associated with a degraded cortical population code that could be explained by greater trial-to-trial response variability. Our findings suggest that the perceptual limitations that attend early hearing loss are best explained by an encoding deficit in auditory cortex.

Activity-dependent synaptic integration and modulation of bilateral excitatory inputs in an auditory coincidence detection circuit

KEY POINTS

Binaural excitatory inputs to coincidence detection neurons in nucleus laminaris (NL) play essential roles in interaural time difference coding for sound localization. Here, we show that the two excitatory inputs are physiologically nearly completely segregated. Synaptic integration shows linear summation of EPSPs, ensuring high efficiency of coincidence detection of the bilateral excitatory inputs. We further show that the two excitatory inputs to single NL neurons are symmetrical in synaptic strength, kinetics and short-term plasticity. Modulation of the EPSCs by metabotropic glutamate receptors (mGluRs) is identical between the two excitatory inputs, maintaining balanced bilateral excitation under neuromodulatory conditions. Unilateral hearing deprivation reduces synaptic excitation and paradoxically strengthens mGluR modulation of EPSCs, suggesting activity-dependent anti-homeostatic regulation, a novel synaptic plasticity in response to sensory manipulations.

ABSTRACT

Neurons in the avian nucleus laminaris (NL) receive bilateral excitatory inputs from the cochlear nucleus magnocellularis, via morphologically symmetrical dorsal (ipsilateral) and ventral (contralateral) dendrites. Using in vitro whole-cell patch recordings in chicken brainstem slices, we investigated synaptic integration and modulation of the bilateral inputs to NL under normal and hearing deprivation conditions. We found that the two excitatory inputs onto single NL neurons were nearly completely segregated, and integration of the two inputs was linear for EPSPs. The two inputs had similar synaptic strength, kinetics and short-term plasticity. EPSCs in low but not middle and high frequency neurons were suppressed by activation of group I and II metabotropic glutamate receptors (mGluR I and II), with similar modulatory strength between the ipsilateral and contralateral inputs. Unilateral hearing deprivation by cochlea removal reduced the excitatory transmission on the deprived dendritic domain of NL. Interestingly, EPSCs evoked at the deprived domain were modulated more strongly by mGluR II than at the counterpart domain that received intact input in low frequency neurons, suggesting anti-homeostatic regulation. This was supported by a stronger expression of mGluR II protein on the deprived neuropils of NL. Under mGluR II modulation, EPSCs on the deprived input show transient synaptic facilitation, forming a striking contrast with normal hearing conditions under which pure synaptic depression is observed. These results demonstrate physiological symmetry and thus balanced bilateral excitatory inputs to NL neurons. The activity-dependent anti-homeostatic plasticity of mGluR modulation constitutes a novel mechanism regulating synaptic transmission in response to sensory input manipulations.

Pitch and Duration Pattern Sequence Tests in 7- to 11-Year-Old Children: Results Depend on Response Mode

BACKGROUND

Pitch pattern sequence (PPS) and duration pattern sequence (DPS) tests are frequently used in the assessment of auditory processing disorder. Current recommendations suggest alternate, interchangeable modes for responding to stimuli.

PURPOSE

The objective of the study is to evaluate the influence of response mode (i.e., humming, pointing, and labeling) and age on PPS and DPS performance of 7- to 11-year-old children.

RESEARCH DESIGN

Laboratory-based testing of school children. Cross-sectional comparison of age, with repeated measures of age, test, ear, and response mode.

STUDY SAMPLE

From 452 children recruited, 228 right-handed children (109 girls) aged 7 years to 11 years 11 months (mean age 9 years 4 months) completed at least one test (PPS: 211, DPS: 198), and 181 children completed both tests. Audiology inclusion criteria include normal hearing thresholds (≤15 dB HL at octave frequencies 250-8000 Hz); word recognition in quiet ≥92%; tympanogram peak compensated static acoustic compliance 0.4-1.6 mmhos; and tympanometric peak pressure -100 to +50 daPa, all in both ears. Other inclusion criteria were Portuguese as first language; right handed; no musical training; no related, known, or observed phonological, learning, neurologic, psychiatric, or behavioral disorder; otologic history; and delayed neuropsychomotor or language development.

