The changes occur in the amygdala, a region of the brain that serves as an "alarm" to activate a cascade of other biological systems to protect the body in times of danger, said Matthew D. Lieberman, assistant professor of psychology at UCLA and lead author of the study.
The findings will be published May 8 in the online version of Nature Neuroscience, and later in the print version.
Five out of eight African Americans (63 percent) responded with significantly more amygdala activity when presented with expressionless photographs of African Americans than when they were shown expressionless photographs of Caucasians, Lieberman and his colleagues found. Seven of 11 Caucasians (64 percent) in the study also responded with greater activity in the amygdala when viewing the African American photographs.
Although a third of participants in each race did not show this effect, no participant in the study responded with greater amygdala activity to the Caucasian photographs than to the African American photographs, Lieberman said.
"We didn't see any differences in amygdala activity between the racial groups," Lieberman said. "From looking at the amygdala, you couldn't tell if the scans were from African American or Caucasian participants.
"Many people of either race may not be happy to find out that a part of their brain involved in responding to potential threats responds more to African Americans than Caucasians," Lieberman said. "Even people who believe to their core that they do not have prejudices may still have negative associations that are not conscious."
Why do African Americans have this amygdala response?
"One theory," Lieberman said, "is that people are likely to pick up the stereotypes prevalent in a
Contact: Stuart Wolpert
University of California - Los Angeles