Biophysics of the Cochlea. Theory, Experiments and Applications

This work attempts to bring together theoretical and experimental aspects of cochlear biophysics. In both cases, the focus is on the relationship between the motility of outer hair cells and the filtering properties of the basilar membrane, as this seems the key for understanding the functioning of the peripheral auditory system. From the theoretical side, the hydrodynamics of the cochlea is studied in detail. A possible mechanism for coupling the outer hair cells to the mechanics of the basilar membrane is proposed and analysed mathematically. From the experimental side, the effects of stimulating the cochlea with extracellular current are investigated by means of laser interferometry. The necessary apparatus and the software for data acquisition were engineered in the course of this investigation. A rapid return in the realm of mathematical modelling concludes this work, with an eye on possible applications of physiological knowledge to speech recognition. The newcomer is given a succint introduction to the cochlear world in Chapter 1. A new model of cochlear biomechanics is presented in Chapter 2. A set of experiments aiming at clarifying the role of outer hair cell motility in the control of the vibration pattern of the basilar membrane are described in Chapter 3. The role of active cochlear mechanics in the processing of speech is explored in Chapter 4. Chapters 2 and 4 are the result of an intense collaboration with Prof. Renato Nobili at the Department of Physics of Padova University, Italy, following a preparatory period with Prof. Campbell L. Searle at the Massachusetts Institute of Technology, Boston, U .S.A. The results of Chapter 3 were obtained thanks to the expertise of Dr. Jonathan Ashmore, in his laboratory at the Department of Physiology of Bristol University, England.