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 designed to identify and treat patients in the earliest stages of Alzheimer's, before memory loss begins.

Patients accepted into the trial already have deposits of beta amyloid, the other protein associated with Alzheimer's. The addition of the tau scan will allow scientists to get a much clearer picture of the events that lead to Alzheimer's.