Cochlear outer hair cell system is a logarithmic compressor

In general, sensors of the sensory organs are ultrasensitive, so that a gain control function would be essential to protect the sensors from high intensity stimuli. This holds for the cochlea, an acoustic sensor of high sensitivity. Above all, the cochlea has to be equipped with the organ mechanically protecting the vulnerable sensor from high amplitude sounds. In addition, to expand the apparent dynamic range of the cochlear sensor, the stimulus intensity i.e. amplitude, should be considerably compressed in the cochlea. Of course, the amplitude should be compressed logarithmically so as not to miss the low level signals as much as possible. Thus, it is very convenient if a logarithmic compressor (LC) exists in the cochlea. Then, we examined literatures on this subject, and finally we reached the conclusion that the outer hair cell (OHC) system is none other than the LC. Here we propose ‘the LC theory’ that the OHC system is the LC properly compressing the signal intensity together with the tectorial membrane. However, this theory is quite contradictory to the generally accepted theory that OHCs are selective amplifiers of the basilar membrane vibrations (CA theory). In our opinion, this contradiction is due to that the logic of the CA theory is not sound. If you enumerate all possible explanations of experimental data and examine them logically, you will never conclude to the CA theory. In a word, the CA theory confuses the effect of the LC with that of the selective amplifier. Certainly, they are very mistakable. On the other hand, because the LC theory is a logical result of the well-known experimental data, it is consistent with any of them. Moreover, the LC theory can easily explain the causes of such phenomena as otoacoustic emissions, two-tone suppression and loudness recruitment that have been difficult to be reasonably explained up to now. Needless to say, if the OHC system is the LC, you will have to re-create the auditory theory fundamentally. This means that every aspect of otology such as the clinical examination, the design of cochlear implant and the etiology of hearing impairments should be re-evaluated. The conclusion is that the CA theory should be corrected as quickly as possible.