We can't talk specifically to brain-training for alzheimer's, and we know, for instance, that brain-training doesn't work for actually making you smarter.
But the biggest protective effect against Alzheimers is years of education (ie >13 years of education is protective and it goes up from there). So it's plausible
But the biggest protective effect against Alzheimers is years of education (ie >13 years of education is protective and it goes up from there). So it's plausible