"Old dogs" may really find it hard to learn new tricks, a study of how memories form has suggested.
A neuron - there are about 10,000 separate synapses on this cell
University of Oxford scientists say that adults may find learning more difficult than children because their brains store memories differently.
The study, in the journal Neuron, looked at nerve cell activity - the basis of learning and memory - in rats.
Experts said younger brains may learn things more easily, but older brains may store information more efficiently.
The researchers, backed by the Medical Research Council and the Wellcome Trust looked at the nerve cell processes in young and old rats.
Nerve cells communicate by sending signals though synapses, junctions between the cells.
But some synapses are "silent" and are not activated when chemical signals are passed between cells.
The team used highly detailed laser imaging, which looked at images one micron wide - a 100th the width of a human hair, to look at how synapses behave.
They focused on electrical activity and the movement of molecules called calcium ions.
They found that silent synapses are more prevalent in young brains, and are called on when new memories are laid down.
When this happens, key receptors - which detect stimuli - are called to the surface of the cell, transforming it into an active synapse.
In older brains, there were fewer silent synapses - which the researchers believe is because they have been used up.
This means older brains have to reuse the "un-silenced" synapses, boosting their power with increased amounts of neurotransmitters, chemicals which fuel the transmission of the chemical signals.
Dr Nigel Emptage, who led the research, said the findings could help understand the differences between how the young and old learn.
"It might be the case that this is the reason infants are so able to store new information, such as language.
"But later in life, remembering things proves harder. That might be because the way we have to store information is fundamentally different, using parts of the system that have been used already."
Emrah Duzel, honorary consultant neurologist at London's Institute of Cognitive Neuroscience at University College London, said: "It is an exciting possibility that these lifespan changes in memory capacity are linked to cellular mechanisms of connectivity.
"Different mechanisms are apparently involved in the acquisition of entirely new connections and the modification of existing connections."
Professor Keith Kendrick, head of cognitive and behavioural neurosciences at the Babraham Institute in Cambridge, said: "Young brains do tend to be able to absorb new information better than old ones, although not necessarily to integrate it as well with what has been learned previously."
But he added: "More extensive learning experience could perhaps also lead to more efficient representation and integration of information using existing 'active' synapses leading to a reduced dependence upon the presence of naive 'silent' ones.
"This study sets out an interesting idea, but it is one that still needs much more experimental verification."