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

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.

Age-related auditory dysfunction affects half of all individuals 60 years and older, yet its causes are poorly understood. While commonly associated with cochlear dysfunction, a growing body of literature suggests that dysfunction originating in the auditory cortex itself is also a major contributor. Here, we review recent literature that describes the effects of aging on the primary auditory cortex in humans, non-human primates, rodents, and a variety of other species. During aging, individuals with auditory cortical dysfunction experience deficits in spectral and temporal processing of sounds, resulting not only from a loss of inhibition but also from an extensive restructuring of cortical circuits. Importantly, aging in the auditory cortex is sex-dependent, yet few studies account for this variable. A lack of comprehensive knowledge on aging in the auditory cortex hinders the path toward restoring cortical function through auditory training or broader cortical rehabilitation paradigms. Thus, we propose a cohesive mechanism of aging in the primary auditory cortex that involves a complex interaction between excitatory and inhibitory neurons, which several factors can modify. These factors include input from higher-order cortical areas, such as the orbitofrontal cortex, as well as the wide-ranging effects of neuromodulators and the external sensory environment, which must be accounted for in a sex-dependent manner.

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.

Purpose: Frequency selectivity plays a crucial role in auditory perception, yet its precise characterization in humans remains debated. Most behavioral or physiologic estimates of frequency selectivity in humans have historically been obtained from individuals with clinically normal audiograms. However, emerging evidence suggests that even within this population, subclinical cochlear deficits may be prevalent, potentially skewing prior tuning estimates toward broader bandwidths. Here, we tested the hypothesis that human cochlear tuning is sharper when subclinical deficits, specifically hearing sensitivity above 8000 Hz, are considered.

Methods: Using stimulus frequency otoacoustic emission (SFOAE) delays, we obtained physiological estimates of cochlear tuning sharpness (Q_ERB). We applied the Stockwell transform, optimized through in silico experiments, to accurately extract SFOAE delays in adults with normal audiograms (n = 37) while systematically accounting for hearing thresholds above 8000 Hz.

Results: Our findings demonstrate that controlling for subclinical deficits results in significantly sharper (higher) tuning estimates at 2000 and 2828 Hz among the tested frequencies. Additionally, applying a normative criterion for extended high-frequency hearing, we observed narrower equivalent rectangular bandwidths-approximately two times sharper-in individuals with better extended high-frequency sensitivity. The Q_ERB estimates aligned closely with forward masking data in the literature, reinforcing the view that humans possess sharper cochlear tuning than common laboratory animals.

Conclusion: These findings highlight the influence of subclinical hearing deficits on cochlear tuning estimates and suggest that humans with optimal cochlear health may possess even sharper biological frequency selectivity than previously reported.

Purpose: This study aimed to investigate changes in auditory processing using auditory steady state responses (ASSR) in patients with idiopathic tinnitus.

Methods: 19 tinnitus patients (7 females) and 24 control subjects (9 females) without tinnitus were examined with multiple ASSRs. Three modulation frequencies of 20, 40, and 80 HZ were tested, and the steady state responses were compared between tinnitus and control group. Further, the thresholds in ipsi- and contralateral side to ear with tinnitus were compared.

Results: Our findings showed no significant difference in ASSR thresholds in ipsi- and contralateral side in tinnitus patients. However, we observed enhanced ASSRs at 40 and 80 Hz modulations in patients with idiopathic tinnitus compared to no-tinnitus control subjects.

Conclusion: The results of this study suggest possible sensory deficits along higher order auditory regions in patients with idiopathic tinnitus. Further, our data indicates a bilateral involvement of auditory pathway in these regions in patients with lateralized tinnitus.

The microvasculature plays a crucial role in maintaining auditory health by delivering essential nutrients such as glucose, ions, growth factors, and hormones, while also facilitating the elimination of metabolic waste. Simultaneously, the innate immune system acts as a protective barrier against cochlear damage caused by infections, toxic substances, and foreign agents. The normal functioning of these two systems creates an appropriate microenvironment that supports the health of sensory hair cells and spiral ganglion neurons. Disruptions in blood flow or inappropriate activation of the immune response can result in cochlear hypoxia and inflammation, both of which are linked to various auditory disorders. Understanding the characteristics and functions of these two systems could offer valuable insights into their distinct roles, potentially leading to the development of new treatments for hearing disorders associated with their dysfunction. This review covers the cellular characteristics and functions of both the vascular network and the innate immune cells within the stria vascularis, with a particular focus on how changes in both systems contribute to age-related hearing loss (ARHL), a common sensory deficit affecting the elderly population.

Purpose: Measures of the human medial olivocochlear reflex (MOCR) typically rely on long duration (> 100 ms) or continuously presented broadband elicitors. MOCR gain reduction measured by otoacoustic emissions (OAE) exhibits multiple time constants, including in the hundreds of milliseconds, when elicited by broadband noise. Psychoacoustic studies of gain reduction have largely adopted these elicitor characteristics, but less is known about how broadband elicitor duration affects auditory perception. Additionally, the literature on the relationship between psychoacoustic and OAE measures of gain reduction has yielded mixed results, which is counterintuitive if both measures reflect the same mechanism. In this study, the effects of ipsilateral broadband elicitor duration were evaluated using forward masking psychoacoustic and transient-evoked OAE (TEOAE) paradigms in individuals with normal hearing (N = 19; m = 7, f = 12).

Methods: Ipsilateral pink broadband noise was used as the elicitor in both experiments, presented at 50 dB SPL (50-800 ms) for the psychoacoustic measures and 50 dB FPL (50-400 ms) for the TEOAE measures. Gain reduction was quantified as the change in signal threshold (2 kHz) and the change in TEOAE level (1/3rd-octave band centered at 2 kHz) with and without the presence of the elicitor.

Results: The average time constants for psychoacoustic and TEOAE gain reduction were similarly short (< 100 ms), with near-maximal effects observed for elicitor durations of 200 ms. However, individual comparisons of TEOAE and psychoacoustic gain reduction revealed mixed results. Potential factors contributing to this discrepancy are discussed.

Conclusion: The human MOCR reduces cochlear gain on relatively short time scales (< 100 ms) with ipsilateral broadband elicitors.

Purpose: The goal of this research was to determine where in the organ of Corti (ooC) sound-induced, longitudinal vibrations occur, and how they depend on the health of the cochlea.

Methods: Sound-evoked vibrations of the ooC in the cochlea's middle turn of adult anesthetized gerbils were measured using optical coherence tomography (OCT). Vibratory responses, evoked with acoustic tone complexes, were recorded at multiple, closely spaced (20 μm), tonotopic locations which changed the "viewing angle" of the vertical OCT beam re. the longitudinal motion. After spatial alignment of the responses, within-ooC regions exhibiting sound-induced longitudinal motion were identified from a conspicuous 180° phase flip.

Results: Longitudinal motion was restricted to the outer hair cells (OHC), Deiters' cells and the tunnel of Corti (i.e., the ooC's "core"). They were frequency and level-independent but did depend on the ear's metabolic state; after death, they disappeared.

Conclusion: There can be little doubt about the presence of longitudinal motions within the cochlea. Their disappearance postmortem and spatially restricted occurrence suggest these longitudinal vibrations arise from active processes within the OHC. Whether this involves cycle-by-cycle feedback or some other, as-of-yet undetermined, mechanism remains to be resolved.