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Monday, 16 October, 2000, 09:50 GMT 10:50 UK
Electric dreams reveal memory secrets
Tetris graphic
Dreams of tetris could help unravel memory secrets
Amnesiacs given computer games to play went on to dream about them - even though they could not actually remember playing them.

Their experiences have given scientists clues as to the way the body uses sleep to store away memories for future use.

Volunteers - including five people with no ability to store long-term memories - were asked to play the classic game Tetris. This involves rotating different shaped blocks as they fall so they will fit into gaps left below.

Many of the volunteers reported that they actually dreamed about the game the following night, seeing images of blocks falling and rotating.

REM sleep appears to have some significance in learning

Dr Paul Fletcher, Addenbrooke's Hospital
The amnesiacs had no actual memories of playing the game when asked the following morning and, unlike their normal colleagues, never improved their game-playing skills from day to day.

However, three of the five reported having dreams which appeared related to Tetris.

However, these dreams, they said, had a somewhat surreal quality when compared to those of the non-amnesiac players.

Dr Robert Stickgold, a psychiatrist at Harvard Medical School, who conducted the research, said he believed that the brain used dreams as a way of filing away memories from the previous day.

"Dreams are just the body's way of clearing out the mental 'in-box'," he said.

Weird dreams

When dreams seemed weird, he said, it could be because the brain was trying to cross-reference new against old memories - and in the case of the amnesiacs, it was unable to do this.

"What these results, especially from the amnesiacs, tells us, is that when the brain puts dreams together, it does it without knowledge of and access to memories of actual events in our life."

The researchers believe that this is further evidence of two different centres in the brain concerned with the storage and processing of memory.

The amnesiacs in the study had suffered damage to the hippocampus - one of the key areas concerned with memory - either through a head injury or stroke. This is thought to deal with specific memories of events, whereas more general memories are processed elsewhere.

Dr Stickgold said: "When you go for that general information you go to the neocortex. An amnesiac can tell you what they like for breakfast - they can't tell you what they had for breakfast."

It is possible, say the researchers, that the neocortex plays a more significant part in the production of dream images.

Dr Paul Fletcher, a cognitive neuroscientist from Addenbrooke's Hospital near Cambridge, UK, said that while more than ever was understood about how the brain laid down and retrieved memories, many questions still remained unanswered.

He said: "There is evidence that the hippocampus is important in memory in certain circumstances, and this research is plausible. And REM sleep appears to have some significance in learning."

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