Elliptical sound-induced motion in the bushcricket hearing organ

The bushcricket Mecopoda elongata can hear a wide range of frequencies, utilizing less than 50 sensory units. It is known that transduction takes place in the sensory dendrite but the underlying mechanisms are still unexplained. In a recent study we used optical coherence tomography (OCT) to characterize the relative motion in the dorsal-ventral direction between anatomical structures near the transduction site. In the current study, we combined OCT vibrometry with the use of a mirror to measure vibrations of the same structures from two different angles. By developing a method to identify measurement locations across the two viewing angles, we were able to decompose the motion into an anterior-posterior and a dorsal-ventral component. In the structures surrounding the transduction site we observed elliptical sound-induced motion that varied systematically with frequency. The motion in the cap cells (CC) was more tilted towards the anterior-posterior axis than that of the dorsal wall (DW). Finally, the two-dimensional relative motion between the DW and the CC, a candidate for the drive of transduction, was sharply tuned, and for ultrasound it was similar to the neural tuning described in the literature for this species.