The dura of the middle fossa lies superior the temporal line in >80% of specimens and at least 5 mm superior in nearly half. This indicates the temporal line or a line slightly inferior to this is reliably inferior the middle fossa dura.

Intracochlear pressures reveal lower middle-ear transfer function magnitudes (i.e. reduced gain relative to the ear canal) for high sound pressure levels, thus revealing lower than expected cochlear exposure based on extrapolation from cochlear pressures measured at more moderate sound levels. These results are consistent with lowered transmissivity of the ossicular chain at high intensities, and are consistent with our prior report measuring middle ear transfer functions in human cadaveric temporal bones with high intensity tone pips.

Simulating effusion leads to a frequency-dependent reduction in intracochlear sound pressure levels consistent with audiological presentation and prior reports. Results reveal that intracochlear pressure measurements (PSV and PST) decrease less than expected, and less than the decrease in PDiff. The observed decrease in umbo velocity is greater than in the differential intracochlear pressures, suggesting that umbo velocity overestimates the induced conductive hearing loss. These results suggest that an alternate sound conduction pathway transmits sound to the inner ear during effusion.

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.