Auditory Research publications

Hearing loss is one of the most prevalent sensory disorders, but no commercial biological treatments are currently available. Here, we identify an East Asia-specific founder mutation, the homozygous c.220 C > T mutation in MPZL2, that contributes to a significant proportion of hereditary deafness cases in our cohort study. We find that the disease-causing mutation can be targetable by adenine base editors (ABEs) that enable A·T-to-G·C base corrections without DNA double-strand breaks. To demonstrate this, we develop a humanized mouse model (hMPZL2Q74X/Q74X) that recapitulates human MPZL2 deafness and leads to progressive hearing loss. A PAM-flexible ABE variant with reduced bystander and off-target effects (ABE8eWQ-SpRY:sgRNA3) is packaged in dual adeno-associated viruses (AAVs) and injected into the inner ear of hMPZL2Q74X/Q74X mice and effectively corrects the mutation. This treatment significantly restores hearing function, improves inner ear structural integrity, and reverses altered gene expression. Base editing may hold therapeutic potential for hereditary deafness, including most cases of MPZL2 deafness.

Diverse biological factors, such as sex and age, confer heterogeneity on sensory processing challenges in autism. These factors result in major difficulties in the processing of contextual information in social and non-social situations. To assess divergence in autistic traits, it is critical to consider sex- and age-related variability. Nevertheless, these differences remain largely elusive. Animal models of autism offer the possibility to examine contextual processing at the single-neuron level. Here, we investigated predictive processing of contextual auditory cues in the auditory midbrain of control and prenatally valproic acid-induced rats, a well-established animal model of autism. The rats were prepubertal and adult female and male animals. We performed single-unit recordings in the inferior colliculus of control and prenatally, or in utero , exposed rats under the classical oddball paradigm and non-repetitive cascade control sequences to study neuronal mismatch. This is the neuronal correlate of mismatch negativity, the brain’s automatic response to interruptions in environmental regularity. When comparing control and exposed rats, our results demonstrated a reduction in neuronal mismatch in rats exposed to valproic acid. However, exposed adult females exhibited an increased neuronal mismatch compared to their control counterparts. With respect to sex distinctions, valproic acid induced sex differences in neuronal mismatch of prepubertal and adult rats that are not observable in control animals. Moreover, we detected an age-dependent refinement in prediction error that is not affected by the drug. But valproic acid altered typical developmental trajectory of neuronal mismatch in both sexes. Such observations support sex- and age-related effects of in utero valproic acid exposure in contextual auditory processing at the neural level of the inferior colliculus. In autism, atypical predictive processing of environmental regularities underlies unusual responses to novel experiences. The present study highlights the importance of sex and age, that confer heterogeneity to these challenges.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by complex sensory processing deficits, which continue to elude comprehensive mechanistic understanding. A key unresolved question is how alterations in neural connectivity and communication translate into the behavioral manifestations seen in ASD. Here, we investigate how oligodendrocyte dysfunction alters myelin plasticity and neuronal activity, leading to auditory processing disorder associated with ASD. We focus on the SCN2A gene, an ASD-risk factor, to understand its role in myelination and neural processing within the auditory nervous system. Transcriptional profiling suggests alterations in the expression of myelin-associated genes in Scn2a conditional knockout mice, highlighting the cellular consequences engendered by Scn2a deletion in oligodendrocytes. The results reveal a nuanced interplay between oligodendrocytes and axons, where Scn2a deletion causes alterations in the intricate process of myelination. This disruption instigates changes in axonal properties, presynaptic excitability, and synaptic plasticity at the single cell level. Furthermore, oligodendrocyte-specific Scn2a deletion compromises the integrity of neural circuitry within auditory pathways, leading to auditory hypersensitivity. Our findings reveal a pathway linking myelin deficits to synaptic activity and sensory abnormalities in ASD.

