Hearing Research最新文献

In vivo measurements show that the basilar membrane (BM) exhibits sharp frequency tuning and high sensitivity to low-level stimuli. This has led most cochlear theories to assume that outer hair cells (OHCs) amplify traveling waves by delivering power directly to the BM. However, recent experiments revealed that the main bodies of Deiters cells (DCs), which are sandwiched between the OHCs and the BM, deform significantly in response to acoustic inputs. These findings challenge the hypothesis that power is transmitted by OHCs to the BM through the DCs. In this work, we consider a cochlear model that includes a micromechanical model of the organ of Corti with deformable DCs. The micromechanical model includes not only the BM, OHCs and DCs, but also other components of the organ of Corti, including the reticular lamina (RL) and pillar cells (PCs). We find that the amplitude and phase of the OHC-DC junction is consistent with in vivo measurements only if (1) the DC stiffness is comparable to that of OHCs; and (2) the joint between the RL and PCs is relatively stiff. Under these conditions, the model predicts that OHC electromotility does not deliver power to the BM through the classical OHC-DC-BM pathway, but rather through an alternative pathway through the RL and PCs. This result points to a new theoretical framework in which the RL and PCs, rather than DCs, serve as the primary conduit for the transfer of OHC-generated power to the BM and offers new insight into how the cochlea may achieve its remarkable sensitivity and frequency selectivity.

The two ears of many non-mammalian vertebrates are acoustically coupled through an interaural cavity, providing mechanical directional sensitivity for sound localization. Previous studies using lizards demonstrate that this coupling affects the spontaneous otoacoustic emissions (SOAEs) measured at each ear, with properties indicative of binaural synchronization. In other words, each active inner ear could influence the function of the other. However, it is unclear how binaural coupling and, consequently, synchronization contribute to SOAE generation, which is typically modeled as being localized to an individual ear. We simultaneously measured SOAEs at both ears of green anole lizards (Anolis carolinensis) and found robust relationships between them, including evidence that binaural synchronization could not be attributed to one ear uniformly driving the other. Instead, we observed frequency-dependent phase-locking between the two ears, primarily at frequencies where SOAE peaks occurred in both ears. Notably, these relationships could also occur in the regions between SOAE peaks. While binaural synchronization was stronger in some individuals than others, we consistently found that binaural coupling could have greater effects on the resulting emissions than the coupling between generators within the same ear. We propose a heuristic model for active hearing that incorporates binaural coupling, accounting for its effects on SOAE generation and sound localization in the green anole. Our data strengthen the evidence that, in lizards, emissions can be generated binaurally, a principle that can inspire new strategies for designing hearing assistive technologies.

Introduction: Dexamethasone-eluting cochlear implant (CI) electrode arrays aim to reduce mean electrode impedance and enhance stability. However, longitudinal data on intra-day impedance dynamics are lacking. This study compared postoperative impedance profiles between users of dexamethasone-eluting FLEX28 (DEX) and conventional FLEX28 (NoDEX) electrodes, focusing on mean impedance levels and intra-day fluctuations.

Methods: Participants were assigned to DEX or NoDEX groups based on electrode type. Both groups measured impedance twice daily (morning and evening) for four months postoperatively via an app. Primary outcomes were mean impedance levels and intra-day fluctuations, represented by the morning-to-evening difference (MED). Analyses were conducted descriptively and by group comparisons using the start of electrical stimulation (t₀) as reference. Four postoperative phases were examined: early postoperative (days 1-10), late postoperative (day 11-t₀), intensive fitting (t₀-day 21), and regular hearing phase (day 22-4 months).

Results: The DEX group exhibited consistently low and stable impedance values throughout, with no detectable effect of the start of electrical stimulation (t₀). Daily impedance was consistently lower in DEX than in NoDEX, but the differences reached high statistical significance from the late postoperative phase onward (p < 0.0001). Intra-day fluctuations were abolished in DEX (MED ≈ 0), whereas NoDEX showed measurable fluctuations during intensive fitting (DEX: 0.0 kΩ, n = 7 vs. NoDEX: 0.75 kΩ, n = 11; p < 0.001) and regular hearing phase (DEX: 0.0 kΩ, n = 8 vs. NoDEX: 0.56 kΩ, n = 11; p = 0.02).

