Even among medical experts, you will find differing opinions on how much someone with advanced dementia of any type understands. Alzheimer's, particularly, can render a person mute and uncommunicative, especially during the last stages of the disease.
Loving family members, and others who care for and about people with dementia, would like an answer to their question about how much a person understands. My non-medical viewpoint is that it varies. No, I'm not "copping out." The dementia I've witnessed, some of it Alzheimer's and some of it other types, has suggested to me that people likely do understand their surroundings on some level, even if it's just the body language or mood of his or her caregiver. Also, some people with dementia will have inexplicable moments of clarity where they seemingly come out of the walled-off state and momentarily return to a state that is indicative of their pre-dementia personality.
Moments of Clarity
Recently, I was chatting with a group of students from a university class that uses my book as a text. A young woman shared a story about her grandmother that started an interesting discussion.
The young woman's name was Anna. Although she'd never known her grandmother without Alzheimer's disease, they still had a close relationship. Twenty years is a long time for the disease to progress, and some people decline more quickly than others. Anna was fortunate to know her grandmother during years when she was still able to communicate.
Of course, as her grandmother's disease worsened, the communication became more difficult. Yet, Anna never gave up. She visited her grandmother regularly. As she was leaving her grandmother's room after one such visit—and this was during the late stages where her grandmother seemed to recognize no one—Anna hugged her goodbye, as was her habit. As she did so, she said, "I love you, Grandma." To her astonishment, her grandmother said with great clarity, "I love you, too, Anna." Then, her grandmother slipped back into the grip of her disease.
My dad suffered from a different type of dementia, one caused by a failed brain surgery. He spent most of his last decade in a state of delusion. Yet, there were times when, out of nowhere, my dad would look at me with clear, comprehending eyes, and he'd make a profoundly coherent statement, as when he thanked me for helping him live out his "fantasies," meaning the work life I created for him as his pretend office manager. Those moments were just that: moments. Then, he'd relapse back into his delusional world.
To me, moments of clarity that appear and disappear within a flash of time are a kind of proof that there is still a great deal going on in the brain of a person with advanced dementia.