Data from: Non-invasive biophysical measurement of travelling waves in the insect inner ear

Frequency analysis in the mammalian cochlea depends on the propagation of frequency information in the form of a travelling wave (TW) across tonotopically arranged auditory sensilla. TWs have been directly observed in the basilar papilla of birds and the ears of bush-crickets (Insecta: Orthoptera) and have also been indirectly inferred in the hearing organs of some reptiles and frogs. Existing experimental approaches to measure TW function in tetrapods and bush-crickets are inherently invasive, compromising the fine-scale mechanics of each system. Located in the forelegs, the bush-cricket ear exhibits outer, middle and inner components; the inner ear containing tonotopically arranged auditory sensilla within a fluid-filled cavity, and externally protected by the leg cuticle. Here, we report bush-crickets with transparent ear cuticles as potential model species for direct, non-invasive measuring of TWs and tonotopy. Using laser Doppler vibrometry and spectroscopy, we show that increased transmittance of light through the ear cuticle allows for effective non-invasive measurements of TWs and frequency mapping. More transparent cuticles allow several properties of TWs to be precisely recovered and measured in vivo from intact specimens. Our approach provides an innovative, non-invasive alternative to measure the natural motion of the sensilla-bearing surface embedded in the intact inner ear fluid.

哺乳动物耳蜗的频率解析依赖于以行波（travelling wave，TW）形式存在的频率信息，沿拓扑频率排列的听觉感受器（auditory sensilla）进行传播。行波已在鸟类的基底乳头（basilar papilla）以及螽斯（bush-crickets，昆虫纲：直翅目）的耳部被直接观测到，同时在部分爬行动物与蛙类的听觉器官中也得到了间接推断。现有用于检测四足动物与螽斯的行波功能的实验方法均具有内在侵入性，会破坏各系统的精细力学特性。螽斯的耳部位于前足，具有外、中、内三部分结构；内耳位于充满液体的腔体中，包含拓扑频率排列的听觉感受器，且外部由足角质层（leg cuticle）保护。本研究报道了一类耳部角质层透明的螽斯，可作为直接、无创检测行波与频率拓扑（tonotopy）的潜在模式物种。本研究借助激光多普勒测振术（laser Doppler vibrometry）与光谱术（spectroscopy）技术，证实耳部角质层的光透过率提升后，可实现行波与频率映射的有效无创检测。对于角质层透明度更高的个体，可从完整活体标本中精准复原并检测行波的多项特性。本方法为检测嵌入完整内耳液体中的感受器所在表面的自然运动提供了一种创新性的无创替代方案。