Researchers at Oxford University showed 40 volunteers a series of images depicting serious injuries. After 30 minutes, half of the volunteers played Tetris for 10 minutes, while the other half did nothing. Over the next week, those who had played the game experienced far fewer flashbacks to the disturbing images.

The team suspects that Tetris has spatial game play which requires a lot of mind power, making it affect the way recent memories are embedded in the brain. (Source)