Auditory Research publications

Background: Noise-induced hearing loss (NIHL) is a pervasive occupational health challenge, yet the individual susceptibility mechanisms remain unclear. Ferroptosis, an iron-dependent form of programmed cell death, has been implicated in cochlear hair cell damage. This study aims to elucidate the regulatory role of the transcription factor FOXA2 and the deacetylase SIRT1 in ferroptosis and to investigate the association between SIRT1 genetic polymorphisms and NIHL susceptibility in occupational populations. Methods: We employed a multi-level study design combining epidemiological investigation, animal models, and cellular experiments. First, a case–control study was conducted involving 1314 noise-exposed workers (639 cases vs. 675 controls) from a chemical fiber enterprise in Jiangsu Province to analyze the association between SIRT1 single nucleotide polymorphisms (SNPs) and NIHL risk. Second, a C57BL/6J mouse model exposed to 120 dB white noise was established to assess cochlear morphology and protein expression. Third, in HEI-OC1 cochlear hair cells, we performed siRNA-mediated knockdown of Foxa2 and dual-luciferase reporter assays to verify the transcriptional regulation of SIRT1 and its downstream effects on the ferroptosis pathway. Results: Population analysis revealed that the SIRT1 rs12778366 C allele was significantly associated with increased NIHL risk (OR = 1.386, 95% CI: 1.084–1.772, p = 0.009), and this association remained significant after adjustment (p = 0.041). Stratified analysis further revealed a significant gene–environment interaction in workers with >15 years of noise exposure (OR = 2.126, 95% CI: 1.401–3.226, p < 0.001). In vivo, noise exposure led to significant downregulation of Sirt1 and Foxa2 in cochlear tissues, accompanied by elevated ferroptosis markers (Fe2+, MDA) and depleted antioxidant defenses (GSH, xCT, and GPX4). Mechanistically, we demonstrate that FOXA2 transcriptionally activates SIRT1 by binding to its promoter. Knockdown of FOXA2 in vitro suppressed SIRT1 expression, suppressed xCT, a key component of the System Xc−/GPX4 antioxidant axis, and promoted ferroptosis-related cellular changes. Conclusions: This study identifies a novel protective axis where FOXA2 prevents noise-induced ferroptosis in cochlear hair cells by transcriptionally upregulating SIRT1 and maintaining xCT-mediated antioxidant defense. Furthermore, the SIRT1 rs12778366 polymorphism is identified as a candidate variant warranting further investigation in independent cohorts before clinical translation.

Introduction Sensory processing depends on interactions between neural circuits that convey and regulate information across cortical and subcortical networks. Classical frameworks distinguish driving inputs, which transmit sensory content via suprathreshold activation, from modulatory inputs, which alter neuronal excitability without directly eliciting spiking. However, physiological signatures of these circuit types that generalize widely across distributed brain regions remain unclear. Methods We functionally differentiated driving and modulatory circuits in the awake macaque brain by jointly quantifying suprathreshold multiunit activity (MUA) and oscillatory phase coherence (inter-trial coherence, ITC) across eight cortical and thalamic structures during auditory, visual, and eye-movement conditions. Results Preferred sensory stimuli elicited broadband ITC increases accompanied by robust MUA, yielding relatively uniform spectral distributions across adjacent frequency bands, consistent with driving inputs. In contrast, non-preferred sensory and eye-movement related events produced narrowband, frequency-specific ITC modulation without concurrent firing, characterized by dominant peaks at stimulation or event rates, consistent with modulatory inputs. These two response types were observed within individual regions, revealing two separable modes of neural activity. Discussion This narrowband ITC modulation is indicative of coordinated phase alignment, capable of dynamically regulating information transfer mediated by driving inputs across thalamocortical circuits. These findings identify distinct spectrotemporal signatures of driving and modulatory circuit properties across cortical and thalamic levels and demonstrate that subthreshold oscillatory modulation is a widespread phenomenon reflecting cross-modal and saccadic-related influences on neural excitability.

