Introduction

In the mammalian nervous system, myelin provides electrical insulation for the neural circuit by forming a highly organized, multilayered thin-film around the axon fibers. Recently, we have investigated the colorful reflectance from this subcellular nanostructure and devised a new label-free technique based on a spectroscopic analysis of reflected light, enabling nanoscale imaging of myelinated axons in their natural living state. Harnessing this technique, we demonstrated 3-dimensional mapping of the axon diameter and sensing of dynamic changes in the substructure of myelin at nanoscale. We further revealed the prevalence of axon bulging in the brain cortex after mild compressive trauma. Our novel tool opens new avenues of investigation by creating unprecedented access to the nanostructural dynamics of live myelinated axons in health and disease.