Structural Connectivity Sets the Stage for Later Reasoning Ability

“Everything that is beautiful and noble is the product of reason and calculation,” wrote 19^th century poet and essayist Charles Baudelaire. The Western tradition of philosophy generally holds that reason—the ability to think, process, and ultimately understand the world in a thorough, logical way—is the highest form of cognition. Many studies have shown that strong reasoning abilities are positively correlated with better school performance and career success. Yet despite decades of research, it’s been unclear just how such capacities develop in the brain. New research from the University of California at Berkeley suggests that structural connections, or white matter tracts, between key reasoning brain areas in childhood may lay the foundation for stronger functional connections and reasoning abilities later in life.

The Science of Reason

Vinod Goel, professor of cognitive neuroscience at Canada’s York University, has been studying reasoning ability for most of his career. He says it’s long been considered a large part of what separates humans from the animals.

“In the Judeo-Christian tradition, the ability of reason is associated with the human soul. People reason, animals don’t. Man was considered sort of half in the animal world, half with the angels. And it was reasoning that allowed us to share some space with the angels,” he says.

“When I began working in this area, the consensus within cognitive psychology was that there must be something called reasoning that we would be able to find in the brain. We thought there would be one system—but over the years, we’ve found many reasoning systems in the brain. And we’ve learned that there are many different types of reasoning.”

Carter Wendelken, formerly a researcher at the University of California at Berkeley now working at Vicarious, an artificial intelligence company, says that a key aspect of understanding the neurobiological bases of reasoning is to understand how they might develop in the growing brain.

“It’s a difficult thing to try to study. Reasoning involves many parts of the brain, if not the whole brain. And it’s many different competencies,” he says. “But given that it is so important to achievement, we’d like to understand how it develops and how it might change with experience.”

Reason and Relationships

Silvia Bunge, director of the Building Blocks of Cognition Laboratory at Berkeley, has been interested in these different aspects of reasoning ability for some time. Her lab published the first neuroimaging study involving analogical reasoning and has discovered a core set of brain regions involved with relational processing, or the ability to process relationships between two objects to solve problems (as done in analogy or transitive inference tasks).

“Our work suggests that the interior parietal lobe is involved with maintaining relations between two items—I think that’s fundamentally what parietal cortex does, to relate things together, and why it’s so important to encoding space, time, and numbers,” she says. “But this region interacts with rostrolateral prefrontal cortex (PFC), and that interaction allows integration of those relations or the ability to compare them or consider them jointly so we can solve complex problems.”

Bunge, Wendelken, and colleagues’ previous work had showed that these two brain regions needed to work together to help adolescents solve reasoning problems. The stronger the two coordinated through functional connections, the better an adolescent was at solving the tasks. But it raised the question for Bunge: What drove that strong functional connectivity in the better problem solvers?

To find an answer, the researchers analyzed brain imaging data from three longitudinal data sets, which included more than 500 participants who had cognitive, reasoning, and brain imaging tests multiple times when they were between 6 and 22 years old. By looking at those scans across time, the researchers found that strong structural connections, or white matter tracts, between the inferior parietal lobe and the rostrolateral PFC in younger children were associated with both strong functional connectivity and improved reasoning in their young adult years.

“Reasoning and other complex cognitive abilities require the coordinated activity of different brain regions,” Bunge says. “In order for those regions to be coordinated, you need to have strong cables to connect them. It appears to be important, particularly in childhood, to lay down those strong cables to build up those abilities.”

Building the Foundation for Reason         

Goel says this study is quite interesting and offers us a new way to think about this specific type of relational processing aspect of reason.

“This idea of the functional connectivity being built on the structural connectivity makes a lot of sense,” he says. “But this is just one kind of task. It may not be the same for all kinds of reasoning tasks. So we need to do more of these kind of studies to really understand what’s going on.”

Bunge plans to do more work in this area. Ultimately, she hopes to gain a better understanding of how experience might change this brain circuit over the course of development, strengthening those white matter “cables” in younger children to help them gain better reasoning abilities later in life. She’s already done a small study that suggests that targeted interventions could be successful.

“We see that kids, even as young as six, already engage all the right brain regions for reasoning. What’s really changing is just how quickly those regions can communicate with one another,” she says. “So we’d like to see if, with practice, we can show improvements in the reasoning as well as changes to the circuit there. Given the massive ramping up of both reasoning ability and connectivity in childhood, just prior to adolescence, we may be able to find a way to intervene with to make those improvements. That’s where we’re headed.”