In nature, animals learn to replace predisposed behaviors with new strategies, yet the neural constraints on these transitions are unclear. Using an ethological search task in mice, we reveal medial prefrontal cortical (mPFC) neural correlates of a predisposed win-stay strategy that decays as animals learn to follow a more reliable auditory cue. Auditory cortex (ACx) activity predicts correct trial-by-trial sound-guided search, even on day one of training. This prognostic coding strengthens with learning and emerges from suppressed spiking, most pronounced in neurons tuned laterally to the cue’s spectrum. Chemogenetic disruption reveals ACx contributions to improving performance. Unexpectedly, the global silencing of mPFC accelerates successful usage of sound-tracking, contrary to its canonical role in flexible or stimulus-dependent behavior. Instead, a decentralized multiexpert competition model best predicts behavior and causal perturbations. These findings suggest that mPFC implements a default strategy based on prior knowledge, which actively hinders the expression of more efficient strategies.

The auditory nerve (AN) glial transition zone (GTZ), where myelination shifts from Schwann cells in the peripheral AN to oligodendrocytes in the central AN, is a unique biological niche housed within the cochlear modiolus. Although age-related hearing loss (ARHL) is associated with AN degeneration, the neuroimmune mechanisms contributing to age-related myelin pathology and altered immune cell function remain poorly defined. We hypothesized that the AN GTZ is especially vulnerable to age-related immune activity which may contribute to AN degeneration and myelin pathology. Using an ARHL mouse model, we combined large-field light sheet microscopy of tissue-cleared mouse temporal bones, three-dimensional high-resolution imaging, and quantitative immunohistochemistry to evaluate the AN GTZ. RNA-sequencing was used to evaluate age-related changes in gene expression of the whole AN. Human temporal bones were also examined to evaluate the AN and its macrophages/microglia. RNA-sequencing revealed age-associated enrichment of neuroinflammation and myelin degeneration-related pathways. Aging was associated with an increase in Iba1 + macrophages/microglia throughout the AN, with prominent accumulation at the AN GTZ. The aged AN GTZ contained Iba1 + subpopulations expressing CD206, Gal3, CD163, and Lamp1, suggesting enhanced phagocytic activity and altered activation state at the AN GTZ. CD68 + cells were also increased at the AN GTZ, as well as the central AN, with aging. Macrophages/microglia contained significantly more internalized myelin debris across all regions of the AN with aging, including myelin localized within Lamp1 + lysosomes of Iba1 + cells. More importantly, normal-appearing myelin was frequently observed within macrophages/microglia at the AN GTZ, but not in the peripheral or central regions of the AN. Myelin debris within Iba1 + cells was also found in the human AN, consistent with our findings in mouse. Together, these findings identify the AN GTZ as a unique microenvironment with age-related alterations in phagocytic activity and immune activation. The immune cell heterogeneity and enhanced myelin phagocytosis observed in the aging AN emphasize the importance of defining how distinct macrophage/microglia populations contribute to AN degeneration and ARHL.

Mutations in transmembrane channel-like protein 1 (TMC1), the pore-forming component of the mechano-electrical transducer (MET) channel in auditory hair cells, cause cell death and deafness in 3-wk old mice. We studied mice with mutations Tmc1 p.T416K, p.M412K, p.D528N, and p.D569N, which possessed functional MET channels at postnatal day (P)6 but became deaf before P21. These Tmc1 mutants had channels with reduced Ca 2+ permeability and lower expression of the PMCA2 calcium pump in outer hair cell (OHC) stereocilia. The reduction in PMCA2 density was directly correlated with reduced Ca 2+ entry via the MET channel. Over the first postnatal week, PMCA2 expression decreased in cochlear cultures containing lowered extracellular Ca 2+ , but after P11, PMCA2 density was insensitive to Ca 2+ changes. The lower PMCA2 density in mutants was maintained into adulthood and may contribute to hair cell death. Before the onset of hearing, PMCA2 continuously turns over, and its insertion into stereocilia from an identified vesicular compartment is regulated by cytoplasmic [Ca 2+ ]. PMCA2 turnover was strongly inhibited by the endocytosis blocker, Pitstop2, and by PtdIns(4,5)P 2 blockers like phenylarsine oxide (PAO), which was shown to elevate stereociliary [Ca 2+ ]. We argue the effects of PAO on mechanotransduction may be partly due to this Ca 2+ increase. OHC bundles also expressed Neuroplastin (NPTN), a PMCA2 accessory protein, whose development paralleled PMCA2, and we propose it stabilizes the pump complex in stereocilia. NPTN expression was delayed about 2 d relative to PMCA2 and was less Ca 2+ sensitive, implying it originates from a different internal pool of vesicles.