Noise can induce hearing loss. In particular, noise can induce cochlear synapse degeneration leading to hidden hearing loss, which is the most common type of hearing disorders in the clinic. Currently, there is no pharmacological treatment, especially no post-exposure (i.e., therapeutic) treatment available in the clinic. Here, we report that systemic administration of K+ channel blockers by intraperitoneal injection before or after noise exposure significantly ameliorated noise-induced hearing loss (NIHL) and cochlear synapse degeneration. After systemic administration of a general K+-channel blocker tetraethylammonium (TEA) before or after noise exposure, the noise-induced threshold elevation of auditory brainstem responses (ABRs) and reduction of suprathreshold responses were significantly attenuated. The impairment on the active cochlear mechanics measured by distortion product otoacoustic emission (DPOAE) was also reduced. The therapeutic effect was further improved as the post-exposure administration time extended. BK channel is a predominant K+ channel in the inner hair cell. We further found that post-exposure administration of a BK channel blocker GAL-021 could ameliorate NIHL and improved the hearing behavioral responses examined by acoustic startle response (ASR). Finally, both TEA and GAL-021 significantly reduced noise-induced ribbon synapse degeneration. These findings demonstrate a promise of systemic administration of K+ channel blockers to treat synapse degeneration and NIHL after noise exposure, which currently is urgently required in the clinic.

Prestin (SLC26A5) promotes mechanical feedback via outer hair cells (OHC) within the organ of Corti, governed by voltage-dependent kinetics of its charge movements; namely, nonlinear-capacitance (NLC). We study NLC frequency response in mouse OHC membrane patches. The characteristic frequency cut-off (Fis) is 27 kHz. Single point mutations within prestin's chloride binding pocket (S396E and S398E) lack usual anion influence. In agreement, we show absence of anion binding in these mutants through molecular dynamics (MD) simulations. NLC Fis in S396E knock-in mice is unaltered, indicating that high frequency activity is not governed by chloride but likely by viscoelastic loads. Also, the allosteric action of chloride does not underlie piezoelectric-like behavior in prestin, since tension sensitivity of S396E NLC is comparable to WT. Because structures of all studied species appear indistinguishable, with analogous chloride binding pockets, prestin performance likely evolved by modifying, not its protein-anion interaction, but instead mechanical loads on the protein.

Fragile X Syndrome (FXS) is a leading genetic cause of autism spectrum disorders (ASD)- associated behaviors, including sensory processing deficits. Sensory sensitivity and temporal processing deficits in the auditory domain will affect development of language and cognitive functions. The mouse model for FXS, Fmr1 KO, has shown remarkably similar auditory processing phenotypes to patients with FXS. In vitro cortical slice recordings show layer-specific differences in Fmr1 KO mouse local circuits, but it is unclear how these differences translate to changes in sensory processing. In this study, we used a depth multielectrode to record in vivo spikes and local field potentials across layers of the auditory cortex in Fmr1 KO and wildtype mice (WT), converting the latter to current source density (CSD) profiles for improved spatial resolution analysis. We observed reduced CSD sink amplitudes and inter-trial phase coherence, and an increase in trial-to-trial variability for temporally modulated stimuli in the KO mice. Results indicated a differential cortical layer pattern of activity in KO mice, with higher baseline gamma power in superficial and deep layers and higher resting delta and theta power in granular layers. Significantly elevated inter-trial variability was observed for CSD and spikes in KO mice. Auditory steady state responses to clicks or gaps at 40 Hz showed considerable trial-to-trial variability in a layer-specific manner in KO mice. Neural generators in the Fmr1 KO mouse auditory cortex failed to detect short gaps in noise, indicating severe temporal processing deficits. Altogether, this study indicates layer-specific cortical mechanisms of sensory hypersensitivity and temporal processing deficits in FXS.

