A LIFETIME of daily intellectual stimulation could help prevent the formation of plaques that are the hallmark of Alzheimer's disease.

Although previous research has suggested that engaging in mentally demanding activities - such as reading, writing and playing games - may help stave off the disease, a new study identifies the biological target at play.

The study, led by researchers at the University of California, says the discovery could guide future research into effective prevention strategies.

"Rather than simply providing resistance to Alzheimer's, brain-stimulating activities may affect a primary pathological process in the disease," said principal investigator Dr William Jagust of UC Berkeley's Helen Wills Neuroscience Institute.

"This suggests that cognitive therapies could have significant disease-modifying treatment benefits if applied early enough, before symptoms appear," he said.

In the first study of its kind, researchers used brain scans to examine the amount of beta amyloid deposits in the brains of healthy seniors with no signs of dementia.

Beta amyloid - the protein fibres folded into tangled plaques that accumulate in the brain - is the top suspect in the pathology of Alzheimer's disease.

But the buildup of amyloid can also be influenced by genes and aging.

People who reported doing daily brainy activities from age six onward had very low levels of amyloid plaque - on par with an average person in their early 20s. Those who never or rarely engaged in these activities had higher plaque levels.

"This is the first time cognitive activity level has been related to amyloid buildup in the brain," said study scientist Susan Landau of the Neuroscience Institute.

Amyloid is believed to start accumulating many years before symptoms appear - so by the time patients have memory problems, there is little that can be done. Scientists hope to intervene sooner, so it's important to identify whether lifestyle factors might help.

The study was published in the January 23 issue of the Archives of Neurology