Just days before her 61st birthday, Gerda Saunders made a wretched discovery at the neurologist’s office: “Dement” is a verb. “I dement, you dement, he/she/it dements,” Saunders writes in “Memory’s Last Breath: Field Notes on My Dementia.” It’s an unlovely conjugation if ever there was one. Why is it that disorders of the body so often involve disfigurements of language as well? Even before that day, Saunders knew her memory was deserting her. In conversation with colleagues, she’d lose her bearings midsentence. (Before retiring, she was the associate director of the gender studies program at the University of Utah.) She’d misplace the names of books and authors she knew by heart. Once, at an important meeting, she asked all of the participants to go around the table and introduce themselves. They’d already done so. So she went to the doctor, described her symptoms, wedged herself inside an M.R.I. machine. Her scans revealed “white matter lesions,” or stoppered microvessels that were compromising the flow of blood in her brain. A neurologist told her she’d need two more evaluations at two-year intervals before she could be given a definitive diagnosis of dementia. “But in my heart,” Saunders writes, “I already knew: […]