Supplemental Data Justification of gene selection

The DARPP-32 gene is associated with an intracellular protein that is highly concentrated in striatum. When phosphorylated by D1 receptor stimulation, protein photophase-1 is inhibited, thereby facilitating corticostriatal synaptic plasticity (Stipanovich et al., 2008). Carriers of two copies of the T allele (TT carriers) show greater DARPP-32 mRNA expression (Meyer-Lindenberg et al., 2007), which has been linked to a superior ability to learn about action that lead to positive outcomes relative to individuals with at least one C allele (C carriers) (Doll et al., 2011; Frank et al., 2007, 2009). Given the anatomical evidence suggesting that the BG/DA feedback loop would primarily modulate phasic bursts of DA (Joel and Weiner, 2000; Lee et al., 2004), we targeted DARPP-32 as our gene of interest. We also collected DRD2 and COMT gene labels as part of a suite we commonly collect for the purpose of replication. DRD2 has been associated with D2 receptor affinity. D2 receptors are primarily expressed by striatopallidal (indirect NoGo) medium spiny neurons, which are sensitive to fluctuations of DA below baseline levels (Hirvonen et al., 2009). Thus, genetic variation of DRD2 has been argued t