Maybe…. It has been observed that Alzheimer’s Disease affects the areas of the brain known as Wernicke’s area (which is correlated to speech comprehension) and Broca’s area (which is correlated to speech production) and that these affect peoples ability to communicate their intentions. People with dementia may still have intentions but may find it more difficult to communicate them. This may be because (amongst other things) the damage to the brain makes it more difficult to actively construct new sentences.
It has also been observed that when people reminisce those memories are more likely to be well-rehearsed pieces of autobiographical narrative. Little stories that have been told and re-told until they are honed and fit for purpose. As such, when a reminiscence is evoked, the reminiscer is (possibly) not constructing new sentences or expressing a new idea but re-telling a well-honed, oft-told story. This is a different process, in the same way that singing a song is a different process, and both are therefore less susceptible to the cognitive slights of dementia because of it. There are a lot of caveats and uncertainties in this entry but, if this is correct, then it would represent another way in which reminiscence works through the cognitive strengths of someone with dementia.