Our brain has to forget the things which we have learned earlier in order to grasp new things, according to a new study.
Once you have learned to ride a bicycle, you never forget how to do it. But new research from European Molecular Biology Laboratory (EMBL) and University Pablo Olavide in Spain suggests that while learning, the brain is actively trying to forget.
"This is the first time that a pathway in the brain has been linked to forgetting, to actively erasing memories," said Cornelius Gross from EMBL.
At the simplest level, learning involves making associations, and remembering them. Working with mice, researchers 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 they blocked this main route, scientists found that the mice were no longer capable of learning a Pavlovian response - associating a sound to a consequence, and anticipating that consequence.
But if the mice had learned that association before the scientists stopped information flow in that main route, they could still retrieve that memory.
This confirmed that this route is involved in forming memories, but is not essential for recalling those memories. The latter probably involves the second route into the hippocampus, researchers suggest.
But blocking that main route had an unexpected consequence - the connections along it were weakened, meaning the memory was being erased.
"Simply blocking this pathway should not have an effect on its strength. When we investigated further, we discovered that activity in one of the other pathways was driving this weakening," said Agnes Gruart from University Pablo Olavide.
This active push for forgetting only happens in learning situations. When scientists blocked the main route into the hippocampus under other circumstances, the strength of its connections remained unaltered.
"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," said Gross.
"To learn new things, you have to forget things you've learned before," he said.
The findings were published in the journal Nature Communications.
