A comparison of kid brains and grownup brains may explain why our ability to recognize faces keeps getting better until about age 30.
Brain scans of 25 adults and 22 children showed that an area devoted to facial recognition keeps growing long after adolescence, researchers report in the journal Science.
The area didn't acquire more neurons, says Jesse Gomez, a graduate student in neurosciences at Stanford University and the study's lead author. Instead the brain region became more densely populated with the structures that connect and support neurons.
"You can imagine a 10-foot by 10-foot garden, and it has some number of flowers in there," Gomez says. "The number of flowers isn't changing, but their stems and branches and leaves are getting more complex."
To see whether that sort of change occurred elsewhere in the brain, the researchers also looked at a nearby area that responds to places, instead of faces. In this area, there was no difference between children and adults.
The results suggest that brain development is more varied than researchers once thought.
For years, scientists have focused on a process known as synaptic pruning, which shapes the brain by eliminating unused connections among neurons. Most synaptic pruning takes place in the first few years of life.
"After age 3, the textbooks are pretty silent about what's going on in the brain," Gomez says.
The continuing growth in facial recognition areas may be a response to the need to recognize more and more faces as children grow older, says Kalanit Grill-Spector, a professor in the psychology department at Stanford.
"When you're a young child, you need to recognize your family and a handful of friends," she says. "But by the time you've reached high school or college your social group has expanded to hundreds or even thousands of people."
And recognizing all those people requires a lot of brain power, Grill-Spector says, because "all faces have the same features and the same configuration."
Ongoing changes in the brain may also help children focus on different sorts of faces at different stages of development, says Suzy Scherf, an assistant professor of psychology at Penn State University.
"Children's face recognition early on is very much tuned to adult faces," Scherf says. "In adolescence it changes to be highly tuned toward adolescent faces."
Understanding how facial recognition develops throughout childhood could make it easier to figure out why some people have difficulty recognizing faces, researchers say.
Gomez hopes to scan the brains of people with "face blindness," a disorder that can leave a person unable to recognize even familiar faces.
And Scherf wants to know whether people with autism, who often struggle to recognize faces, have abnormal development in the facial recognition area of their brains.
ARI SHAPIRO, HOST:
A lot of our mental abilities peak when we turn 20. We can't process information as quickly as we once did. It takes longer to solve math problems in our heads. There is at least one notable exception. Our ability to recognize faces improves all the way into our 30s. Now scientists say they are starting to understand why.
NPR's Jon Hamilton reports on evidence that brain areas involved in facial recognition keep growing well into adulthood.
JON HAMILTON, BYLINE: Long before babies learn to walk or talk, they can recognize a familiar face, and Kalanit Grill-Spector of Stanford University says this ability improves dramatically as kids grow up.
KALANIT GRILL-SPECTOR: When you're a young child, you need to recognize your family and a handful of friends. But by the time you've reached maybe high school or college, your social group has expanded to hundreds or even thousands of people.
HAMILTON: Think Facebook. Grill-Spector says it's remarkable that our brains can keep track of all those faces because frankly they look pretty similar.
GRILL-SPECTOR: Face recognition is very difficult computational problem, and the reason is that all faces have the same features and the same configuration.
HAMILTON: Grill-Spector wanted to know more about how the brain is able to tell the subtle differences among so many different faces, so she and a team of researchers scanned the brains of several dozen people, including adults as old as 28 and children as young as 5. The brain scans focused on an area that responds specifically to faces. And Jesse Gomez, a Ph.D. student who did much of the work, says the scans showed something surprising.
JESSE GOMEZ: Brain tissue actually seemed to be growing from childhood into adulthood.
HAMILTON: Gomez says the number of neurons stayed the same, but the structures that connected and supported the neurons increased.
GOMEZ: You can imagine, like, a 10-foot by 10-foot garden, and you know, it has some number of flowers in there. And so the number of flowers isn't changing, but it's really - their stems and the branches and leaves are getting more complex, and there's more of them over time.
HAMILTON: Meanwhile, in a nearby area of the brain that responds to places rather than faces, there was no difference between kids and adults. The results, published in the journal Science, help explain how the ability to recognize faces keeps getting better until about age 30 even as other mental abilities have plateaued or are in decline.
But why does this area of the brain continue to grow? It may not be just about recognizing more faces. Suzy Scherf of Penn State University says as we grow up, the faces we pay attention to change.
SUZY SCHERF: Children's face recognition early on is very much tuned to adult faces. And in adolescence, it changes to be highly tuned towards adolescent faces.
HAMILTON: Scherf says understanding how facial recognition develops could make it easier to figure out why some adults are very bad at recognizing faces, a condition known as face blindness. She says it could also lead to a better understanding of why faces are so difficult for many people with autism. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.