Any research that shows decreasing risk of dementia in persons who perform daily "mental exercise", or brain training games, like Sudoku Lumosity , Elevate or Skillz Apps?
probably, you won't find an answer for this question. I would suggest to search for molecular modifications in dementia and how video games influence those modifications. Maybe the answer would be imprecise and inaccurate, but at least you will have idea to start.
Lifetime cognitive engagement has been associated with lower deposition of beta-amyloid in the brain, according to studies of amyloid PET images (see Landau et al 2012; PMID 22271235). Another study showed that lifetime intellectual enrichment (high education, high midlife cognitive activity) is associated with lower amyloid accumulation in the brains of AD patients who are APOE-e4 carriers (Vemuri et al 2016; PMID 26911640).