Over and over, research shows we build new neural networks through real life activities. Conversation with friends, volunteering, physical activity, and so on. Sure, your performance will appear to go up as you play pricey "brain boosting" games but that improvement is only relevant to the game and doesn't transfer to other areas of life.
Even more upsetting are programs that allege dementia can be reversed, like the proprietary SAIDO Learning Method. A cruel scam now brought to you by greedy nursing homes. Here's more on that: http://geekmom.com/2013/04/method-for-reversing-dementia/