The relationship between distortion product otoacoustic emissions and audiometric thresholds in the extended high-frequency range.

Distortion product otoacoustic emissions (DPOAEs) and behavioral audiometry are routinely used for hearing screening and assessment. These measures provide related information about hearing status as both are sensitive to cochlear pathologies. However, DPOAE testing is quicker and does not require a behavioral response. Despite these practical advantages, DPOAE testing is often limited to screening only low and mid- frequencies. Variation in ear canal acoustics across ears and probe placements has resulted in less reliable measurements of DPOAEs near 4 kHz and above where standing waves commonly occur. Stimulus calibration in forward pressure level and responses in emitted pressure level can reduce measurement variability. Using these calibrations, this study assessed the correlation between audiometry and DPOAEs in the extended high frequencies where stimulus calibrations and responses are most susceptible to the effect of standing waves. Behavioral thresholds and DPOAE amplitudes were negatively correlated, and DPOAE amplitudes in emitted pressure level accounted for twice as much variance as amplitudes in sound pressure level. Both measures were correlated with age. These data show that with appropriate calibration methods, extended high-frequency DPOAEs are sensitive to differences in audiometric thresholds and highlight the need to consider calibration techniques in clinical and research applications of DPOAEs.

Hearing outcomes in children with Congenital Cytomegalovirus: A multi-center, single-enterprise experience.

BACKGROUND: Cytomegalovirus (CMV) is the most common cause of non-genetic sensorineural hearing loss (SNHL) in the United States; yet screening for congenital CMV (cCMV) remains controversial. CMV related SNHL can be present at birth, or develop in a delayed manner, and it is a consistent feature in children with either symptomatic or asymptomatic disease. A retrospective chart review was performed to determine the characteristics of patients diagnosed with cCMV and SNHL. METHODS: The electronic database warehouse of the Nemours Children's Health System (NCHS) was queried from 01/01/2004 to 10/05/2019. ICD 9 (771.1) and ICD 10 (B25.9, P35.1) diagnostic codes were used to identify patients throughout the system with a diagnosis of cCMV infection. Patient demographics including gender, race/ethnicity, age of diagnosis, results of newborn hearing screening (NBHS), detection and progression of hearing loss, presence of antiviral therapy, and frequency of monitoring were collected, and descriptive statistics performed. RESULTS: Of the 170 patients confirmed to have cCMV, 153 (90%) were symptomatic and 17 (10%) were asymptomatic. CNS involvement (63.5%), radiographic evidence of disease present (69.4%), and SNHL (50.6%) were the most common manifestations of the disease. Of these 170 patients, 83 (48.8%) were determined to have SNHL eligible for evaluation. For these patients with SNHL, the average time of hearing monitoring was 50.6 months. At the time of initial reported detection 63 of 83 (76%) had bilateral hearing loss and 20 (24%) had unilateral loss. Over the study period 3 (15%) progressed from unilateral to bilateral involvement, and 32 (47%) had a deterioration in hearing, with severe to profound SNHL in at least one ear identified at the last visit in 53 (64%) patients. Newborn hearing testing results were available for 69 (83%) of those with hearing loss and 26 patients passed initial testing. However, of the 26 patients who passed, 22 (85%) eventually developed SNHL by their last visit. Within our cohort, females with cCMV were significantly more likely to have SNHL than males with cCMV (62.3% versus 37.6%; p < 0.01). CONCLUSION: In the absence of targeted or universal cCMV screening, the majority of children identified with this condition present symptomatically. Approximately one half of children with symptomatic cCMV failed NBHS at birth while at least 25% develop SNHL later in life. Children with cCMV are at high risk of delayed onset loss and such children, particularly females, should be monitored closely.

Cross-species experiments reveal widespread cochlear neural damage in normal hearing.

Animal models suggest that cochlear afferent nerve endings may be more vulnerable than sensory hair cells to damage from acoustic overexposure and aging. Because neural degeneration without hair-cell loss cannot be detected in standard clinical audiometry, whether such damage occurs in humans is hotly debated. Here, we address this debate through co-ordinated experiments in at-risk humans and a wild-type chinchilla model. Cochlear neuropathy leads to large and sustained reductions of the wideband middle-ear muscle reflex in chinchillas. Analogously, human wideband reflex measures revealed distinct damage patterns in middle age, and in young individuals with histories of high acoustic exposure. Analysis of an independent large public dataset and additional measurements using clinical equipment corroborated the patterns revealed by our targeted cross-species experiments. Taken together, our results suggest that cochlear neural damage is widespread even in populations with clinically normal hearing.

Individualized Assays of Temporal Coding in the Ascending Human Auditory System.

Neural phase-locking to temporal fluctuations is a fundamental and unique mechanism by which acoustic information is encoded by the auditory system. The perceptual role of this metabolically expensive mechanism, the neural phase-locking to temporal fine structure (TFS) in particular, is debated. Although hypothesized, it is unclear whether auditory perceptual deficits in certain clinical populations are attributable to deficits in TFS coding. Efforts to uncover the role of TFS have been impeded by the fact that there are no established assays for quantifying the fidelity of TFS coding at the individual level. While many candidates have been proposed, for an assay to be useful, it should not only intrinsically depend on TFS coding, but should also have the property that individual differences in the assay reflect TFS coding per se over and beyond other sources of variance. Here, we evaluate a range of behavioral and electroencephalogram (EEG)-based measures as candidate individualized measures of TFS sensitivity. Our comparisons of behavioral and EEG-based metrics suggest that extraneous variables dominate both behavioral scores and EEG amplitude metrics, rendering them ineffective. After adjusting behavioral scores using lapse rates, and extracting latency or percent-growth metrics from EEG, interaural timing sensitivity measures exhibit robust behavior-EEG correlations. Together with the fact that unambiguous theoretical links can be made relating binaural measures and phase-locking to TFS, our results suggest that these "adjusted" binaural assays may be well suited for quantifying individual TFS processing.

Non-Invasive Assays of Cochlear Synaptopathy - Candidates and Considerations.

Studies in multiple species, including in post-mortem human tissue, have shown that normal aging and/or acoustic overexposure can lead to a significant loss of afferent synapses innervating the cochlea. Hypothetically, this cochlear synaptopathy can lead to perceptual deficits in challenging environments and can contribute to central neural effects such as tinnitus. However, because cochlear synaptopathy can occur without any measurable changes in audiometric thresholds, synaptopathy can remain hidden from standard clinical diagnostics. To understand the perceptual sequelae of synaptopathy and to evaluate the efficacy of emerging therapies, sensitive and specific non-invasive measures at the individual patient level need to be established. Pioneering experiments in specific mice strains have helped identify many candidate assays. These include auditory brainstem responses, the middle-ear muscle reflex, envelope-following responses, and extended high-frequency audiograms. Unfortunately, because these non-invasive measures can be also affected by extraneous factors other than synaptopathy, their application and interpretation in humans is not straightforward. Here, we systematically examine six extraneous factors through a series of interrelated human experiments aimed at understanding their effects. Using strategies that may help mitigate the effects of such extraneous factors, we then show that these suprathreshold physiological assays exhibit across-individual correlations with each other indicative of contributions from a common physiological source consistent with cochlear synaptopathy. Finally, we discuss the application of these assays to two key outstanding questions, and discuss some barriers that still remain. This article is part of a Special Issue entitled: Hearing Loss, Tinnitus, Hyperacusis, Central Gain.