MAPT and Alzheimer disease: Using Tg12099(+/−) rats, we bilaterally injected tau prions into the thalamus from 1) the brains of aged, sick Tg12099(+/+) rats, 2) postmortem brain samples from human patients with clinically diagnosed AD and PSP, and 3) a postmortem brain sample from a cognitively unimpaired control human patient.