To understand the structure and function of the brain, we need to study the highly complex, 3D neuronal connections. To enable a correct reconstruction of the nerve fiber pathways, it is crucial to know the detailed substructure of the tissue, especially in regions with crossing fibers. Neuroimaging techniques such as 3D polarized light imaging (3D-PLI) reveal the fiber pathways with micrometer resolution, but fiber crossings still pose a major problem. Here, we show how light scattering can be used to detect fiber crossings in 3D-PLI images and to reveal their substructure.

In various experimental and simulation studies, we find that the transmitted light intensity strongly depends on the angle between the fibers and the direction of light propagation. It can be used not only to reveal 3D information but also to identify crossing fibers. Furthermore, we demonstrate that optical scattering reveals the substructure of brain tissue such as the crossing angles of nerve fibers. To explain our experimental observations, we develop a simulation framework for polarization microscopy that allows us to study light scattering on fibrous tissue models using high-performance computing.

Our results provide an improved reconstruction of nerve fiber pathways in the brain at neuronal scales and allow for a better understanding of the brain’s microstructure. We anticipate that scattering microscopy, which reveals difficult-to-access information about brain tissue at micrometer resolution, will become an integral part of future neuroimaging techniques. Also, the simulation framework and results can easily be generalized to other microscopy techniques and fibrous tissue samples, enabling applications beyond neuroscience.