Measurements and models of cochlear mechanics are built upon understanding the fluid mechanics within the cochlear scalae and the fluid interactions within the organ of Corti, basilar membrane (BM), and tectorial membrane, which together make up the organ of Corti complex (OCC). Even in the absence of an active mechanism, the passive cochlea exhibits a traveling wave, which peaks at a location slightly basal of the active peak for a given stimulus frequency, and terminates at a location similar to that of the active traveling wave. The mechanics that result in the termination of the traveling wave are not fully understood. Here, we examine motion in the lateral region of the guinea pig OCC, including the BM, Boettcher's cells (BCs), and Hensen's cells, using optical coherence tomography. We explore this motion as a potential source of viscous forces due to motion gradients. The BCs lie on the BM and were found to move at the same amplitude as the BM. Beyond the BCs, displacement amplitudes exponentially decreased, suggesting that the lateral region motion is "fluid-like." The displacement amplitude decay rates in the lateral region were similar to motion decay rates previously observed in the scala tympani fluid. We compare our results to predictions from a 3D cochlear model and estimate power dissipation as a result of the viscous forces associated with the displacement gradients in the lateral region. The fluid-like motion and viscous forces in the lateral region may serve as a source of power dissipation and thus traveling wave damping.

Tinnitus involves peripheral auditory damage and aberrant central plasticity, with dysregulated BDNF signaling linking injury to compensation. Yet, direct evidence connecting BDNF/AKT/mTOR pathway activation to behavioral phenotypes is limited. This study examined BDNF/AKT/mTOR expression in the inferior colliculus (IC) of sodium salicylate (SS)-induced tinnitus rats and assessed therapeutic inhibition. Rats received intraperitoneal SS, showing decreased GPIAS ratios, elevated ABR thresholds, and upregulated BDNF/TrkB/AKT/mTOR phosphorylation in the IC-changes associated with tinnitus-like behavior. Bilateral IC microinjection of BDNF siRNA or systemic rapamycin revealed that siRNA suppressed BDNF/TrkB and ameliorated tinnitus without improving hearing, while rapamycin reduced mTOR phosphorylation and partially alleviated behavior. These results first demonstrate that BDNF/AKT/mTOR upregulation in the IC contributes to tinnitus in SS rats, and its inhibition improves behavioral manifestations without reversing peripheral hearing loss.

Sleep is critical for consolidating recent experiences into memories. A key mechanism underlying this process is hippocampal sharp-wave ripples (SWRs). Although SWR-dependent memory consolidation is often viewed as an "offline" process, sounds heard during sleep are processed by a highly active auditory system that projects to medial temporal lobe structures, providing a pathway by which sounds may modulate hippocampal activity. While processing salient sounds during sleep can be adaptive, whether ongoing processing of environmental sounds interferes with SWR-dependent memory consolidation remains unknown. To address this question, we recorded neural activity in the CA1 region of the hippocampus in sleeping rats and used a closed-loop system to deliver non-waking broadband noise (BBN) stimuli during or outside of SWRs. We found that BBN suppressed ripple power and reduced SWR rates. BBN delivered during SWRs (On-SWR) produced a greater reduction in ripple power than BBN delivered outside SWRs (Off-SWR). This suppression was accompanied by substantial changes in SWR-associated spiking. We next tested the influence of BBN on memory consolidation using a conditioned place preference paradigm. On-SWR BBN presentation during post-learning sleep abolished memory retention 24 h after learning while sparing memory immediately after sleep. By contrast, Off-SWR BBN weakened memory at both time points. Notably, On-SWR BBN induced a significantly larger impairment in memory 24 h after learning as compared with Off-SWR BBN. These findings suggest that exposure to noise during sleep disrupts hippocampal activity and impairs memory consolidation in a manner that depends on the timing of sounds relative to SWRs.

