for National Geographic News
The brain of the macaque monkey has a distinct area dedicated to recognizing faces, according to a new study.
This brain region is the first one in any animalincluding humansfound to have nearly all of its nerve cells focused on a specific visual form.
The finding adds weight to the theory that the brain works like a Swiss Army knife, with separate modules set to different tasks.
"When we put an electrode in, it was clear from the very first day that every single cell just responded to faces," said study co-leader Doris Tsao, a neuroscientist at the Harvard Medical School in Boston. The study is reported in today's issue of the journal Science.
Like humans, monkeys are social animals. They benefit from recognizing other individuals in their group and from deciphering their peers' facial expressions. (See "Babies Recognize Faces Better Than Adults, Study Says.")
Scientists already know that humans have areas of the brain that are adept at face processing. For example, some stroke victims lose the ability to identify faces yet can still recognize everyday objects.
Functional magnetic resonance imaging (fMRI) experiments on humans have demonstrated that blood flow to these regions increases during face-recognition tasks, just as it does in an area of the macaque brain known as the middle face patch.
But to find out exactly how many of the nerve cells in the region are involved, researchers needed to record the cells' activity directly using an electrode.
While two macaques looked at a succession of pictures, some of which depicted faces, Tsao and colleagues logged the activity of more than 400 neurons in the monkeys' middle face patches.
Ninety-seven percent of the cells in this brain region responded when a monkey saw a picture of a face.
"It doesn't matter if it's a monkey, human, or even a cartoon face," said Tsao, who is planning several follow-up experiments.
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