Prions are not usually

Prions, abnormal proteins which change normal proteins into copies of themselves, are thought to cause neurodegenerative diseases.

But researchers at New York's Columbia University say a protein which behaves in the same way may help make memories.

Writing in Nature magazine, they say prions may perform other beneficial roles in the body.

Benefits

In diseases such as variant Creutzfeldt-Jakob Disease, prions enter the brain and reproduce, converting other proteins into copies of themselves.

We're at quite an early stage in terms of finding out what memory is and how it's formed Professor Mike Stewart, Open University

These accumulate in the brain and progressively damage and destroy cells.

The researchers from Columbia found a protein called cytoplasmic polyadenylation element-binding protein (CPEB) reproduces in the same way, but this time with a beneficial result.

The team, whose work has also been published in the journal Cell, looked at CPEB found in the brains of sea-slugs. A form of CPEB is also found in humans and other mammals.

It is found at synapses, the connections between nerve cells, where it triggers the production of other proteins which help nerve cells form strong links with each other - a process which is crucial in forming memories.

The scientists investigated its function by inserting sea-slug CPEB into yeast cells.

They found CPEB was switching into a prion-like form that replicates and is inherited by other cells.

'No animal research'

The researchers suggest that electrical signals triggered by an experience could trigger synapses, the connections between nerve cells, which then switch CPEB into its active, prion-like form.

Dr Eric Kandel, who led the research, said: "It behaves exactly like a prion."

Mike Stewart, professor of neuroscience at the Open University, told BBC News Online: "This is potentially very interesting. But the problem is that they haven't actually shown that it exerts a prion-like effect in animal cells."

But he said the work could be prove to be extremely useful in adding to knowledge about how the brain makes memories.

"We're at quite an early stage in terms of finding out what a memory is and how it's formed," he added.