Background Chronic suppurative otitis media (CSOM) can lead to sensorineural hearing loss (SNHL), but the underlying mechanisms remain incompletely understood. This study aimed to investigate whether the outer membrane vesicles (OMVs) from Pseudomonas aeruginosa ( P.aeruginosa ), a common CSOM pathogen, can induce ototoxicity via activation of NLRP3 inflammasome. Methods A CSOM model was established in C57BL/6 mice by intratympanic injection of P.aeruginosa -derived OMVs. The pathological changes in the middle and inner ear and the activation of the NLRP3 inflammasome pathway were evaluated using cochlear tissues from model mice, together with in vitro models employing organ of Corti-derived (HEI-OC1) cells and postnatal day 4 (P4) mouse cochlear explants, through histopathological staining, immunoassays, and RNA sequencing. The protective role of the NLRP3 inhibitor MCC950 was additionally investigated. Results P. aeruginosa OMVs induced dose- and time-dependent reductions in cellular metabolic activity in the HEI-OC1 organ of Corti cell line, as well as cochlear hair cell damage and NLRP3 inflammasome activation in postnatal P4 cochlear explants. In vivo, OMV inoculation provoked CSOM and inner ear injury within 14 days, accompanied by significant hair cell loss. RNA-sequencing analysis of CSOM mouse cochleae identified 2583 differentially expressed genes, predominantly enriched in inflammatory pathways, with marked upregulation of NLRP3, Pycard, Casp1, GSDMD, and IL-1β. Treatment with MCC950 significantly alleviated inner ear inflammation, preserved cochlear morphology, reduced hair cell damage, and suppressed the expression of NLRP3, ASC, caspase-1, and GSDMD. Conclusion These findings provide evidence supporting the hypothesis that P. aeruginosa OMVs contribute to CSOM-associated cochlear damage both in vivo and in vitro, a process associated with NLRP3 inflammasome activation within the inner ear. While causality cannot be fully established, inhibition of NLRP3 signaling with MCC950 mitigated inner ear injury and suppressed pyroptosis-related effectors, implying its potential as a novel therapeutic strategy for CSOM-related SNHL.

Aminoglycoside antibiotics such as kanamycin induce sensorineural hearing loss by killing hair cells, resulting in secondary degeneration of spiral ganglion neurons (SGNs). Previous studies show that anti-inflammatory agents reduce SGN death, implicating a causal role of the immune response. This is consistent with observations of increased numbers of macrophages and lymphocytes, including T and NK cells, in the spiral ganglion after exposure to aminoglycosides. Here, we directly test the role of T cells and other lymphocytes in SGN degeneration in kanamycin-deafened rats. Homozygous RNU nude rats that lack T cells – but retain NK and B cells– show neurodegeneration similar to rats with a normal T cell complement, indicating that T cells are not necessary for neurodegeneration. Homozygous SRG rats lacking all lymphocytes (i.e., T, B, and NK cell-deficient), exhibit remarkable regional variation in the pattern of spiral ganglion degeneration post-deafening. In the basal half of the ganglion, SGN degeneration is significantly reduced in deafened SRG rats, implying a role for lymphocytes, presumably NK cells of the innate immune system, in SGN death. In the apical half of the deafened ganglion, SGN degeneration is not significantly affected by the lack of all lymphocytes, implying a role for other cellular mechanisms.

Spontaneous calcium (Ca 2+ ) waves play a critical role as internal stimuli in the early developing auditory system before the onset of sensory experiences. However, neither the spatiotemporal control of spontaneous Ca 2+ waves nor their impacts on auditory development are well understood. Here we report that a lateral array of inner supporting cells (ISCs) beneath the inner hair cells displays a spontaneous ultra‐long, ultra‐fast, transient Ca 2+ flash, termed “Ca 2+ lightning”, which triggers a series of simultaneous bursts of Ca 2+ waves in the whole cochlea, before the ear canal opening. The Ca 2+ lightning margins the cochlear ISCs at different developmental stages that correspondingly exhibit different Ca 2+ activities. Triggered by an ATP‐induced high‐level Ca 2+ wave, the Ca 2+ lightning rapidly propagates laterally into neighboring ISCs through the intricate interplay of the T‐type Ca 2+ channel, Anoctamin 1 (Ano1) Ca 2+ ‐activated Cl − channel and Connexin 26 (Cx26). The genetic deletion of Cav3.2, Ano1, or Cx26 abrogates Ca 2+ lightning flashes and dysregulates cell development and functions in peripheral cochleae. We propose that cochlear Ca 2+ lightning flashes orderly with Ca 2+ waves together orchestrate the spatiotemporal maturation processes of the peripheral auditory system before the onset of hearing.

