Feb. 20, 1998 PHILADELPHIA --The recognition of faces is so fast and effortless it's easy to overlook the complexity of the brain systems responsible, says a Duke University Medical Center researcher who has helped identify two critical brain regions involved in our ability to process faces.
The first region lies on the underside of the brain and appears specialized for rapidly distinguishing faces from other objects. The second region is located on the side of the brain, and it becomes involved when one views a face in which the eyes or mouth are moving.
"There is something special, and fascinating, about face perception," said Gregory McCarthy who prepared a report on his work for the annual meeting of the American Association for the Advancement of Science.
"It ties together sensation, recognition, emotion, and memory in different areas of the brain within 200 milliseconds after viewing a face," said McCarthy, director of the Brain Imaging and Analysis Center at Duke.
The results of his newest study, undertaken at Yale University and the West Haven Veterans Administration Medical Center before he came to Duke, will be published in the March 15 issue of the Journal of Neuroscience. Co-authors of the findings are Truett Allison and Aina Puce at Yale.
They found that the area that processes eye and mouth movements is close to, but distinct from, other brain regions that respond to most other kinds of movements.
"The brain may need a dedicated region to process facial movements," McCarthy speculated in an interview, "because eye and mouth movements convey a lot of information, including important social signals." He added that knowledge about what people say is aided by unconsciously watching their lips move. That might be why, for example, people are disturbed by a video in which the visual and audio tracks are not synchronized.
McCarthy's group earlier mapped a region in the underside of the brain that discerns faces from among other everyday objects such as telephones and bicycles. Other groups have identified other brain regions such as the amygdala that identifies the emotional state of the face being seen. It appears then that different brain systems work together to identify a face and to extract important information related to social and verbal communication, McCarthy said.
Among the many questions about face perception yet to be answered is how the brain developed this sophisticated system to recognize and process faces. McCarthy asked, "Is this something that is learned or is it present in the brain from early on? I favor the idea that this is a primitive process that is tuned by experience -- there is a definite survival advantage to recognizing friend from foe."
McCarthy and his colleagues gathered information about these brain areas by functional magnetic resonance imaging (MRI), and by making electrical recordings directly from the brain surface in patients in whom electrodes were implanted by surgeons to identify brain areas involved in epileptic seizures. Functional MRI measures changes in blood oxygenation in small areas of the brain that are activated by a stimulus, such as the picture of a face. The active brain tissue requires more blood flow to deliver oxygen, just as a leg or arm muscle would require during exercise.
The machine does not use damaging X-rays, so it can be used repeatedly to study the architecture of a patient's brain. And because the location of some important brain areas related to language may be different in different people, this information can be helpful to surgeons in reducing neurological deficits following neurosurgery.
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