Auditory Research publications

Anxiety is characteristic comorbidity of noise-induced hearing loss (NIHL), which causes physiological changes within the dentate gyrus (DG), a subfield of the hippocampus that modulates anxiety. However, which DG circuit underlies hearing loss-induced anxiety remains unknown. We utilize an NIHL mouse model to investigate short- and long-term synaptic plasticity in DG networks. The recently discovered longitudinal DG-DG network is a collateral of DG neurons synaptically connected with neighboring DG neurons and displays robust synaptic efficacy and plasticity. Furthermore, animals with NIHL demonstrate increased anxiety-like behaviors similar to a response to chronic restraint stress. These behaviors are concurrent with enhanced synaptic responsiveness and suppressed short- and long-term synaptic plasticity in the longitudinal DG-DG network but not in the transverse DG-CA3 connection. These findings suggest that DG-related anxiety is typified by synaptic alteration in the longitudinal DG-DG network.

CasRx, a recently discovered member of the type VI CRISPR system with minimum size, offers a new approach for RNA manipulation with high efficiency and specificity in prokaryotes and eukaryotes. However, in vivo studies of functional recovery using the CasRx system have not been well characterized. Here, we sought to establish an adeno-associated virus (AAV)-CasRx-guide RNA (gRNA) system for the specific knockdown of Htra2 transcript to protect mice from aminoglycosides-induced hearing loss. For the study, we verified an optimized gRNA in vitro, which was packaged into a single AAV with CasRx, and injected the packaged AAV into mice with hearing loss induced by neomycin and auditory functions investigated by auditory brainstem response tests. Upon using the AAV-CasRx-gRNA system, we found the knockdown of Htra2 transcript led to less cochlear hair cell loss and improved auditory function, with low off-target and adverse side effects. Additionally, the decrease in Htra2 significantly inhibits mRNA expression of Casp3 and Casp9. In conclusion, the AAV-CasRx-gRNA-mediated knockdown of Htra2 transcript in mice has been proved effective and safe for preventing hearing loss induced by aminoglycosides and, thus, represents a promising genetic approach for the future clinical applications for treating non-inherited hearing loss.

Objectives. Noise exposure leads to an increase in the macrophage population. This increment is thought to be caused by the transformation of infiltrated monocytes into macrophages rather than by proliferation of the cochlear resident macrophages. However, studies on infiltrated monocytes in the cochlea are scarce. Thus, we aimed to investigate the infiltration of monocytes and their transformation into macrophages after noise exposure.Methods. In wild-type and CX3CR1+/GFP C57/B6 mice, inflammatory monocytes were identified by immunofluorescence of mouse cochlear cells. The findings were confirmed and quantitated by flow cytometry.Results. One day after noise exposure, monocytes were identified in the spiral ligament. Flow cytometric analysis confirmed that the monocyte population peaked on post-noise exposure day 1 and decreased thereafter. On day 3 after noise exposure, amoeboid-type macrophages increased in the crista basilaris, and on day 5, they spread to the basilar membrane.Conclusion. Infiltrated monocytes were successfully observed 1 day after noise exposure, preceding the increase in the macrophage population. This finding supports the proposal that infiltrated monocytes transform into macrophages.

In almost every natural environment, sounds are reflected by nearby objects, producing many delayed and distorted copies of the original sound, known as reverberation. Our brains usually cope well with reverberation, allowing us to recognize sound sources regardless of their environments. In contrast, reverberation can cause severe difficulties for speech recognition algorithms and hearing-impaired people. The present study examines how the auditory system copes with reverberation. We trained a linear model to recover a rich set of natural, anechoic sounds from their simulated reverberant counterparts. The model neurons achieved this by extending the inhibitory component of their receptive filters for more reverberant spaces, and did so in a frequency-dependent manner. These predicted effects were observed in the responses of auditory cortical neurons of ferrets in the same simulated reverberant environments. Together, these results suggest that auditory cortical neurons adapt to reverberation by adjusting their filtering properties in a manner consistent with dereverberation.

