Neurologist Bruce Miller calls tau—a floppy, free-form protein—“the holy grail of dementia.” That designation may come as a surprise to anyone who has even a passing interest in the science of end-of-life brain diseases. A different protein, amyloid-beta (Aß), has become famous as the culprit responsible for the so-called senile plaques that gum up the brains of people with Alzheimer’s disease. Yet tau also plays a role in Alzheimer’s, by far the most prevalent type of dementia, and it’s not Aß but tau, escapi…