The mind actively erases memories to create space for new information

By Kate Devlin, Medical Correspondent Published: 7:30AM GMT 19 Feb 2010

Scientists believe the breakthrough in understanding how short-term memories are lost solve the mystery of how they are created in the first place.

Scientists have previously speculated that they "drop out" to make room for new ones, but the theory has been difficult to prove.

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New research suggests that chemicals in the brain actively remove short-term memories.

And they speed up their work when faced with large amounts of information.

"Learning activates the biochemical formation of memory," said Yi Zhong of Tsinghua University, in Beijing, who led the study.

"But you need to remove memories for new information to come in.

"We"ve found that forgetting is an active process to remove memory."

The findings could help scientists to understand how our minds store memories in the first place.

"We still don"t really understand … memory in terms of what is formed and what is erased," Mr Zhong said.

"The study of forgetting may be a better way to identify the material basis of memory."

The memories are erased by a protein in the body known as Rac.

When that protein is blocked, the brain retains information for far longer than it would normally.

But Rac is released faster when the brain is attempting to juggle large amounts of information, clearing more space as it is needed.

The study was conducted in fruit flies trained to avoid certain smells.

The flies forgot which odours to evade when confused by new information, the research published in the journal Cell, shows.

But when the scientists turned off the Rac protein the flies remembered the smells for much longer than they had previously, more than a day instead of just a few hours.

The researchers believe that memories could work in the same way for all organisms, and say there has been recent evidence of a similar pattern in mice.

Rac proteins have also recently been linked to intelligence in humans, they add.