The brain areas that mediate the formation of auditory threat memory and perceptual decisions remain uncertain to date. Candidates include the primary (A1) and secondary (A2) auditory cortex, the medial division of the medial geniculate body (MGm), amygdala, and the temporal association cortex. We used chemogenetic and optogenetic manipulations with in vivo and in vitro patch-clamp recordings to assess the roles of these brain regions in threat memory learning in female mice. We found that conditioned sound (CS) frequency-dependent plasticity resulted in the formation of auditory threat memory in the temporal association cortex. This neural correlated auditory threat memory depended on CS frequency information from A1 glutamatergic subthreshold monosynaptic inputs, CS lateral inhibition from A2 glutamatergic disynaptic inputs, and non-frequency-specific facilitation from MGm glutamatergic monosynaptic inputs. These results indicate that the A2 and MGm work together in an inhibitory-facilitative role. SIGNIFICANCE STATEMENT: The ability to recognize specific sounds to avoid predators or seek prey is a useful survival tool. Improving this ability through experiential learning is an added advantage requiring neural plasticity. As an example, humans must learn to distinguish the sound of a car horn, and thus avoid oncoming traffic. Our research discovered that the temporal association cortex can encode this kind of auditory information through tonal receptive field plasticity. In addition, the results revealed the underlying synaptic mechanisms of this process. These results extended our understanding of how meaningful auditory information is processed in an animal's brain.

Background Calcific aortic valve disease (CAVD) is often undiagnosed in asymptomatic patients, especially in underserved populations. Although artificial intelligence has improved murmur detection in auscultation exams, murmur manifestation depends on hemodynamic factors that can be independent of aortic valve (AoV) calcium load and function. The aim of this study was to determine if the presence of AoV calcification directly influences the S2 heart sound. Methods Adult C57BL/6J mice were assigned to the following 12-week-long diets: (1) Control group ( n = 11) fed a normal chow, (2) Adenine group ( n = 4) fed an adenine-supplemented diet to induce chronic kidney disease (CKD), and (3) Adenine + HP ( n = 9) group fed the CKD diet for 6 weeks, then supplemented with high phosphate (HP) for another 6 weeks to induce AoV calcification. Phonocardiograms, echocardiogram-based valvular function, and AoV calcification were assessed at endpoint. Results Mice on the Adenine + HP diet had detectable AoV calcification (9.28 ± 0.74% by volume). After segmentation and dimensionality reduction, S2 sounds were labeled based on the presence of disease: Healthy, CKD, or CKD + CAVD. The dataset (2,516 S2 sounds) was split subject-wise, and an ensemble learning-based algorithm was developed to classify S2 sound features. For external validation, the areas under the receiver operating characteristic curve of the algorithm to classify mice were 0.9940 for Healthy, 0.9717 for CKD, and 0.9593 for CKD + CAVD. The algorithm had a low misclassification performance of testing set S2 sounds (1.27% false positive, 1.99% false negative). Conclusion Our ensemble learning-based algorithm demonstrated the feasibility of using the S2 sound to detect the presence of AoV calcification. The S2 sound can be used as a marker to identify AoV calcification independent of hemodynamic changes observed in echocardiography.

Elevated neural plasticity during development contributes to dramatic improvements in perceptual, motor, and cognitive skills. However, malleable neural circuits are vulnerable to environmental influences that may disrupt behavioral maturation. While these risks are well-established prior to sexual maturity (i.e., critical periods), the degree of neural vulnerability during adolescence remains uncertain. Here, we induce transient hearing loss (HL) spanning adolescence in gerbils, and ask whether behavioral and neural maturation are disrupted. We find that adolescent HL causes a significant perceptual deficit that can be attributed to degraded auditory cortex processing, as assessed with wireless single neuron recordings and within-session population-level analyses. Finally, auditory cortex brain slices from adolescent HL animals reveal synaptic deficits that are distinct from those typically observed after critical period deprivation. Taken together, these results show that diminished adolescent sensory experience can cause long-lasting behavioral deficits that originate, in part, from a dysfunctional cortical circuit.

