MRI reveals brain connections behind face recognition
Despite their apparent differences, monkeys and people have some things in common. One is face recognition, which, in both species, is handled by a series of specific areas in the brain. In the case of macaques, there are six sites. What has been unclear is how those sites are connected to each other and to the rest of the brain.
Using six categories of stimuli (top), researchers found selective brain regions that respond more to the faces than to the five nonface object categories in monkeys that were shown the stimuli. On the bottom is the timing of the stimulus sequence used to identify face recognition patches.
To find out more about the connection, Sebastian Moeller, Winrich A. Freiwald and Doris Y. Tsao from the University of Bremen in Germany used a new combination of techniques to examine how macaque monkeys recognize faces. Combining functional MRI and electrical microstimulation allowed them to trace the connections within the brain.
They used a Siemens MRI scanner to perform functional MRI on conscious animals. This allowed them to see which parts of the brain responded to stimuli because these areas would light up as blood oxygen levels changed.
The researchers showed the monkeys a blank screen and then microstimulated a face recognition patch. They tracked the response of the other patches and the rest of the brain through fMRI. They then moved on to the next patch, repeating the procedure for each of four targeted areas. Finally, they microstimulated areas around the patches and watched what happened in response.
Facial recognition takes place in six interconnected areas in macaque monkeys. Researchers have mapped out the connections between the face recognition patches. Images courtesy of Doris Y. Tsao, University of Bremen.
Working with live animals enabled them to trace the brain’s circuitry sequentially, said Tsao, who heads an independent brain research group at Bremen. Once they discovered that A connects to B, they could then see what else connected with B. They found that stimulating one patch produced a strong response within the others. Microzapping outside a patch produced a response, but that activation largely avoided the facial recognition areas. From these results they concluded that facial recognition patches form a strongly interconnected hierarchical network with specific linkages between areas.
“We were very surprised by how strong and specific the connections were,” Tsao said.
Such a conclusion is of interest to more than monkeys. Most people can recognize faces despite changes in size or age. Such recognition even works when faces are partially hidden. However, a small group of people, called prosopagnosics, do not recognize faces at all.
Tsao hopes that this and subsequent research will be able to help these individuals. “When we understand the steps necessary to wire up a face area normally, we should be able to figure out what happens abnormally in people suffering face blindness.”
Science, June 6, 2008, pp. 1355-1359.
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