DRD4 and attention deficit-hyperactivity disorder: Regarding the PFC, the SNPs of dopamine receptors (DRD) in the pyramidal neurons are also involved in cognition: the TaqIA DRD2 variant has been shown to influence verbal memory, learning, and visuospatial abilities, while the 4R variant of the 48 bp VNTR SNP in the DRD4 gene has been consistently related to poorer performances in attention, executive functioning, and inhibition, suggesting a crucial role in Attention Deficit/Hyperactivity Disorder (ADHD) [12].