Compressive sound waves in some mammalian cochleae determine the onset latencies of basal cochlear-partition responses

Wenxiao Zhou, Ph.D. Student, Department of Mechanical Engineering, Advised by Jong-Hoon Nam

Hopeman 224

Stapes footplate location in the rodent cochlea’s vestibule implies that compressive waves from that footplate strike a section of the basal cochlear partition within microseconds. Recent evidence shows that throughout the basal end of chinchilla cochlea, the signal-fronts of intense clicks and high-frequency tones indeed arrive at the cochlear partition with ~4 μs latency, too quickly for “slow” traveling waves to provide. However, all measured onset latencies in the apical region are much longer, consistent with slow-wave propagation. It is proposed that this physiological segmentation of response-onset behavior occurs because of a corresponding segmentation in cochlear anatomy, with key anatomical features being the relatively large scalar volumes of the sound-port regions and the location of the footplate. Supporting the proposal are published experimental data which show that the segmentation of the cochlea into regions having similar response-onset latencies to clicks and high-frequency tones approximates the anatomical segmentation of this cochlea. Support is also given by a model of the gerbil’s cochlea that creates a basal “vestibule” by relocating the sound ports from their placements in conventional models.

This representation of the vestibule was a key to the model’s ability to generate segmented response-onset latency characteristics similar to those obtained experimentally.