Skin Color and Brain Reaction

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Abstract

Background. Ethnic minority individuals have an increased risk of developing a psychotic disorder, particularly if they live in areas of ethnic segregation, or low own group ethnic density.

The neurobiological mechanisms underlying this ethnic minority associated risk are unknown. We used functional MRI to investigate neural responses to faces of different ethnicity, in individuals of black ethnicity, and a control group of white British ethnicity individuals.

Results.
–  At the within-group level, both groups showed greater right amygdala activation tooutgroup faces.
–  Between groups, the black ethnicity group showed greater right amygdala activation to white faces, compared to the white ethnicity group.
–  Within the black ethnicity group, individuals living in areas of lower own group ethnic density showed greater right amygdala reactivity to white faces .

Conclusions. This is the first time an increased amygdala response to white faces has been demonstrated in individuals of black ethnicity. In the black ethnicity group, correlations were observed between amygdala response and neighbourhood variables associated with increased psychosis risk. These results may have relevance for our understanding of the increased rates of paranoia and psychotic disorders in ethnic minority individuals.

Being a member of an ethnic minority group is one of the most well established environmental risk factors for schizophrenia… In various settings, the increased risk appears greatest for individuals of black ethnicity…This risk also appears to be somewhat specific for psychosis…there is no evidence of increased rates of depression or anxiety in the UK black ethnicity population…Similarly, in the USA a number of studies have reported reduced rates of depression and anxiety in African Americans.

Interestingly, despite the fact that communities with high proportions of ethnic minority individuals are frequently the most deprived, living in an area where one’s own ethnic group forms a larger proportion of the population is relatively protective against schizophrenia…Epidemiological work has also suggested that greater levels of segregation between members of ethnic minority groups and the rest of the community may be linked to a greater incidence of psychotic disorders…The amygdala is also an area of potential interest given it is a key component of the neural circuit processing threatening experiences…A greater right amygdala neural response to pictures of faces of people with an outgroup ethnicity, compared with those with in-group ethnicity, has been interpreted as representing threat appraisal… In psychosis, meanwhile, amygdala hyperactivity has been linked to paranoid symptoms.

Individuals from ethnic minority populations typically have much greater exposure to outgroup individuals than the native population.  Amygdala hyperactivity to frequent outgroup exposure could therefore partially underlie the greater levels of paranoia seen in both ethnic minority patient and population samples ….we hypothesised that

–  individuals who identified as being of black ethnicity would display a greater right amygdala response to white faces, than individuals who identified as being of white ethnicity; who would, in turn, show a greater response to black faces.

–  Within the black ethnic minority group, we further hypothesised that increased amygdala reactivity to white faces would correlate with increased ethnic segregation, and decreased own group ethnic density, as these ethnicity related neighbourhood variables are associated with increased psychosis risk.

There were no significant differences between groups in terms of sex or age…Within the black ethnic minority group right amygdala response to white faces significantly correlated with living in an area of greater ethnic segregation and lower own group ethnic density …The right amygdala response also positively correlated with greater population density and lower levels of deprivation.

Discussion
We demonstrated increased amygdala activation to white faces in
a group of individuals of black ethnicity – both within group compared with black faces and between groups when compared with white British individuals.

  • The white British ethnicity group showed a greater amygdala response to black faces both within, and between the group.
  • lower own group ethnic density was significantly associated with greater amygdala reactivity to white faces.
  • Our finding of increased right amygdala reactivity to black faces in the white

While our findings suggest a general out-group effect, this finding may potentially have a greater psychological impact for ethnic minority groups given their generally greater exposure to outgroups….Living in areas of low own group ethnic density has been shown to increase the risk of psychosis in ethnic minorities…lower own group ethnic density is also linked to greater amygdala response to outgroup faces in black individuals.

Living in an environment where one is more isolated from one’s own ethnic group (i.e. an area of low own group ethnic density), could conceivably contribute to outgroup individuals being perceived as a greater threat.  Taken with evidence that experiences of racism are correlated with amygdala activation to white faces in black individuals this suggests that environmental exposures are associated with functional alterations in the brain circuits involved in threat processing…The right amygdala appears to be particularly implicated in the processing of race

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