Conclusion: Dexamethasone-eluting FLEX28 electrodes not only reduce mean impedance but also maintain stable values over time and effectively abolish intra-day fluctuations.

Atg7-dependent autophagy is critical for the long-term maintenance of the post-mitotic cells, yet its role in spiral ganglion neurons (SGNs) remains incompletely defined. Here, we conditionally ablated Atg7 in SGNs by generating Bhlhe22^Cre/+Atg7^flox/flox mice and examined cellular p62 aggregates, ultrastructure, and auditory function at postnatal day (P)30 and P60. At P30, Atg7 was markedly reduced in SGNs. Immunofluorescence revealed progressive enlargement of p62-positive condensates from nano-scale at P30 to micron-scale by P60. Excess p62 activated the antioxidant transcription factor Nrf2. Transmission electron microscopy demonstrated progressive axonal degeneration, including vacuolated axoplasm, mitochondrial abnormalities, and disorganization of myelin lamellae with a characteristic wavy appearance. Functionally, ABR thresholds were preserved at P30 but became significantly elevated by P60 (approximately 30 dB on average), indicating age-dependent hearing loss. The amplitude and latency analysis of ABR waves implied that hearing loss may primarily attributed to autophagy-impaired SGNs rather than other auditory brain neurons of Bhlhe22 lineage. The postsynaptic GluR2 receptors, but not presynaptic CtBP2, dramatically decreased at P60. Together, these data show that Atg7-dependent autophagy is required to preserve SGN over time, thereby maintaining the auditory function.

This study aims to investigate differences in brain oxyhemoglobin concentrations among preschool children with varying auditory processing (AP) abilities, as screened by the Preschool Auditory Processing Assessment Scale (PAPAS). The study selected 36 children with AP deficits and 52 typically developing (TD) children as subjects, all screened using the PAPAS. An fNIRS system measured cerebral hemodynamic responses during a speech recognition task performed under noisy and silent conditions. Behavioral results from the fNIRS task showed that children with AP deficits exhibited lower accuracy in speech recognition under noisy conditions compared with TD children. Region of interest activation analysis at the group level revealed significant activation in the left superior temporal gyrus, left middle temporal gyrus, right inferior frontal gyrus, right superior temporal gyrus, and right middle temporal gyrus in TD children during the speech-in-noise recognition task. In contrast, children with AP deficits did not show significant activation in these regions at the group level. Comparative analyses indicated that activation in the right inferior frontal gyrus, right superior temporal gyrus, and right middle temporal gyrus was significantly lower in the AP deficits group than in the TD group.

The human auditory ossicles -malleus, incus, and stapes- are critical for hearing, yet the middle ear that houses them is frequently affected by inflammatory conditions such as chronic otitis media with and without cholesteatoma, leading to ossicular chain damage. In cases of severe degradation, reconstructive surgery often involves ossiculoplasty using sculpted autografts. However, the impact of inflammation and surgical sculpting on the in-depth microarchitecture of ossicles remains poorly understood. This study investigates the structural integrity of ossicles (incudes and mallei) affected by cholesteatoma, previously sculpted autografts, and healthy controls using high-resolution synchrotron-based X-ray microtomography. Quantitative spatial analysis of mineral density, porosity, vascular canal density, and lacunar volume density reveals that cholesteatoma induces not only surface degradation but also significant internal alterations, including reduced mineral density and increased porosity, particularly around vascular canals. These changes suggest compromised structural stability, which may affect the suitability of ossicles for autologous grafting. Our findings highlight the need for improved assessment criteria during ossiculoplasty and underscore the importance of understanding ossicle microarchitecture and its alterations to optimize surgical outcomes.