On inner ear function and the origin of oto-acoustic emissions

The extremely low hearing threshold of the mammalian ear suggests the presence of a special amplifying mechanism, because the stereocilia of the outer hair cells (OHCs) are not likely to be sensitive enough themselves, although their mechanical embedding may provide some amplification. In the past decades, biophysicists have increasingly turned to the chaos theory for explanation. a theory the implications of which are considerable. One of its major tenets, self-organization, is not easily understood at first glance, but is easily reproducible mathematically. With self-organization, the processes involving the OHCs can readily be simulated: Self-organization can help to explain why OHCs vibrate at amplitudes much higher than those of the exciting stimulus. To further our understanding of the process of hearing, vibratory processes, which presumably occur in normal and damaged OHC clusters, are described and compared with a mathematical analysis of data sets obtained from normal subjects using an extremely sensitive microphone.