In a May 19, 2015 file photo, R. Scott Turner, Professor of Neurology and Director of the Memory Disorder Center at Georgetown University Hospital, points to PET scan results that are part of a study on Alzheimer’s disease at Georgetown University Hospital, in Washington.

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In a May 19, 2015 file photo, R. Scott Turner, Professor of Neurology and Director of the Memory Disorder Center at Georgetown University Hospital, points to PET scan results that are part of a study on Alzheimer’s disease at Georgetown University Hospital, in Washington.