Displacement of the stapes differs across species—Implications for studies of auditory function

Abstract

Sound is transferred to the cochlea via the middle ear. The anatomy and physiology of the middle ear varies significantly across species, and these differences impact both the stimulation provided to the inner ear, and the suitability of different animal models for use in various types of research. Studies of auditory trauma from blast, for example, require generation of intracochlear pressures with sufficiently high intensities to cause damage. In some species, e.g., mice and rats, it may not be possible to generate sufficiently high pressures through air conducted sound alone, whereas in humans sufficiently high pressures can readily be generated through air conduction. We hypothesize that this is due to limits on the displacement of the stapes by the stapedial annular ligament, which thereby constrains the energy transferred to the cochlea through the middle ear. To test this hypothesis, we made measurements of the motion of the middle ear bones in response to tones of varying intensities and frequencies in several different species commonly used in laboratory research. Our results reveal peak stapes displacements from ~150 um in humans to 10-20 um in mice and rats. We will discuss the implications of these findings for basic studies of auditory function.