Reactive oxygen species (ROS) and inflammation have been considered major contributors to noise-induced hearing loss (NIHL) that constituted a public health threat worldwide. Nanoantioxidants, with high antioxidant activity and good stability, have been extensively used in the study of ROS-related diseases. In this study, we constructed a superoxide dismutase (SOD)@zeolite imidazolate framework-8 (ZIF-8) nanoparticle based on biomimetic mineralization and applied it to a rat model of NIHL. Our results showed that SOD@ZIF-8 effectively protected the animals from hearing loss and hair cell loss caused by noise. ROS, oxidative damage, and inflammation of noise-damaged cochlea were attenuated considerably after SOD@ZIF-8 administration. Importantly, we found that SOD@ZIF-8 achieved nanotherapy for NIHL in rats via a primary effect on the Sirtuin-3 (SIRT3)/superoxide dismutase2 (SOD2) signaling pathway without obvious adverse side effects. Therefore, our study is expected to open up a new field for NIHL treatment, and lay a foundation for the application of nanomaterials in other ROS-related inner ear diseases.

The ability to process and act upon incoming sounds during locomotion is critical for survival. Intriguingly, sound responses of auditory cortical neurons are on average weaker during locomotion as compared to immobility and these results have been suggested to reflect a computational resource allocation shift from auditory to visual processing. However, the evolutionary benefit of this hypothesis remains unclear. In particular, whether weaker sound-evoked responses during locomotion indeed reflect a reduced involvement of the auditory cortex, or whether they result from an alternative neural computation in this state remains unresolved. To address this question, we first used neural inactivation in behaving mice and found that the auditory cortex plays a critical role in sound-guided behavior during locomotion. To investigate the nature of this processing, we used two-photon calcium imaging of local excitatory auditory cortical neural populations in awake mice. We found that underlying a net inhibitory effect of locomotion on sound-evoked response magnitude, spatially intermingled neuronal subpopulations were differentially influenced by locomotion. Further, the net inhibitory effect of locomotion on sound-evoked responses was strongly shaped by elevated ongoing activity. Importantly, rather than reflecting enhanced “noise”, this ongoing activity reliably encoded the animal’s locomotion speed. Prediction analyses revealed that sound, locomotive state and their integration are strongly encoded by auditory cortical ensemble activity. Finally, we found consistent patterns of locomotion-sound integration in electrophysiologically recorded activity in freely moving rats. Together, our data suggest that auditory cortical ensembles are not simply suppressed by locomotion but rather encode it alongside sound information to support sound perception during locomotion.

Objectives Hearing plays an important role in our ability to control voice, and perturbations in auditory feedback result in compensatory changes in vocal production. The auditory cortex (AC) has been proposed as an important mediator of this behavior, but causal evidence is lacking. We tested this in an animal model, hypothesizing that AC is necessary for vocal self‐monitoring and feedback‐dependent control, and that altering activity in AC during vocalization will interfere with vocal control. Methods We implanted two marmoset monkeys ( Callithrix jacchus ) with bilateral AC electrode arrays. Acoustic signals were recorded from vocalizing marmosets while altering vocal feedback or electrically stimulating AC during random subsets of vocalizations. Feedback was altered by real‐time frequency shifts and presented through headphones and electrical stimulation delivered to individual electrodes. We analyzed recordings to measure changes in vocal acoustics during shifted feedback and stimulation, and to determine their interaction. Results were correlated with the location and frequency tuning of stimulation sites. Results Consistent with previous results, we found electrical stimulation alone evoked changes in vocal production. Results were stronger in the right hemisphere, but decreased with lower currents or repeated stimulation. Simultaneous stimulation and shifted feedback significantly altered vocal control for a subset of sites, decreasing feedback compensation at some and increasing it at others. Inhibited compensation was more likely at sites closer to vocal frequencies. Conclusions Results provide causal evidence that the AC is involved in feedback‐dependent vocal control, and that it is sufficient and may also be necessary to drive changes in vocal production. Level of Evidence N/A Laryngoscope , 133:1–10, 2023

Information flow in the sensory cortex has been described as a predominantly feedforward sequence with deep layers as the output structure. Although recurrent excitatory projections from layer 5 (L5) to superficial L2/3 have been identified by anatomical and physiological studies, their functional impact on sensory processing remains unclear. Here, we use layer-selective optogenetic manipulations in the primary auditory cortex to demonstrate that feedback inputs from L5 suppress the activity of superficial layers regardless of the arousal level, contrary to the prediction from their excitatory connectivity. This suppressive effect is predominantly mediated by translaminar circuitry through intratelencephalic neurons, with an additional contribution of subcortical projections by pyramidal tract neurons. Furthermore, L5 activation sharpened tone-evoked responses of superficial layers in both frequency and time domains, indicating its impact on cortical spectro-temporal integration. Together, our findings establish a translaminar inhibitory recurrence from deep layers that sharpens feature selectivity in superficial cortical layers.

