COMT and DARPP-32 genotype interaction effects on working memory performance. Graphs depict target discrimination (d′ for targets versus lures; mean ± SEM). Under high working memory load (3-back trials), COMT and DARPP-32 genotype significantly interact to affect d′, according to an inverted-U relationship (F(2, 89)=4.37, p=0.016). A post-hoc ANOVA found a significant effect of DARPP-32 genotype on 3-back target/lure detection in COMTValMet individuals, F(1,39)=6.23, p=0.017.