Brain FACTs: A same-section workflow for Fiber Architecture, Cytoarchitecture and cell Types in large-scale brain sections

Abstract

Understanding the human brain's multiscale organization requires linking cells, connections and architecture, yet conventional methods are incompatible within a single specimen, and inter-individual variability confounds cross-brain comparisons. Multiple-label immunohistochemistry for different cell types has been applied in interleaved sections but remains challenging within a single large human brain section and, has never been combined on the same tissue with 3D polarized light imaging (3D-PLI) for three-dimensional fiber architecture. Here we introduce a sequential multimodal workflow integrating 3D-PLI, multiplex chromogenic immunohistochemistry and Nissl staining on the same large human brain section, preserving each technique's quality and specificity. The method was validated on vervet monkey and Wistar rat sections. The resulting paired high-resolution images eliminate inter-subject variability and enable direct micron-scale mapping of fiber tracts relative to molecularly defined cell types, yielding previously inaccessible insights such as molecular identification of white-matter components, refined cortical layering and cytoarchitectural disambiguation.