Kwon, J. et al. Nat. Commun. 8, 1832 (2017).

Myelin tightly wraps around axons and forms an insulating sheath, which enables fast propagation of action potentials. To quantify the degree of myelination and the thickness of the underlying axon, Kwon et al. harness the reflective properties of the multilayered myelin sheath in a label-free and high-resolution imaging approach. The different layers in the myelin sheath have different refractive indices, and therefore incident light is partially reflected at the interphases between layers. The reflections from different interphases interfere with each other, and this information can be used to describe the properties of the myelin sheath. Kwon et al. show that they can determine the degree of myelination, the axonal diameter as well as swelling of myelin with their approach. The researchers applied the technology to assess the changes in myelin after a traumatic brain injury in mice.