Alzheimer's disease could eventually be reversed, claim scientists, after discovering that stem cells can "nurse" the brain back to health.

Researchers have shown for the first time that neural stem cells can rescue memory destroyed by advanced Alzheimer's disease, leading to hopes for a treatment for the condition.

American scientists at the University of California have shown for the first time that stem cells injected into the brain can rescue memory in mice, rebuilding neurons and memory.

They examined the mouse brains after the injection and found six per cent of the stem cells had turned into neurons with the majority becoming other types of brain cells which aided growth.

The stem cells were found to have secreted a protein called brain-derived neurotropic factor, or BDNF which caused existing tissue to sprout new neuritis – the connections between neurons.

The lead author Mathew Blurton-Jones said: "The neural stem cells were helping the brain form new synapses and nursing the injured neurons back to health.

"This gives us a lot of hope that stem cells or a product from them, such as BDNF, will be a useful treatment for Alzheimer's," Prof LaFerla said.

More than 700,000 people in Britain have dementia, of which Alzheimer's is the most common form, but that number is expected to mushroom in coming decades as the population ages.

The findings were published in the Proceedings of the National Academy of Sciences.