The prefrontal cortex has long been described as "terra incognita" by many brain researchers. Scientists know that this region is the most advanced part of the human brain and is responsible for cognitive functions such as memory, reasoning, mental computation and language, but they're still unclear about how the prefrontal cortex processes information.
To unravel the complexity of the prefrontal cortex, scientists at the School of Medicine studied how visual stimuli was processed in the brains of primates. Their findings of this research -- funded by the National Institute of Mental Health and the McDonnell Foundation -- are reported in the Nov. 7 issue of the journal Science.
Patricia S. Goldman-Rakic, professor of neuroscience, led a research team that used physiological techniques to map the prefrontal cortex of primates as they were shown pictures of faces and objects. The team found that some neurons responded only to pictures of faces and to no other stimuli. They further found that the neurons responding to faces were clustered in one area of the prefrontal cortex, called the inferior prefrontal cortex.
"This study has revealed that information related to faces is processed in a specific region of the prefrontal cortex," says Professor Goldman-Rakic, the study's principal investigator. "This shows not only that the prefrontal cortex is modular and specialized by sensory domain, but that each of its neurons has a dedicated function, since individual neurons code individual items of information, for example different faces." In addition to Professor Goldman-Rakic, team members included Séamas P. O Scalaidhe, associate research scientist in neurobiology, and Fraser A. W. Wilson, now an assistant professor in neuroscience at the University of Arizona.
The researchers recorded and thoroughly analyzed close to 2,500 cells. The responsiveness of the neurons was tested with many different stimuli. Their research also revealed that cells in the prefrontal cortex were able to maintain information even after the stimuli disappeared.
"This work shows that the neurons in the prefrontal cortex are activated when different faces are maintained in memory," says Professor Goldman-Rakic. "Even in primates who were not trained to remember pictures, neurons continue firing long after the stimulus is gone, showing that an intrinsic property of these neurons is to maintain that activity in the absence of stimuli."
Past studies of brain function have focused mostly on sensory and motor areas, which have been found to be modular and specialized. Some scientists have theorized that the prefrontal cortex might function in a different way. Mr. O Scalaidhe, the study's first author, points out that in this respect, the organization of the prefrontal cortex resembles that of other brain areas.
"Our study indicates that the prefrontal cortex is modular, like other brain areas that have been more closely examined," says Mr. O Scalaidhe. "This research has brought us closer to understanding how the higher centers of the human brain works."