Brain Has "Face Place" for Recognition, Monkey Study Confirms
for National Geographic News
|February 3, 2006|
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.
"[The nerve cells will] respond more to some faces, less to others, but they will fire some response to almost every face."
Furthermore, most of the remaining 3 percent of the cells reacted to a type of facial image not included in the original experiment, such as the back of a head or a head titled upward.
The discovery casts light on a much debated field of neuroscience.
Though some experts promote the aforementioned Swiss-Army-knife view of the brain, others say that mental processes are performed in a widely distributed way. They argue that the regions involved in face recognition are really used for identifying all sorts of objects.
Margaret Livingstone, a neuroscientist in the same laboratory as Tsao, says that the brain's expertise at recognizing a range of objects may follow from this ability to recognize faces.
"The fact that we found that virtually all the cells are responsive to faces says that it can't just be general expertise," Livingstone said. "There's no machinery left to be expert at [identifying] these other things," such as birds and cars and so on.
However, people might use the face selectivity of these cells to recognize objects that in some way resemble a face, Livingstone says.
Knives, Apples, and Clocks
Some of the monkey brain cells responded, though weakly, to round shapes such as clocks and apples.
This finding, according to Tsao, suggests that cells in the macaque's middle face patch are involved in some intermediate level of face coding.
"[The cells are] not yet coding a particular identity, but they are coding the basic structure and measurement of a face," Tsao said.
There are three face patches in each side of the macaque brain. The human brain has a similar distribution.
According to Winrich Freiwald, a former Harvard postdoctoral student who co-led the study with Tsao, it remains a mystery why the brain has multiple face-recognition areas, rather than just one.
"Ultimately the answer, I think, will depend on what the areas surrounding these patches do and which are the areas they're connected to," said Freiwald, now with the Brain Research Institute at the University of Bremen in Germany.
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