Level-growth functions of auditory steady state responses (ASSR) as indicator of cochlear synaptopathy
* Presenting author
Recent animal studies showed that acoustic overexposure with subsequent temporal threshold shift leads to a synaptic damage between the inner hair cell the auditory nerve. It is unclear if this phenomenon also exists in human listeners. The main difficulty to investigate this "cochlear synaptopathy" in humans is the requirement to use noninvasive techniques rather than invasive electrophysiology. One measure to quantify neural activity in human listeners is the electrical steady-state response of the auditory system to a modulated sound(ASSR). The present study investigated ASSR level-growth functions as a potential biomarker of synaptopathy. It is hypothesized that ASSR amplitudes decrease for high stimulus intensities and shallow modulation depths where it is assumed that the in cases of synaptopathy affected low-spontaneous-rate fibers encode intensity fluctuations. The data of normal-hearing and hearing-impaired listeners was compared to simulated ASSRs using a modified state-of-the art model of the auditory nerve (AN). The results indicate that not only a narrow but a broad frequency region, and not only one but a large proportion of all types of AN fibers need to be affected by synaptopathy in order to account for the data. The findings also imply that off-frequency contributions are important for processing of suprathreshold sounds.