Sensory cortex encompasses the regions of the cerebral cortex that receive primary sensory inputs and is crucial for conscious sensory perception in humans. Yet, some forms of perception are possible without sensory cortex. For example in animal models, the association of a sound detection to a simple behavior resists to the inactivation of auditory cortex. In contrast, post-training inactivation experiments conducted in visual or somatosensory cortex led to much stronger effects. Here we show that muscimol inactivation of visual or auditory cortex in the same detection protocol transiently abolishes visual but not auditory detection. We also observe that cortex-dependency correlates with longer reaction times. This suggests that auditory cortex is more easily bypassed by other circuits for stimulus detection than other primary sensory areas, which may be due to timing differences between auditory and visual associations.

The dynamics of information flow within the auditory cortical hierarchy associated with speech processing and the emergence of hemispheric specialization remain incompletely understood. To study these questions with high spatiotemporal resolution, intracranial recordings in 29 human neurosurgical patients of both sexes were obtained while subjects performed a semantic classification task. Neural activity was recorded from posteromedial portion of Heschl's gyrus (HGPM) and anterolateral portion of Heschl's gyrus (HGAL), planum temporale (PT), planum polare, insula, and superior temporal gyrus (STG). Responses to monosyllabic words exhibited early gamma power increases and a later suppression of alpha power, envisioned to represent feedforward activity and decreased feedback signaling, respectively. Gamma activation and alpha suppression had distinct magnitude and latency profiles. HGPM and PT had the strongest gamma responses with shortest onset latencies, indicating that they are the earliest auditory cortical processing stages. The origin of attenuated top-down influences in auditory cortex, as indexed by alpha suppression, was in STG and HGAL. Gamma responses and alpha suppression were typically larger to nontarget words than tones. Alpha suppression was uniformly greater to target versus nontarget stimuli. Hemispheric bias for words versus tones and for target versus nontarget words, when present, was left lateralized. Better task performance was associated with increased gamma activity in the left PT and greater alpha suppression in HGPM and HGAL bilaterally. The prominence of alpha suppression during semantic classification and its accessibility for noninvasive electrophysiologic studies suggests that this measure is a promising index of auditory cortical speech processing.SIGNIFICANCE STATEMENT Understanding the dynamics of cortical speech processing requires the use of active tasks. This is the first comprehensive intracranial electroencephalography study to examine cortical activity within the superior temporal plane, lateral superior temporal gyrus, and the insula during a semantic classification task. Distinct gamma activation and alpha suppression profiles clarify the functional organization of feedforward and feedback processing within the auditory cortical hierarchy. Asymmetries in cortical speech processing emerge at early processing stages. Relationships between cortical activity and task performance are interpreted in the context of current models of speech processing. Results lay the groundwork for iEEG studies using connectivity measures of the bidirectional information flow within the auditory processing hierarchy.

Kv3 potassium currents mediate rapid repolarisation of action potentials (APs), supporting fast spikes and high repetition rates. Of the four Kv3 gene family members, Kv3.1 and Kv3.3 are highly expressed in the auditory brainstem and we exploited this to test for subunit-specific roles at the calyx of Held presynaptic terminal in the mouse. Deletion of Kv3.3 (but not Kv3.1) reduced presynaptic Kv3 channel immunolabelling, increased presynaptic AP duration and facilitated excitatory transmitter release; which in turn enhanced short-term depression during high-frequency transmission. The response to sound was delayed in the Kv3.3KO, with higher spontaneous and lower evoked firing, thereby reducing signal-to-noise ratio. Computational modelling showed that the enhanced EPSC and short-term depression in the Kv3.3KO reflected increased vesicle release probability and accelerated activity-dependent vesicle replenishment. We conclude that Kv3.3 mediates fast repolarisation for short precise APs, conserving transmission during sustained high-frequency activity at this glutamatergic excitatory synapse.

