Figure 2.

A, B, Mean ± SE of BOLD response in caudate (A) and in middle frontal gyrus (PFC; B) during working memory in compound genotype groups. Since we expected that the genotypes potentially associated with putative intermediate levels of dopamine would show more focused activity for a similar level of behavioral performance, genotype groups are ordered from putative less dopamine reuptake (DAT 9-carriers have less DAT expression) and release (DRD₂ GG subjects have greater presynaptic D₂ mRNA) to greater reuptake and release (DAT 10–10 repeat DRD₂ GT subjects). The relationship between compound genotype and BOLD response is nonlinear. Genotypes on the y-axis are ordered to reflect the nature of our hypothesis about the relationship between putative levels of dopamine stimulation determined by compound genotypes and BOLD activity for a given level of performance. Thus, genotypes at the two extremes of the curve are hypothesized to have intermediate levels of dopamine stimulation and more efficient BOLD activity (less activity for a given behavioral performance).