For years, the two patients had come to the Penn Memory Center at the University of Pennsylvania, where doctors and researchers follow people with cognitive impairment as they age, as well as a group with normal cognition. Both patients, a man and a woman, had agreed to donate their brains after they died for further research. “An amazing gift,” said Dr. Edward Lee, the neuropathologist who directs the brain bank at the university’s Perelman School of Medicine.