Jaro-Journal of the Association for Research in Otolaryngology最新文献

Introduction: The human cochlea is encased within the otic capsule, the densest bone in the body, posing significant challenges for anatomical imaging of cochlear structures. Because of difficult access and the fragility of cochlear structures, our understanding of intracochlear anatomy has historically relied on postmortem histology. We thus have a limited understanding of human cochlear anatomy in its native, unfixed state. Clinical diagnostics for hearing loss, such as audiometry and otoacoustic emissions, offer functional assessments but fail to elucidate the often diverse underlying structural pathologies with any degree of precision.

Methods: To address the critical need for assessing the human cochlear anatomy and associated pathologies without the risk of traumatizing cochlear structures, we imaged fresh cochleae (N = 23, 15 males, 8 females) in situ soon after death through the intact round window membrane with Optical Coherence Tomography (OCT) without inserting instruments inside or opening the cochlea.

Results: Micron-resolution OCT cross-sectional images of the human intracochlear structures were acquired and compared with corresponding histology systematically to aid in the identification of fine structural features and possible pathologies. With OCT imaging, we observed varied anatomy of the organ of Corti, and developed a cochlear "integrity" rating system to differentiate healthy-appearing cochleae from various pathological states.

Conclusion: These results demonstrate the capability of OCT to non-traumatically visualize cochlear integrity, highlighting its potential as a diagnostic tool. This work shows promise in translating the ability to determine the likelihood of existing or lack of hair cells and supporting cells in live patients, which would enable appropriate targeted treatments.

Purpose: Although human temporal bones suggest that cochlear synapse numbers decline with age and noise exposure, no validated diagnostic method exists. In animal models, cochlear synaptopathy is associated with reduced auditory brainstem response (ABR) wave 1 amplitude and envelope following response (EFR) magnitude for a sinusoidally amplitude modulated (SAM) tone. However, measuring SAM EFR at the optimal modulation frequency (1000 Hz) is difficult in humans. A rectangular amplitude modulated (RAM) tone may be more sensitive to synaptopathy, but this has not been validated in animals. In addition, because synaptopathy likely co-occurs with outer hair cell dysfunction (OHC), a diagnostic assay needs to be robust to abnormal auditory thresholds. The objective of this study was to evaluate the relative ability of ABR and EFR measures to predict synapse numbers in mice with varying degrees of synaptopathy and OHC dysfunction.

Methods: Distortion product otoacoustic emissions (DPOAEs), ABR, SAM EFR, and RAM EFR were recorded from 57 mice with a range of auditory thresholds and degrees of synaptopathy. Cross-validation was used to compare the relative ability of linear regression models incorporating different measures to predict synapse numbers. Predictions were confirmed histologically.

Results: RAM EFR modulated at 1000 Hz was the single best predictor of synapse numbers for broad synapse loss across frequency, while combining RAM EFR with ABR further improved predictions. In contrast, ABR best predicted focal synaptopathy. Incorporating DPOAEs improved predictions for EFR, but not ABR.

Conclusion: RAM EFR, ABR, and DPOAEs should be used in the future when predicting synapse numbers.

Purpose: Perceiving the sound source distance is important in many everyday activities. For sources near the listener, two dominant intensity-independent cues are available, the direct-to-reverberant energy ratio (DRR) and the interaural level difference (ILD). Previous studies identified the planum temporale (PT) and posterior superior temporal gyrus (pSTG) as auditory cortical areas important for distance processing. However, it is not clear whether the identified areas represent integrated percepts of distance, per se, or the discrete cues based on which it is created. To address this, we combined behavioral and neuroimaging experiments with advanced computational modeling.

Methods: We conducted human behavioral (15 participants with 5 self-reported females) and fMRI experiments (15 participants with 5 self-reported females) in a virtual reverberant environment using broadband noise stimuli. The availability and congruency of the DRR and ILD cues were manipulated to identify cortical areas encoding distance cues vs. distance percepts.

Results: Behavioral results showed that distance percepts were stronger when both cues were available and congruent, confirming that both cues are used when listeners judge distance. A univariate fMRI analysis identified areas in the PT + pSTG as encoding the DRR cue. An ROI-based multi-voxel pattern analysis (MVPA) over the whole PT + pSTG region found a significant difference between Congruent and Incongruent stimuli, likely representing the distance percept.

Conclusion: The PT + pSTG region encodes both the distance cues and percepts. However, while the cue encoding is local, the percepts are encoded in a distributed network.