Aging leads to degeneration of the peripheral and central auditory systems, hearing loss, and difficulty understanding sounds in noise. Aging is also associated with changes in susceptibility to or recovery from damaging noise exposures, although the effects of the interaction between acute noise exposure and age on the perception of sounds are not well studied. We tested these effects in the CBA/CaJ mouse model of age-related hearing loss using operant conditioning procedures before and after noise exposure and longitudinally measured changes in their sensitivity for detecting tones in quiet or noise backgrounds. Cochleae from a subset of the behaviorally tested mice were immunolabeled to examine organ of Corti damage relative to what is expected based on aging alone. Mice tested in both quiet and noise background conditions experienced worse behavioral sensitivity immediately after noise exposure, but mice exposed at older ages generally showed greater threshold shifts and reduced recovery over time. Surprisingly, day-to-day stability in thresholds was markedly higher for mice detecting signals in the presence of a noise masker compared with detection in quiet conditions. Cochlear analysis revealed decreases in the total number of outer hair cells (OHCs) and the number of ribbons per inner cell in high-frequency regions in aged, noise-exposed mice relative to aging alone. Our findings build on previous work showing interactions between age and noise exposure and add that background noise can increase the stability of behavioral hearing sensitivity after noise damage.

Collapsin response mediator protein 1 (CRMP1), also known as dihydropyrimidinase-related protein 1, participates in cytoskeleton remodeling during axonal guidance and neuronal migration. In cochlear hair cells, the assembly and maintenance of the cytoskeleton is of great interest because it is crucial for the morphogenesis and maintenance of hair cells. Previous RNA sequencing analysis found that Crmp1 is highly expressed in cochlear hair cells. However, the expression profile and functions of CRMP1 in the inner ear remain unknown. In this study, the expression and localization of CRMP1 in hair cells was investigated using immunostaining, and was shown to be highly expressed in both outer and inner hair cells. Next, the stereocilia morphology of Crmp1-deficient mice was characterized. Abolishing CRMP1 did not affect the morphogenesis of hair cells. Interestingly, scanning electron microscopy detected hair cell loss at the basal cochlear region, an area responsible for high-frequency auditory perception, in Crmp1-deficient mice. Correspondingly, an auditory brainstem response test showed that mice lacking CRMP1 had progressive hearing loss at high frequencies. In summary, these data suggest that CRMP1 is required for high-frequency auditory perception.

Lexical bias is the tendency to perceive an ambiguous speech sound as a phoneme completing a word; more ambiguity typically causes greater reliance on lexical knowledge. A speech sound ambiguous between /g/ and /k/ is more likely to be perceived as /g/ before /ɪft/ and as /k/ before /ɪs/. The magnitude of this difference—the Ganong shift—increases when high cognitive load limits available processing resources. The effects of stimulus naturalness and informational masking on Ganong shifts and reaction times were explored. Tokens between /gɪ/ and /kɪ/ were generated using morphing software, from which two continua were created (“giss”–“kiss” and “gift”–“kift”). In experiment 1, Ganong shifts were considerably larger for sine- than noise-vocoded versions of these continua, presumably because the spectral sparsity and unnatural timbre of the former increased cognitive load. In experiment 2, noise-vocoded stimuli were presented alone or accompanied by contralateral interferers with constant within-band amplitude envelope, or within-band envelope variation that was the same or different across bands. The latter, with its implied spectro-temporal variation, was predicted to cause the greatest cognitive load. Reaction-time measures matched this prediction; Ganong shifts showed some evidence of greater lexical bias for frequency-varying interferers, but were influenced by context effects and diminished over time.

