That is the most troubling part of Alzheimer’s: We don’t know what someone in the late stages of the disease thinks or feels. My mother reassures me that he’s unaware and unconcerned, but I’m not so sure. I am pretty confident that my call didn’t do any good.

In-person visits can be traumatic for him as well. The last time I went to see him, my older brother Gabi also came. Several times during our visit, Dad asked me who the stranger talking to our mother was. “Why is that guy here?” he would say. I told him it was his son. “If you say so,” he replied. When we sat at the table for dinner, I could sense that he was struggling to understand who we were and to follow the conversation. Is it good for him that we put him through these episodes?

The Alzheimer’s Association says that the time that families spend with a sufferer “has a lasting, positive impact” and it offers some guidelines for families about how to communicate with the patient — like not asking him or her to identify you, as I can’t seem to help but do, to be patient, calm and reassuring. I will try harder to follow those directions the next time I see my dad.