On autopsy, the brain of an Alzheimer's patient can weigh as little as 30 percent of a healthy brain. The tissue grows porous. It is a sieve through which the past slips. As her mother loses her grasp on their shared history, Elizabeth Kadetsky sifts through boxes of the snapshots, newspaper clippings, pamphlets, and notebooks that remain, hoping to uncover the memories that her mother is actively losing as her dementia progresses. These remnants...