PET scans reveal amyloid plaques, which appear as warm colors such as red, yellow and orange. On the left is a patient with Alzheimer's disease, and on the right is a person with no detectable amyloid deposits in the brain. The middle scan is of a normal person with no symptoms of cognitive problems, but with evident levels of amyloid plaque in the brain. (Credit: Susan Landau and William Jagust, UC Berkeley)

Keep in mind that the people in this study, many of them in their 70s and 80s, did not show any symptoms of Alzheimer's. Scientists are still trying to understand the connection between beta-amyloid deposits in the brain and dementia.

Aging and a family history of Alzheimer's are both considered risk factors, but we can't control those. And even if your brain hasn't been particularly active up until now, Landau says it's not too late to start ratcheting up your mental activities.

"I think that cognitive stimulation is probably beneficial at any age. But, what our findings from this study show, is that the more cognitively active you can be over the course of your lifespan, the better"

Landau says she and her colleagues plan to follow the volunteers in this study as they age, to see whether there is a link between lifetime mental activity and Alzheimer's symptoms as some of them develop dementia in the years ahead. That may help the researchers better understand the relationship between stimulating mental activities, beta-amyloid deposits and dementia.