Neural Correlates Involved in Processing Happy Affect on Same Race Faces

Abstract

Neuroimaging studies have shown that the face-related regions of the brain, including the amygdala and the fusiform gyrus, are activated when subjects viewed the faces of their own race as compared to those of other races. These regions have been regarded as the neural correlates of “in-group advantage,” a phenomenon showing superior performance for the same-race face than for other-race faces in behavioral experiments. However, in these neuroimaging studies, faces of notably different races have been used for comparisons, and thus far, no study has investigated brain activity associated with positive expression. In the present functional magnetic resonance imaging study involving the Japanese participants, we investigated brain activation in response to viewing happy and neutral faces of Japanese, non-Japanese Asian, and Caucasian races. Analysis of covariance using the mean happiness rating as a covariate revealed that as compared to viewing of neutral faces, viewing of happy faces by the Japanese subjects resulted in greater activation of the posterior cingulate cortex under the same-race condition than under other-race conditions. In addition, parametric modulation analysis showed that clusters in a part of the posterior cingulate cortex and in the superior temporal gyrus were associated with subjective judgment of the facial features that resembled those of the Japanese race. The left amygdala activity differed between the races; however, it is more likely that this difference was related to the differences in the subjective rating of facial happiness than to the recognition of the race per se. Therefore, we considered that the posterior cingulate cortex is the neural correlate that is specifically involved when Japanese subjects judge the happy expression on the same-race face. These results may indicate that in the Japanese participants a sense of familiarity played a role in the neural processing of a positive expression on the same-race face.