Gerda Saunders is “dementing.” That’s what her neurologist told her in 2010 just before her 61st birthday, confirming what Saunders had already suspected: Her recent mental missteps were a sign of something serious.

They were also something that Saunders wanted to chronicle, which she soon found herself with time to do after retiring as associate director of gender studies at the University of Utah. (The final straw was when she was chairing a meeting, and in a moment of confusion recommended that everyone introduce themselves — for the second time.)

Her journal has morphed into a memoir, “Memory’s Last Breath: Field Notes on My Dementia,” that explores her life and her brain.

Even before her diagnosis, Saunders had a remarkable story to tell. It starts in South Africa, where she was raised on her Afrikaner family farm, a place without electricity but with black laborers that her father had “inherited.” That she can mine recollections from this childhood in vivid detail is as surprising to her as it may be to her readers. She also marvels at her ability to write a book — an undoubtedly complex mental task — when her daily life is filled with instances of unintentional shoplifting and being baffled by how to use a glass that is upside down.

“I am not the only person who appears to be ‘faking,’ ” Saunders writes, sharing the results of her scientific inquiry into her condition. She weaves in neurological research, accounts of other individuals with dementia, and plenty of talk of dendrites and the cerebral cortex.

All the while, she continues to sketch out her path, from the farm to boarding school to ­post-university married life with two children. When her husband was offered a job in the United States in 1984, they all left South Africa — and the resulting culture clash often left her discombobulated. It’s a sensation that returned after the dementia diagnosis, Saunders writes.

The book closes with Saunders addressing the realities to come, including what she refers to as “my eventual suicide.” She surveys the right-to-die landscape, which is particularly treacherous in America for a person who expects not to be “of sound mind” someday. But she has traveled across oceans before, and she’s willing to do it again, she writes, “when people will rightly say, ‘Gerda is no longer Gerda.’ ”