Several mechanical manipulations of the wall of the inner ear do not affect air and bone conduction auditory thresholds

Objectives: According to classic theories, auditory stimulation, whether air- or bone-conducted, has been thought to begin with sound-induced relative motion between the cochlear shell and the stapes footplate, producing a passive mechanical traveling wave along the basilar membrane. This study was designed to assess the effect of experimental mechanical manipulations of the cochlea on the auditory thresholds to air-conducted and bone-conducted stimulation. Methods: The left ear of Psammomys obesus (highest auditory sensitivity between 0.5 and 5.0 kHz) was initially ablated in all animals studied. After baseline recording of auditory nerve-brain stem evoked response (ABR) thresholds to airand bone-conducted broadband click stimulation from the right ear, a hole was drilled in the vestibule of that ear in 3 animals. In 2 other animals, the round window of the animals was immobilized. In 3 additional animals, the round window was widely perforated. Repeat ABR thresholds were then determined. Results: There was no change in ABR thresholds to both air- and bone-conducted stimulation following these manipulations. The ABR wave latency also did not change. Conclusions: It is likely that an alternative mode of cochlear excitation is possible.