DATA COLLECTION AND ANALYSIS

PPS: 30 trials per ear and response condition of three consecutive 500 msec duration intermixed high (1430 Hz) or low (880 Hz) frequency tones presented monaurally at 50 dB HL. The first response condition was humming followed by labeling (naming: high or low). DPS: As per PPS except 1000 Hz tones of intermixed 500 (long) and 250 msec (short) duration. First response was pointing (at a symbolic object) followed by labeling. Trends across age and between tests were assessed using repeated measures generalized linear mixed models. Correlation coefficients were calculated to assess relations among test scores. The two-sided significance level was 0.05.

RESULTS

Older children performed better than younger children in all tasks. Humming the tone pattern (PPS humming) produced generally better performance than either articulating the attributes of the tones (labeling) or pointing to objects representing tone duration. PPS humming produced ceiling performance for many children of all ages. For both labeling tasks and DPS pointing, performance was better on the PPS than on the DPS, for stimulation of the right than the left ear, and in boys than girls. Individual performance on the two tasks was highly correlated.

CONCLUSIONS

Response mode does matter in the PPS and DPS. Results from humming should not be combined with or be a substitute for results obtained from a labeling response. Tasks that rely on labeling a tonal stimulus should be avoided in testing hearing in children or other special populations.

Association between language and hearing disorders - risk identification

OBJECTIVE:

To identify children at risk for hearing and/or language disorders and to investigate the association between these risks by conducting pre-validated hearing and language screenings.

METHODS:

The study was conducted during a polio vaccination campaign in August of 2013 in basic health units in western São Paulo. Parents of children between 2 and 5 years of age were asked to complete two screening tools: a hearing questionnaire (regarding hearing development) and a language production and comprehension scale (including the major language development milestones). The screening tools were administered by different researchers. We compared the risk of having language disorders among children at risk for hearing loss versus children not at risk, as well as the attributable risk and odds ratios. Chi-squared tests and logistic regression analyses were used.

RESULTS:

The study included 479 children with a mean age of three and one-half years, of whom 26.9% were identified as at risk for deficits in language production, 8.6% were at risk for deficits in language comprehension and 14% were at risk for hearing disorders. The children at risk for hearing disorders were twice as likely as those not at risk to exhibit language production and comprehension deficits.

CONCLUSION:

The results of this study highlight the importance of establishing and adopting low-cost procedures such as screenings to identify children at risk of developing language and/or hearing disorders in early childhood.

Auditory deprivation modifies the expression of brain-derived neurotrophic factor and tropomyosin receptor kinase B in the rat auditory cortex

The development and plasticity of central auditory system can be influenced by the change of peripheral neuronal activity. However, the molecular mechanism participating in the process remains elusive. Brain-derived neurotrophic factor (BDNF) binding with its functional receptor tropomyosin receptor kinase B (TrkB) has multiple effects on neurons. Here we used a rat model of auditory deprivation by bilateral cochlear ablation, to investigate the changes in expression of BDNF and TrkB in the auditory cortex after auditory deprivation that occurred during the critical period for the development of central auditory system. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry methods were adopted to detect the mRNA and protein expression levels of BDNF and TrkB in the auditory cortex at 2, 4, 6 and 8 weeks after surgery, respectively. The change in the expression of BDNF and TrkB mRNAs and proteins followed similar trend. In the bilateral cochlear ablation groups, the BDNF-TrkB expression level initially decreased at 2 weeks but increased at 4 weeks followed by the reduction at 6 and 8 weeks after cochlear removal, as compared to the age-matched sham control groups. In conclusion, the BDNF-TrkB signaling is involved in the plasticity of auditory cortex in an activity-dependent manner.