Intratympanic (IT) injection of corticosteroids is a standard clinical treatment for sensorineural hearing loss; however, achieving both biocompatibility and efficient cochlea drug delivery remains a significant challenge. Herein, we engineered a novel drug nanocrystal (NS)-loaded thermo-reversible hydrogel (NS-TG) system of dexamethasone-21-palmitate (DEX-P), a lipophilic prodrug of dexamethasone (DEX), for improved IT delivery. NSs with a mean diameter of 835.0 nm were fabricated using a dual centrifugation process with polyvinyl alcohol as the stabilizer. The NS-TG system, comprising NSs in a 19% (w/v) Poloxamer 407 hydrogel, exhibited rapid gelation (2–3 min) and a 31-fold increase in drug solubility (1.57 ± 0.02 mg/mL) compared to NS alone, through micellar solubilization. In vitro cytotoxicity assays in HEI-OC1 cells revealed that NS-TG is highly biocompatible, maintaining cell viability, whereas the commercial lipid emulsion (Lipothason®) induced significant cytotoxicity. In vivo pharmacokinetic evaluation in mice revealed that IT NS-TG provided superior cochlear drug absorption compared to DEX-SP solutions and DEX-P NS, despite showing lower absorption than the lipid emulsion. These findings suggest that the DEX-P NS-TG system, pending further investigation, could serve as a promising platform for cochlear steroidal delivery, offering an optimal balance between delivery efficiency and local safety for treating inner ear diseases.

Like mammals, some reptiles possess sensitive and frequency-selective hearing at mid- to high-kilohertz frequencies. Both groups employ a place-frequency map within the inner ear to encode sound stimuli, but the mechanisms by which they achieve tuned nerve activation along the cochlea are believed to be distinct. To investigate the mechanical origins of auditory sensation in the reptiles, we measured sound-evoked displacement responses in the hearing organ of the tokay gecko ( Gekko gecko ), known as the basilar papilla. Using optical coherence tomography, we were able to resolve sub-nanometer-scale vibrations throughout the organ both in vivo and ex vivo . We saw that tuning was not present in the tissue-scale mechanics at any position within the organ; it instead exhibits an untuned rotational motion. We developed a mathematical model which predicted that this motion induces hair-bundle-stimulating fluid displacement, and is due to an anatomical asymmetry seen in many reptile species. These results are consistent with the theory that hair-bundle-level mechanics are primarily responsible for tuning in the tokay gecko cochlea, and we argue that our proposed mechanisms generalize to many other species across the Reptilia class. SIGNIFICANCE We present the most comprehensive picture of tissue-scale mechanics in a reptile hearing organ to-date: sound-evoked displacement responses within the basilar papilla of the tokay gecko ( Gekko gecko ) both ex vivo and in vivo , across the animal’s auditory frequency range, and along all three spatial dimensions. We observed that place-frequency tuning is not present in the mechanics of the tissue as it is in mammals. Instead, this organ relies on an untuned rocking mechanism to stimulate hair bundles. A mathematical model shows that this may be at play in other reptile species, indicating a unifying mechanism of hearing in the class Reptilia in which hair bundle mechanics play the leading role in frequency tuning.

Auditory decision-making requires transforming sensory inputs into meaningful choices by integrating external stimuli with internal cognitive processes. Classical hierarchical models propose sequential processing, where primary sensory areas relay sensory information to higher-order regions that compute decision-related processes. However, whether this sequential hierarchy fully captures cortical dynamics remains unclear. Here, we analyzed simultaneous neuronal recordings from primary auditory cortex (A1) and dorsolateral prefrontal cortex (PFC) in two male macaque monkeys performing a spatial auditory decision-making task. Our analyses revealed a clear temporal hierarchy: sensory information was unidirectionally transferred from A1 to PFC, while decision-related information exhibited a bidirectional transfer, first from PFC to A1, and crucially back from A1 to PFC. These findings extend classical hierarchical assumptions, demonstrating a recurrent loop between A1 and PFC during decision-making, and offer a dynamic perspective on the integration of sensory and cognitive processes in the cerebral cortex.

