“We are constantly being swamped with sensory impression,” Professor Lars Olson, who led the study, said in a statement.
“After a while, the brain must decide what's to be stored long term. It's this mechanism for how the connections between nerve fibers are altered so as to store selected memories that we've been able to describe.”
Short-term memories occur as a result of chemical changes caused by altered signaling between different nerve cells in the brain, a process which is relatively well understood.
But scientists are less certain about how the brain converts sensory impressions into lasting memories, which are then stored in the cerebral cortex.
The researchers discovered that signaling via the nerve membrane's nogo receptor 1 (NgR1) receptor molecule plays a key role in the formation of long-term memories.
When nerve cells are activated, the gene for NgR1 is switched off, leading the team to believe that this inactivation might be important in the creation of long-term memories.
Using genetically modified mice with an extra NgR1 gene that could remain active even when the normal NgR1 was switched off, Olson and his team were able to switch the animal's ability to form lasting memories on and off by adding a substance to their drinking water.
“We found that the ability to retain something in the memory for the first 24 hours was normal in the genetically modified mice,” said Olson.
“However, two different memory tests showed that the mice had serious difficulties converting their normal short-term memories to long-term ones, the kind that last for months.”
The scientists hope that their findings will help in the development of new treatments for a variety of conditions which affect people's memory, including those related to Alzheimer's and strokes.
Medicines which target the NgR1 receptor system, for example, could improve the brain's ability to form long-term memories.
The research was conducted in collaboration with American researchers at the National Institute on Drug Abuse (NIDA) at the National Institutes of Health (NIH).
The findings are published in the Proceedings of the National Academy of Sciences (PNAS).