This study is a rare example that demonstrates actual enhancement of memory formation

Professor Thomas Carew

A typical neuron makes thousands of these connections - called synapses - with other neurons.

However, only a proportion of these synapses play a role in a particular memory.

Neuroscientists are investigating chemicals that appear to strengthen synapses.

The latest research suggests that one such chemical is a protein called PKM.

Key candidate

The researchers believe that PKM selectively strengthens synapses that are involved in the storing of a particular memory.

A team led by Dr Jerry Yin, at Cold Spring Harbor Laboratory, trained fruit flies to avoid a particular odour.

They did this by giving the flies a mild electric shock every time they encountered the smell.

They then measured the flies' ability to remember to avoid the odour.

In general, flies are initially good at remembering to stay away, but their memory tends to fade away completely over the course of a week.

However, when the researchers used a genetic trick to boost the level of PKM in the flies, a substantial proportion of flies retained the "avoid that odour" for a much longer period.

Professor Thomas Carew, an expert in neurobiology at the University of California, Irvine, said: "Much of what we know about memory processing comes from studies in which memory is disrupted.

"This study takes on added significance because it is a rare example that demonstrates actual enhancement of memory formation."

Side effects

Professor Seth Grant, an expert in the molecular mechanism of learning and memory at Edinburgh University, told BBC News Online that PKM was a particular version of an enzyme called protein kinase C (PKC) that had long been implicated in learning.

He said: "The notion that PKC is involved in memory is not new, but the fact that this team has shown that artificially increasing levels can somehow trigger memory enhancement is interesting."

Finding drugs that result in memory enhancement is one of the goals of molecular neuroscientists.

These drugs may help in childhood learning disability, in the memory loss with ageing and even in recovery from brain damage. Understanding PKM and other molecular mechanisms is likely to be a productive way forward.

Previous experiments have also shown that modifying PKC levels to which a developing embryo is exposed could have an impact on subsequent behaviour after birth.

However, Professor Grant said the molecular mechanism behind the effect was not known.

He also warned that PKC had been linked to the development of certain types of cancer.

"This is dangerous stuff to be messing around with in humans.

"If we could only restrict its effect to the nerve cells then that might be a different matter."

The research is published in the journal Nature Neuroscience.