Matched Behavioral and Neural Adaptations for Low Sound Level Echolocation in a Gleaning Bat, Antrozous pallidus

In active sensing, animals make motor adjustments to match sensory inputs to specialized neural circuitry. Here, we describe an active sensing system for sound level processing. The pallid bat uses downward frequency-modulated (FM) sweeps as echolocation calls for general orientation and obstacle avoidance. The bat's auditory cortex contains a region selective for these FM sweeps (FM sweep-selective region, FMSR). We show that the vast majority of FMSR neurons are sensitive and strongly selective for relatively low levels (30-60 dB SPL). Behavioral testing shows that when a flying bat approaches a target, it reduces output call levels to keep echo levels between ∼30 and 55 dB SPL. Thus, the pallid bat behaviorally matches echo levels to an optimized neural representation of sound levels. FMSR neurons are more selective for sound levels of FM sweeps than tones, suggesting that across-frequency integration enhances level tuning. Level-dependent timing of high-frequency sideband inhibition in the receptive field shapes increased level selectivity for FM sweeps. Together with previous studies, these data indicate that the same receptive field properties shape multiple filters (sweep direction, rate, and level) for FM sweeps, a sound common in multiple vocalizations, including human speech. The matched behavioral and neural adaptations for low-intensity echolocation in the pallid bat will facilitate foraging with reduced probability of acoustic detection by prey.

lncRNA expression in the auditory forebrain during postnatal development

The biological processes governing brain development and maturation depend on complex patterns of gene and protein expression, which can be influenced by many factors. One of the most overlooked is the long noncoding class of RNAs (lncRNAs), which are known to play important regulatory roles in an array of biological processes. Little is known about the distribution of lncRNAs in the sensory systems of the brain, and how lncRNAs interact with other mechanisms to guide the development of these systems. In this study, we profiled lncRNA expression in the mouse auditory forebrain during postnatal development at time points before and after the onset of hearing (P7, P14, P21, adult). First, we generated lncRNA profiles of the primary auditory cortex (A1) and medial geniculate body (MG) at each age. Then, we determined the differential patterns of expression by brain region and age. These analyses revealed that the lncRNA expression profile was distinct between both brain regions and between each postnatal age, indicating spatial and temporal specificity during maturation of the auditory forebrain. Next, we explored potential interactions between functionally-related lncRNAs, protein coding RNAs (pcRNAs), and associated proteins. The maturational trajectories (P7 to adult) of many lncRNA - pcRNA pairs were highly correlated, and predictive analyses revealed that lncRNA-protein interactions tended to be strong. A user-friendly database was constructed to facilitate inspection of the expression levels and maturational trajectories for any lncRNA or pcRNA in the database. Overall, this study provides an in-depth summary of lncRNA expression in the developing auditory forebrain and a broad-based foundation for future exploration of lncRNA function during brain development.

The Norwegian Hearing in Noise Test for Children

OBJECTIVES

The aims of this study were to create 12 ten-sentence lists for the Norwegian Hearing in Noise Test for children, and to use these lists to collect speech reception thresholds (SRTs) in quiet and in noise to assess speech perception in normal hearing children 5 to 13 years of age, to establish developmental trends, and to compare the results with those of adults. Data were collected in an anechoic chamber and in an audiometric test room, and the effect of slight room reverberation was estimated.

DESIGN

The Norwegian Hearing in Noise Test for children was formed from a subset of the adult sentences. Selected sentences were repeatable by 5- and 6-year-old children in quiet listening conditions. Twelve sentence lists were created based on the sentences' phoneme distributions. Six-year-olds were tested with these lists to determine list equivalence. Slopes of performance intensity (PI) functions relating mean word scores and signal to noise ratios (SNRs) were estimated for a group of 7-year-olds and adults. HINT normative data were collected for 219 adults and children 5 to 13 years of age in anechoic and audiometric test rooms, using noise levels 55, 60, or 65 dBA. Target sentences always originated from the front; whereas, the noise was presented either from the front, noise front (NF), from the right, noise right (NR) or from the left, noise left (NL). The NR and NL scores were averaged to yield a noise side (NS) score. All 219 subjects were tested in the NF condition, and 95 in the NR and NL conditions. Retest of the NF at the end of the test session was done for 53 subjects. Longitudinal data were collected by testing 9 children as 6, 8, and 13 years old.

