MAPT and Alzheimer disease: However, when stratifying the groups into symptomatic AD, CU, and other CI, we found that tau368/t-tau was increasingly associated with tau PET SUVR in brain regions commonly being affected later by fibrillar tau deposition in participants with symptomatic AD (limbic regions: ρ = − 0.58, P < 0.01; isocortical regions: ρ = − 0.67, P < 0.001), with no strong associations observed between tau368/t-tau and tau PET SUVR in any of the brain regions in the groups encompassing other participants (Fig. 2A–C).