Noise-damaged cochleas keep low-side suppression normal while high-side thresholds rise

Evidence

Neurophysiological data on suppression in hearing-impaired (HI) mammals are limited. We present data on firing-rate suppression measured in auditory-nerve-fiber responses in a chinchilla model of noise-induced hearing loss, and in normal-hearing (NH) controls at equal sensation level. Hearing-impaired (HI) animals had elevated single-fiber excitatory thresholds (by ~ 20–40 dB), broadened frequency tuning, and reduced-magnitude distortion-product otoacoustic emissions; consistent with mixed innerand outer-hair-cell pathology. We characterized suppression using two approaches: adaptive tracking of two-tone-suppression threshold (62 NH, and 35 HI fibers), and Wiener-kernel analyses of responses to broadband noise (91 NH, and 148 HI fibers). Suppression-threshold tuning curves showed sensitive low-side suppression for NH and HI animals. High-side suppression thresholds were elevated in HI animals, to the same extent as excitatory thresholds. We factored second-order Wiener-kernels into excitatory and suppressive sub-kernels to quantify the relative strength of suppression. We found a small decrease in suppression in HI fibers, which correlated with broadened tuning. These data will help guide novel amplification strategies, particularly for complex listening situations (e.g., speech in noise), in which current hearing aids struggle to restore intelligibility. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3814

Categorization

• DEFINE: Defines two-tone suppression and the Wiener-kernel decomposition into excitatory versus suppressive sub-kernels.
• XREF: Connects to two-tone suppression physiology and otoacoustic emissions literature on outer-hair-cell function. — connects to: Loud noise damage can make the cochlea spontaneously generate its own noise — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 675