Jessica Cantlon seeks the origins of numerical thinking

Brain scans and behavioral tests add up to explain an intriguing evolutionary question

Jessica Cantlon

Cognitive neuroscientist Jessica Cantlon wants to find out how humans understand numbers and where that understanding comes from.

J. Adam Fenster/University of Rochester

Jessica Cantlon, 40
Cognitive neuroscientist
University of Rochester

The SN 10The first time Jessica Cantlon met Kumang at the Seneca Park Zoo, the matriarch orangutan regurgitated her previous meal right into Cantlon’s face. “I was retching,” Cantlon recalls. “It was so gross.” But Cantlon was there to kick off a series of behavioral experiments, and her students, who would be working with Kumang regularly, were watching. “Does anyone have any towels?” she remembers asking, knowing she had to keep her cool.

Cantlon’s deliberate nature and whatever-it-takes attitude have served her well. As a cognitive neuroscientist at the University of Rochester in New York, she investigates numerical thinking with some of the most unpredictable and often difficult study subjects: nonhuman primates, including orangutans, baboons and rhesus macaques, and — most remarkably — children as young as age 3. Both groups participate in cognitive tests that require them, for example, to track relative quantities as researchers sequentially add items to cups and to distinguish between quantities of assorted dots on touch screens. The kids also go into the functional MRI scanner where, in a feat impressive to parents everywhere, they lie completely still for 20 to 30 minutes so Cantlon and colleagues can get pictures of their brains.

“She takes steps carefully, and she thinks very hard about where she is going,” says Daniel Ansari, a developmental cognitive neuroscientist at the University of Western Ontario in London, Canada, who is familiar with Cantlon’s work. “She goes for the big questions and big methodological challenges.”

The central question in Cantlon’s research is: How do humans understand numbers and where does that understanding come from? Sub-questions include: What are the most primitive mathematical concepts? What concepts do humans and other primates share? Are these shared concepts the foundation for fancier forms of mathematical reasoning? In addressing these questions, Cantlon draws on a wide range of methods. “Very few people can combine work on cognitive skills — studies from the point of view of behavior — with imaging work in very young children, and very few people do that same combination in nonhuman primates,” says Elissa Newport, who chaired the brain and cognitive sciences department at Rochester for more than a decade and now leads the Center for Brain Plasticity and Recovery at Georgetown University.

As a graduate student, Cantlon determined that neuroimaging studies would add an independent source of data to the cognitive questions under exploration in Elizabeth Brannon’s lab at Duke University. So she identified collaborators and taught herself functional MRI. “By the time she graduated, she had something like four dissertations’ worth of work,” says Brannon, now of the University of Pennsylvania.

In the years since, Cantlon has identified a type of “protocounting” in baboons; they can keep tabs on approximate quantities of peanuts as researchers increase those quantities (SN Online: 5/17/15). In her most attention-grabbing work, Cantlon studied activity in the brains of children while they watched Sesame Street clips that dealt with number concepts — an unexpected success that proved everyday, relatively unaltered stimuli can yield meaningful data. An ongoing study in Cantlon’s lab seeks to find out how monkeys, U.S. kids and adults, and the Tsimané people of Bolivia, who have little formal education, distinguish between quantities. Do they determine the number of dots presented on the computer screen or do they rely on a proxy such as the total area covered by the dots?

The work explores how the brain understands everyday concepts, but it could also inform strategies in math education. “If we understand the fundamental nature of the human brain and mind, that might give us a better insight into how to communicate number concepts to kids,” Cantlon says.

Growing up outside of Chicago, Cantlon enjoyed digging deep into a topic and becoming an expert. She and a friend turned themselves into ice skating superfans one summer, reading up on the Olympic skaters and checking videos out of the local library. In another project, Cantlon decided to learn everything possible about the price of gold. When she moved to a school where she could no longer take Latin, she taught and tested herself. Despite the fact that neither of her parents went to college, no one ever questioned that Cantlon would go. She studied anthropology as an undergraduate at Indiana University in Bloomington. “I was interested in the question of where we come from,” Cantlon says. “I was interested in studying people.”

Sabina, an olive baboon, participates in tests that help reveal how primates understand quantities. J. Adam Fenster/Univ. of Rochester

During college, she went on an archaeological dig in Belize and studied lemurs in Madagascar. For a year after graduation, she observed mountain gorillas in Rwanda, detailing their behavior every 10 minutes. “What they were thinking was something that was constantly on my mind,” she says. “‘How are we similar? Are you thinking what I’m thinking?’” Though she might have succeeded in any number of careers, she wanted exploration to be a big part of her life: “I don’t think doing a less exotic type of work would have been as satisfying.”

Today, Cantlon, who at age 40 recently earned tenure, doesn’t spend much time in the field. And even in the lab, she leaves much of the data collection to her graduate students and research assistants. “At this point, we are a well-oiled system,” she says, referring to the brain scan studies on kids.

To make the kids comfortable, Cantlon’s team does trial runs in a mock scanner, describing it as a spaceship and providing “walkie-talkies” for any necessary communication. To keep them interested, the researchers treat it as a team activity and offer a ton of positive reinforcement, with prizes including Lego sets and a volcano-making kit. The kids receive pictures of their brains, which typically interest the parents most. The older of Cantlon’s two daughters, a 5-year-old extrovert named Cloe, has participated in behavioral tests and will no doubt be excited for her first brain scan.

The Sesame Street study was in part inspired by a paper by Uri Hasson, a neuroscientist at Princeton University who imaged the brains of volunteers while they watched The Good, the Bad and the Ugly. To better understand brain development, Cantlon wanted to see how brain activity compared in kids and adults exposed to math in a natural way. Of particular interest was a region called the intraparietal sulcus, or IPS, thought to play a role in symbolic number processing. The results, reported in PLOS Biology in 2013, showed that kids with IPS activity more closely resembling adults’ activity performed better on mathematical aptitude tests.

“It was the clearest, cleanest — did not have to come out this way — result,” Cantlon says.

Cantlon is notable for her diverse set of tools, says Steve Piantadosi, a computational neuroscientist and colleague at Rochester. “But she has something which is even more powerful than that. If you have different hypotheses and you want to come up with the perfect experiment that distinguishes them, that is something she is very good at thinking about. She is a great combination of critical and creative.”

To add another methodological approach, Cantlon next plans to collaborate with Piantadosi to develop computational models that explain the operations the brain performs as it counts or compares quantities. She would also like to add data analyses from wild primates into the mix. When researchers talk about the evolution of a primitive number sense, they often speak about foraging activity — identifying areas of the forest with more food, for example. But Cantlon wonders whether social interactions also require some basic understanding of quantities. 

As for a recent question from a colleague about what risky project she’ll pursue now that she has tenure, Cantlon says nothing in particular comes to mind: “I feel like we’ve been doing the crazy things all along.”

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