Memantine has been useful for slowing down Alzheimer's and temporarily improving responsiveness. However, Memantine has not shown any effectiveness in reversing Alzheimer's or fully stopping its progression (sadly). Memantine does seem to increase self-awareness clarity but, counterintuitively, seems to also disrupt memory recall. Word of caution, in one rat study, I had read that Memantine could have long term side-effects of hindering memory recall.
Amantadine has a fascinating structure, but it seems like it's not super useful by itself from studies. It seems more like a very promising 'base structure' to build future compounds upon (like Memantine and bromantane).
Anyways, this family is rather interesting for a number of its properties and are still not very well known or understood. Please do share any more insights.