MAPT and red-green color blindness: Solid-state NMR spectroscopy in combination with biochemical experiments revealed that the rigid/semi-rigid core of the heparin-free tau fibrils is formed by the tau residues ~270 to ~380, i.e., a similar size and location of the fibril core region as in tau fibrils purified from a CBD patient brain (Figs. 2, 3).