Although such views did not prevent the doctor from going on to accept a post at Oxford University, one he retained until his death at age 70, his contention that brainpower, creativity and innovation have an early expiration date was, unfortunately, widely accepted by others. Until recently, neurologists believed that brain cells died off without being replaced. Psychologists affirmed the supposition by maintaining that the ability to learn trudged steadfastly downward through the years.

Of course, certain capabilities fall off as you approach 50. Memories of where you left the keys or parked the car mysteriously vanish. Words suddenly go into hiding as you struggle to remember the guy, you know, in that movie, what was it called? And calculating the tip on your dinner check seems to take longer than it used to.

Yet it is also true that there is no preordained march toward senescence.

Some people are much better than their peers at delaying age-related declines in memory and calculating speed. What researchers want to know is why. Why does your 70-year-old neighbor score half her age on a memory test, while you, at 40, have the memory of a senior citizen? If investigators could better detect what protects one person’s mental strengths or chips away at another’s, then perhaps they could devise a program to halt or reverse decline and even shore up improvements.

As it turns out, one essential element of mental fitness has already been identified. “Education seems to be an elixir that can bring us a healthy body and mind throughout adulthood and even a longer life,” says Margie E. Lachman, a psychologist at Brandeis University who specializes in aging. For those in midlife and beyond, a college degree appears to slow the brain’s aging process by up to a decade, adding a new twist to the cost-benefit analysis of higher education — for young students as well as those thinking about returning to school.