Machine learning (ML) techniques are increasingly being used to improve disease diagnosis and treatment. However, the application of these computational approaches to the early diagnosis of age-related hearing loss (ARHL), the most common sensory deficit in adults, remains underexplored. Here, we demonstrate the potential of ML for identifying early signs of ARHL in adult mice. We used auditory brainstem responses (ABRs), which are non-invasive electrophysiological recordings that can be performed in both mice and humans, as a readout of hearing function. We recorded ABRs from C57BL/6N mice (6N), which develop early-onset ARHL due to a hypomorphic allele of Cadherin23 (Cdh23ahl), and from co-isogenic C57BL/6NTacCdh23+ mice (6N-Repaired), which do not harbour the Cdh23ahl allele and maintain good hearing until later in life. We evaluated several ML classifiers across different metrics for their ability to distinguish between the two mouse strains based on ABRs. Remarkably, the models accurately identified mice carrying the Cdh23ahl allele even in the absence of obvious signs of hearing loss at 1 month of age, surpassing the classification accuracy of human experts. Feature importance analysis using Shapley values indicated that subtle differences in ABR wave 1 were critical for distinguishing between the two genotypes. This superior performance underscores the potential of ML approaches in detecting subtle phenotypic differences that may elude manual classification. Additionally, we successfully trained regression models capable of predicting ARHL progression rate at older ages from ABRs recorded in younger mice. We propose that ML approaches are suitable for the early diagnosis of ARHL and could potentially improve the success of future treatments in humans by predicting the progression of hearing dysfunction.

The insular cortex is involved in a wide range of auditory functions in the mammalian brain. We studied the organization and basic response properties of auditory neurons in the insular cortex and adjacent areas by recording responses to sound stimuli in anesthetized female rats. Auditory neurons were present in an insulo-parietal auditory field that spans the boundary between the posterior insula, particularly in the granular insular cortex, and the ventral part of the adjacent nonprimary somatosensory fields. Confirming previous reports, neurons in this field had narrow tuning and were preferentially tuned to relatively low frequencies (<16 kHz). Intriguingly, auditory units in this field displayed shorter minimal latencies than units in the primary auditory cortex, as well as weaker sensitivity to deviance. These results establish the existence of a rapid auditory information stream with distinct properties through the insulo-parietal cortex that may parallel the pathway through the primary and anterior auditory fields.

Background: Although several evidence demonstrates a "gut-microbiota-brain axis", suggesting a bidirectional communication between gut microbiota and the central nervous system, less is known about a possible link between the gut and the peripheral nervous system, including the inner ear. Methods: Here, we investigated the impact of intestinal inflammation and the modulation of gut microbiota through fecal microbiota transplantation on hearing sensitivity. Female C57BL/6 mice were assigned to four groups: control (Ctrl), DSS-induced colitis (DSS), FMT from patients with active ulcerative colitis (FMT aUC), and FMT from patients with ulcerative colitis in remission (FMT rUC). Auditory function was evaluated by auditory brainstem responses (ABR). Morphological and molecular analyses on cochlear tissues were performed using immunofluorescence, histological staining, and Western blot to assess inflammation, oxidative stress, and blood-labyrinth barrier integrity. Donor microbiota composition was characterized by 16S rRNA sequencing, and systemic inflammation was evaluated by measuring serum lipopolysaccharide (LPS) levels. Results: We found that intestinal dysbiosis is associated with functional, morphological, and molecular alterations in the cochlea, such as increased oxidative stress, inflammation, and altered blood-labyrinth barrier permeability. This leads to macrophage infiltration and immune response activation through the MyD88/NF-κB pathway. Notably, these effects were exacerbated by FMT from subjects with aUC, while FMT from patients with rUC provided a protective effect on cochlear functions. Conclusions: Overall, our findings suggest that gut inflammation, microbiota alteration, or its therapeutic modulation can impact inner ear pathology: worsening gut inflammatory status negatively affects hearing sensitivity, while the restoration of gut microbiota positively impacts auditory function.

