MECHANICAL RESPONSES OF THE MAMMALIAN COCHLEA

Recent findings in auditory research have significantly changed our vi ews of the processes involved in hearing. Novel techniques and new app roaches to investigate the mammalian cochlea have expanded our knowled ge about the mechanical events occurring at physiologically relevant s timulus intensities. Experiments performed in the apical, low-frequenc y regions demonstrate that although there is a change in the mechanica l responses along the cochlea, the fundamental characteristics are sim ilar across the frequency range. The mechanical responses to sound sti mulation exhibit tuning properties comparable to those measured intrac ellularly or From nerve fibres. Non-linearities in the mechanical resp onses have now clearly been observed at all cochlear locations. The me chanics of the cochlea are vulnerable, and dramatic changes are seen e specially when the sensory hair cells are affected, for example, follo wing acoustic overstimulation or exposure to ototoxic compounds such a s furosemide. The results suggest that there is a sharply tuned and vu lnerable response related to the hair cells, superimposed on a more ro bust, broadly tuned response. Studies of the micromechanical behaviour down to the cellular level have demonstrated significant differences radially across the hearing organ and have provided new information on the important mechanical interactions with the tectorial membrane. Th ere is now ample evidence of reverse transduction in the auditory peri phery, i.e. the cochlea does not only receive and detect mechanical st imuli but can itself produce mechanical motion. Hence, it has been sho wn that electrical stimulation elicits motion within the cochlea very similar to that evoked by sound. In addition, the presence of acoustic ally-evoked displacements of the hearing organ have now been demonstra ted by several laboratories. (C) 1997 Elsevier Science Ltd.