CHAT and Mental deterioration: With respect to the major confounders (Figs. S2 and S4), we found a negative correlation between ChAT-ir areas with Braak stage in control subjects (Fig. S2f), and a negative correlation between the GA-ir areas and Braak stage in control and T2DM subjects (Fig. S4f), indicating the NBM neuronal activity declines along the course of cognitive decline.