Histological visualization of long fiber tracts in the white matter of adult human brains.

The position and extent of fiber pathways and their intersubject variability in the white matter of the forebrain have not been analyzed with histological techniques in the adult human brain. This is due mainly to the lack of a staining procedure with which the different fiber tracts can be visualized with sufficient contrast. The here described modification of the Heidenhain-Woelcke myelin stain yields increased contrast between heavily and less heavily myelinated pathways, facilitating identification and tracing of single fiber tracts. The modification makes the microscopical resolution possible which is necessary for preparing comprehensive maps of fiber tracts. Such maps are valuable tools for clinical diagnosis, since they provide a basis for localizing anatomically the structures involved in subcortical lesions. Correlations between the size of a lesion and its location relative to identified fiber tracts on the one hand and postlesional functional alterations and recovery on the other can only be made on the basis of topographic and morphometric maps of these structures in the normal adult human brain.