Purpose Best practices in audiology recommend assessing speech understanding in noisy environments, especially for those with communication difficulties. Speech-in-noise (SiN) assessments such as the QuickSIN are used for validating signal processing in hearing aids (HAs) and are linked to HA satisfaction. This project seeks to enhance QuickSIN test efficiency by applying recent advancements in automatic speech recognition (ASR) technologies. Method Twenty-three adults with sensorineural hearing loss were fitted bilaterally with Unitron Moxi HAs and were administered the QuickSIN test in low and high reverberation environments. Testing was performed with two different HA programs: an omnidirectional program and a fixed directional microphone program. QuickSIN sentences were presented from 0° azimuth and competing babble from either 0°, laterally from 90° or 270°, or simultaneously from 90°, 180°, and 270° azimuths. Participants’ verbal responses to QuickSIN stimuli were scored by an audiologist and were recorded in parallel for offline transcription and scoring by ASR models from Amazon, Microsoft, NVIDIA, and Picovoice. The ASR-derived QuickSIN scores were compared to the corresponding audiologist-derived scores. Results Repeated Measures ANOVA results revealed that all ASR models overestimated the QuickSIN scores across most test conditions. Bland-Altman analyses showed that the Amazon ASR model had the least bias and the narrowest range for the limits of agreement, in comparison to the manual scoring by an experienced audiologist. Conclusions Some ASR models, such as Amazon, demonstrated performance comparable to that of an audiologist in automatically scoring QuickSIN tests. However, further refinements are necessary to increase the robustness of the ASR models in scoring low SNR loss test conditions.

Age-related hearing loss is common in the human population but it is highly heterogeneous in aetiology which has hampered efforts to develop ways of stopping its progression. Three major sites of the initial dysfunction are the sensory hair cells, their innervation, and the stria vascularis which generates the high potassium endolymph maintained at a high endocochlear potential bathing the apical surface of hair cells. Treatments aimed at the initial site-of-lesion may be useful, and diagnostic tools to distinguish the primary site would help stratify clinical trials and facilitate selection of the most suitable treatment for each person. Here we report a new non-invasive test that distinguishes mutant mice with known stria vascularis dysfunction and reduced endocochlear potential from mice with sensory hair cell or neural defects but with normal endocochlear potential. It is based on measuring inter-trial coherence in auditory brainstem responses to individual stimuli. Mice with reduced strial function show good inter-trial coherence compared with the amplitude of the averaged response, while mice with sensory or neural deficits show poor coherence. This method might be useful in humans to predict whether they have reduced strial function, which cannot be measured directly, and identify who would benefit from treatments aimed at boosting strial function.

Middle age represents a critical period of accelerated brain changes and provides a window for early detection and intervention in age-related neurological decline. Hearing loss is a key early marker of such decline and is linked to numerous comorbidities in older adults. Yet, ~10% of middle-aged individuals who report hearing difficulties show normal audiograms. Cochlear neural degeneration (CND) could contribute to these hidden hearing deficits, though its role remains unclear due to a lack of objective diagnostics and uncertainty regarding its perceptual outcomes. Here, we employed a cross-species design to examine neural and behavioral signatures of CND. We measured envelope following responses (EFRs) – neural ensemble responses to sound originating from the peripheral auditory pathway – in young and middle-aged adults with normal audiograms and compared these responses to young and middle-aged Mongolian gerbils, where CND was histologically confirmed. We observed near-identical changes in EFRs across species that were associated with CND. Behavioral assessments revealed age-related speech-in-noise deficits under challenging conditions, while pupil-indexed listening effort increased with age even when behavioral performance was matched. Together, these results demonstrate that CND contributes to speech perception difficulties and elevated listening effort in midlife, which may ultimately lead to listening fatigue and social withdrawal.

Circadian sensitivity significantly influences the severity of noise-induced hearing loss (NIHL), but the underlying mechanisms remain unclear. Here, we applied single-cell RNA sequencing to 97,043 cochlear cells, identifying macrophages as the primary immune responders to acoustic trauma, with a notable increase in their proportion in the cochlea. Immunofluorescence confirmed significant recruitment and activation of cochlear macrophages following noise exposure, while in vivo macrophage depletion resulted in the recovery of hearing. Furthermore, analyses of differentially-expressed genes and pathways revealed pronounced activation of NLRP3 inflammasome signaling in macrophages during night-time noise exposure. Measurements of elevated IL-1β and IL-18 expression in cochlear macrophages by multiplex immunohistochemistry correlated with heightened inflammation in the night-time exposure group. These findings were further confirmed by the administration of the selective NLRP3 inhibitor CY-09, which mitigated inflammasome activation, preserved synaptic integrity, and protect against hearing loss. In conclusion, our findings underscore the role of macrophage-driven NLRP3 inflammasome activation in mediating circadian variations in cochlear damage, offering a potential therapeutic target for mitigating NIHL.

