More studies linking metal exercise with improved resistance to degeneration are rolling in: "complex mental activity across people's lives significantly reduces the risk of dementia. The researchers found that such activity almost halves the incidence of dementia. ... It is a case of 'use it or lose it'. If you increase your brain reserve over your lifetime, you seem to lessen the risk of Alzheimer's and other neurodegenerative diseases. ... individuals with high brain reserve have a 46 percent decreased risk of dementia, compared to those with low brain reserve. All the studies assessed agreed that mentally stimulating leisure activities, even in late life, are associated with a protective effect. ... brain reserve is not a static property, nor that it is determined by early life experiences such as level of education, socio-economic deprivation or poor nutrition. It is never too late to build brain reserve."

Link: http://www.unsw.edu.au/news/pad/media/2006/jan/Dementia_brain_reserve.html