How do you advise older adult patients with cognitive impairment and/or caregivers who inquire about commercial cognitive apps/games for the prevention of cognitive decline?

There is no data that suggests that participating in cognitive apps/games can help patients who already have cognitive impairment. That said, my bias is that doing something is better than doing nothing, so any cognitive challenge is better than just watching TV.

There is some data that cognitive stimulation can help to prevent cognitive decline, but most particularly in conjunction with other interventions such as a healthy diet, social connectedness, and physical activity (i.e., the U.S. POINTER study). I tell my patients that if the same activity is done over and over, you get better at that activity, but that doesn't translate into better cognitive health overall. So, playing sudoku makes you a better sudoku player, not a better Scrabble...