Alzheimer's researchers at Harvard for the first time are scanning the brains of healthy patients for the presence of a hallmark protein called tau, which forms toxic tangles of nerve fibers associated with the fatal disease.

The new scans are part of a large clinical trial called Anti-Amyloid Treatment in Asymptomatic Alzheimer's or A4, the first designed to identify and treat patients in the earliest stages of Alzheimer's, before memory loss begins.