Comment on "Measuring power production in the mammalian cochlea" [Curr. Biol. 17, 1340 (2007)] (L)

Recently, a paper by Lakashkin (2007) ("Power amplification in the mammalian cochlea," Curr. Biol. 17, 1340-1344) was published on how power can be measured in the mammalian cochlea. The general subject is of current widespread interest, so the question of whether the method used by Lakashkin is valid may be of interest to the readers of this journal. Power generation in the cochlea can account for the extraordinary sensitivity of hearing. Lukashkin claimed to provide a direct proof of cochlear power generation. A first-order spring-dashpot system was used to model the organ of Corti. The power flux direction can be derived from the sign of the phase difference between the force and displacement, which can be presented as a "hysteresis plot." Basilar membrane (BM) vibration near the characteristic frequency (CF) was measured while applying a low-frequency modulation tone together with the CF tone. A force was derived from the modulation profile of the BM CF vibration and when plotted versus the displacement at the modulation frequency, the function had a counterclockwise direction of hysteresis, suggesting power generation. In this letter, we present comments on the analysis in the report: (1) that it is not appropriate to analyze at the modulation frequency to derive the power generation at CF; (2) that the derivation of a force from just the displacement profile is not justified, followed by an alternative interpretation of the experimental data.