MAPT and Alzheimer disease: Using three large cohorts of cognitively unimpaired older adults, from the Anti‐Amyloid Treatment in Asymptomatic Alzheimer's (A4) and its companion study, Longitudinal Evaluation of Amyloid Risk and Neurodegeneration, the Alzheimer's Disease Neuroimaging Initiative, and the Harvard Aging Brain Study, the investigators identified regions of the brain with high rates of tau accumulation and attempted to estimate how these rates might evolve over a continuous spectrum of amyloid deposition, beginning at baseline.