Being older is no bar to having a razor sharp mind - but it may well work in a different way, US scientists suggest.
Research suggests the elderly store memories differently
A Johns Hopkins University team, who studied rats, found older animals stored memories in a different way than younger ones.
They say that, if the findings are true for humans, it could lead to treatments to prevent memory loss which were tailored to older brains.
The research is published in Nature Neuroscience.
Old v young
The researchers compared the brains of six-month-old "young" rats with those of two-year-olds "old" rats, who were deemed to be relatively sharp because they had performed well in various learning tasks.
These rats' brains were also compared with those of older rats which had showed declines in their abilities to learn new things.
The researchers looked at a key set of nerve cell connections that store information by modifying the strength of chemical communications at synapses - the tiny gaps between nerve cells, where chemicals released by one cell act upon another.
Synaptic communication is the way brains register and preserve information to form memories.
The team found that while the older rats that were less able to learn new things had brains that had lost the ability to adjust the force of those synaptic communications, the sharper older rats still had that capacity.
And the successful older rats also relied far less than did younger rats on a synaptic receptor that is linked to a common mechanism for storing memories.
Dr Michela Gallagher, who worked on the study, said: "We found that aged rats with preserved cognitive abilities are not biologically equivalent to young rats in some of the basic machinery that neurons use to encode and store information in the brain.
"Instead, successful agers relied more than young rats on a different mechanism for bringing about synaptic change.
"This 'switch' could serve the same purpose - storing memories - but through a different neurochemical device."
Professor Shane O'Mara, of the Institute of Neuroscience, at Trinity College Dublin, said: "This is a fascinating paper that seeks to address a difficult but important question.
"Why are some people mentally productive until late old age - such as the philosopher Bertrand Russell, and why do others not show this resilience - such as the writer Iris Murdoch?
"Modern brain imaging shows that there are differences between the brains of those who age 'successfully' compared to the brains of young people.
"However, brain imaging does not disclose why this difference exists."
Professor O'Mara added: "This study suggests that there is a difference in the regulation of a key biochemical messenger in the brain.
"If these findings prove to be generally applicable, then they show that the resistance to mental ageing shown by some people has a biochemical basis, and they point to what this biochemical basis is.
"In turn, this suggests a target for drugs to rescue or reduce the effect of ageing on brain function and hence on cognitive or memory function with ageing."