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Tetris is a tile-matching puzzle video game, originally designed and programmed by Russian game designer Alexey Pajitnov. It was released on June 6, 1984, while he was working for the Dorodnicyn Computing Centre of the Academy of Science of the USSR in Moscow. He derived its name from the Greek numerical prefix tetra- (all of the game’s pieces contain four segments) and tennis, Pajitnov’s favorite sport.

How to play Tetris
Tetris is a deceptively simple game to play. With only a handful of moves to learn, anyone can begin to enjoy Tetris in no time at all. This introduction is designed to teach you the fundamentals of Tetris, providing you the minimum information necessary to get going.

Tetris is played on a 10 by 20 grid called the Matrix. Shapes called Tetriminos fall from the top of the Matrix and come to rest at the bottom. Only one Tetrimino falls at a time. At first the Tetriminos fall rather slowly; as the game progresses they will fall faster and faster. There are seven shapes of Tetriminos, each made up of four small squares called Minos.

Using the arrow keys, you can adjust where and how the Tetriminos fall. By pressing the LEFT and RIGHT Arrow keys, you can slide the falling Tetrimino from side to side. You can’t slide a Tetrimino past the edge of the Matrix. By pressing the UP Arrow key, you can rotate the Tetrimino 90 degrees clockwise. You can move the Tetriminos even after they land at the bottom of the Matrix briefly. The Tetrimino will Lock Down as soon as you stop trying to move it. At that point, the next Tetrimino will begin to fall.

As your game improves and you begin to pay attention to the Tetriminos in your Next Queue, you might find yourself getting a little impatient waiting for the piece to fall. You have two options to speed up the game—the Soft Drop and the Hard Drop—and they’re both really easy to do.

The Soft Drop is performed by pressing the DOWN Arrow key—the Tetrimino will fall much faster than usual while you hold down the key, but as soon as you let go the piece will resume its normal pace. You retain complete control over the piece while doing a Soft Drop.

The Hard Drop is much less forgiving—hit the Space Bar to cause the Tetrimino to fall straight down, forgoing any further opportunity to move it. The Hard Drop is great for timed games where your goal is to get pieces into position as quickly as possible. Pay attention to the Ghost Piece to help you see where the Tetrimino will fall, and don’t press the space bar until you’re ready!

Effect of Tetris on the brain
According to research from Dr. Richard Haier, et al. prolonged Tetris activity can also lead to more efficient brain activity during play. When first playing Tetris, brain function and activity increases, along with greater cerebral energy consumption, measured by glucose metabolic rate. As Tetris players become more proficient, their brains show a reduced consumption of glucose, indicating more efficient brain activity for this task. Moderate play of Tetris (half-an-hour a day for three months) boosts general cognitive functions such as “critical thinking, reasoning, language and processing” and increases cerebral cortex thickness.

In January 2009, an Oxford University research group headed by Dr. Emily Holmes reported in PLoS ONE that for healthy volunteers, playing Tetris soon after viewing traumatic material in the laboratory reduced the number of flashbacks to those scenes in the following week. They believe that the computer game may disrupt the memories that are retained of the sights and sounds witnessed at the time, and which are later re-experienced through involuntary, distressing flashbacks of that moment. The group hopes to develop this approach further as a potential intervention to reduce the flashbacks experienced in post-traumatic stress disorder but emphasized that these are only preliminary results.

Professor Jackie Andrade and Jon May, from Plymouth University’s Cognition Institute, and Ph.D. student Jessica Skorka-Brown have conducted research that shows that playing Tetris could give a “quick and manageable” fix for people struggling to stick to diets, or quit smoking or drinking.

Another notable effect is that, according to a Canadian study in April 2013, playing Tetris has been found to treat older adolescents with amblyopia (lazy eye), which was better than patching a victim’s well eye to train his weaker eye. Dr. Robert Hess of the research team said: “It’s much better than patching – much more enjoyable; it’s faster, and it seems to work better”. Tested in the United Kingdom, this experiment also appears to help children with that problem.

The game has been noted to cause the brain to involuntarily picture Tetris combinations even when the player is not playing (the Tetris effect), although this can occur with any computer game or situation showcasing repeated images or scenarios, such as a jigsaw puzzle.

Possibility of infinite gameplay
The question Would it be possible to play forever? was first encountered in a thesis by John Brzustowski in 1992. The conclusion reached was that the game is inevitably doomed to end. The reason has to do with the S and Z Tetriminos. If a player receives a large sequence of alternating S and Z Tetriminos, the naïve gravity used by the standard game eventually forces the player to leave holes on the board. The holes will necessarily stack to the top and, ultimately, end the game. If the pieces are distributed randomly, this sequence will eventually occur. Thus, if a game with an ideal, uniform, uncorrelated random number generator is played long enough, any player will top out.

In practice, this does not occur in most Tetris variants. Some variants allow the player to choose to play with only S and Z Tetriminos, and a good player may survive well over 150 consecutive Tetriminos this way. On an implementation with an ideal uniform randomizer, the probability at any given time of the next 150 Tetriminos being only S and Z is (2/7)150 (approximately 2×10−82). Most implementations use a pseudorandom number generator to generate the sequence of Tetriminos, and such an S–Z sequence is almost certainly not contained in the sequence produced by the 32-bit linear congruential generator in many implementations (which has roughly 4.2×109 states). The “evil” algorithm in Bastet (an unofficial variant) often starts a game with a series of more than seven Z pieces.

Modern versions of Tetris released after 2001 use a bag-style randomizer that guarantees players will never receive more than four S or Z pieces in a row. This is one of the “Indispensable Rules” enforced by the Tetris Guideline that all officially licensed Tetris games must follow.

Recent versions of Tetris such as Tetris Worlds allow the player to repeatedly rotate a block once it hits the bottom of the playfield, without it locking into place (see Easy spin dispute, above). This permits a player to play for an infinite amount of time, though not necessarily to land an infinite number of blocks.