In the late 1980s, psychology researcher Dr. Randall Engle presented his study subjects with a “dippy little task,” as he calls it. “I gave them a simple arithmetic problem to solve, and then I gave them a letter to remember, and then another arithmetic problem, and then another letter, and so on. And then I asked, ‘Now what were all of the letters that I just told you, in order?’” The exercise was designed to test something called working memory, or what you can recall when you’re shifting your attention away from the task at hand and then back again. It turned out that the number of letters that subjects could remember correlated strongly with a variety of real world cognitive aptitudes, including reading comprehension and complex problem solving.
“I wondered, Why would this relationship exist?” says Engle, who now runs the Attention & Working Memory Lab at Georgia Tech, which focuses on the role memory and attention play in human cognition. We recently spoke with Engle about intelligence and memory, why it declines as we age, and what we can do to help (or hurt) our brainpower.
Twenty-five years ago, you showed that working memory was closely related to “fluid intelligence.” Can you explain what that means? Most theories of intelligence contend that there are two types. One is crystallized intelligence, which is everything that you’ve learned: knowledge you gained in school or on the job, languages you speak. I’m nearly 70 years old, and I can still recite “Jabberwocky.” Fluid intelligence, on the other hand, is the biological side of intelligence. This is what you do when you haven’t learned what to do: your ability to solve a novel problem that you’ve never encountered before, complex reasoning. It’s also what’s most heritable. We had a discovery in the early 1990s that these working memory scores that we’d been measuring were correlated quite highly with fluid intelligence. The question was why.
And what is the connection? About 10 or 15 years ago, we discovered the relationship really had to do with how well you focus and maintain your attention. It’s your ability to not be distracted, which varies greatly from person to person. And attention control is something that declines as we get older.
So this is not about dementia. It’s just normal decline that happens with aging? Yes. Mind wandering happens at a very molecular level. We’re not talking about your mind wandering during a boring lecture. We’re talking about a biological tendency to quickly shift your attention from topic to topic. Some people are just easily distracted, and as we get older our attention is more easily captured by events that are off-task. That creates a bit of a problem because it affects working memory and fluid intelligence and our ability to do complex things.
So you’re saying that we get less smart as we get older? Well, yes and no. Crystallized intelligence continues to increase over the course of most of your life span. At age 75, your vocabulary, for example, will be as high as it ever was and probably higher. If we look at fluid intelligence, however, it increases to about age 22, and then it kind of levels off. Then at about age 40, it starts going down, and it drops like a rock.
Fantastic. Do we know why? It likely has to do with the breakdown of insulation surrounding our neurons, called a myelin sheath. Similar to the way insulation that’s wrapped around an electrical cord prevents the wires from touching each other, the myelin sheath keeps signals in that neuron from leaking into other neurons. This myelinating process happens in the frontal lobe of the brain, and it’s completed around age 22. And that’s also when fluid intelligence hits its peak; then, later, it starts to degrade.
Is there anything that you can do to curb that decline? What about this idea of “training your brain” by playing games or using specialized apps or computer software programs? Brain training is a wonderful promise, and as a soon-to-be 70-year-old, if I thought that playing these games for an hour every day would retard that decline, then I would be doing it. But I’ve done tons of work evaluating these programs, and the evidence is quite compelling that when you do a well-controlled study—and that’s key—you find no benefit.
What I tell people is, if you enjoy playing this game, you should play it. If you love crossword puzzles, then do it for the joy of solving them—not because it will magically fix your declining memory. Do it because it adds life to your years, not because it adds years to your life.
I’ve been a sudoku addict for a long time. But I have no illusion that it’s making me smarter. It’s just making me a better sudoku player.
Do you think that bad habits—like relying on our smartphones to remember things for us—make the problem worse? Not really. Technology is not the culprit for declining memory, though it has certainly given us a lot more stuff that we need to remember. But that’s just the product of living in a complex world. I think it’s a good thing to make use of technology to help you manage it, for example to keep track of your calendar or to send notes to yourself.
What about multitasking? Is it a bad thing? The reality is that you can attend to one thing at a time. That’s it. You can’t divide your attention. Even the best multitaskers are just shifting their attention very rapidly. But it’s your ability to retain information while you’re switching your attention back and forth that’s the real issue. You have to remember what you were doing at task A when you return from task B. Fluid intelligence is really important in your ability to do that. But nobody has enough fluid intelligence that they can text and drive at the same time. There’s a reason why you see these videos of people walking and texting on a cell phone, and then they walk right into an open manhole.
That said, if all of the tasks are pretty simple, or if they can be done relatively mindlessly, then no, it’s not bad. Think about reading your kids a bedtime story. After you’ve read The Cat in the Hat 40 times, you can think about something else while you’re reading it and still do a perfectly good job as a reader. But the more complex the tasks are, the more thought they require, the less capably you will be able to switch between them. It’s really a case of diminishing returns.
So is there anything we can do to help preserve our brainpower as we age? A friend of mine, a neuroscientist named Art Kramer, has shown that the answer to this is exercise. Research has proven over and over again that aerobic exercise—lifting doesn’t do it, calisthenics doesn’t do it—will lead to improvements in working memory and fluid intelligence. It’s not going to make that decline go away, but it retards it a little bit. And it’s true for children as well as old people. You take kids who are fairly slothful, and you give some of them stretching exercises and some of them aerobic exercises and you keep some of them as a control group, and then you look at all three groups. And you find that the kids who are doing aerobic exercise are doing better in school, and they’re doing better on tests that measure fluid intelligence.
What is it about exercise that makes it so protective of intelligence? The physiological mechanisms are still being worked out. There’s a gene called brain derived neurotropic factor that leads to the growth of new blood cells if you exercise. It’s not just increased blood flow or oxygen to the brain, though that’s part of it, too. But for now, I tell people: Just take a brisk 30-minute walk every day, and it will give you all the benefits that you’re going to get.
Engle on the presidential debates:
When you watch Hillary Clinton in a debate, it’s amazing how much information she can remember: details about all of these policies, all of the countries she has visited. She’s also notorious for remembering names and faces. When she walked out on stage, she’d point and wave to all of these people that she recognized. She had acquired a lot of that information on the job as senator or Secretary of State—that’s crystallized intelligence—but she also had to pack it into her mind quickly to prepare for the debates, and that’s what fluid intelligence is all about. Your crystallized knowledge reflects your fluid intelligence at the time that you learned it; the higher your fluid intelligence, the more (and the faster) you can learn. Of course, Trump hadn’t spent his life in politics, immersed in these same kinds of policy details. But he also wasn’t prepared to—or else wasn’t willing to—put in the effort to learn them. And neither was Gary Johnson, who infamously couldn’t remember what Aleppo was. Independent of politics, there’s a clear difference in what these people know and how much they were able to learn in a given period of time.
This article originally appeared in our January 2017 issue.