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Tetris is a relatively basic yet compelling video game. The aim is to line up falling blocks so they fit together in horizontal rows. When a perfect line with no gaps is made, it will vanish, making room for more play and point-scoring.

Scientists say it's Tetris's immersive simplicity that makes it a potentially powerful therapeutic tool.

Prof Emily Holmes, an expert in psychology at the University of Karolinska, has spent many years exploring the game's medical merits.

"We wanted to have a task that really tapped into visual memory. With Tetris, it's the colours, shapes and movements that are very absorbing.

"Other games in the lab, like pub quiz games or counting tasks, didn't work. So we think it needs to be visual."

Such is its pull, some people say that after playing the game they see falling blocks in their thoughts and dreams - a phenomenon dubbed the Tetris effect.

Here's how it might help people.

Post-traumatic stress disorder

Prof Holmes has just published a study that shows Tetris therapy may lessen the psychological impact of traumatic events.

Her team at the University of Oxford gave Tetris therapy to patients admitted to a large UK hospital emergency department in a state of shock following road traffic accidents.

The patients were asked to visualise the crash they had just encountered and then begin playing Tetris on a Nintendo console.

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Twenty minutes of game play appeared to be enough of a distraction to stop disturbing memories of the accident being formed.

Prof Holmes explains: "Our findings suggest that if you engage in very visually demanding tasks soon after a trauma, this can help block or disrupt the memory being stored in an overly vivid way."

She says there is roughly a six-hour window of opportunity after a traumatic event to intervene.

In the study, the group of patients who had the Tetris therapy were far less likely to experience troublesome flashbacks of their accident than those who did not receive this intervention.

She says bigger studies are now needed - hers involved 71 volunteers. If those prove beneficial, it could be a treatment that other hospitals start to use.

Cravings

Scientists from Plymouth University and Queensland University of Technology, Australia, say playing Tetris can help people curb cravings for things like coffee, cigarettes and alcohol.

They asked 31 students to take part in an experiment.

The students were sent text messages throughout the day asking them to rate their current level of cravings for drugs, food and drink, and activities including exercise and sex.

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Fifteen of the students were also given an iPod to play short bursts of Tetris to see if it would have any effect.

Cravings decreased in the Tetris group.

Researcher Prof Jackie Andrade explained: "We think the Tetris effect happens because craving involves imagining the experience of consuming a particular substance or indulging in a particular activity. Playing a visually interesting game like Tetris occupies the mental processes that support that imagery; it is hard to imagine something vividly and play Tetris at the same time."

Lazy eye

A small study some years ago found an adapted version of Tetris helped treat a condition known as lazy eye or amblyopia.

The video game trains both eyes to work together, which is counter to previous treatments for the disorder.

Conventionally, doctors recommend covering the "good" eye with a patch to make the "lazy" one work harder.

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Dr Robert Hess, from McGill University in Canada, who ran the study said: "Using head-mounted video goggles we were able to display the game dichoptically, where one eye was allowed to see only the falling objects, and the other eye was allowed to see only the ground plane objects."

This forced the eyes to work together.

The researchers tested the treatment on 18 adults with amblyopia. Half played regular Tetris with the stronger eye patched, while the other half played the modified game with both eyes open.

At the end of the two-week study, the group who used both eyes had more improvement in their vision than the patched group.

When the monocular patching group, who had showed only a moderate improvement, switched to the dual eye training, the vision of this group also improved dramatically.