Application of force to the cochlear wall: Effect on auditory thresholds, outer hair cell transduction, and distortion‐product otoacoustic emissions

Abstract

Described are the changes in cochlear sensitivity and mechanoelectrical transduction during a novel cochlear perturbation: the application of force to the cochlear wall. While numerous methods exist to create transient shifts in the operating point of the outer hair cell (OHC) transducer, including low‐frequency acoustic bias [G. Frank and M. Kössl, Hear. Res. 113, 57–68 (1997)] and hydrostatic bias [A. N. Salt and J. E. DeMott, Hear. Res. 123, 137–147 (1998)], attempts to create prolonged operating point shifts are largely thwarted by the numerous sources of ac coupling in the auditory system which prevent transmission of dc stimuli to the hair cells. The application of force sufficient to deform the otic capsule produced a consistent drop in neural thresholds and a sustained bias of the OHC operating point that did not rapidly adapt back to normal. Near‐simultaneous measurements of compound action potential thresholds, distortion‐product otoacoustic emissions, the OHC transfer curves derived from low‐frequency cochlear microphonic waveforms, and the endocochlear potential were performed. The data provide ample evidence of the resistance of the cochlea to dc mechanical stimuli, particularly those which do not cause a large pressure differential across the basilar membrane. [The authors gratefully acknowledge the surgical assistance of Dr. Peter Sellick.]