Ethnicity, the amygdala, and the social environment: a neuroimaging study

Abstract

BackgroundEthnic minorities have greatly increased rates of schizophrenia. The risk is most pronounced when individuals are living in areas with few people of the same ethnicity as them. Amygdala hyperactivity has been linked to paranoid symptoms in psychosis, and increased levels of paranoia have been observed in ethnic minority individuals. White individuals show an increased amygdala response when viewing black faces; however, whether a similar effect is seen in black individuals is not clear. Methods20 individuals of white British ethnicity, and 20 of black ethnicity underwent a 3T MRI scan while viewing faces of black and white ethnicity. Participants were aged 18–45 years, with no history of mental illness. Population density, indices of multiple deprivation, and percentage own-group ethnic density were obtained from the 2011 census. Neighbourhood segregation was quantified with the Index of Dissimilarity method. Ethics approval was granted by the West London National Research Ethics Service Committee. FindingsAt the within-group level, both groups individually showed greater right amygdala activation to the out-group faces (white ethnicity t=2·08, p=0·02; black ethnicity t=2·38, p=0·015). Between groups, the black ethnicity group showed a greater increase in right amygdala activation for the white faces compared with baseline than did the white ethnicity group (t=1·84, p=0·038). Within the black ethnicity group, amygdala reactivity to white faces showed significant correlations with measures of neighbourhood population density (r=0·61, p=0·01), segregation (r=0·71, p=0·003), deprivation (r=0·67, p=0·04), and own-group ethnic density (r=–0·51, p=0·04). InterpretationWe have shown for the first time, to our knowledge, increased amygdala response to white faces in individuals of black ethnicity. Significant correlations were observed between amygdala response and neighbourhood variables associated with increased psychosis risk. This finding has relevance for our understanding of the increased rates of paranoia and psychotic disorders in ethnic minority individuals. Further research in patient populations will help clarify aetiological relevance. FundingNational Institute for Health Research, Medical Research Council, Wellcome Trust.