Methods for multiscale structural and functional analysis of the mammalian cochlea

The mammalian cochlea is a snail-shaped structure deeply that is embedded in the temporal bone and harbors the auditory sensory epithelium - the organ of Corti. Since the discovery of this remarkable hearing organ in the middle of the 19th century, generations of anatomists and physiologists have been attracted to study the structural and functional details of this intricate and delicate structure and thereby contributed to establishing our current understanding of peripheral sound encoding. Since these early days, the continued development of novel imaging technologies - both on light and electron microscopic level - has driven the auditory research field and now enables the visualization of cochlear structures across multiple scales with unprecedented clarity and exquisite detail. To honor these achievements, this review aims to provide a concise overview of current multi-scale imaging methodologies to investigate cochlear anatomy and cellular function in the peripheral auditory pathway. For this purpose, we will outline the technological concepts underlying these techniques - ranging from label-free to label-containing approaches - highlight their respective strengths and limitations and provide specific examples of their use in modern auditory research. We will focus on traditional as well as less conventional imaging techniques that present essential tools for unraveling the protein composition, nanoscale assembly, and physiology of the first auditory synapse and associated structures. In addition, we will introduce novel non-invasive large-scale methodologies that allow for high-resolution in situ imaging of the structurally-unperturbed cochlea and point out potential future applications. In combination, these techniques allow for a comprehensive multi-scale analysis of cochlear structure and function.