How might the senator's mind deteriorate over the next eight years?
John McCain is old and, as several news outlets have reported, he's only getting older. This wouldn't be a problem if his opponent in the general election were equally chronologically gifted. But Barack Obama is one of the youngest Democratic nominees ever. If he won, he'd be the third-youngest U.S. president. The contrast is stark. Standing side-by-side, the two candidates look like a still from Finding Forrester.
McCain's age is already causing problems. His slip-ups are billed as "senior moments," while Obama's are innocent mistakes. In response, the McCain campaign has mastered the swift and stinging rebuke. When Obama backhandedly praised McCain's "50 years of service," McCain's camp cried foul. When Obama suggested McCain was "losing his bearings," strategist Mark Salter wrote a memo accusing Obama of ageism. To calm speculation, the McCain camp released 1,173 pages of McCain's medical records last month. Despite repeated operations to treat melanoma, he's quite fit. The pages did not include mental-health records, presumably because McCain has not had any mental evaluation in the past eight years. (The records McCain released during the 2000 campaign showed no lasting psychological wounds from his years as a prisoner of war.)
But that doesn't change the fact that a 72-year-old's brain is different from that of a 46-year-old. Even the most healthy human brains undergo chemical and anatomical changes in their sunset years—changes that can and do affect behavior. We don't know the details of McCain's mental health, but it's worth examining what happens to the minds of normal people at his age.
As everyone with a grandparent knows, certain types of memory are affected by aging. Episodic memory—the ability to remember things that happened to you—declines. Same for prospective memory, or the ability to remember lists or agendas. You could argue these skills are less essential for a president, who has speechwriters to produce anecdotes and handlers to keep his schedule. But age also affects working memory, which we use to process, sort, and recall information on the fly. Mental arithmetic, for example, requires a good working memory. Fortunately, presidents have calculators. But working memory also translates into debating skills—the better your short-term retention, the better you can rebut your opponent's arguments.
Oldsters show fewer deficits in semantic memory, which includes vocabulary and general knowledge. So while McCain's ability to synthesize facts into a compelling argument might degrade over time, his verbal arsenal is likely to grow. Semantic memory generally peaks in the sixth decade of life and doesn't decline until the ninth. Similarly, behaviors that are considered overlearned—actions you repeat over and over, like driving a car or saying that cutting taxes raises revenue—are less easily forgotten.
An elder president might show some other cognitive symptoms, too. Aging is known to affect our ability to suppress an instinctual response to a given stimulus. A famous example is the "Stroop interference" test. Imagine you're looking at the word blue written in red ink. Now say the name of the color of the ink. Your instinct is probably to say blue, but you force yourself to say red. The speed with which you complete the task is supposedly an indicator of mental flexibility; older people generally take longer to say red. Likewise, inhibition control declines over time. If you're at a party and your nemesis walks through the door, you might be inclined to sock him in the nose. Instead, you shake his hand. Older people aren't likely to feel any different—they're just less likely to suppress their first instinct.
This doesn't explain McCain's famous temper; if anything, he has mellowed of late. But it does suggest that we may see a further development of McCain's shoot-from-the-hip style. When a questioner in New Hampshire asked what he thought of "staying in Iraq for 50 years," McCain cut him off: "Make it a hundred." The line has dogged McCain since, largely because of its lack of context. If he had resisted the urge to jump in, it would have been harder for opponents to distort his words.
All of these behavioral changes have their basis in anatomy. As the brain ages, it starts to look different. It loses about 2 percent of its weight and volume every decade, starting around age 20. Certain areas of the cortex get smaller and thinner, and its grooves and ridges become more pronounced. The spaces between the gyri—the wormy coils you might call brains—often get wider as well. (Gaps are especially pronounced in Alzheimer's patients.) But when it comes to cognition—memory, attentiveness, decision-making—it's not the stuff that matters so much as the stuff that connects the stuff, called "white matter." White matter is largely made up of conductive nerve strands sheathed in myelin that carry information from one area of the brain to another. In general, the more intact your white matter, the smoother your cognitive function. The quantity of myelin is thought to peak around age 50, after which white matter begins to disappear. (The opposite problem, white matter hyperintensity, is associated with late-life depression.)
The brain's chemistry also changes with age. Levels of dopamine, a neurotransmitter associated with sensations of happiness, generally decline. (Some schizophrenics, who experience abnormally high dopamine levels, recover suddenly when they reach a certain age.) Same with hormones like testosterone; on average, men in their 80s have testosterone levels 40 percent lower than men in their 20s. (Forget McCain, just ask Bob Dole.) The behavioral effects of lowered testosterone aren't known, but it's correlated with weaker cognition. But as recent history has shown, a president with low testosterone isn't necessarily a bad thing.
Emotional changes are harder to quantify, but on average, emotional stability increases over time—a so-called mellowing effect. Older people tend to concentrate on positive events over negative events. One study found that older adults shown positive images (like a bowl of ice cream) and negative images (like a dead animal) were 30 percent less reactive to the negative images than younger adults. Some attribute this response to end-of-life perspective—perhaps death doesn't seem quite so negative. Others point to a slowing of the limbic system, which regulates emotion.
Many studies now emphasize the cognitive benefits of aging. Researchers describe a greater appreciation for ambiguity among older people—some might even call it "wisdom." While the elderly are easily distracted, that inability to filter information efficiently often means they can take in more information. Likewise, while we know younger brains are speedier, there's little evidence that healthy older brains can't perform the same tasks, albeit more slowly. Roberto Cabeza of Duke University has conducted studies showing older adults often perform just as well as their younger counterparts because of what he calls "compensation." If one area of the brain is weaker, the theory goes, other areas will pick up the slack. For example, while younger people use the right side of their prefrontal cortex for high-level cognitive processing, some elderly people use the left side as well, resulting in equal performance.
How much of this describes McCain's brain? Who knows. It's impossible to apply general trends to an individual case, since so much depends on lifestyle (exercise, diet, smoking), genetics (there's a reason McCain trots out his 96-year-old mom), and environmental conditions (being educated helps; being tortured doesn't). Plus, changes in brain structure are highly variable. Average cognitive ability declines precipitously over time, but variability increases: Plenty of 70-year-olds outperform plenty of 20-year-olds. (My 90-year-old grandmother is sharp enough to be president 10 times over.) And don't forget all the ancient CEOs out there. Companies regularly hire septuagenarians for their wisdom, contacts, and job-specific skills. A recent survey of senior professionals found that 53 percent say they would hire a qualified 72-year-old CEO. And rightly so: Some jobs simply demand experience, even if it means having a leader who can't do long division in his head.
Whether the presidency is that sort of gig is for voters to decide.
Thanks to Suzanne Corkin of the Massachusetts Institute of Technology, Jeri Janowsky of Oregon Health and Science University, and Jennifer Manly of Columbia University.
Christopher Beam is a writer living in Beijing.
Photograph of John McCain by Paul J. Richards/AFP/Getty Images.