McGovern Institute investigator and professor of cognitive neuroscience
Is the brain like a Swiss Army knife?
In a sunny, fourth-floor office in the McGovern wing of the BCS complex, Nancy Kanwisher thinks small. Kanwisher ‘80, PhD ‘86, has spent a decade strengthening the case that a blueberry-sized area of the brain is active only when you look at another person’s face. It is not interested in images of apples, trucks, or even other body parts.
“The general emphasis in my lab has largely been to focus on parts of the brain that are very strikingly specialized for one particular cognitive function,” says Kanwisher. In addition to the face response area, she and her colleagues have identified three other brain regions that respond only to images of places, bodies, and written words in almost every person tested.
Kanwisher’s interest has plunged her into a fierce, 200-year-old debate about the human brain. Is the brain like a Swiss Army knife, made up of specialized parts that perform specific tasks? Or is the brain a generalist, able to solve problems on the fly without any customized tools? “Pretty much everyone has agreed for a long time,” Kanwisher says, that the cerebral cortex or higher brain has a motor area that specializes in the mental processes that guide the taking of a step or the shaking of someone else’s hand. But the notion that abstract thought processes – such as guessing what other people are thinking, parsing the syntax of a sentence, or recognizing faces – may have dedicated areas in the brain is much more controversial. “A lot of people in my field prefer to have ideological debates, but I prefer just to stick subjects in the scanner and find out,” Kanwisher says.
In order to stick subjects in a scanner, Kanwisher used to have to commute off campus. “We’ve been lucky to use the scanners at the Martinos Center in Charlestown for the last 10 years,” she says. “But it’s always a nuisance to drive across town and then discover that something’s wrong with one of your computers.” Kanwisher will soon be able to stay within the BCS complex and use the new brain scanner in the Martinos Imaging Center at the McGovern Institute.
To locate regions of the brain specialized for particular tasks, Kanwisher uses functional magnetic resonance imaging (fMRI), which measures neural activity in terms of local blood flow. She initially found the face-specialized region by looking for areas that were more active when subjects looked at faces than when they looked at objects.
Then she had to rule out other possible reasons for the stronger signals. The putative face region might have been wired to respond to round things or to human body parts generally; or it might have been part of an attention-boosting mechanism, which faces activated because social interaction is so crucial for humans. “There are literally dozens of alternative accounts. The signature of my work,” Kanwisher says, “is to take all of these alternative accounts seriously and test them, every one if we can.” This process takes years.
“One of the biggest questions I’d love to answer is where all this structure in the brain comes from,” Kanwisher says. She finds the same specializations in the same brain regions in nearly every single subject she scans. “It’s like the liver or the kidney. They’re just parts of the system.” Are they the result of natural selection, since identifying faces, places, and bodies are such vital human tasks? Or might they be the result of changes in individuals’ brains?
Kanwisher’s recent work with postdoc Chris Baker, which examines a brain structure involved in reading, suggests that experience can train brain regions to respond selectively to different stimuli. When people who read Hebrew look at Hebrew words, for instance, they have twice as strong a response in the written-language area of the brain as people who do not read Hebrew.
Kanwisher doesn’t believe the entire brain is specialized. “I think some domains of [abstract thought] get their own bit of brain and others don’t. The question of why some do and others don’t is a very big, interesting one, and it’ll keep us busy for a long time.” – By Katherine Bourzac, SM ‘04