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分析，依赖于以行波（travelling wave, TW）为载体的频率信息，在按音调拓扑排布的听觉感受器（tonotopically arranged auditory sensilla）间的传播。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）的耳部中被直接观测到，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。当前用于测量四足动物与螽斯中行波功能的实验方法，本质上均具有侵入性，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；其内耳包含充满液体的腔体，腔内的听觉感受器按音调拓扑排布，且耳部外部被足角质层（leg cuticle）所保护。本文报道了一类耳部角质层透明的螽斯，可作为直接、非侵入式测量行波与音调拓扑的潜在模式物种。借助激光多普勒振动测量法（laser Doppler vibrometry）与光谱法（spectroscopy），我们证实，耳部角质层对光线的更高透过率，可实现对行波与频率映射的有效非侵入式测量。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测量行波的多项特性。本研究方法为测量内嵌于完整内耳体液中的、带有听觉感受器的表面的自然运动，提供了一种创新性的非侵入式替代方案。