Here's one (behind paywall unfortunately) by the Max Planck Institute for Human Development that "found significant gray matter (GM) increase in right hippocampal formation (HC), right dorsolateral prefrontal cortex (DLPFC) and bilateral cerebellum in the training group" that was trained for 2 months for at least 30 min per day with a platformer game:-

http://www.nature.com/mp/journal/v19/n2/pdf/mp2013120a.pdf

But it seems brain training games don't seem to provide any conclusive benifit:- http://longevity3.stanford.edu/blog/2014/10/15/the-consensus...