Dr Valenzuela said that until the UNSW review, international research had provided mixed messages about the role of what's referred to as brain reserve - education, occupation, IQ and mentally stimulating leisure activities - in protecting people from dementia.

The Australian findings, published in the journal Psychological Medicine, possibly explain why between 10 and 40 per cent of people who have clear pathological signs of Alzheimer's disease at autopsy show no mental impairment before death.

http://www.theage.com.au/news/National/Mental-activity-reduces-dementia-risk/...