Playing Tetris can become an addiction for many people, as many video games. An interesting phenomenon which a lot of gamers have observed is that after playing the game, they see the pieces falling from the sky in real life. Many even see the game in their dreams! This happens because of the cognitive afterimage, an optical illusion that makes the image appear in front of your eyes after you have been exposed to it. With Tetris, your mind continues the game even after you stop playing it.
In 1991 an American psychologist Richard Haier, known for his studies on human intelligence and Neural Connections, used the game in brain studies. He observed, that while gamers were playing the game, their brain scans were showing increasingly lit up neural networks, which means that neurons were working hard to help the player resolve the puzzle. Interestingly, after a few days of playing, the activity of neurons in the brain has substantially decreased. In other words, the brain was consuming less power to solve the puzzles. The brain has learned how to automate the process, the phenomena now known in psychology as the Tetris Effect.