Fluent speech production is mediated by serially ordering and preparing motor plans corresponding to target speech sounds, a process known as speech-motor sequencing. Here we used high-density direct cortical recordings while 14 participants spoke utterances with varying phonemic and syllabic sequence complexity after reading a target sequence and a delay period. Phasic activations corresponding to speech production and auditory feedback were observed, but also sustained neural activity that persisted throughout all task phases including the target presentation, the delay period and production of the sequence. Furthermore, sustained activity in a specific area, the middle precentral gyrus (mPrCG), was both modulated by sequence complexity and predicted reaction time, suggesting a role in speech-motor sequencing. Electrocortical stimulation of the mPrCG caused speech disfluencies resembling those seen in apraxia of speech. These results suggest that speech-motor sequencing is mediated by a distributed cortical network in which the mPrCG plays a central role.

Hearing hinges upon the ear’s ability to enhance its responsiveness by means of an energy-expending active process that amplifies the very mechanical inputs that it detects. This process is defined by four properties that, although seemingly unrelated, consistently occur together: amplification, sharp frequency tuning, compressive nonlinearity, and spontaneous otoacoustic emission. In nonmammal tetrapods, the active process is evident in individual hair cells. The hair bundles of the bullfrog, for example, exhibit all four attributes by operating near a Hopf bifurcation—a critical regime in which these properties naturally coalesce. In mammals, however, the delicate nature of the cochlea has restricted the evidence for an active process to studies in vivo, where it is generally attributed to the collective effort of the outer hair cells that energize the traveling wave along the cochlear spiral. As a result, the cellular mechanisms that underlie the properties of mammalian hearing remain contested, with uncertainty about whether criticality plays a role in the cochlea’s active process. Here we show that, when placed in a recording chamber that closely mimics the in vivo physiological environment, a segment of the mammalian cochlea ex vivo displays the features of the active process—amplification, frequency tuning, compressive nonlinearity, and the generation of distortion products. We show that this process operates locally, independently of traveling waves, and that the sensory epithelium achieves active amplification by operating near criticality at a Hopf bifurcation. The results reveal the existence of a unified biophysical principle that underlies auditory processing across species and even phyla.

In the mammalian inner ear, cochlear inner hair cells (IHCs) enable accurate and faithful synaptic sound encoding, while outer hair cells (OHCs) perform frequency-specific sound amplification and fine-tuning through their intrinsic voltage-dependent somatic electromotility. This latter process is facilitated by the unique trilaminate structure of the OHC lateral wall, which consists of the plasma membrane that is densely occupied by the transmembrane motor protein Prestin, the submembrane actin- and spectrin-based cytoskeleton, and the endomembranous subsurface cisternae. This complex system provides mechanical resilience while allowing for cell expansion and contraction during electromotility. Whereas the ultrastructure of the lateral wall is well described, its molecular architecture remains largely elusive. Here, we identified Paralemmin-3 (Palm3) as a novel protein specifically localized to the lateral walls of auditory HCs to play a crucial role in connecting the plasma membrane to the underlying cytoskeleton and subsurface cisternae. Palm3 -KO mice display early-onset and progressive hearing impairment that results from diminished cochlear amplification. Subsequent multiscale morphological analyses revealed structural collapse of OHCs that led to progressive and extensive OHC loss along the tonotopic axis. Palm3 -KO OHCs exhibited disrupted expression and distribution of several membrane-associated proteins – including spectrin isoforms and Prestin – suggesting an essential role of Palm3 in plasma membrane scaffolding. Electron tomography of OHC lateral walls revealed significantly fewer and structurally perturbed subsurface cisternae. Finally, adeno-associated virus (AAV)-mediated rescue of Palm3 during early postnatal development partly restored hearing function, enhanced OHC survival, and restored OHC cell shape as well as membrane protein expression levels. In summary, Palm3 is a key component of the submembrane cytoskeleton in cochlear hair cells, playing a fundamental role in hair cell biology and hearing, and emerges as an attractive candidate for the long-elusive “pillar” component of the hair cell lateral wall ultrastructure.

