Interestingly, the enrichment direction for immune-related pathways varied according to brain region, increasing with AA proportion in the caudate nucleus and with EA proportion in the other brain regions. Therefore, there is no simple ‘up or down’ bias in functional associations across brain regions. For example, if AA proportion is a risk factor for immune response in the caudate nucleus, then by the same reasoning AA proportion would be a protecting factor for immune response in the hippocampus and DLPFC. We considered that differences in directionality across regions may reflect variation in cell composition because the caudate nucleus was the only brain region without a laminar architecture. However, laminar architecture in the brain has generally implicated neuronal biology39, which was not the case in this study (that is, enrichment of immune-related pathways).
