These gene polymorphisms affected the expression of catechol-o-methyltransferase, which catabolizes synaptic dopamine primarily in the prefrontal cortex (COMT Val158Met polymorphism), D2 dopamine receptors primarily in the striatum (DRD2/ANKK1-Taq1a polymorphism), and dopamine transporters, which clear synaptic dopamine in the striatum (DAT 3' VNTR variant).
We found a double dissociation for temporal discrimination: the DRD2/ANKK1-Taq1a polymorphism (A1+ allele) was associated with significantly greater variability for the 500-msec duration only, whereas the COMTVal158Met polymorphism (Val/Val homozygotes) was associated with significantly greater variability for the 2000-msec duration only.