Purpose: Biasing of the cochlear partition by tones below 100 Hz is commonly used to investigate cochlear non-linearity. Their long periodicity allows resolution of the suppression of cochlear responses as the partition is displaced periodically away from its resting position. The purpose of this study was to quantify by how much the biasing tone (BT) level needed to be increased to keep an equal suppression depth in OAE and an equal criterion suppression of loudness while the levels of the response-evoking stimuli were increased.

Method: Suppression-period patterns were obtained for the distortion-product and stimulus-frequency otoacoustic emissions (DPOAE: N = 8 ears, SFOAE: N = 6 ears) using a 55-Hz BT, conditions in which the primary frequencies were at least 3 octaves above the BT frequency. A prior search for primary parameters that allowed the highest recording SNR was conducted, including an optimization of the lower primary tone level (L1) for the DPOAE. The BT level was adjusted so that the maximum suppression depth was kept constant at 9 dB for both OAEs, for various primary levels. Also, the BT level required to reach an equal criterion suppression in the loudness of 1- and 2-kHz tone-pip probes was measured psychoacoustically (N = 4) at various probe levels using the same BT.

Results: The increase in suppressor level per increase in probe level was similar (~ 0.4 dB/dB) for equal-loudness suppression of the tone pips, 9-dB suppression of the SFOAE, and the 2F1-F2 DPOAE, when the increase in L1 was considered. Average BT levels increased linearly over the whole range of probe levels tested.

Conclusion: As the observed iso-suppression rate is broadly consistent with the growth of basilar membrane vibration with increasing stimulus level in the active region of the traveling wave, we conclude that equal suppression of cochlear responses during partition biasing occurs when bias displacement grows in proportion to the probe's traveling wave amplitude in its active region.

Purpose: Auditory-nerve fiber (ANF) responses to sound are processed by several distinct neural circuits in the cochlear nucleus (CN). One of the main cochlear nucleus cell types that projects to higher auditory nuclei is bushy cells (BCs), which can be divided into two subtypes, globular and spherical, depending on the shape of their soma and their innervation patterns. Apart from receiving excitatory inputs from ANFs and inhibitory inputs from D-Stellate and tuberculoventral cells, BCs receive excitation via gap junctions (a.k.a. electrical synapses) from neighboring BCs. One of the distinctive features of the BCs is the enhancement of the synchronization behavior in ANFs. For globular BCs, which receive subthreshold inputs from many ANFs, a coincidence-detection mechanism is proposed, whereas for spherical BCs, the mechanism for the synchronization enhancement is still not fully understood.

Methods: In this study, fully connected bushy cell network models were created. The effects of gap junctions on the synchronization of the BCs were inspected by connecting the membrane potentials of clusters of five fully connected BCs.

Results: As the strength of the gap junction connections was increased within a given cell network, the synchronization was enhanced. The effects of inhibition on the synchronization were also explored and were found to be non-monotonic.

Conclusion: Synchronization index values of the simulated network models with different gap junction strengths indicated that gap junctions can strongly contribute to the synchronization of models for both globular and spherical BCs.

Purpose: Sound pressure recordings at different positions at the head such as ear canal, nasal cavity, or on the skin are effective tools to verify, fit, or follow up the output of bone conduction devices (BCDs) intra- and post-operatively. Here, we investigated the possibility of using a surface microphone (SM) as a non-invasive alternative to laser Doppler vibrometry (LDV) measuring cochlear promontory (CP) vibrations in human heads.

Methods: A percutaneous BCD (Ponto system) was implanted at the standard position in five human (four males/one female) cadaver heads (ten ears). CP vibration was measured using LDV in response to the BCD stimulation. Simultaneously, the sound pressure level (SPL) emitted by the skin was measured by the SM attached to the forehead of the specimens. A linear regression model estimated the vibration amplitudes based on the measured SPL.

Results: A frequency-independent linear regression between recorded SM SPL and CP velocity showed a significant correlation (slope = 1.012; r² = 0.535, p < 0.001). An enforced fixed slope (constant = 166.7 dB) of one resulted in a mean absolute error of MAE = 7.7 ± 2.7 dB across frequencies. Although the initial linear model with a fixed slope of one showed frequency-dependent deviations, applying a frequency-specific correction significantly improved the prediction accuracy (r² = 0.557, MAE = 6.5 ± 1.5 dB).

Conclusion: Microphone-based recording of acoustic surface emissions offers a non-invasive alternative to LDV to assess BCD output.

