A paper in the Archives of General Psychiatry has the first quantitative proof that a life driven by purpose and goals can preserve the brain from cognitive decline. 

The data comes from a study started in 1997 on people with no signs of dementia when they entered the research group.  The participants were assessed on their baseline physical, social, psychological and cognitive health and were rated on their sense of purpose based on their answers to 10 questions. 

When the study participants die, their brain is autopsied, allowing researchers to compare the physical health of their brain with each person's assessment. 

So far, 246 people in the study have died and researchers found that the people who rated highly on the purpose of life scale had a 30 percent lower rate of cognitive decline than those with low 'purpose of life' scores.