Amygdala reactivity in ethnic minorities and its relationship to the social environment: an fMRI study

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.

Methods: In total 20 individuals of black ethnicity, and 22 individuals of white British ethnicity underwent a 3T MRI scan while viewing faces of black and white ethnicity. Own group ethnic density was calculated from the 2011 census. Neighbourhood segregation was quantified using the Index of Dissimilarity method.

Results: At the within-group level, both groups showed greater right amygdala activation to outgroup 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 (r = -0.61, p = 0.01).

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.

Keywords: Amygdala; ethnic density; ethnic minority; ethnicity; fMRI; paranoia; psychosis; risk factors; schizophrenia.

Fig. 1.

fMRI task. Participants judge whether an image is to the left or right of a fixation cross. Each face trial (top row) is followed by four white square trials (bottom row).

Fig. 2.

(a) Increased amygdala activation in black ethnicity group compared with white British ethnicity group for white > black faces contrast during 525 ms presentations. Functional maps are unmasked and thresholded at p < 0.001 whole brain, uncorrected for display purposes. (b) Mean parameter estimates for right amygdala region of interest (ROI) for both groups, for faces (525 ms) v. white square contrasts, error bars = ±SEM. *p < 0.05.

Fig. 3.

Scatter plots for right amygdala response to whitefaces within the black ethnicities group, against: (a) % own group ethnicity of current lower layer super output area (LSOA) (r_s = −0.611, p = 0.009) (b) Index of segregation (r_p = 0.831, p < 0.001).