Abstract 406, Date 2:00 pm - 4:45 pm, Tuesday, February 19, 2008 Session M: Podium
Mechanical Preprocessing of Amplitude Modulated Sounds in the Apex of the Cochlea
*Nigel Cooper
A displacement-sensitive laser interferometer was used to record the sound-evoked vibrations of individual Hensenís cells in the apical turns of living guinea-pig cochleae. The mechanical responses to amplitude modulated (AM) tones were investigated, and are shown to be physiologically vulnerable. In healthy cochleae, the AM responses are demodulated strongly at both moderate and high sound pressure levels (e.g. 60-80dB SPL). In less healthy and post-mortem cochleae, AM demodulation is weaker and is only seen at high stimulus levels (e.g 85-90dB SPL). The physiologically vulnerable component of the demodulation is considered to be an analogue of the baseline position shifts that can be seen in the apical cochleaís responses to pure-tone stimuli. The simplified computational model of Cooper & Dong (2003) is used to support a suggestion that both the baseline position shifts and the AM demodulation (i) originate from an asymmetry in the outer hair cellsí mechano-electrical transduction process and (ii) are put into effect via a voltage-dependent electro-mechanical transduction process such as the somatic motility (but not the hair-bundle motility) of the outer hair cells. Acknowledgements Supported by the Royal Society and by Deafness Research UK. References Cooper, N.P. and Dong, W (2003) Baseline position shifts and mechanical compression in the apical turns of the cochlea. In: Gummer, A.W. (ed.) The Biophysics of the Cochlea: Molecules to Models. Singapore: World Scientific, pp. 261-270.