Sensory-motor control requires the integration and monitoring of sensory feedback resulting from our behaviors. This self-monitoring is thought to result from comparisons between predictions about the expected sensory consequences of action and the feedback actually received, resulting in activity that encodes feedback error. Although similar mechanisms have been proposed during speech and vocal production, including sensitivity to experimentally perturbed auditory feedback, evidence for a vocal “error signal” has been limited. Here, we recorded from the auditory cortex of vocalizing nonhuman primates, using real-time frequency shifts to introduce feedback errors of varying magnitude and direction. We found neural activity that scaled with the magnitude of feedback error in both directions, consistent with vocal error monitoring at both the individual unit and population levels. This feedback sensitivity was greater than expected based upon passive sensory responses and was specific for units in the vocal frequency range. Feedback responses also predicted subsequent compensatory changes in vocal production. These results provide evidence that the auditory cortex encodes the degree of vocal feedback error using both unit-level error calculations and changes in the population of neurons involved. These mechanisms may provide critical error information necessary for feedback-dependent vocal control.

Damage to the cochlear outer hair cell (OHC) is a major cause of deafness in mammals. OHCs amplify the auditory signals to enhance the sensitivity and sound frequency selectivity of the auditory system. However, detailed mechanisms underlying functional OHC regulation remain unclear. Here, it is demonstrated that volume‐regulated anion channels (VRACs) are essential for OHC function. VRAC subunits are highly expressed in OHCs. Genetic deletion of leucin‐rich repeat containing 8A (LRRC8A), the obligatory VRAC subunit, in hair cells results in hearing loss, whereas re‐expressing LRRC8A in the cochlea restores hearing in LRRC8A‐deficient mice. By employing patch‐clamp electrophysiology, it is shown that VRAC in OHCs is activated by hypotonicity and is involved in regulating cell volume. Furthermore, the nonlinear capacitance (NLC), a measure of electromotility, is decreased in the OHCs from LRRC8A‐deficient mice. Therefore, LRRC8A deficiency compromises electromotility of OHCs and impairs signal amplification. In conclusion, the findings highlight the essential role of VRAC in OHC electromotility and its necessity for auditory function.

The first-spike latency (FSL) is an important temporal characteristic of a neurophysiological response. We study the FSLs of sound-driven responses in individual neurons in the rat’s auditory midbrain. Responses were elicited by a train of stimuli created using multiple presentations of two tone bursts with different frequencies. Presentations of the two sounds were interleaved temporally in a random order. We found that the mean and the temporal variation of FSL of the response elicited by a sound was increased when the sound was presented more frequently or when it was moved from the ear that drove an excitatory response to the ear that drove an inhibitory effect. Furthermore, the FSL of response to one sound was dependent on the spatial location of the other sound. Results suggested that the timing of the first spike could be used by midbrain neurons to encode information related to the probability of occurrence and spatial location of a sound. It could also be used to gauge how the sound was related to the other sound in spatial location. These results enhance our understanding of neural bases of binaural hearing, especially in an environment with temporally separated competing sounds.

Age-related hearing loss (ARHL) is the most common sensorineural hearing loss, and the dysfunction of spiral ganglion neurons (SGNs) and ribbon synapses plays a crucial role in the pathogenesis. The fibroblast growth factor 13 (FGF13) is considered to be associated with neuronal survival and synaptic transmission. However, whether FGF13 is involved in degeneration of SGNs and ribbon synapses, the typical changes of ARHL, is still unknown. Firstly, the expression of FGF13 mRNA and protein, was all dramatically decreased in the SGNs of aged mice, accompanied by impaired SGNs and ribbon synapses. More importantly, specific upregulation of FGF13 in SGNs significantly reduced hearing threshold, improved wave I amplitude, and alleviated loss of SGNs as well as ribbon synapses. Furthermore, the proteomic analysis and verification results suggested that the decrease of FGF13 induced the loss of SGNs and ribbon synapses partly by regulating the ORC1. Taken together, our data revealed that FGF13 might protect SGNs and ribbon synapses by regulating the expression of ORC1, which could provide a new idea and targets for the prevention and treatment of ARHL.