RESULTS

NF and NS group means for adults were -3.7 and -11.8 dB SNR, respectively. Group means for 13-year-olds were -3.3 and -9.7, and for the 6-year-olds group means were -0.3 and -5.7 dB SNR, as measured in an anechoic chamber. NF SRTs measured in an audiometric test room were 0.7 to 1.5 higher (poorer) than in the anechoic chamber. Developmental trends were comparable in both rooms. PI slopes were 8.0% dB SNR for the 7-year-olds and 10.1% for the adults. NF SRTs in the anechoic chamber improved by 0.7 dB per year over an age range of 5 to 10 years. Using a PI slope 8 to 10% per dB, the estimated increase in percent intelligibility was 4 to 7% per year. Adult SRTs were about 3 dB lower than those for 6-year-olds, corresponding to 25 to 30% better intelligibility for adults.

CONCLUSIONS

Developmental trends in HINT performance for Norwegian children with normal hearing are similar to those seen in other languages, including American English and Canadian French. SRTs approach adult normative values by the age of 13; however, the benefits of spatial separation of the speech and noise sources are less than those seen for adults.

Influence of medial olivocochlear efferents on the sharpness of cochlear tuning estimates in children

The present study objectively quantified the efferent-induced changes in the sharpness of cochlear tuning estimates and compared these alterations in cochlear tuning between adults and children. Click evoked otoacoustic emissions with and without contralateral broadband noise were recorded from 15 young adults and 14 children aged between 5 and 10 yrs. Time-frequency distributions of click evoked otoacoustic emissions were obtained via the S-transform, and the otoacoustic emission latencies were used to estimate the sharpness of cochlear tuning. Contralateral acoustic stimulation caused a significant reduction in the sharpness of cochlear tuning estimates in the low to mid frequency region, but had no effect in the higher frequencies (3175 and 4000 Hz). The magnitude of efferent-induced changes in cochlear tuning estimates was similar between adults and children. The current evidence suggests that the stimulation of the medial olivocochlear efferent neurons causes similar alterations in cochlear frequency selectivity in adults and children.

Benefits of Stimulus Exposure: Developmental Learning Independent of Task Performance

Perceptual learning (training-induced performance improvement) can be elicited by task-irrelevant stimulus exposure in humans. In contrast, task-irrelevant stimulus exposure in animals typically disrupts perception in juveniles while causing little to no effect in adults. This may be due to the extent of exposure, which is brief in humans while chronic in animals. Here we assessed the effects of short bouts of passive stimulus exposure on learning during development in gerbils, compared with non-passive stimulus exposure (i.e., during testing). We used prepulse inhibition of the acoustic startle response, a method that can be applied at any age, to measure gap detection thresholds across four age groups, spanning development. First, we showed that both gap detection thresholds and gap detection learning across sessions displayed a long developmental trajectory, improving throughout the juvenile period. Additionally, we demonstrated larger within- and across-animal performance variability in younger animals. These results are generally consistent with results in humans, where there are extended developmental trajectories for both the perception of temporally-varying signals, and the effects of perceptual training, as well as increased variability and poorer performance consistency in children. We then chose an age (mid-juveniles) that displayed clear learning over sessions in order to assess effects of brief passive stimulus exposure on this learning. We compared learning in mid-juveniles exposed to either gap detection testing (gaps paired with startles) or equivalent gap exposure without testing (gaps alone) for three sessions. Learning was equivalent in both these groups and better than both naïve age-matched animals and controls receiving no gap exposure but only startle testing. Thus, short bouts of exposure to gaps independent of task performance is sufficient to induce learning at this age, and is as effective as gap detection testing.