A recent study conducted by the University of Illinois, the University of Pittsburgh, and MIT surprised several people when it found that brain size is proportional to video game performance. The experiments consisted of people with relatively little gaming experience playing two games specially developed for the study. One game had players concentrate on a single task (think Tetris), the other shifted their attention between multiple jobs (think a strategy or simulator game). Presumably these were non-competitive games, and results were compared via a scoring system. If I'm reading the article right, the team found that they could predict the best player 25% of the time based on the size of their brain.
They also note that, while the size of the nucleus acclumbens, which controls our sense of achievement, was a heavy influence on players during the early parts of the tests, the players with larger caudates and putamens won out in the end. Apparently the caudate and putamen affect our ability to concentrate, especially on multiple tasks. Glad they spent money finding out that better concentration = higher scores.
Source: BBC News