Purpose: In anesthesia research and clinical practice, the level of consciousness is often assessed by stimulating subjects and observing their responses. It is possible that such stimulation alters the very state of consciousness being assessed. Whether this phenomenon is accompanied by specific cortical activities remains unknown. Here, we tested the effects of behavioral assessments on neuronal activity in the rat primary auditory cortex (A1) and perirhinal cortex (PrC). Methods: Neuronal spiking activity was recorded from microwire arrays targeting A1 and/or PrC in rats (n = 9), whilst presenting 40 Hz click-trains and gradually increasing infusion rates of propofol, remifentanil, ketamine or dexmedetomidine. We assessed righting reflex, pain withdrawal, whisking reflex, and corneal reflex every 12 minutes (every 360 auditory trials). We searched for significant changes in baseline firing rate and stimulus-evoked activities (where present) due to the behavioral assessments, by comparing 4 min intervals before and after the behavioral tests. Results: Out of 1004 units in 20 sessions, we found significantly elevated activity (p < 0.01) following behavioral tests in 32% and 20% of A1 auditory-responsive units and 8.6% and 5.3% of auditory-unresponsive units under propofol and dexmedetomidine, respectively, but not under remifentanil or ketamine. A higher proportion of units modulated their firing following behavioral tests in A1 compared to PrC, with median gains ranging from +0.23 to +1.06, depending on the specific response feature. Conclusion: Behavioral testing increases ongoing firing rate and responses to sounds in some cortical neurons. This increase is more prevalent in A1 than in PrC, mirroring clinical observations that patients exhibit basic responses under sedation, while complex processing, such as memory encoding, is impaired. The degree of neuronal modulation due to behavioral testing varies between anesthetic agents, mirroring their clinical phenotypes.

Auditory and vestibular symptoms in vestibular migraine, cochlear migraine, and Ménière's disease overlap, yet mechanisms linking migraine biology to inner ear dysfunction remain unclear. Calcitonin gene–related peptide (CGRP) is a key mediator of trigeminovascular activation and a major therapeutic target in migraine, but its contribution to cochlear dysfunction is not well defined. Using a repeated nitroglycerin (NTG) paradigm in male Wistar rats, we investigated whether a systemic migraine‐like state affects cochlear function and whether these effects are dependent on CGRP. Rats received saline, NTG, or NTG followed by the CGRP receptor antagonist olcegepant (OLC). NTG increased plasma TNF‐ α and elevated trigeminal c‐Fos; olcegepant partially normalized these markers, whereas behavioral changes in the open‐field test were interpreted cautiously because baseline immobility differed across groups before treatment. NTG produced frequency‐dependent changes in distortion‐product otoacoustic emissions and auditory brain stem response thresholds. Electrocochleography showed limited changes, and scala media proportions did not differ significantly among groups, indicating no evidence of overt endolymphatic hydrops at the studied time point. Inner hair‐cell synaptic markers showed no significant group differences for CtBP2, whereas GluR2 puncta differed between NTG and NTG + OLC ( p = 0.012). Olcegepant attenuated NTG‐associated cochlear functional changes and was associated with differences in postsynaptic GluR2 puncta, alongside region‐specific changes in cochlear CGRP immunoreactivity. These findings support a mechanistic link between migraine‐like trigeminovascular activation and early cochlear dysfunction and suggest that CGRP receptor blockade may benefit migraine patients with cochlear or vestibular symptoms. Future studies should assess females, estrous cycle tracking, hormones, and sex‐specific auditory responses.

Hypercholesterolemia is a recognized risk factor for sensorineural hearing loss. This study investigated the mechanistic link between blood-labyrinth barrier (BLB) disruption and hypercholesterolemia-associated cochlear damage. Low-density lipoprotein receptor knockout (Ldlr -/-) mice fed a high-fat diet for 8 weeks were used as the experimental model. Auditory assessments showed elevated auditory brainstem response (ABR) thresholds and distortion product otoacoustic emissions (DPOAEs), especially at high frequencies, consistent with hearing loss driven by outer hair cell dysfunction. BLB disruption occurred before hearing impairment, manifest as increased vascular permeability, damaged tight junctions and downregulated junctional protein levels. Cochlear histopathology confirmed outer and inner hair cell loss. These findings demonstrate a sequential and identify BLB as a key therapeutic target for preventing hypercholesterolemia-associated hearing impairment.