Ossicular motion related to middle ear transmission delay in gerbil

The middle ear transmits sound efficiently from the air in the ear canal (EC) to the fluid filled cochlea. In gerbil, middle ear transmission produces a constant pressure gain between the EC and the cochlea of similar to 25 dB from 2 to 40 kHz, and a delay-like phase corresponding to a similar to 25-30 mu s delay. The mechanisms by which the air-born signal is collected and delivered to the cochlea are not thoroughly understood, and the source of the delay is controversial. We investigated these issues by observing ossicular motion along a single line of sight, roughly parallel to the EC and perpendicular to the stapes footplate. Measurements were made at the umbo, the long process of the manubrium, across the malleus-incus joint, at the long process of the incus, and the stapes head. While the overall delay between EC pressure and stapes velocity was fairly constant with frequency, subcomponents of the delay were frequency dependent. Up to similar to 17 kHz, most of the overall delay was between the EC and umbo with a much smaller contribution along the ossicles, whereas in the range from similar to 17 to 30 kHz, more of the overall delay was along the ossicles. (C) 2010 Elsevier B.V. All rights reserved.