Does Reticular Lamina Active Gain Explain Broad Suppression Tuning of SFOAEs?

Stimulus frequency otoacoustic emissions (SFOAEs) appear to originate primarily in the cochlear region of the CF place of the evoking probe tone. It is commonly believed that SFOAE generation is a byproduct of the cochlear amplifier that enhances basilar membrane vibrations near the characteristic frequency place. However, evidence from studies of SFOAEs revealed by suppressors more than an octave above that of the probe tone suggests generation extends basal to the region thought to contribute to mechanical amplification [3, 4]. This finding complicates the interpretation of the SFOAE phenomenon, because this basal region shows no evidence of nonlinear suppression in studies of basilar membrane vibrations. The recent reports from the Ren and Oghalai labs [7, 8, 10] show substantial active and vulnerable gain in the reticular lamina motion basal to the peak, where the basilar membrane appears passive and linear. It is thus plausible that basal SFOAE contributions arise from hair-cell-mediated reticular lamina amplification that is subject to two-tone suppression.