The video game Tetris can be found on computers in almost any lab; grad students need entertainment too, after all. Now researchers have put the game to scientific use--and found that vivid images of Tetris appear to new players as they are drifting off to sleep. Amnesics also see the pieces, a finding that narrows down how memories take hold during sleep.

There are many kinds of memories; some, called "explicit," mean that you can remember a past experience. People with damage to their hippocampus and surrounding brain structures can't build new explicit memories. If amnesics play Tetris, take a short break, and then return to the game room, they don't remember the game or even having met the experimenter who just taught them how to play.

In what he calls a serendipitous design, psychologist Robert Stickgold of Harvard Medical School in Boston and colleagues decided to include five people with amnesia in a study of sleep and learning, using Tetris as an example of learning a complex skill. The amnesics, along with 12 novice Tetris players, spent several hours playing the game over the course of 3 days. The experimenters then woke the players up repeatedly during the first hour of sleep on the following nights, during a phase of light sleep called Stage 1. Nine of 12 novices reported seeing Tetris pieces spinning and falling--just as they do in the game--as they were drifting off. Similarly, the amnesics reported seeing, in the words of one, "images that are turned on their side. I don't know what they are from. I wish I could remember, but they are like blocks."

The finding, reported in the 13 October issue of Science, suggests that the "parts of the brain responsible for the inability to learn must be different from those responsible for the images," says Richard Haier of the University of California, Irvine. Stickgold suspects Stage 1 sleep images occur as people unconsciously relive their day's experiences and extract what's meaningful. Even though amnesics can't remember the game because of damage to the hippocampus, he says, their brains still reprocess the images.

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