Remember the Fox television show Are You Smarter Than a 5th Grader?
In November 2011, results of the ultimate extreme version of that kind of contest were reported in Seattle at the annual meeting of the Psychonomic Society. Gene Brewer, a psychologist at Arizona State University, was the first author of a paper entitled “Working Memory in Rats and Humans.”i Working memory is the ability to juggle multiple items of information in your head, to not simply remember the numbers 13 and 4 but to multiply them in your mind. According to the abstract, “The quintessential instrument used by animal researchers for measuring working memory in rodents is the radial-arm maze. We constructed an 11-arm human version of the radial-arm maze and assessed individual differences in maze ability, general-fluid intelligence, and working memory capacity.” A key phrase in the abstract’s conclusion caught my attention: “Human behavior in the maze paralleled that found in rodents.”
I asked Brewer if that meant what I thought it did: had he actually asked people to compete against rats in a maze, almost literally running in a rat race, and found that the people did no better than the rats?
“It is kind of eyebrow-raising, I guess,” Brewer told me. “But to step out on a limb and then say that because the rats learn this maze as well as humans do, that we have similar cognitive abilities, that’s probably not a good idea. We just happened to notice a peculiar similarity between how well our volunteers learned it and how well the rats did.”
To test human participants, Brewer and his colleagues constructed the walls of an eleven-arm radial maze on a basketball court, out of plastic tarps. Center court was where the eleven arms of the maze met in the middle. At the end of each arm was money.
“But it wasn’t money they were going to keep,” Brewer said. “We’ve now collected data on 150 participants. Animals need a reward to motivate them, but humans usually find motivation in just trying to succeed at a task. That’s a big difference between rats and humans.”
Yes, that’s one of them. But what was it like for the participants who tried to complete the maze?
“When you’re going through that maze, man, you’re good for about seven or eight arms,” Brewer said. “And then you’re, like—what? Where am I? You just lose it. As you start coming around the second time, it’s just very hard to keep track of eleven arms when you can’t do it in a simple order.”
Although Brewer refused to infer from his study any conclusions about the intelligence of mice, a neuroscientist at Rutgers University in New Jersey has recently come out of the closet on the question.
“I once was reluctant to use the term ‘intelligence’ in mice, because it’s such a loaded term,” said Louis D. Matzel when we met at his office in the psychology building on the university’s Piscataway campus. “The first grant proposal I submitted to NIH, in 1992, used the word. The reviewer said there is no place in biology for studying intelligence because everybody knows that intelligence is just a social construct. That gives you a sense of why some animal scientists are so reluctant to discuss it. I even had a dean here at Rutgers who once told me I shouldn’t discuss intelligence because it’s such a difficult topic. But she was an idiot and got fired soon after, so I felt vindicated.”
I was beginning to like this guy. Matzel is a wiry middle-aged smoker with graying brown hair, a trim mustache, and photographs of the dead British punk rockers Sid Vicious and Ian Curtis on his office wall. His latest studies of mice have offered perhaps the most astonishing proof imaginable that brain training really can make people smarter. He trained mice to practice learning how to navigate two radial mazes at once, and found that after the training, they performed better on other tests of problem solving and attention.
“The thing is,” Matzel told me, “if I ask the mouse to work on only one maze, he’s really good at it. A well-trained animal will typically make no errors. He’ll navigate around and get his eight pieces of food. With two mazes, it’s really hard. At first they all make many errors. But here’s what we found: over days of trying it again and again, they get good at it. A smart mouse will eventually get really good at it and make no errors. This is a task where some rodents are at least as good as humans. So they do have a working memory.”
I asked him what he meant by a “smart” mouse.
“We test intelligence in the mouse on a battery of six learning tests, each one different from the other. Occasionally, we get an animal who turns out to be the best on all six tests compared to fifty other mice. That’s a really smart mouse, we would say. We teach them to avoid a shock or avoid a bright light. Navigate through a dry maze. Navigate in a water maze. We also have a reasoning task.”
The reasoning task requires the mice to make an inference by exclusion. “I show an animal a star symbol,” he said, “and it learns to walk over to an object shaped like a circle; underneath is a treat. So the animal learns that when it sees the star, if it goes to the circle, it gets a piece of food. Star means circle. Then I train it on a square and a triangle. If you see a square, you’ll get food under the triangle. So square means ‘go to triangle.’ And then one day I show the animal a symbol it’s never seen before, let’s say a crescent, and out in the field of objects it can choose from, it might have a triangle, might have the circle, and a novel object it’s never seen before. It looks at the triangle and the circle and thinks, ‘It can’t be under those, so it must be under the novel object.’ It infers by exclusion that the food must be under the novel object. This is the amazing thing—mice are decent at doing that. This kind of reasoning task is considered a quintessential example of human’s ability to reason. And yet mice do it. I’m so amazed they can do it. Because I don’t believe my dog can do it. My dog just seems really stupid. For years I’d let my dog out in the yard on a rope, and he’d always wrap himself around a tree.”
Using the reasoning task, Matzel demonstrated that, just as in humans, a general intelligence factor can be discerned in mice: those who are better at the reasoning tasks tend to be faster at learning the other tasks. In 2010, he reported that the mice who practiced on the dual maze actually got smarter on tests of general cognitive abilities. Finally, and most significantly of all, mice who trained on the dual-maze task when they were younger showed less age-related loss of attention and learning abilities by the time they had reached the mouse equivalent of old age. Matzel and colleagues concluded in that study: “These results suggest that general impairments of learning, attention, and cognitive flexibility may be mitigated by a cognitive exercise regimen that requires chronic attentional engagement.” Or, as he told me, “It was our intention to manipulate working memory in mice and see if that manipulation had a direct effect on their intelligence. In fact Jaeggi’s work demonstrates the same thing we found.”
If training increases intelligence in mice, imagine what it might have done for Sid Vicious.
From SMARTER: The New Science of Building Brain power by Dan Hurley. Reprinted by arrangement with Hudson Street Press, a member of Penguin Group (USA) LLC, a Penguin Random House Company. Copyright © Dan Hurley, 2013.
[i] “Human behavior in the maze paralleled that found in rodents”: Brewer GA, Grunfeld IS, et al., “Working memory in rats and humans.” Presented at the Psychonomic Society annual meeting, 2011.