Jun 9, 2007
Writing in the journal Science, British and US scientists said a small region called the dentate gyrus is important.
When mice were genetically altered to interfere with brain cells in this area, they became confused and disorientated.
It is hoped that the finding could help unlock treatments for memory disorders in old age.
Dr Matthew Jones, from the University of Bristol, and one of the scientists working on the project based at MIT and Harvard University, said one specific network of brain neurons was involved in a quickfire process which allows humans to realise when in a familiar space.
He said: "We constantly make split-second decisions about how best to behave at a given place and time.
"To achieve this, our nervous system must employ highly efficient ways of recognising and learning changes in our environment."
In the experiment, mice, which have similar brain structures to humans, were trained to differentiate between different locations by giving them a tiny electric shock when they entered a particular spot.
Normally, a mouse returning to the place where they had received a shock will freeze, showing researchers that they recognise it.
Brain scans pinpointed neurons "firing" in the dentate gyrus at this precise moment as the mice realised where they were.
The same experiment was repeated on a group of mice who had been genetically altered to knock out the "NMDA receptor" - part of a brain signalling pathway previously linked with learning and memory.
The altered mice did not respond in the same way, wandering into the shock location time after time.
This clearly suggests that the receptor - in this small area of the brain - has a key part to play in the instant development of these fast memories.
Dr Paul Dudchenko, from Stirling University, said that experiment revealed more about the parts of the brain involved in memory.
He said: "What's interesting is that by the 17th day of receiving a shock, even the genetically altered mice had learned not to go into the space, suggesting that the brain can use another pathway.
"It is possible that this may be of some relevance to people with Alzheimer's disease, or older people generally."
Dr Jones said that the next step for researchers would be to take mice with the equivalent disease to Alzheimer's in humans and try to boost the NMDA receptors to see if this relieved symptoms.
"What we have now is a very obvious target for medication, although we are still some way away from having a treatment we can use in humans."