ANN ARBOR, Mich.---New evidence suggests our brains are hardwired before birth to recognize faces and places. But in contrast, the neural circuitry we use to recognize words develops mainly as a result of experience.
That's according to new findings from the University of Michigan.
"There's been a big debate about whether face recognition is a function we're wired to perform for survival. This is the first study to look at that question using brain imaging in twins," said psychology professor Thad Polk, the first author of a paper on the results that are published in the Dec. 19 edition of The Journal of Neuroscience.
Polk and his colleagues used functional MRI to examine brain activity in sets of identical and fraternal twins who viewed pictures of faces, houses, chairs, made-up words and abstract control images. Faces, houses, and words are known to elicit distinct patterns of activity in the brain's ventral visual cortex, on the bottom of the brain, behind and around the ears.
The scientists used photos of houses to stimulate what's called the "parahippocampal place area." And they included pronounceable made-up words rather than actual words to make sure that the meaning didn't affect brain activity.
For each category the participants viewed, they had to press a button to say whether a picture was the same picture as the one before it.
Functional MRI of the brain indirectly measures the activity of firing neurons. The tests gave scientists color-coded maps of brain activity. By comparing each participant's MRI results with his or her twin's, Polk could gauge how similarly their brains worked when tasked with recognizing images in the different categories.
The brain circuits used to recognize chairs or made-up words were no more similar in identical twins than in fraternal twins. That suggests that the neural circuitry underlying these behaviors is not innate. Instead, that circuitry is primarily learned through experience, Polk said.
But in the face and house categories, the scientists saw a different story. The neural pathways used to process these images were more similar in identical than fraternal twins. This suggests that genes play a significant role in this type of brain function. Identical twins are genetic copies of one another. Fraternal twins are as genetically different as regular siblings.
These results cannot be chalked up to greater structural similarity in identical twins' brains, the study says. If they could be, then the brain activity patterns for made-up words and chairs should also have been more similar in identical twins. They weren't.
"Face and place recognition are older than reading on an evolutionary scale," Polk said. "They are shared with other species and they provide a clearer adaptive advantage. It's therefore plausible that evolution would shape the cortical response to faces and places, but not symbols such as words and letters."
He said that this research could help scientists understand what's innate and what is learned. "If we can figure out the extent to which the brain can change as a result of experience and what makes it change, we could potentially develop therapies for people with brain damage," Polk said. When parts of the brain are damaged, other areas often compensate.