London, March 20 (IANS): They say that once you have learned to ride a bicycle, you never forget how to do it. But discovery of a new brain mechanism suggests that while learning, the brain also actively tries to forget apparently to make space for new memories to form.

"This is the first time that a pathway in the brain has been linked to forgetting, to actively erasing memories," said one of the researchers Cornelius Gross from European Molecular Biology Laboratory (EMBL).

"One explanation for this is that there is limited space in the brain, so when you are learning, you have to weaken some connections to make room for others," Gross said.

"To learn new things, you have to forget things you have learned before," Gross explained.

The study was published in the journal Nature Communications.

At the simplest level, learning involves making associations, and remembering them. Working with genetically engineered mice, Gross and colleagues studied the hippocampus, a region of the brain that is long been known to help form memories.

Information enters this part of the brain through three different routes. As memories are cemented, connections between neurons along the 'main' route become stronger.

When the scientists blocked this main route, the connections along it were weakened, meaning the memory was being erased.

Interestingly, this active push for forgetting only happens in learning situations. When the scientists blocked the main route into the hippocampus under other circumstances, the strength of its connections remained unaltered.