How Smart Is Grandpa?

How much can you expect from a septuagenarian brain?

Sen. John McCain, R-Ariz.

Sen. John McCain announced his intent to run for president in 2008 on Wednesday. If elected, he would take office at age 72, the oldest first-time president ever to do so. “I’m not the youngest candidate. But I am the most experienced,” he said during a speech in Portsmouth, N.H. Just how much can you expect from a typical septuagenarian brain?

It depends on the septuagenarian. Visual-spatial skills—like those involving hand-eye coordination—often deteriorate first, typically before the age of 40. While politicians don’t need to have a killer tennis serve, they do need to learn new things, and retain them in short-term and intermediate memory. Those abilities are usually the next to decline. On average, people lose about a fifth of their working memory capacity between the ages of 40 and 70. But the loss of mental function varies widely among individuals—from as little as 3 percent to as much as 50 percent—and is greatly affected by disease. After memory begins to slip away, we gradually lose the ability to make good decisions based on new information. (Septuagenarians who start with high cognitive function—like McCain, perhaps—are less likely to experience mental deterioration as they age.)

Older people develop ways to compensate for their mental decline, such that many can function just as well as the young. Someone who’s 60 might take a bit longer to process information than a 40-year-old, but he might find new ways to perform the same cognitive task. (He might rely more on past experience, for example.) That can explain why many CEOs and doctors peak in middle age, when they have a healthy balance between their capacity for learning and their life experience. Ronald Reagan’s superb communication skills, for instance, helped him compensate for presidential gaffes—like toasting “the people of Bolivia” while at a banquet in Brazil.

Bonus Explainer: So what exactly does aging do to the brain? The connections between cells start to break down. You don’t have to worry about losing whole neurons, since most brain cells stick around, and the ones that die don’t have much of an effect. But researchers have found that we lose synapses as we get older. Advancing age also causes a deterioration of each cell’s insulating layer, called the myelin sheath. With age, the myelin loosens, which slows down the electrical transmission of nerve impulses from one cell to the next.

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Explainer thanks Amy Arnsten of Yale University and John Morley of Saint Louis University School of Medicine.