Electrically evoked compound action potentials (ECAPs) generated in the subthalamic nucleus (STN) contain features that may be useful for titrating deep brain stimulation (DBS) therapy for Parkinson’s disease. Delivering a strong therapeutic effect with DBS therapies, however, relies on selectively targeting neural pathways to avoid inducing side effects. In this study, we investigated the spatiotemporal features of ECAPs in and around the STN across parameter sweeps of stimulation current amplitude, pulse width, and electrode configuration, and used a linear classifier of ECAP responses to predict electrode location. Four non-human primates were implanted unilaterally with either a directional (n=3) or non-directional (n=1) DBS lead targeting the sensorimotor STN. ECAP responses were characterized by primary features (within 1.6 ms after a stimulus pulse) and secondary features (between 1.6-7.4 ms after a stimulus pulse). Using these ECAP features, a linear classifier was able to accurately differentiate electrodes within the STN versus dorsal to the STN in all four subjects. ECAP responses varied systematically with recording and stimulating electrode locations, which provides a subject-specific neuroanatomical basis for selecting electrode configurations in the treatment of Parkinson’s disease with DBS therapy.

Non-sensory cells in the sensory epithelium of the cochlea are connected extensively by gap junctions. Functionally null mutations in GJB6 (encoding Cx30) cause hearing loss in humans. In this study, we injected AAV1-CB7- Gjb2 into the scala media between P0-2 in the cochlea of Gjb6 −/− mice. The injection increased Cx26 expression and significantly preserved auditory functions. However, the hearing preservation gradually declined and essentially disappeared 3 months after the injections. In contrast, the morphological preservation was still significant at 3 months post-injection. We found that the expression of Cx26, at both the mRNA and protein levels, showed substantial decreases during the 3-month period. Curiously, treatments by injecting AAV1-CB7- Gjb6 with the identical approach failed to yield any hearing preservation. Our results demonstrated the first successful cochlear gene therapy treatment in mouse models by virally expressing a companion gene of Gjb6 .

Aminoglycosides exhibit ototoxicity by damaging mitochondria, which in turn generate reactive oxygen species that induce hair cell death and subsequent hearing loss. It is well known that damaged mitochondria are degraded by mitophagy, an important mitochondrial quality control system that maintains mitochondrial homeostasis and ensures cell survival. However, it is unclear whether dysregulation of mitophagy contributes to aminoglycoside-induced hair cell injury. In the current study, we found that PINK1-PRKN-mediated mitophagy was impaired in neomycin-treated hair cells. Our data suggested that mitochondrial recruitment of PRKN and phagophore recognition of damaged mitochondria during mitophagy were blocked following neomycin treatment. In addition, the degradation of damaged mitochondria by lysosomes was significantly decreased as indicated by the mitophagic flux reporter mt-mKeima. Moreover, we demonstrated that neomycin disrupted mitophagy through transcriptional inhibition of Pink1 expression, the key initiator of mitophagy. Moreover, we found that neomycin impaired mitophagy by inducing ATF3 expression. Importantly, treatment with a mitophagy activator could rescue neomycin-treated hair cells by increasing mitophagy, indicating that genetic modulation or drug intervention in mitophagy may have therapeutic potential for aminoglycoside-induced hearing loss. Abbreviations: AAV: adeno-associated virus; ABR: auditory brainstem response; ATF3: activating transcription factor 3; ATOH1/MATH1: atonal bHLH transcription factor 1; BafA1: bafilomycin A1; CCCP: carbonyl cyanide m-chlorophenyl hydrazone; COX4I1/COXIV: cytochrome c oxidase subunit 4I1; CTBP2/RIBEYE: C-terminal binding protein 2; DFP: deferiprone; EGFP: enhanced green fluorescent protein; FOXO3: forkhead box O3; GRIA2/GLUR2: glutamate receptor, ionotropic, AMPA2 (alpha 2); HC: hair cell; HSPD1/HSP60: heat shock protein 1 (chaperonin); IHC: inner hair cell; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MYO7A: myosin VIIA; OPTN: optineurin; OMM: outer mitochondrial membrane; PRKN: parkin RBR E3 ubiquitin protein ligase; PINK1: PTEN induced putative kinase 1; RT-qPCR: real-time quantitative polymerase chain reaction; TOMM20/TOM20: translocase of outer mitochondrial membrane 20; TUNEL: Terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling; USP30: ubiquitin specific peptidase 30; XBP1: X-box binding protein 1.