Cultural Variation in the Gray Matter Volume of the Prefrontal Cortex is Moderated By the Dopamine D4 Receptor Gene (Drd4)

It has been well-established that people from different cultures vary in cognitive, emotional, and motivational processes and the brain activities underlying them. Further, initial evidence suggested that these cultural differences are linked to structural properties of the brain, such that more interdependent individuals (e.g., East Asians) have smaller gray matter (GM) volume in certain prefrontal regions. The directionality of this relationship, however, remains unclear. In the present study, we addressed this gap by adopting a unique genetic approach. People who carry the 7- or 2-repeat allele of the dopamine D4 receptor gene (DRD4) have been described as more sensitive to environmental influences, including cultural influences. We thus predicted that if culture shapes the brain, this link should be moderated by DRD4. We analyzed structural MRI images of 132 subjects (both European Americans and East Asians). Approximately half in each cultural group carried the 7- or 2- repeat allele of DRD4. Voxel-based morphometry (VBM) analysis revealed significantly greater GM volume in certain prefrontal regions among European Americans than among Asian Americans, after controlling for total brain volume, age, and sex. Moreover, this group difference was significantly more pronounced among the carriers than among the non-carriers. This pattern was robust in Freesurfer analysis assessing cortical thickness. Importantly, among Asian sojourners, the prefrontal regions showed an increase in GM volume as a function of the number of years spent in the U.S., but only among carriers not non-carriers. The present evidence is consistent with a view that culture modulates the structural properties of the brain by mobilizing epigenetic pathways that are gradually established through socialization and enculturation.