Sorry, I can't remember what this article was about. http://www.pcgamer.com/study-suggests-first-person-shooters-may-be-damaging-your-brain/
It also depends on how the FPS is designed. If it triggers things that force you to use that part of your brain... well then you increase grey matter in that region. But interesting nonetheless.
Yeah but what about all the junk gamers consume while gaming? Was that the same for everyone in the study? Same amounts, same brands and so on. Or did one guy have snickers and red bull while someone else had trail mix and snapple? Or was no one allowed to have anything?