According to new research by neuroscientist Richard Haier, Tetris makes your brain more efficient, as it helps develop some parts of it. In fact, according to Haier, any "challenging visuospatial task" will affect it.
This is the second part of the research. The previous one showed how some brain parts used more glucose as the subjects get more experienced with the game, making it less challenging. This study uses new imaging techniques to check for changes in adolescent girls during a three month period. According to Haier, adolescent girls' brains are still developing. Obviously, boys' brains stop functioning properly around age ten.