Brain scans reveal racial biases

18:00:08 May 2005
NewScientist.com news service
Anna Gosline

Negative feelings about black people may be subconsciously learned by both white and black Americans, suggests a brain imaging study. The research is among the first to test the brain physiology of racial biases in both black and white subjects.

The new study showed that both white and black people had increased activity in an area of the brain called the amygdala - which responds to fearful or threatening situations - when completing a matching task with images of black faces.

“ I think the results are very specific to being raised in this society where the portrayal of African Americans is not very positive, on average,” says Matthew Lieberman at the University of California, Los Angeles, US, who led the study. “It suggests that those cultural messages are not harmless.”

But the amygdala also responds to novelty. The spike in activity upon viewing black faces shown in previous studies with solely white participants could just be the unconscious reaction to seeing an unfamiliar, or “outgroup”, face.

Pervasive cultural cues

So to tease apart the novelty factor, Lieberman and his colleagues conducted a similar experiment - using a functional MRI scanner - with 11 white and eight black Americans. Each participant completed three matching tasks; a visual task where they had to match the race of a target photo to one of two comparison photos; a verbal task where they had to match a target photo to either the words “African American” or “Caucasian American” and a control test where they matched geometrical shapes.

Both black and white people showed increased amygdala activity on the visual matching task with black target photos. The same task with a white target face produced no such activity. Because black faces are presumed not to be “novel” to black subjects, Lieberman concluded they must have learned, through pervasive cultural cues, to associate black people with fear.

The results mimic studies which measure hidden biases using association tests called Implicit Attitude Tests (IAT), says William Cunningham at the University of Toronto, Canada. IATs use subtle tasks, such as the time it takes for subjects to associate ideas of race and positive or negative words, to uncover unconscious attitudes. Many studies have found that black Americans show preferentially positive associations for white people in IATs.

Friends and neighbours

However, Cunningham cautions that increased amygdala activity and IAT scores cannot simply be translated as evidence of prejudice. Furthermore, black Americans often show highly variable responses on IATs, depending on their personal history and the diversity of their friends and neighbours, for example.

“ Measuring one's experience rather than the colour of their skin will probably get us closer to understanding what an amygdala response to an outgroup face means,” says neuroscientist and amygdala expert Paul Whalen at the University of Wisconsin, Madison, US.

Interestingly, when the subjects performed the verbal matching tasks, the race-biased amygdala effect disappeared. The scans showed that when word processing, areas of the brain involved in fighting impulses or inhibitory control took over.

“ The moment you start thinking about race in words you know you’re thinking about it and can make decisions,” says Lieberman. “In general, putting your feelings into words seems to regulate or dampen those feelings.”

Journal Reference: Nature Neuroscience (DOI: 10.1038/nn1465)

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