Studies point to brain areas that respond to faces, human bodies
THURSDAY, Sept. 27, 2001 (HealthDayNews) -- Your eyes aren't the only things to light up when you see someone you know. Your brain does, too. And that has scientists debating: Does the brain have a certain area specifically wired to react to other people, or does the the reaction occur over a more widespread region of the organ?
Two separate teams of researchers are drawing these opposite conclusions on how people respond to images of faces and bodies.
One study suggests that a crucial response pattern occurs across a section of the brain's visual cortex, while the other suggests the key is activity in a single brain structure.
Both reports appear in the Sept. 28 issue of Science.
The first study was led by research scientist James Haxby at the National Institute of Mental Health in Bethesda, Md. His team examined the functional magnetic resonance imaging (fMRI) scans of the brains of six volunteers as they looked at a series of images: faces, cats, five types of man-made objects and nonsense images. The fMRI scans show blood-flow changes in various areas of the brain, a sign of mental activity.
Viewing faces created a flurry of activity in an area of the brain called the fusiform face area (FFA), which has been linked to face recognition. Other images triggered lower levels of activity in that area. At the same time, each image created a specific pattern across a larger region of the brain, almost like a fingerprint.
"The surprising thing is that we can look at the pattern of response in an individual's brain to a given category, like chairs, and tell that that person is looking at chairs," says Haxby. In fact, the researchers could say with 96 percent accuracy what the subjects were looking at just by examining the brain pattern it produced.
Haxby says, "Faces are very important for our social communication so we really have to have very sensitive, sophisticated systems for face perception." He says the findings might someday provide information about disorders like face blindness, where people are unable to recognize faces easily.
In the second study, scientists describe a modular view, which suggests that the brain is divided into separate, independently operating parts. Each section has its own function, and when its task is complete, that information is shared with other components so it can be used.
In previous research, the authors had found evidence of two key regions of the brain:: the FFA that responded to faces and the parahippocampal place area (PPA) that responded to places.
Now, the researchers have identified a region of the lateral occipital cortex (located towards the back of the brain), which they have called the extrastriate body area (EBA) that appears to respond strongly to visual perceptions of the human body.
The researchers showed 19 people a variety of images, including pictures, line drawings and silhouettes of humans, while the volunteers were inside a fMRI scanner.
In all 19 people the fMRI scans showed the EBA has much more activity in response to pictures of the human body than to images of animals or common objects such as umbrellas or hammers. Increased activity also was seen when subjects were shown line drawings, stick figures or silhouettes of the human form.
"There's no other explanation that we can come up with," says lead author Paul Downing, a lecturer at the Centre for Cognitive Neuroscience at the University of Wales in Bangor, U.K. "[The EBA] really does seem to be a body area."
Downing says that having such an area makes sense from an evolutionary perspective, since it would allow us to recognize whether another human is attractive or if they posed some kind of threat.
However, he says much still must be learned about this area. For example, he says it may help us to recognize other people, to determine how other people's bodies are oriented to us, or to help guide our own body movements. Downing says at this stage, the findings don't have immediate clinical applications.
Dr. Jonathan Cohen, director of Princeton's Center for the Study of Brain, Mind and Behavior, says the theories described in the two studies represent the extreme ends of the same spectrum, but that most scientists don't subscribe to these exact viewpoints.
"In the case of the [Downing] study, the suggestion is that there's a part of the brain that's specifically responsible for recognizing parts of bodies," says Cohen. "Each part of the brain has its own dedicated function. It's specialized to do something very specific, and the way the brain works is to combine all these different specialized processes into a group that talks to one another and shares information about what they know."
At the other end of the spectrum, the other study describes graded specialization in the brain, meaning that there is no one part of the brain that only does one thing. "In the case of the current paper representations of faces are not necessarily located to a very specific area, but rather engage much broader expanses of the brain," says Cohen.
Cohen says one of several intermediate theories actually may be closer to the truth. One intermediate positions suggests some brain areas are particularly specialized but don't operate alone. "This is called distributed representation," says Cohen.
One benefit of this theory is that if a one section of the brain is damaged, other sections can adapt to perform, albeit less effectively, the functions of the damaged area.
"We see in many cases of brain injury -- you start out with this horrible deficit, but with time you actually regain function," says Cohen. "That must mean that that area couldn't have been the only area to do the function that was lost."
Another intermediate position suggests that the area of the brain that appears to respond to faces is actually responding to some other unknown stimuli, but pays special attention to faces, says Cohen.
"The value of the present studies is simply to help provoke further research to really get down to the nitty-gritty," he says. While brain imaging studies are invaluable, he says examining the activity of single neurons may be necessary to determine exactly how the systems work.
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