Figure 13.

Illustrations show the Braak τ staging system in Alzheimer disease in three different imaging planes. Braak stages I and II (orange areas) are characterized by abnormal τ aggregation at the entorhinal cortex, with early involvement at the hippocampus. Braak stages III and IV (green areas) are characterized by more advanced hippocampal aggregation and further involvement of the limbic system. Braak stages V and VI (purple areas) are characterized by extension into the neocortex, specifically involving the precuneus, temporal lobes, and lingual gyrus. This staging predicts the sequence of findings at structural imaging, FDG PET, and τ-based PET.