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: […]