WELL-educated people and those in high-status jobs appear to be better able to fend off the symptoms of mental decline in later life.
A growing number of studies show that the higher a person's IQ, the less likely they are to succumb to dementia and even brain damage caused by injuries.
It should even be possible to fight senility with some well-chosen mental gymnastics, according to a report in New Scientist magazine.
Researchers have puzzled over why people who lead more intellectually stimulating lives are somehow protected from mental decline.
Some psychologists and neuroscientists have started referring to this as their "cognitive reserve".
One theory is thatthe brains of people with higher levels of "cognitive reserve" are better able to switch to "plan B" when there are problems. Other experts believe they are more able to increase the efficiency of their existing brain networks.
The idea could explain why it appears that people with high IQ levels go downhill unusually quickly when they do show symptoms of a disease such as Alzheimer's.
Michael Rutter, from the Institute of Psychiatry in London, said people with a good education and who have Alzheimer's disease are able to combat the symptoms more effectively, so that by the time the problems appear, they are at a relatively late stage of the disease.
Researchers believe the best predictor of cognitive ability in middle-age is a person's IQ score when they are eight years old.
But people can take steps later in life to try to boost their "cognitive reserve". Yaakov Stern, of Columbia University in the US, said: "This is as powerful as any drug we will ever have to stop Alzheimer's progression."