Toward a Differential Diagnosis of Hidden Hearing Loss in Humans

Abstract

Recent work suggests that hair cells are not the most vulnerable elements in the inner ear; rather, it is the synapses between hair cells and cochlear nerve terminals that degenerate first in the aging or noise-exposed ear. This primary neural degeneration does not affect hearing thresholds, but likely contributes to problems understanding speech in difficult listening environments, and may be important in the generation of tinnitus and/or hyperacusis. To look for signs of cochlear synaptopathy in humans, we recruited college students and divided them into low-risk and high-risk groups based on self-report of noise exposure and use of hearing protection. Cochlear function was assessed by otoacoustic emissions and click-evoked electrocochleography; hearing was assessed by behavioral audiometry and word recognition with or without noise or time compression and reverberation. Both groups had normal thresholds at standard audiometric frequencies, however, the high-risk group showed significant threshold elevation at high frequencies (10–16 kHz), consistent with early stages of noise damage. Electrocochleography showed a significant difference in the ratio between the waveform peaks generated by hair cells (Summating Potential; SP) vs. cochlear neurons (Action Potential; AP), i.e. the SP/AP ratio, consistent with selective neural loss. The high-risk group also showed significantly poorer performance on word recognition in noise or with time compression and reverberation, and reported heightened reactions to sound consistent with hyperacusis. These results suggest that the SP/AP ratio may be useful in the diagnosis of “hidden hearing loss” and that, as suggested by animal models, the noise-induced loss of cochlear nerve synapses leads to deficits in hearing abilities in difficult listening situations, despite the presence of normal thresholds at standard audiometric frequencies.

Cortical and Sensory Causes of Individual Differences in Selective Attention Ability Among Listeners With Normal Hearing Thresholds

“…Indeed, cochlear synaptopathy reduces the strength of auditory nerve responses; the auditory system then seems to respond by increasing some internal gain to amplify the weak response that remains (e.g., see Chambers et al, 2016). Based on these findings, one proposed method for identifying cochlear synaptopathy in humans computes the ratio of the summation potential (the response of the hair cells in the cochlea) to the action potential (the auditory nerve response; Liberman, Epstein, Cleveland, Wang, & Maison, 2016); however, neither this metric nor any other has yet been proven to be diagnostic of cochlear synaptopathy in humans (see comments in the section on Future Impact in the Clinic).…”

Stress is irrelevant to the onset and exacerbation of sensorineural hearing loss: Evaluation using various types of stress models in mice

“…In noiseexposed humans and animals, acoustic trauma (noise-induced hearing loss) leads to hair cell damage and causes a threshold shift [19,20]. Recent studies have indicated that ageing and/or moderate noise exposure can result in hidden hearing loss [21][22][23], which causes difficulties in speech discrimination and temporal processing in a noisy environment [24]. It can be detected physiologically, and is characterized by reduced amplitude in the sound-evoked spiral ganglion neuron activity (the first peak of the ABR waveform) [25][26][27].…”

Biomarkers for Hearing Dysfunction: Facts and Outlook

“…While CAP responses are, to date, typically used to extract the CAPs generated by sound in animal models, ear canal electrodes in humans are successfully used at this time to analyze deficits in auditory processing in subject groups who had normal audiometric thresholds up to 8 kHz [67] . Accordingly, CAPs were recorded in humans using tiptrodes inserted deep into the ear canal [67] .…”