Micron-resolution fiber mapping in brain histology independent of sample preparation.

Detailed knowledge of the brain's nerve fiber pathways is essential for understanding brain function, improving surgeries, and studying neurological diseases ( 1 , 2 ). Microscopy techniques allowing to disentangle this dense fiber network in macroscopic tissue sections, like polarization microscopy ( 11-13 ) or Nissl-based structure tensor analysis ( 26 ), require birefringence or specific staining, limiting their use on histological tissue sections, which are often formalin-fixed paraffin-embedded with little birefringence contrast or prepared with other stains ( 26 ). Here, we present a light scattering-based microscopy technique that reveals interwoven fiber architectures with high resolution across large fields of view, independent of birefringence and staining. We demonstrate its broad applicability on both label-free and stained, paraffin-embedded and deparaffinized, fresh and century-old archived, animal and human brain tissues. Notably, we uncover detailed fiber structures in whole-brain sections from the BigBrain atlas ( 24 ), and identify altered microstructures in diseases like demyelination and hippocampal neurodegeneration. We compare our results to diffusion magnetic resonance imaging, polarization microscopy, and structure tensor analysis, demonstrating our technique's superiority in resolving interwoven fiber pathways with high resolution and accuracy. Finally, we show that it can also reveal fiber structures in non-brain tissues - including muscle, bone, and blood vessels. Our fast and accessible technique enables laboratories worldwide to study intricate fiber networks in all kinds of histological tissue sections, offering a new dimension to neuroscientific and biomedical research.