Many of us have experienced being introduced to someone only to forget their name seconds later. However, it's often easier for us to remember someone's face than their name. Now, researchers at Stanford University have found out why: the brain region associated with face recognition grows even stronger as we age.
This is surprising since brain development is believed to involve synaptic pruning, the connection between neurons, rather than growth. In other words, the brain develops by becoming more streamlined, not by growing new tissue.
“What’s surprising here is that the changes involve a different mechanism, expansion not pruning,” Kalanit Grill-Spector, study author, and neuroscientist at the Stanford University School of Medicine in California, told New Scientist.
We are born with a number of neurons and connections, which eventually chip away over time, and by the time we’re 25, our brains will have fully developed, according to the University of Rochester Medical Center. At birth, we learn how to distinguish faces from other images. However, what gives us the ability to do so, and how exactly we develop these skills, remains a mystery.
In the study, published in Science, Grill-Spector and his colleagues found the fusiform gyrus, a brain region that specializes in facial recognition, becomes larger, and develops more branched-out neurons from adolescence into adulthood. This means we become better at recognizing faces as we age.
Changes in the fusiform gyrus reflect the importance of facial recognition in our lives; we’re constantly increasing our social circles.
“By the time we’re in college or high school, we know thousands of people,” said Grill-Spector. “Then we continue to learn new faces throughout life.”
A total of 22 children (aged five to 22) and 25 adults (aged 22 to 28) underwent a qualitative magnetic resonance imaging scan (qMRI) to detect changes in density in the fusiform gyrus between the age groups. The researchers used qMRI because a standard MRI cannot give absolute values of brain-cell density that could be comparable. qMRI works by exciting protons in the water in brain tissue. The time it takes for those protons to calm back down to their resting state is what lets us know about someone's brain density. So, a quicker time to relaxations means a denser brain region, according to LiveScience.
Inside the MRI, the participants were asked to look at two sets of images: one of different faces, the other of different places.
The researchers concluded the denser a person's face-recognition area, the better he or she performed on tests of facial recognition in the MRI scanner.
To explore what sort of brain tissue was causing density increase with age, the researchers ran computer simulations to test various possibilities. The simulations showed myelin — a fatty substance that insulates the long axons of neurons — could not explain brain density. This prompted them to look at anatomical samples of donated brains from deceased adults to see the cause for brain density.
The samples revealed the fusiform gyrus in adult brains didn't have any more cell bodies than the place-recognition area in childhood — it had fewer. The researchers narrowed it down to a “neural fill,” which refers to the tissues surrounding the cell bodies, like axons, synapses, and dendrites, the branched structures at the ends of axons that end the synapses. This means the tissue that is growing can't be the cell bodies, so it must be the “neural fill,” according to the researchers.
Jesse Gomez, study leader, and a doctoral candidate in neuroscience at Stanford University, compared brain density in this region to a garden.
“You can imagine a 10-foot-by-10-foot garden, and it has some number of flowers in there,” he told NPR. “The number of flowers isn’t changing, but their stems and branches and leaves are getting more complex.”
Facial-recognition abilities are known to peak in our late 20s or early 30s, which is slightly older than most of the adults in the study. The researchers plan to follow up with these participants over time.
This can lead to a better understanding of neurological conditions, such as facial blindness, or why those with autism have trouble recognizing faces.
Source: Gomez J, Barnett MA, Natu V et al. Microstructural proliferation in human cortex is coupled with the development of face processing. Science. 2017.