Purpose: Vestibular implants that target the three semicircular canal branches of the vestibular nerve can partially restore the 3-dimensional vestibulo-ocular reflex (3D VOR) in individuals disabled by bilateral vestibular hypofunction. A key goal of implant design is optimizing the number, spacing, and placement of stimulating and return electrodes to maximize response strength and selectivity. While computational models provide initial insights, empirical data are essential to validate performance.

Methods: We unilaterally implanted stimulating electrodes in each semicircular canal and positioned return electrodes both inside the labyrinth and outside the temporal bone in three female rhesus macaques. Using mixed-effects ANOVA, we quantified how electrode location influenced 3D VOR response magnitude and misalignment.

Results: We found that: (1) the deepest stimulating electrode in each canal generally yielded the strongest and most aligned responses; (2) a 600-750 µm difference in electrode position significantly impacted VOR outcomes; (3) return electrodes placed inside the labyrinth produced significantly larger VOR responses than those placed outside the temporal bone when stimulus current is constrained to levels that elicit no sign of facial nerve excitation; and (4) "near-bipolar" stimulation-using a return electrode in the same ampulla as the stimulating electrode-yielded better alignment.

Conclusion: Although including multiple stimulating electrodes per canal may lower the risk of missing the target, a VI limited to one deep stimulating electrode per canal and one common return electrode can suffice if array design and surgical technique ensure placement near the crista ampullaris. Unused stimulator channels could be repurposed in designs intended to stimulate the utricle, saccule and/or cochlea. Moreover, spatial selectivity is improved by placing return electrodes within the labyrinth or ampullae, rather than outside the temporal bone. VIs that use a single common return electrode shared by all stimulation channels could achieve better performance in the future by incorporating multiple independent return electrode channels to permit near-bipolar stimulation.

Purpose: To evaluate whether optical coherence tomography (OCT) vibrometry can differentiate causes of conductive hearing loss (CHL) following ossiculoplasty, specifically distinguishing among effusion, soft-tissue fixation, and prosthesis disconnection.

Methods: We simulated three post-surgical CHL conditions, effusion, soft-tissue fixation, and prosthesis disconnection, in a cadaveric temporal bone model (N = 10 per condition), with a partial ossicular replacement prosthesis (PORP) and cartilage graft implanted via a retrotympanic approach. A custom-built swept-source middle-ear OCT system (λ₀ = 1550 nm, Δλ = 40 nm) was used to capture cross-sectional images and mobility measurements at the umbo and center of the cartilage graft across six stimulus frequencies (500, 750, 1000, 1500, 2000, and 3000 Hz). Mobility values (point velocity normalized to sound pressure) served as input features for a Random Forest classifier. Changes in mobility from baseline were also statistically analyzed.

Results: The classifier achieved 90.9% accuracy (40/44 datasets) in differentiating conditions in leave-one-out cross-validation, and 100% when trained on the full dataset. Simulated effusion and soft-tissue fixation were associated with broadband mobility decreases of 17.5 dB and 8.0 dB, respectively, averaged across both locations. Prosthesis disconnection at the stapes and at the tympanic membrane led to low-frequency (500 and 750 Hz) mobility increases of 9.9 dB and 11.1 dB, respectively, averaged across both locations.

Conclusion: In a cadaveric model of post-surgical CHL, OCT vibrometry accurately distinguished effusion, soft-tissue fixation, and prosthesis disconnection. The ability to identify the cause of post-surgical CHL highlights OCT vibrometry's potential to assist clinical decision-making in revision surgery.

Brief acoustic tinnitus suppression (BATS) is a well-known phenomenon among tinnitus patients. Most knowledge about BATS comes from experiments applying filtered, modulated, or customized stimuli in selected patient populations. Testing BATS in clinical routine could provide valuable information for patient subtyping and assistance in treatment decision-making. Here, we investigated the feasibility of BATS tests beyond controlled experimental settings. Seventy individuals with tinnitus (29 female) were tested for BATS using white noise as part of a first consultation visit at the Interdisciplinary Tinnitus Center in Regensburg. The procedure turned out to be feasible under clinical routine conditions. Thirty-five patients (50%) reported some form of tinnitus suppression, with 6 (8.6%) reporting at least 50% reduction and 1 (1.4%) complete absence of their tinnitus percept. The degree of suppression was rated as relevant improvement by most patients. In summary, the integration of BATS assessments was feasible and provided valuable information about the patients' tinnitus.