Technological advances in 3D micro-scanning laser Doppler vibrometry: investigation of the locust ear

In order to better understand insect hearing, different approaches must be combined to investigate how insect ears detect the different properties of a sound wave, how this signal is transmitted to the central nervous system, and how this information translates into an appropriate behavioural response. The tympanal hearing of the desert locust Schistocerca gregaria has already been the subject of numerous studies investigating membrane mechanics, neurophysiology, and ethology over the past few years.
In this context, we are studying the impact of tympanal structure on frequency analysis in the locust. Membrane mechanics have already been investigated in locusts using laser Doppler vibrometry to record tympanal displacement in previous studies. Owing to this approach it is known that, in locusts, sounds of given frequencies will generate travelling waves across the tympanum that propagate to different locations depending on the frequency of the initial stimulus. These travelling waves thus allow for the incoming stimulus to be concentrated in the region of the tympanum best tuned to its frequency, a phenomenon which can be regarded as a first, mechanical step in the process of frequency analysis. The research addressed in this work applies recent technological advances in 3D micro-scanning laser Doppler vibrometry to measure membrane displacement. Thus, in addition to the travelling waves identified through vibration measurements in only one dimension by previous studies, this work has for the first time detected and identified membrane oscillations in three dimensions simultaneously. The results allow us to improve our understanding of the impact of membrane mechanics on frequency analysis in the locust ear.