This photo provided by Washington University shows associate professor of neurology at Washington University School of Medicine Beau Ances MD, PhD, right, and Matthew Brier an MD/PhD student at the university, examining PET (positron emission tomography) scans of Alzheimer’s disease patients, in St. Louis. Scientists are peeking inside living brains to watch for the first time as a toxic duo of plaques and tangles interact to drive Alzheimer's disease, with implications for better treatments. (Robert Boston/Washington University via AP)