Children may be exceptionally good at spotting their parent’s face from across the room, but beyond family and some friends, they’re not terribly good at recognizing faces.
It’s a task that requires a lot of brain power, in part because all faces have the same features and the same configuration. And it’s also a task that we get better at with age. Even after adolescence, brain areas devoted to facial recognition keep developing.
For years, scientists assumed that brain development throughout one’s life depended almost exclusively on synaptic pruning, or the weeding out of unnecessary connections between neurons. Most of the pruning happens in the first few years of life.
Popular belief dictates tissue is slowly lost as you get older. In actuality, the tissue that’s left after pruning in infancy grows. But it’s not like there are more neurons in your brain. Studies show that the number of neurons in the brain is pretty consistent from birth to death.
The researchers examined a region of the brain that distinguishes faces from other objects. They scanned 25 adults and 22 children using two types of MRI: one that indirectly measures brain activity, a functional MRI, and one that measures the proportion of tissue to water in the brain, a quantitative MRI.
Here’s Jon Hamilton, reporting for NPR:
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.”
Kalanit Grill-Spector, a psychologist at Stanford University and senior authors of both papers, speculates that, from an evolutionary standpoint, this adaptation would have been necessary to survive and thrive in large, social communities. Today, children go from recognizing the faces of parents and close relatives to recognizing hundreds, even thousands, of people by the time they reach high school or college.
In the future, the team wants to see if there’s similar tissue growth happening in other parts of the visual cortex. They hope to shed light on disorders such as prosopagnosia—known as face blindness—and on whether people with autism, who often struggle to recognize faces, have abnormal development in the part of their brains associated with facial recognition.